# DNV Classification Note 31.1 Strength Analysis of Hull Structure in

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DNV Classification Note 31.1 Strength Analysis of Hull Structure in

CLASSIFICATION NOTES No. 31.1 Strength Analysis of Hull Structure in Bulk Carriers DECEMBER 2012 The electronic pdf version of this document found through http://www.dnv.com is the officially binding version The content of this service document is the subject of intellectual property rights reserved by Det Norske Veritas AS (DNV). The user accepts that it is prohibited by anyone else but DNV and/or its licensees to offer and/or perform classification, certification and/or verification services, including the issuance of certificates and/or declarations of conformity, wholly or partly, on the basis of and/or pursuant to this document whether free of charge or chargeable, without DNV's prior written consent. DNV is not responsible for the consequences arising from any use of this document by others. DET NORSKE VERITAS AS FOREWORD DET NORSKE VERITAS (DNV) is an autonomous and independent foundation with the objectives of safeguarding life, property and the environment, at sea and onshore. DNV undertakes classification, certification, and other verification and consultancy services relating to quality of ships, offshore units and installations, and onshore industries worldwide, and carries out research in relation to these functions. Classification Notes Classification Notes are publications that give practical information on classification of ships and other objects. Examples of design solutions, calculation methods, specifications of test procedures, as well as acceptable repair methods for some components are given as interpretations of the more general rule requirements. © Det Norske Veritas AS December 2012 Any comments may be sent by e-mail to [email protected] If any person suffers loss or damage which is proved to have been caused by any negligent act or omission of Det Norske Veritas, then Det Norske Veritas shall pay compensation to such person for his proved direct loss or damage. However, the compensation shall not exceed an amount equal to ten times the fee charged for the service in question, provided that the maximum compensation shall never exceed USD 2 million. In this provision "Det Norske Veritas" shall mean the Foundation Det Norske Veritas as well as all its subsidiaries, directors, officers, employees, agents and any other acting on behalf of Det Norske Veritas. Classification Notes - No. 31.1, December 2012 Changes – Page 3 CHANGES General This document supersedes Classification Notes No. 31.1, June 2011. Text affected by the main changes in this edition is highlighted in red colour. However, if the changes involve a whole chapter, section or sub-section, normally only the title will be in red colour. Main Changes Items related to Ore Carriers are removed from this Classification Note and used as a basis for a new Classification Note No. 31.10 Strength Analysis of Hull Structures in Ore Carriers. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Contents – Page 4 CONTENTS 1. 1.1 1.2 1.3 1.4 2. 2.1 2.2 2.3 3. 3.1 3.2 3.3 3.4 4. 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 5. 5.1 5.2 5.3 5.4 5.5 6. 6.1 6.2 6.3 6.4 General.................................................................................................................................................... 5 Introduction...............................................................................................................................................5 Bulk Carriers.............................................................................................................................................5 Procedure ..................................................................................................................................................6 Definitions.................................................................................................................................................7 Design Loads......................................................................................................................................... 10 General....................................................................................................................................................10 Bulk cargo filling part of hold (heavy cargo) .........................................................................................10 Bulk cargo expanded to fill hold.............................................................................................................11 Design Loading Conditions – Local Strength.................................................................................... 12 General ...................................................................................................................................................12 Summary for Bulk Carriers.....................................................................................................................12 Design Loading Conditions for Bulk Carriers ........................................................................................16 Fatigue Loads..........................................................................................................................................23 Cargo Hold Analysis ............................................................................................................................ 24 General....................................................................................................................................................24 Model Extent...........................................................................................................................................24 Modelling of geometry ...........................................................................................................................25 Elements and Mesh Size .........................................................................................................................26 Boundary Conditions ..............................................................................................................................29 Loading Conditions.................................................................................................................................31 Presentation of input and results .............................................................................................................32 Evaluation of results and applicable acceptance criteria ........................................................................33 Local Structure Analysis ..................................................................................................................... 36 General....................................................................................................................................................36 Stiffeners subject to large deformations .................................................................................................36 Other fine mesh models ..........................................................................................................................38 Documentation and result presentation...................................................................................................38 Acceptance Criteria.................................................................................................................................39 Additional Requirements Considering Flooding .............................................................................. 39 General....................................................................................................................................................39 Global Bending Moment and Shear Force Limitation............................................................................39 Transverse Bulkhead Strength ................................................................................................................40 Diaphragm and shear plates in double bottom below bulkhead stool, considering flooding (evaluation of the effectiveness) .............................................................................................................41 6.5 Limit to Hold Loading, Considering Flooding .......................................................................................42 7. Cargo Hold Load Limitations............................................................................................................. 42 7.1 General....................................................................................................................................................42 7.2 Definitions...............................................................................................................................................42 7.3 Procedure for preparation of Hold Mass Diagrams ...............................................................................43 7.4 Hold mass diagrams................................................................................................................................49 7.5 Local Tank Top Loading ........................................................................................................................54 8. Wave Torsion Induced Stresses ......................................................................................................... 57 8.1 General....................................................................................................................................................57 9. Shear Force Correction ....................................................................................................................... 57 9.1 General....................................................................................................................................................57 9.2 Definitions...............................................................................................................................................57 9.3 Rule Requirement ...................................................................................................................................57 9.4 Allowable Shear Force............................................................................................................................58 9.5 Corrected Shear Force.............................................................................................................................59 Appendix A. Checklist for Finite Element Analysis .......................................................................................................... 62 Appendix B. Beam Modelling.............................................................................................................................................. 65 DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.1. General – Page 5 1. General 1.1 Introduction 1.1.1 This Classification Note covers only the strength analysis of hull structure in non CSR bulk carriers. For bulk carriers with CSR notation, the strength analysis of hull structure is covered in Rules Pt.8 Ch.2. This Classification Note is applicable for ships with class notation HC-A, HC-B, HC-C and HC-B. For ships with class notation HC-M, design load cases are given in Rules Pt.5 Ch.2 Sec.5 Table C1 based on the ships’ loading manual. For application of sea pressure load, cargo load and hold mass diagrams, relevant parts of this Classification Note may be applied. 1.1.2 The “Rules for Classification of Ships” require a direct structural analysis to be carried out in order to cope with the complexity in the loading of bulk carriers and the many possible loading conditions. The scope for the analysis is to verify that stresses in the girder structure are within specified limits when the structure is loaded in accordance with the specified design load conditions. 1.1.3 The structural analysis is generally related to primary strength members of the midship region of bulk carriers arranged with double bottom and single or double side. However, additional calculations may have to be carried out for fore- and aftmost holds as the hopper/top wing tank construction normally is changed significantly compared to the midship construction. 1.1.4 Where in the text it is referred to the Rules, the references refer to the July 2011 edition of “Rules for Classification of Ships”. 1.1.5 Any recognised calculation method or computer program may be applied provided the effects of bending, shear axial and torsion deformations are considered when relevant. 1.1.6 Strength analysis carried out in accordance with the procedure outlined in the Classification Note will normally be accepted as basis for class approval. Nauticus Hull is a computer program offered by DNV that is suitable for the calculations specified in this Classification Note. 1.2 Bulk Carriers 1.2.1 Bulk carriers are ships designed primarily for the transportation of solid bulk cargoes. Such cargoes are generally uniform in composition, and are loaded directly into the cargo space without any intermediate form of containment. The range of cargoes carried in bulk carriers is considerable. Leading bulk cargoes in the world trade are iron ore, coal, grain, bauxite/alumina and phosphate rock, along with substantial quantities of concentrates, petroleum coke, steel, ores, cement, sugar, quarts, salt, fertilisers, sulphur, scrap, aggregates and forestry products. Further, the receivers of bulk cargoes have very varied requirements for tonnage delivered per month or per year. The size of vessels that they choose to carry their cargoes and the frequency that such vessels are employed will be influenced by a variety of factors, including the receivers’ storage capacity, depth of water in the berth, regularity of the demand for the commodity and the financing of its purchase. This large variety in demand and the variety in pattern of international trade have created a versatile world fleet of very varied ship sizes. These may be categorised as follows: Handy-size bulkers: This is the most common size of bulk carriers with a deadweight of 25 000 to 35 000 tonnes and a draught less than 11.5 m. The handy-sized bulker is so called because her comparatively modest dimensions permit her to enter a considerable number of ports, world-wide. Such vessels are used in many trades in which the loading or discharging port imposes a restriction upon the vessel’s size, or where the quantity of cargo to be transported requires only a ship able to carry 35 000 tonnes or less. Handymax bulkers: The trend is for each category of bulker to increase in size, and some commentators now consider the larger handy-sized bulkers, in the 35 000 to 50 000 tonnes range, to be a separate category, the handy-max bulker. Panamax bulkers: Larger than the handy-sized vessel is the Panamax bulk carrier, so named because she is designed to the maximum dimensions (particularly the maximum breadth) which can pass through the Panama Canal. The limiting dimensions for canal transit are Loa 289.5 m, extreme breadth 32.2 m and maximum draught 12.04 m. The typical tonnage range is 50 000 to 100 000 tonnes. Panamax bulkers are extensively employed in the transport of large volume bulk cargoes such as coal, grain, bauxite and iron ore in the long haul trades. Cape-sized bulkers: Cape-sized bulk carriers have dead weights in the range of 100 000 to 180 000 tonnes. While most lie within the range of 100 000 to 140 000 tonnes, new-building in recent years have been DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.1. General – Page 6 concentrated in the 140 000 to 180 000 tonnes range. Cape-sized vessels, with loaded draughts usually in excess of 17 m can be accepted fully laden at only a small number of ports world-wide and are engaged in the long haul iron ore and coal trades. The range of ports which they visit is increased by the use of two port discharges, the ship being only part laden on reaching the second discharge port. Very Large Bulk Carriers (VLBCs): VLBCs are bulkers greater than 180 000 tonnes dead weight. These are mainly employed on the Brazil/Europe and the Australia/Japan routes. 1.2.2 In light of the variety both in cargoes, vessel size, hold arrangement and not least the trading routes, including multi port loading and discharging it is evident that the masters and officers of such vessels, will be in great need of information about relevant loading limitations of the vessel, such as: — maximum allowable/minimum required mass in each individual hold as a function of draught — maximum allowable/minimum required mass in two (or more) adjacent holds. i.e. block loading as a function of draught — maximum allowable mass on deck and hatch cover loading — allowable container loading arrangement both in holds and on deck/hatch cover — maximum allowable tank top pressure (steel coil loading) — still water bending moment and shear force limitations — still water torsion moment limitations. In Sec.1.2.3 and 1.2.4 the most important local load limitations and those most frequently not adhered to have been highlighted. 1.2.3 In order to exemplify the need for information about limitations related to the maximum allowable mass in each individual hold we have described below two situations in which the master may decide to place an excessive tonnage of cargo in a particular hold. — Many bulk carriers load iron ore in ports, which are located within the tropical zone (Brazil, Australia, West Africa, India). When such vessels are loaded to tropical marks, and take only small quantities of bunkers, the total cargo tonnage carried will be substantially (5 to 10%) larger than the standard loading shown in the loading manual. In this situation each alternately loaded hold is likely to be overloaded by tonnage approaching 5 to 10%. — When a ship is asked to load two or more different grades or consignments of ore (e.g. fines and pellets) it is sometimes necessary to juggle with the quantities in each hold, to take account of draught, trim and longitudinal strength at each stage in the voyage. In these circumstances it is easy to decide to load an excessive tonnage in one or several holds, if the maximum permitted tonnage is not prominently displayed and well known aboard ship. 1.2.4 In recent years there has been reported structural damages in which there are reason to believe that incorrect adjacent hold loading, (block loading), has caused such structural damages. The reason for such maloperation is not easy to explain exactly; however, below we have indicated some arguments which should be sufficient to justify the need for proper instruction for such load limitations. — there are reasons to believe that the vast majority of ship operators and ships’ personnel are completely unaware that adjacent hold loading (block loading) can cause problems — a ship can be incorrectly block loaded without creating excessive hull girder shear forces or bending moments, so there is normally no evidence to warn the ship’s officer that his loading may cause damage — adjacent hold loading (block loading) is likely to be considered as a method of loading when several grades of ore are to be loaded, or several consignments of cargo carried, and has recently been used increasingly, for a third reason. In order to cope with the above need for information a procedure for calculating the necessary cargo hold load limitations is given in Sec.7. 1.3 Procedure This classification note describes methods for performing calculations with respect to structural strength of bulk carriers with conventional design. The calculations are based on requirements given in Rules for Classification of Ships. For vessels with notation NAUTICUS(Newbuilding), it is required that FEM analysis is carried out, while for other vessels beam analysis may be acceptable. The flow chart in Fig.1-1 gives an overview of the applicable chapters depending on the method of calculation. The chapters are briefly described in the following: Sec.2. Design Loads, gives description or references to the applicable local loads, like sea pressure and pressure from cargo. Sec.3. Loading Conditions, gives a description of applicable loading conditions. The conditions described in DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.1. General – Page 7 detail here are normally covering all relevant conditions for a typical design of bulk carriers. Some conditions represent the Rule minimum loading while others represent the extreme loading conditions as defined in the loading manual. Steel coil loading and container loading are to be evaluated separately. Sec.4. Cargo Hold Analysis, gives a description of an acceptable procedure for Finite Element Analysis for bulk carriers. It is here focused on extent of model, the structure that shall be included, boundary conditions, mesh topology and results that shall be evaluated. Sec.5. Local Structure, Analysis gives a description of how to perform Finite Element Analysis of local structures of bulk carriers. Sec.6. Flooding Conditions, gives a description of additional requirements for vessels where this is applicable. These requirements ascribe from unified rules given by IACS (International Association of Classification Societies) and are applicable to bulk carriers above 150 meters carrying heavy cargoes with density above 1.0 ton/m3, according to Rules Pt.5 Ch.2 Sec.5 Table A3. Finite element analysis Beam analysis Sec.2 Design loads Sec.3 Load conditions Sec.4 Cargo hold analysis Appendix B Beam modelling general Sec.5 Local structure analysis Sec.6 Flooding conditions Yes Flooding calculations required No Sec.7 Cargo hold load limitations Sec.8 Torsional stress calculations Sec.9 Shear force correction Figure 1-1 Flowchart of applicable sections in this Classification Note depending of calculation method Sec.7. Cargo Hold Limitations, gives a procedure for preparation of local load diagrams for individual holds and for any two adjacent holds. Such limitations do generally define maximum allowable and minimum required mass as a function of the vessel draught. Sec.8. Wave Torsion induced Bending Stresses gives a method to calculate torsion induced stresses. Sec.9. Shear force correction, describes the method and background for shear force corrections. Appendix A, Checklist for FE Analysis, gives checklists related to modelling of Finite Element Models. The checklists are suitable for verification of the model. Appendix B, Beam Modelling, gives a description of acceptable methods for performing structural strength calculations by use of 2- or 3-dimensional beam models for bulk carriers. 1.4 Definitions 1.4.1 Symbols not mentioned in the following list are given in connection with relevant formulae. The general symbols may be repeated when additional definition is found necessary in connection with specific formulae. L B = Rule length in m. * = Rule moulded breadth in m. * DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.1. General – Page 8 D T CB V h hdb E go Cw av at σ τ ρ, δ = = = = = = = = = = = Rule moulded depth in m. * Mean moulded summer draught in m. * Block coefficient. * Maximum service speed in knots on draught T. Cargo or ballast head in m. Height of double bottom in m. Modulus of elasticity = 2.06·105 N/mm2 for steel. Acceleration of gravity. go = 9.81 m/s2. Wave coefficient. ** Combined vertical acceleration in m/s2. ** Combined transverse acceleration in m/s2. ** = Normal stress. = Shear stress. * For details see the Rules for Classification of Ships Pt.3 Ch.1 Sec.1. ** For details see the Rules for Classification of Ships Pt.3 Ch.1 Sec.4B. = as given in the Rules for Classification of Ships Pt.3 Ch.1 Sec.4 C. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.1. General – Page 9 1.4.2 The structural terminology adopted in this Note is illustrated in Fig.1-2, showing a typical structural arrangement of a bulk carrier in the midship area. Strength deck plating Top wing tank webframe Hatch coaming Strength deck longitudinal Top wing tank plating vertical strake Top wing tank Top wing tank sloping plating Top wing tank sloping plating longitudial Side longitudinal Side plating CARGO HOLD Main frame Hopper tank sloping plating Inner bottom Hopper tank sloping plating plating longitudinal Double bottom Inner bottom longitudinal girder longitudinal Hopper side webframe Side longitudinal Bilge longitudinal Keel plate Bottom plating Hopper tank Double Bottom bottom tank longitudinal Double bottom floor Cross deck structure Bilge plating Hatch and coaming Hatch and beam Cross deck structure transverse beam Cross deck structure cantilever beam Shedder plate Lower stool diaphragm Upper stool Upper stool bottom plate Corrugated transverse bulkhead Bottom stool top plate Lower stool Inner bottom Double bottom longitudinal girder Figure 1-2 Typical nomenclature for bulk carrier sections in way of cargo hold and transverse bulkhead DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.2. Design Loads – Page 10 2. Design Loads 2.1 General 2.1.1 Design pressure loads applied in direct calculations representing external sea pressure, liquid in tanks and cargo in holds, are to be taken as given in the Rules for Classification of Ships Pt.3 Ch.1 Sec.12. Loads from cargo in holds are further specified in 2.2 to 2.3 in the following. 2.2 Bulk cargo filling part of hold (heavy cargo) 2.2.1 Design pressure: The design lateral pressures with bulk cargo filling partly of hold are in accordance with Rules for Classification of Ships Pt.3 Ch.1 Sec.12 and shall be taken as: P K α δ hc H bf ρ M VHR V0.3H lh = ρ (go + 0.5av) K hc (kN/m2) = sin2α tan2(45 − 0.5 δ) + cos2α, minimum cos α = Angle between panel in question and the horizontal plane in degrees. = Angle of repose. In general to be taken as 20° for light bulk cargo (grain etc.), 25° for cement cargo (associated cargo density 1.3 t/m3) and 35° for heavy bulk cargo (associated cargo density ≥ 1.78 t/ m3). Otherwise it is to be taken as 30°. = Assumed height of cargo surface above the inner bottom in hold, see the Rules for Classification of Ships Pt.5 Ch.2 Sec.5, see also Fig.2-1. For bulk carriers, it is to be taken as 0.3 H + 0.14 bf within 60% of the middle length and breadth of hold, and linearly reduced to a level 0.3 H at hold sides and to 0.3 H + 0.07 bf at transverse bulkheads. = Height of hold (including hatchway) above plane part of inner bottom in m = Breadth of hold in m at level 0.3 H above inner bottom at hold midlength. = M / VHR, as given in Pt.5 Ch.2 Sec.5 B104. = Mass of cargo in hold, in (t), in accordance with the Rules for Classification of Ships Pt.5 Ch.2 Sec.5. = Volume of cargo hold below the level of hc. Specially for conventional bulk carriers, it may be taken as V0.3H + 0.10267 bf2 lh for regularly shaped cargo holds. For irregularly shaped holds, VHR may be specially considered. = Volume of hold in m3 below level 0.3 H above inner bottom. = Length of hold above lower stool in m, measured to the middle of corrugation depth. See also Fig.2-1. H 0.6 bf 0.14 bf hc 0.3 H bf 0.6 lh 0.07 bf hc lh Figure 2-1 Cargo distribution filling part of cargo hold of bulk carriers DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.2. Design Loads – Page 11 2.2.2 Shear load: A design shear load, ps, has been added in order to obtain the correct total downward force in way of sloping elements i.e. transverse bulkhead stools and hopper tank construction, corresponding to the cargo mass, see also Fig.2-2. The shear load, ps acting on sloping parts of bulkheads is to be taken as: ( 1 – K )h c p s = ρ ( g o + 0.5a v ) ----------------------tan α 2 ( kN ⁄ m ) ρ, α, K, hc = as given in 2.2.1. Ps2 Ps2 2 2 Ps1 Ps1 1 Figure 2-2 Cargo shear load on sloping elements 2.3 Bulk cargo expanded to fill hold 2.3.1 Design pressure: The below pressure distribution assumes that the hold is filled completely up to the top of hatch coaming with bulk cargo. The mass in the hold is then expanded giving a different definition of hc compared with Ch 2.2. The design lateral pressures are to be taken as: p = ρ (go + 0.5av) K hc (kN/m2) K = As defined in Sec.2.2.1. hc = Vertical distance in m from the load point to the highest point of the hold including hatchway in general. For sloping hopper, lower stool, bulkhead and shipside plating the distance may be measured to the deck level only, unless the hatch coaming is in line with or close to the panel considered. (Note that sloping hopper, lower stool, bulkhead and shipside may be taken to be close to the hatch coaming when it is less than 10° out of line from the vertical when measured from the deck, see also Fig.2-3.) Pressure on overhang structure like sloping topwing tank and upper stool may be disregarded. ρ = M/VH, as given in Pt.5 Ch.2 Sec.5 B104. M = Mass of cargo in hold (t). Defined as the mass, according to the loading manual, combined with the corresponding angle of repose that gives the largest nominal lateral pressure on the bulkhead. This is expressed by the largest effective lateral mass, ME, where ME = M tan2 (45 – 0.5δ). ME is not to be less than 0.43 VH, which correspond to a cargo density of 0.88 t/m3 and an angle of repose of 20°. Ref the Rules for Classification of Ships Pt.5 Ch.2 Sec.5 B104 and B203. VH = Cargo hold volume including hatch in m3. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.3. Design Loading Conditions – Local Strength – Page 12 h h 10o Load points Figure 2-3 Design load pressure height for cargo bulkhead 2.3.2 Design shear load: The design shear load, ps, described in 2.2.2, is to be applied for sloping parts of bulkheads. 3. Design Loading Conditions – Local Strength 3.1 General 3.1.1 The following definitions apply: TDAM = damaged water line (m) from damage stability calculations. May be assumed equal to ship’s moulded depth D. TLB = shallowest ballast draught (m) in all seagoing loading conditions. Other definitions refer to Ch 7.2. 3.2 Summary for Bulk Carriers 3.2.1 Table 3-1 and 3-2, lists applicable design loading conditions given in the Rules Pt.5 Ch.2 Sec.5 with indication regarding their applicability with respect to typical class notations, structural part and analysis. These design loading conditions are normally covering all relevant loading conditions for a typical bulk carrier design. The design loading conditions cover the Rule “minimum conditions” in which the intention is to ensure sufficient operational flexibility of the vessel, independent of the specified loading conditions. The loading manual may, however, specify loading conditions for the vessel in question, which are not represented in Table 3-2, such as steel coils, container, lumber, non homogenous loading etc. It is therefore of outmost importance that the loading manual is carefully reviewed prior to defining the final design loading conditions. 3.2.2 Flooding conditions applicable for vessels as described in Sec.1.3, are additionally described in Sec.6. The structure is in general not dimensioned by direct calculations for such conditions. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.3. Design Loading Conditions – Local Strength – Page 13 3.2.3 Design loading conditions are further explained in Sec.3.3. Table 3-1 Applicable design loading conditions for bulk carriers LC 1 2 3a 3b 4 5 6a 6b and 6c 7 8 9 10 11 12 13 14 15 16 17 18 Class notations HC-A HC-B HC-C HC-A No MP HC-B No MP HC-C No MP HC-B* X X X 1) X 2) X 1) X 2) X X 3) X X X 4) X 4) X X X X X X X X X X 4) X 4) X X X X X X X X X X 4) X 4) X X X X X 1) X 2) X X 1) X 2) X 3) X X X X 4) X 4) X X X X X X X X X X 4) X 4) X X X X X X X X X X 4) X 4) X X X X X X X X X 4) X 4) X X X X X: Applicable -: Not applicable 1) applicable to ore holds only 2) applicable to empty holds only 3) applicable only when block loading specified in loading manual. Ref. Sec.7.2 4) applicable only when cargo hold(s) is/are designed for ballast in seagoing conditions Table 3-2 Design loading conditions for bulk carriers Explanation of illustrations shown in Table 3-2: 1. Double bottom tanks: If fuel oil tanks - full If water ballast tanks - empty If fuel oil tanks - full If water ballast tanks - full 2. Cargo holds: DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.3. Design Loading Conditions – Local Strength – Page 14 Table 3-2 Design loading conditions for bulk carriers (Continued) 1 2 3 Description Multiport Condition – Any Single Hold Loaded Application Double bottom structure Mainframes Multiport Condition – Any Single Hold Empty Double bottom structure Mainframes Draught 0.67 T Illustration 0.67T HC-A Condition – Double bottom strucLoading Condition ture with Specified Mainframes Holds Empty M 0.83 T MFULL 0.83T T a) T MHD + 0.1MH b) MHD+0.1MH 4 HC-B* Condition– Double bottom struc- Any Single Hold Empty or Loaded ture Mainframes 0.67T and T a) 0.67T 1.2MFULL b) T 5 No MP Condition Double bottom structure Mainframes T a) b) DET NORSKE VERITAS AS 1.2 MFULL Classification Notes - No. 31.1, December 2012 Sec.3. Design Loading Conditions – Local Strength – Page 15 Table 3-2 Design loading conditions for bulk carriers (Continued) 6 Harbour Condition Double bottom structure Mainframes 0.67 T a) 0.67T MHD b) c) 7 8 Multiport and HC- Compression of B* Condition – transverse deck Adjacent Holds Transverse bulkheads Loaded 0.67 T HC-A Condition – T Adjacent Holds Loaded Compression of transverse deck Transverse bulkheads 0.67T T 9 10 11 No MP Harbour Condition – Adjacent Holds Loaded Compression of transverse deck Transverse bulkheads Adjacent Holds Empty cross deck No MP Condition Transverse bulkhead Top wing tank – Adjacent Holds Empty Bulk Cargo With Filled Hold 0.75T Transverse bulkhead lateral strength MFULL 0.75 T MFULL THB THB 12 MHD + 0.1 MH 0.67 T 0.67T Multiport and HC- Transverse bulkhead. Tensile strength of B* Condition – M T T DET NORSKE VERITAS AS MFULL Classification Notes - No. 31.1, December 2012 Sec.3. Design Loading Conditions – Local Strength – Page 16 Table 3-2 Design loading conditions for bulk carriers (Continued) 13 Heavy Ballast Condition Transverse bulkhead Top wing tank THB THB 14 Heavy Ballast – Heeled Condition Hopper tank girders Top wing tank THB THB 15 Ballast in Top Wing Tank Top wing tank construction THB THB 16 Ballast in Top Wing Tank – Heeled Condition Top wing tank construction THB THB 17 Watertight Bulkhead Loading Transverse bulkhead lateral strength TDAM TDAM 18 Cargo on Deck Top wing tank, cross T 1) deck cantilevers, hatch end and side coamings Note: 1) When load restriction on upper deck in the loading manual is clearly specified, the actual draught for the corresponding loading condition may be used instead of the scantling draught T. 3.3 Design Loading Conditions for Bulk Carriers 3.3.1 LC1 – Multiport Condition – Single Hold Loaded 3.3.1.1 LC1 is applicable for class notations HC-A, HC-B, and HC-C. 3.3.1.2 Any cargo hold is to be capable of carrying M at 67% of maximum draught (0.67T), where, M = MFULL (in loaded hold) 3.3.1.3 Fuel oil tanks in double bottom in way of the loaded cargo hold, if any are to be full, and ballast water tanks in the double bottom in way of the loaded cargo hold are to be empty. All double bottom tanks in way of the empty cargo hold are to be empty. 3.3.1.4 The cargo mass and sea pressure load is to be in accordance with Sec.2.1 and Sec.2.2, with density ρ=M/VHR. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.3. Design Loading Conditions – Local Strength – Page 17 3.3.1.5 This loading condition is applied primarily for the strength evaluation of the double bottom structure. Note that the double bottom strength shall be evaluated on the basis of allowable hull girder still water bending moment. It may however also be decisive for the side frame ends, if rotation of hopper/top wing tank construction becomes significant. 3.3.2 LC2 –Multiport Condition – Single Hold Empty 3.3.2.1 LC2 is applicable for class notations HC-A, HC-B and HC-C. 3.3.2.2 Any cargo hold is to be capable of being empty, with the next cargo holds carrying M, at 83% of maximum draught (0.83 T), where, M = MFULL (in loaded hold) 3.3.2.3 Fuel oil tanks in double bottom in way of the loaded cargo hold, if any are to be full, and ballast water tanks in the double bottom in way of the loaded cargo hold are to be empty. All double bottom tanks in way of the empty cargo hold are to be empty. 3.3.2.4 The cargo mass and sea pressure load is to be in accordance with Sec.2.1 and Sec.2.2, with density ρ = M/VHR. 3.3.2.5 This loading condition is applied primarily for the strength evaluation of the double bottom structure. Note that the double bottom strength shall be evaluated on the basis of allowable hull girder still water bending moment. It may however also be decisive for the side frame ends, if rotation of hopper/top wing tank construction becomes significant. 3.3.3 LC3 – HC-A Condition 3.3.3.1 LC3 is applicable for class notations HC-A and HC-A No MP, and is to cover a loading condition with specified holds empty. In LC3a, the midhold is ore hold. In LC3b, the midhold is empty hold. 3.3.3.2 In LC3a, ore holds, are to be capable of carrying M at maximum draught (T), and in LC3b, empty holds are to be capable of being empty with the next cargo holds carrying M, where, M = MHD + 0.1MH (in loaded hold) 3.3.3.3 Fuel oil tanks in double bottom in way of the loaded cargo hold, if any are to be full, and ballast water tanks in the double bottom in way of the loaded cargo hold are to be empty. All double bottom tanks in way of the empty cargo hold are to be empty. 3.3.3.4 The cargo mass and sea pressure load is to be in accordance with Sec.2.1 and Sec.2.2, with density ρ = M/VHR. 3.3.3.5 A specified reduced allowable hull girder still water bending moment may be applied for the alternative loading condition with empty holds. The limit is defined by the maximum bending moment in hogging and sagging (= 0.5 MSO as given in Pt.3 Ch.1 Sec.5 B), minimum occurrence for these loading conditions, unless higher limits are specified to be used. 3.3.3.6 This loading condition is applied primarily for the strength evaluation of the double bottom structure. Note that the double bottom strength shall be evaluated on the basis of allowable hull girder still water bending moment. It may however also be decisive for the side frame ends, if rotation of hopper/top wing tank construction becomes significant. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.3. Design Loading Conditions – Local Strength – Page 18 3.3.4 LC4 – HC-B* Condition 3.3.4.1 LC4a and LC4b are applicable for class notations HC-B*. 3.3.4.2 In LC4a, any cargo hold is to be capable of carrying M at 67% of maximum draught (0.67T), where, M = 1.2MFULL (in loaded hold) In LC4b, any cargo hold is to be capable of being empty with the next cargo holds carrying M, at maximum draught (T), where, M = 1.2MFULL (in loaded hold) 3.3.4.3 Fuel oil tanks in double bottom in way of the loaded cargo hold, if any are to be full, and ballast water tanks in the double bottom in way of the loaded cargo hold are to be empty. All double bottom tanks in way of the empty cargo hold are to be empty. 3.3.4.4 The cargo mass and sea pressure load is to be in accordance with Sec.2.1 and Sec.2.2, with density ρ = M/VHR. 3.3.4.5 This loading condition is applied primarily for the strength evaluation of the double bottom structure. Note that the double bottom strength shall be evaluated on the basis of allowable hull girder still water bending moment. It may however also be decisive for the side frame ends, if rotation of hopper/top wing tank construction becomes significant. 3.3.5 LC5 – No MP Condition 3.3.5.1 LC5a and LC5b are applicable for the class notations HC-A No MP, HC-B No MP and HC-C No MP, i.e. vessels which have not been designed for loading and unloading in multiple ports. 3.3.5.2 Any single cargo hold is to be capable of carrying M at maximum draught (T), where M = MFULL (in full hold) and the less of M = 0.5 MH (in slack hold) = 1.025 l b (T - THB) (in slack hold) 3.3.5.3 Fuel oil tanks in double bottom in way of the loaded cargo hold, if any are to be full, and ballast water tanks in the double bottom in way of the loaded cargo hold are to be empty. All double bottom tanks in way of the empty cargo hold are to be empty. 3.3.5.4 The cargo mass and sea pressure load is to be in accordance with Sec.2.1 and Sec.2.2, with density ρ = M/VHR. 3.3.5.5 This loading condition is applied primarily for the strength evaluation of the double bottom structure. Note that the double bottom strength shall be evaluated on the basis of allowable hull girder still water bending moment. It may however also be decisive for the side frame ends, if rotation of hopper/top wing tank construction becomes significant. 3.3.6 LC6 – Harbour Condition 3.3.6.1 LC6a is applicable for class notation HC-A and HC-A No MP. The midhold is ore hold. LC6b and LC6c are applicable for class notations HC-A No MP, HC-B No MP and HC-C No MP, i.e. vessels which have not been designed for loading and unloading in multiple ports. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.3. Design Loading Conditions – Local Strength – Page 19 3.3.6.2 For HC-A and HC-A No MP notations, LC6a, any single cargo hold is to be capable of carrying maximum allowable seagoing mass M at 67% of maximum draught (0.67 T) where M = MHD (in loaded hold) and for HC-A No MP, HC-B No MP and HC-C No MP notations, LC6b and LC6c, where M = MFULL (in loaded hold) and the lesser of M = 0.5 MH − 1.025 l b 0.33 T − 0.15 MFULL (in slack hold) = 1.025 l b (0.67 T − THB) − 0.15 MFULL (in slack hold) = minimum 0 3.3.6.3 Fuel oil tanks in double bottom in way of the loaded cargo hold, if any are to be full, and ballast water tanks in the double bottom in way of the loaded cargo hold are to be empty. All double bottom tanks in way of the empty cargo hold are to be empty. 3.3.6.4 The cargo mass and sea pressure load is to be in accordance with Sec.2.1 and Sec.2.2 without dynamic values, with density ρ = M/VHR. 3.3.6.5 This loading condition is applied primarily for the strength evaluation of the double bottom structure. Note that the double bottom strength shall be evaluated on the basis of allowable hull girder still water bending moment. It may however also be decisive for the side frame ends, if rotation of hopper/top wing tank construction becomes significant. 3.3.7 LC7 – Multiport and HC-B* Condition – Adjacent Holds Loaded 3.3.7.1 LC7 is applicable for class notations HC-A, HC-B, HC-C and HC-B*. 3.3.7.2 Any two adjacent cargo holds are to be capable of carrying M at 67% of maximum draught (0.67 T), where, M = MFULL (in loaded hold for HC-A, HC-B and HC-C) = 1.1 MFULL (in loaded hold for HC-B*) 3.3.7.3 Fuel oil tanks in double bottom in way of the loaded cargo hold, if any are to be full, and ballast water tanks in the double bottom in way of the loaded cargo hold are to be empty. All double bottom tanks in way of the empty cargo hold are to be empty. 3.3.7.4 The cargo mass and sea pressure load in any cargo hold is to be in accordance with Sec.2.1 and Sec.2.2, with density ρ = M/VHR. 3.3.7.5 This loading condition is applied primarily for the compression strength of the transverse deck structure between hatches and for the shear strength of the transverse bulkheads. Note that the double bottom strength shall be evaluated on the basis of allowable hull girder still water bending moment. 3.3.8 LC8 – HC-A Condition – Adjacent Holds Loaded 3.3.8.1 LC8 is applicable for class notation HC-A and HC-A No MP, if two adjacent cargo holds, which according to a design loading condition may be loaded with the next hold being empty. 3.3.8.2 Any two adjacent cargo holds are to be capable of carrying 10% of MH in each hold in addition to the maximum cargo load according to that design loading condition, at maximum draught (T), where, M = based on MHD, adj + 0.1MH, adj (in loaded hold,) DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.3. Design Loading Conditions – Local Strength – Page 20 3.3.8.3 Fuel oil tanks in double bottom in way of the loaded cargo hold, if any are to be full, and ballast water tanks in the double bottom in way of the loaded cargo hold are to be empty. All double bottom tanks in way of the empty cargo hold are to be empty. 3.3.8.4 The cargo mass and sea pressure load in any cargo hold is to be in accordance with Sec.2.1 and Sec.2.2, with density ρ = M/VHR. 3.3.8.5 This loading condition is applied primarily for the compression strength of the transverse deck structure between the hatches and for the shear strength of the transverse bulkheads. Note that the double bottom strength shall be evaluated on the basis of allowable hull girder still water bending moment. 3.3.9 LC9 – No MP Harbour Condition – Adjacent Holds Loaded 3.3.9.1 LC9 is applicable for class notations HC-A No MP, HC-B No MP and HC-C No MP, i.e. vessels which have not been designed for loading and unloading in multiple ports. 3.3.9.2 Any two adjacent cargo holds are to be capable of carrying MFULL at 67% of maximum draught (0.67 T), where, M = MFULL (in loaded hold) 3.3.9.3 Fuel oil tanks in double bottom in way of the loaded cargo hold, if any are to be full, and ballast water tanks in the double bottom in way of the loaded cargo hold are to be empty. All double bottom tanks in way of the empty cargo hold are to be empty. 3.3.9.4 The cargo mass and sea pressure load is to be in accordance with Sec.2.1 and Sec.2.2 without dynamic values, with density ρ = M/VHR. 3.3.9.5 This loading condition is applied primarily for the compression strength of the transverse deck structure between hatches and for the shear strength of the transverse bulkheads. Note that the double bottom strength shall be evaluated on the basis of allowable hull girder still water bending moment. 3.3.10 LC10 – Multiport and HC-B* Condition – Adjacent Holds Empty 3.3.10.1 LC10 is applicable for class notations HC-A, HC-B, HC-C, and HC-B*. 3.3.10.2 Any two adjacent cargo holds are to be capable of being empty at 75% of maximum draught (0.75 T), where, M = MFULL (in loaded hold) 3.3.10.3 Fuel oil tanks in double bottom in way of the loaded cargo hold, if any are to be full, and ballast water tanks in the double bottom in way of the loaded cargo hold are to be empty. All double bottom tanks in way of the empty cargo hold are to be empty. 3.3.10.4 The cargo mass and sea pressure load is to be in accordance with Sec.2.1, Sec.2.2, with density ρ=M/VHR. 3.3.10.5 This loading condition is applied primarily for the tensile strength of the cross deck between the hatches and for the shear strength of the transverse bulkheads. Note that the double bottom strength shall be evaluated on the basis of allowable hull girder still water bending moment. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.3. Design Loading Conditions – Local Strength – Page 21 3.3.11 LC11 – No MP Condition – Adjacent Holds Empty 3.3.11.1 LC11 is applicable for class notations HC-A No MP, HC-B No MP and HC-C No MP, i.e. vessels which have not been designed for loading and unloading in multiple ports. 3.3.11.2 Any two adjacent cargo holds are to be capable of being empty at deepest ballast draught (THB), where, M = MFULL (in loaded hold) 3.3.11.3 Fuel oil tanks in double bottom in way of the loaded cargo hold, if any are to be full, and ballast water tanks in the double bottom in way of the loaded cargo hold are to be empty. All double bottom tanks in way of the empty cargo hold are to be empty. 3.3.11.4 The sea pressure load is to be in accordance with Sec.2.1 and Sec.2.2, with density ρ = M/VHR. 3.3.11.5 This loading condition is applied primarily for the tensile strength of the cross deck between the hatches and for the shear strength of the transverse bulkheads. Note that the double bottom strength shall be evaluated on the basis of allowable hull girder still water bending moment. 3.3.12 LC12 – Bulk Cargo With Filled Hold Condition 3.3.12.1 LC12 is applicable to all bulk carriers. 3.3.12.2 Any transverse bulkhead is to be capable of withstand lateral pressure due to M, where, M = MHD + 0.1MH = MFULL = 1.2MFULL (HC-A) (HC-B or HC-C) (HC-B*) 3.3.12.3 The cargo pressure is to be taken according to Sec.2.3 and the sea pressure according to Sec.2.1. The draught is to be taken at maximum draught (T). 3.3.12.4 The load condition is applicable primarily for the transverse bulkhead structure including stool diaphragm plates and in-line shear plates inside double bottom and for local design of the hopper tank. 3.3.13 LC13 – Heavy Ballast Condition 3.3.13.1 LC13 shall be considered if ballast in holds has been specified for the vessel. 3.3.13.2 Cargo holds, which are designed as ballast holds, are to be capable of being full of ballast water including hatchways, with all double bottom tanks being filled, at heavy ballast draught (THB). If data for the ballast draught are not available, the draught may be taken as 0.45T. 3.3.13.3 The ballast and sea pressure load is to be in accordance with Sec.2.1. Load from ballast pressure acting on the hatch cover shall be included as appropriate. 3.3.13.4 This loading condition is applied primarily for the strength evaluation of the transverse bulkhead and for hopper and top wing tank structures, in addition to the double bottom structure of the ballast hold. Note that the double bottom strength shall be evaluated on the basis of allowable hull girder still water bending moment. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.3. Design Loading Conditions – Local Strength – Page 22 3.3.14 LC14 – Heavy Ballast – Heeled Condition 3.3.14.1 LC14 is similar to LC13, and shall be considered if ballast in holds has been specified for the vessel. 3.3.14.2 The ballast and sea pressure load is to be taken according to the Rules Pt.3 Ch.1 Sec.12 for heeled condition. Load from ballast pressure acting on the hatch cover shall be included as appropriate. 3.3.14.3 This loading condition is applied primarily for the top wing tank structure adjacent to the ballast hold, side structure and local scantlings of the transverse bulkhead. 3.3.15 LC15 – Ballast in Top Wing Tank 3.3.15.1 LC15 is applicable for bulk carriers with top wing tank. 3.3.15.2 Top wing tanks are to be filled, with adjacent top wing tanks being empty; draught may be taken according to the heavy ballast draught (THB) when considered relevant. 3.3.15.3 The sea pressure loads may normally be disregarded in this condition, but the ballast pressure load is to be taken in accordance with Sec.2.1. 3.3.15.4 The intention of this condition is to check the top wing tank structure only. Consequently, application of a realistic pressure distribution on the double bottom construction is not necessary. 3.3.16 LC16 – Ballast in Top Wing Tank – Heeled Condition 3.3.16.1 LC16 is similar to LC15, and is applicable for bulk carriers with top wing tank. 3.3.16.2 The ballast pressure load is to be taken according to the Rules Pt.3.Ch.1 Sec.12 for heeled condition. 3.3.16.3 The intention of this condition is to check the top wing tank structure only. Consequently, application of a realistic pressure distribution on the double bottom construction is not necessary. 3.3.17 LC17 – Watertight Bulkhead Loading 3.3.17.1 LC17 is intended to ensure that the watertight subdivision is maintained in case of an emergency flooding. 3.3.17.2 Flooded sea water load is to be according to the Rules, Pt.3 Ch.1 Sec.9 B, with filling of the hold up to the damaged waterline. 3.3.17.3 The sea pressure load may be taken at a draught equal to the damaged waterline, TDAM. Further design criteria are given in the Rules, Pt.3 Ch.1 Sec.9. 3.3.17.4 This loading condition is generally applicable for watertight bulkhead structures including stool diaphragm plates and in-line shear plates inside double bottom. 3.3.18 LC18 – Cargo on Deck 3.3.18.1 LC18 is applicable for bulk carriers with a distinct top wing tank arrangement, where a deck cargo loading capacity has been specified. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.3. Design Loading Conditions – Local Strength – Page 23 3.3.18.2 Forces due to specified cargo load on hatches should be included in the consideration, ref. Rules Pt.3 Ch.1 Sec.4 C. 3.3.18.3 The sea pressure load is to be in accordance with Sec.2.1, at full draught (T). When load restriction on upper deck in the loading manual is clearly specified, the actual draught for the corresponding loading condition may be used instead of the scantling draught T. 3.4 Fatigue Loads 3.4.1 In order to include stresses caused by relative deflection in the fatigue assessment of longitudinals, dynamic load cases as specified in Table 3-3 are to be applied to the cargo hold model for bulk carriers. The results from these load cases may also be used for fatigue assessment of other structural parts e.g. hopper knuckles. The external and internal dynamic pressures are to be calculated according to Classification Note 30.7 “Fatigue Assessment of Ship Structures”. It is emphasised that this is pure dynamic load cases for evaluation of the structures fatigue life. The static part is therefore not included in this chapter. However, static load cases for alternate full load sea, homogeneous full load sea and ballast sea as applicable shall be used to calculate the mean stress factor. Further procedure for fatigue calculations is given in the Classification Note 30.7. Table 3-3 Dynamic load cases for bulk carriers LC Description Draught External Internal pressure pressure Full Dynamic - F1 Alternate Full Load Sea F2 Alternate Full Full Load Sea F3 Homogenous Full Load Sea Full Dynamic - F4 Homogenous Full Load Sea Full - F5 Ballast Sea Normal Dynamic ballast F6 Ballast Sea Normal ballast - Illustration Dynamic Dynamic Dynamic DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.4. Cargo Hold Analysis – Page 24 4. Cargo Hold Analysis 4.1 General 4.1.1 This chapter gives guidance on how to perform finite element calculations for the girder system within the midship area of bulk carriers. 4.1.2 In general the finite element model shall provide results suitable for evaluating the strength of the girder system and for performing buckling analysis of plate flanges and girder webs. This may be done by using a 3D finite element model of the midship area. Several approaches may be applied; ranging from a detailed 3Dmodel of the cargo holds to a coarse mesh 3D-model, supported by finer mesh sub models. Coarse mesh models can be used for calculating deformations and stresses typically suited for buckling control. The deformations may be applied as boundary conditions on sub models for finding the stress level in more detail. The same principles may normally be used on structures outside the midship area but within the cargo area, provided special precautions are taken regarding model extent and boundary conditions. 4.1.3 Fig.4-1 shows a typical 3D-model of a conventional bulk carrier. Whichever approach is used, the model or set of models applied shall give a proper presentation of the following structure: — Typical web frames in hopper and top wing tanks or wing tanks, including floors and mainframes at midhold in midship area — Typical corrugation section of transverse bulkhead with connection to upper and lower stool — Transverse section in way of pipe duct in line with the lower transverse bulkhead stool side — Typical stringer in double side tanks or wing tanks — Typical longitudinal girder in double bottom. In the model description and examples given in the following all these structures are included in one 3D-model of the cargo hold for evaluating the results in these areas directly. This implies that the “cargo hold analysis” and “frame and girder analysis”, in the Rules for Classification of Ships Pt.3 Ch.1 Sec.12 are combined into one model. 4.1.4 In addition, analyses of local structure can be made for determining the detailed stress level in stiffeners subject to large relative support deflections. Such analyses are described in Sec.5 “Local structure analysis”. It is emphasised that this represents one acceptable approach for performing such calculations, and that alternative methods may be equally applicable. Figure 4-1 Example of a 3D-model of a conventional bulk carrier 4.2 Model Extent 4.2.1 General: The extent of the model does in general depend on the structure and the loading conditions, and whether these are symmetric in the longitudinal and transverse direction. The extent of the recommended model is visualized in Table 4-1. 4.2.2 Transverse extent: Normally the structure is symmetric in the transverse direction while the load pattern in the heeled condition, LC14, is not symmetric. This implies that a full breadth model should be made: DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.4. Cargo Hold Analysis – Page 25 For vessels without symmetry about centreline with respect to structure or loads, the analysis model amidships should comprise full breadth of the model. However, even for the heeled condition a half breadth model may be satisfactory if due concern is shown to boundary conditions and their influence of the results in the structure. In the examples in the following, a full breadth model is applied. 4.2.3 Longitudinal extent: Often the transverse bulkheads with upper and lower stools stool are not symmetric in the longitudinal direction. In order to represent this correctly the model must have an extent including one full length cargo hold: For vessels without symmetry about the transverse bulkhead, the analysis model amidships should comprise two hold lengths (½ + 1 + ½). For vessels with symmetry about the transverse bulkhead, the model may be limited to ½ + ½ hold models. 4.3 Modelling of geometry 4.3.1 General model idealisation: All main longitudinal and transverse geometry shall be included in the model. The scantlings shall, according to the Rules for Classification of Ships, be modelled with reduced scantlings; i.e. corrosion addition according to the Rules for Classification of Ships shall be deducted from the actual scantlings. When reduced effectivity of curved flanges is not represented by the model formulation itself, the reduced effectivity shall be defined by assigning reduced thickness of plate elements or cross sectional areas of beam and rod elements. Such reduced effectivity may be calculated as given in the Rules for Classification of Ships Pt.3 Ch.1 Sec.3. Typical structures are: — Curved plate flanges (e.g. bilge plating). — Curved face plates on hopper tank web frame and top wing tank web frame. Half thicknesses shall be applied on plates in symmetry planes on the boundaries of the model. 4.3.2 Girders Free flanges of girders shall be included in the model: In ship structures, openings in the girder webs will be present for access and pipe penetrations. If such cut-outs affect the overall force distribution or stiffness of the girder, the cut-out shall be reflected in the model. This may be done by either; reducing the thickness according to the formula below or by geometrical modelling of the cut-out. The mean girder web thickness may for the first approach be taken as follows: tmean tw hco Ico Figure 4-2 Mean girder web thickness h – hc o t m ea n = ----------------- t w h r co tw = web thickness 1 2 co rco = 1 + ------------------------------2 2.6 ( h – h co ) DET NORSKE VERITAS AS h Classification Notes - No. 31.1, December 2012 Sec.4. Cargo Hold Analysis – Page 26 lco = length of cut-out hco = height of cut-out h = height of girder web When rco is larger than 1.2, (rco > 1.2), it is advised that the cut-out is included in the model in one of the two ways given above. When rco is larger than 2, (rco > 2), it is advised that the cut out is geometrically included in the model. Smaller openings for access and piping may be ignored. However, when such openings are ignored this must be considered when evaluating the results see Sec.4.8.2. 4.3.3 Stiffeners: Continuous stiffeners oriented in the direction of the girders contribute to the overall bending stiffness of the girders and shall be included in the model in such a way that the bending stiffness of the girder is correctly modelled. Non-continuous stiffeners may be included in the model as beam element with reduced effectivity. Sectional area of such stiffeners may be calculated as follows: Sniped at both ends Sniped at one end Connected at both ends 30% of actual area 70% of actual area 100% of actual area Stiffeners on girders perpendicular to the flanges may be included in the model when considered important, alternatively by transferring them to the nearest nodes instead of introducing additional nodes. Buckling stiffeners considered less important for the stress distribution, as sniped buckling stiffeners, may be ignored. 4.3.4 Corrugated bulkhead and stools: Corrugated bulkheads shall be included in the model. Slanted plates (shedder plates) shall, if present, be included in the model as they transfer loads from the flange of the corrugations to the opposite side of the stool. Normally it is difficult to match the mesh from the corrugations directly with the mesh from the stool, so a practical approach is to adjust the mesh of the stools in to the corrugations. The corrugations will then have their true geometrical shape. Diaphragms in the stools and vertical stiffeners on the stool side plating are to be included in the model. It is proposed to use one or two 4-noded element over the depth of the corrugation web. This model formulation gives a good representation of the response of the corrugated bulkhead provided supporting brackets are fitted in line with the corrugations. Modelling of these brackets does normally not change the load transfer from the corrugations to the stool significantly as the vertical flanges are well supported by the vertical or slanted stool plate. Such brackets do therefore not have to be included in a cargo hold analysis due to the fact that finite elements tends to transmit forces more than the real structure through the nodes sheared by the neighbouring elements. The calculated response for designs without such brackets should however be adjusted to represent the reduced efficiency of the web. Alternatively, a model with a fine element mesh, or a separate evaluation, may be used. 4.3.5 Main frames, supporting brackets and connected longitudinals: The cargo hold model shall give a proper representation of deflection of mainframes. In order to achieve this, the mainframes, the supporting brackets in the hopper tank and top wing tank and the connected longitudinals must be represented in the model. A practical approach is to include all the mainframes in the model. In order to evaluate the mainframes, supporting bracket and connected longitudinals, in detail, a fine mesh model must be made. 4.3.6 Hatch coamings, hatch corners and hatches: The hatch coamings shall be included in the model. When it is necessary to evaluate the strength of hatch corners a separate fine meshed model must be made. Hatch covers shall not be included in the model. Unless load conditions including torsional loading of the hull girder is included, the results in these areas will be limited to stress concentrations mainly caused by global hull girder forces. In such cases these forces must be applied to the model. 4.4 Elements and Mesh Size 4.4.1 General: The performance of the model is closely linked to the type-, shape- and aspect ratio of elements, and the mesh topology that is used. The mesh described here is adequate for representing the cargo hold model and frame and girder model as defined in the Rules for Classification of Ships Pt.3 Ch.1 Sec.12. The following guidance on mesh size etc. is based on the assumption that 4-noded shell or membrane elements in combination with 2-noded beam or truss elements are used. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.4. Cargo Hold Analysis – Page 27 Higher order elements such as 8-noded or 6-noded elements with a coarser mesh than described below may be used provided that the structure and the load distribution are properly described. In general the mesh size should be decided on the basis of proper stiffness representation and load distribution of tank and sea pressure on shell- or membrane elements. 4.4.2 Plating: 4-noded shell or membrane elements may be used in connection with mesh size as described below. 3-noded shell or membrane elements with constant strain shall normally not be used. It may however be used to a limited extent for avoiding poor mesh transitions. The element mesh should preferably represent the actual plate panels between stiffeners so that the stresses for the control of yield and buckling strength can be read and averaged from the results without interpolation or extrapolation. In practise, the following may be applied: — there should be minimum three elements over the height of girders. The mesh should in general and as far as practical follow the stiffener system on the girder. For main frames, one element over the web height is acceptable. See Fig.4-3. — one, two or three elements between transverse girders. By using three elements it normally matches with the mainframes. Some local stiffener bending will be included in the results. See comments given in Sec.4.8. Flanges on brackets shall not be connected to the plating, in order to simulate the snipped flange at bracket toe. This applies also to main frame lower and upper end brackets. See Fig.4-4. — one element between longitudinals. See Fig.4-3 and 4-4. This contributes to a correct load transfer from the longitudinal to the transverse frame. — inside hopper tank, top wing areas and wing tanks the mesh are normally limited by the longitudinals in surrounding structures. The mesh should follow the stiffener system on transverse girder webs as far as practicable. The mesh should be fine enough to represent the shape of large openings in the web frame inside the hopper tank. See Fig.4-3 and 4-4. — one element or more on each web and flange on the corrugations in corrugated bulkheads. Two elements are suggested. This is satisfactory for determining the stress level in the bulkhead. An example of mesh on corrugated bulkheads is shown in Fig.4-5. See also Sec.4.3.4. Figure 4-3 Mesh on transverse webframe of a bulk carrier DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.4. Cargo Hold Analysis – Page 28 Flange not to be connected to the plating Figure 4-4 Mesh on lower bracket of main frame in single side skin bulk carriers Figure 4-5 Mesh on corrugated transverse bulkhead of a bulk carrier 4.4.3 Longitudinals and stiffeners: Longitudinals and other continuous stiffeners should be included in the model. These are preferably to be represented by 2-noded eccentric beam elements. If the program used can not consider eccentricity of profiles, precautions shall be taken so that the model gives the correct section modulus for double and single skin structures. However, axial area and shear area of such stiffeners should only represent the profile without the plate flange. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.4. Cargo Hold Analysis – Page 29 Lower stool Beam element Beam element "Overlap Figure 4-6 Overlap of beam elements and shell elements Special attention should be paid when connecting a beam element to one node of a shell or membrane element. The end of the beam elements may then be assumed as hinged in the calculation. This will affect the load distribution. The mentioned effect may be avoided by an overlap between the beam and shell elements. See Fig.4-6. Other stiffeners including buckling stiffeners and free flanges of girders may be modelled as 2-noded beam- or truss elements with effective cross sectional areas calculated according to the Rules. Curved flanges are to be represented with their true effectivity in the model. Stiffeners inside stools may in general be represented by beam elements or alternatively by shell or membrane elements. 4.5 Boundary Conditions 4.5.1 Boundary conditions for the application of local load Symmetric boundary conditions are in general to be applied at the ends of the model. If half breadth models are used, symmetry shall be applied along the centreline of the model. The model may be supported in vertical direction by applying vertical springs in the vertical direction at the line forming the intersection between side and transverse bulkhead. Bulk carriers with double side shall be additionally supported by vertical springs at the intersection between inner side and transverse bulkheads. The spring constant may be calculated as follows, ignoring the effect of bending deflection: K= 8 ASi E 7.8 ⋅ 3lh ASi = shear area for side, inner side or longitudinal bulkhead lh = length of one cargo hold. Alternatively, vertical forces applied in the same intersections may be applied. The model must then be restrained from rigid body translation in the vertical direction. Boundary conditions for the application of local loads for bulk carriers of ordinary design are given in Table 4-1, applying symmetry conditions in one end and, symmetry and linear dependency in the other end. These boundary conditions introduce a horizontal force applied at one of the ends. The purpose of this force is to compensate for the fictitious compression of the hull girder when the mid hold is empty and the holds fore and aft are full. In order to keep the nodes in “plane A” in one plane, the nodes must be linearly dependent in the longitudinal direction of the point (point c) where the force is applied. The magnitude of the force will vary on each load case but shall in general be equal to the net load on the transverse bulkhead. Line C is defined as the intersection between the vertical part of the side shell and the transverse bulkhead. Point a is the point of intersection between the bottom, centreline and transverse bulkhead. As an alternative, boundary conditions with pure symmetry at the ends (Plane A also fixed in the longitudinal direction) without a counteracting force may be applied. The longitudinal stresses should then be corrected for the mentioned fictitious compression. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.4. Cargo Hold Analysis – Page 30 Table 4-1 Boundary conditions for an ordinary bulk carrier with unsymmetrical stool structure Location z x Line C b Line C Line C y Line C Displacement Rotation δy δz θx θy θz Plane A X X Plane B X X Line C S Point a, b X Point c Fh X = Restricted from displacement or rotation L = Linearly dependant of point c = Free S = Springs FV = Vertical forces. When vertical forces are applied the model must in addition be restricted from translation in the vertical direction by fixing it in one node. Fh = Counteracting horizontal force δx L X a Fh c 4.5.2 Boundary conditions for the application of hull girder loads When hull girder loads, i.e. bending moment and shear forces, are intended applied to the model, it is advised that such loads are applied as separate load cases with separate boundary conditions. The resulting stresses may then be manually superimposed to the relevant stresses from the local load model. The described boundary conditions and load application are summarised in Table 4-2 and Table 4-3. Bending moment - boundary conditions: One end should be restricted as shown in Table 4-2. The other end should be kept plane and the displacements of the plane should be as a rigid body. The latter is necessary to apply the hull girder bending moment. In order to keep the nodes in one plane they are to be linearly dependent of each other as a rigid body. Symmetry conditions along the centreline of the model are to be applied for models covering a half breadth of the ship. Application of hull girder bending moment: In general a bending moment shall be applied to the end of the model. The bending moment at the end may be applied as a force pair acting in the opposite direction applied at two points. The points should be positioned vertically above each other with one point in the deck and one point in bottom. The size of the bending moment shall be such that the vertical hull girder bending moment, as described in the Rules, is achieved in the middle of the model. Some modifications to the size of this bending moment are however necessary. The background for this is that the allowable hull girder bending moment (MS + MW) is based on gross scantlings. The FEM model is based on net scantlings (gross scantling reduced by tk). It is therefore necessary to reduce the Hull girder bending moment by a factor of Zmod / Zgross. Where Zmod is the hull girder section modulus as modelled (i.e gross scantling reduced by the corrosion addition, tk) and Zgross, the hull girder section modulus based on actual scantlings. In addition to this bending moment the local loads will also set up a “semi-global hull girder bending moment” that may be compensated for when applying the bending moment. (It is advised that the loads are adjusted to match the acceptance criteria and not the opposite.) The magnitude of the force pair will be as follows: M F = ----h F = Magnitude of force at points in deck and bottom M = Modified bending moment as described above h = Height from base line to point in deck. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.4. Cargo Hold Analysis – Page 31 Table 4-2 Boundary conditions for bulk carrier cargo hold analysis when hull girder bending moments are applied Location Displacement δy δz L L X X X δx L X θx L X X Rotation θy θz L L X X X Plane A Plane B Centreline (when applicable) Point a,b Fa,b X Fixed. L Rigid body linearly dependent. Force according to the above. Forces actFa,b ing in opposite direction at point a and b. z x y Point a e Fa Forc Fb ce For Point b Shear force - boundary conditions: The boundary conditions are given in Table 4-3. Symmetrical boundary conditions are to be applied at ends. Symmetry conditions along the centreline of the model are to be applied for models covering a half breadth of the ship. For models covering the full breadth of the ship the model must be fixed in the transverse direction at the intersections between the transverse bulkhead and the longitudinal centreline girder at inner bottom. Application of shear forces: The shear forces are to be applied at the outer shell at the ends of the model (Line C and F). The shear forces are to be applied as vertical line loads. The forces are to be distributed according to a shear flow calculation with the forces acting in opposite directions at the two ends as shown in Table 4-3. The magnitude of the shear force shall be such that the maximum allowable shear force is achieved within the model. Springs shall be applied at one end. S, Fv Fv Rotation θy θz X X X X X X θx z x Line F y Line F X Fixed. S Springs. Vertical forces acting in opposite directions at Fv the ends. Line C Plane A Plane B Centreline (when applicable) Line Displacement δx δy δz X X X Line C Location Line F Table 4-3 Boundary conditions for bulk carrier cargo hold analysis when global shear forces are applied 4.6 Loading Conditions 4.6.1 General: Normally the basic loading conditions as described in the Rules for Classification of Ships Pt.5 Ch.2 of the Rules, shall be considered. These loading conditions are further elaborated in Sec.3 of this Classification Note. The loading should be applied in the form of lateral pressure on shell elements, (or line loads on membrane elements). Alternative load application may be specially considered. 4.6.2 Fatigue loads: For vessels subject to the class notation NAUTICUS (Newbuilding), see the Rules for Classification of Ships Pt.5 Ch 2 Sec 5A, fatigue strength assessment are in general to be carried out for end structures of longitudinals in bottom, inner bottom, side, inner side and deck in the midship area. For that purpose any deformation of the said longitudinals caused by relative deformation by the supporting strength members may have to be calculated. It is emphasized that such deformations are to reflect dynamic loading only. The dynamic pressure loads are to be calculated according to the Classification Note 30.7 “Fatigue Assessment of Ship Structure”, see Sec.3.6. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.4. Cargo Hold Analysis – Page 32 4.7 Presentation of input and results 4.7.1 The requirements given in the Rules for Classification of Ships Pt.3 Ch.1 Sec.12 regarding proper documentation of the model shall be followed. A practical guidance is given in the following. In appendix A, examples of checklists for internal verification of FEM analyses are given. 4.7.2 Presentation of input data: A reference to the set of drawings the model is meant to represent should be given. The modelled geometry is to be documented, preferably as an extract directly from the generated model. The following input shall be reflected: — — — — — plate thickness free flange sectional area considering efficiency of curved flanges beam section properties boundary conditions load cases. 4.7.3 Presentation of results: The stress presentation should be based on element membrane stresses or gauss membrane stresses at the middle of element thickness, excluding plate bending stress, in the form of iso-stress contours in general. Numerical values should also be presented for highly stressed areas (e.g. areas where stress exceeds 60% of allowable limits or areas in way of openings not included in the model). The following should be presented: — deformed shapes — transverse or vertical membrane stress of shell/plate elements in — — — — — — — — — — — — — bottom plating inner bottom plating deck plating longitudinal bulkhead plating cross deck/upper stool plating hopper tank plating top wing tank bottom plating transverse floors and web frames in hopper and top wing tank and wing tank stringers in wing tank transverse bulkhead plating upper and lower stool plating side and inner side if double side skin construction mainframes — longitudinal membrane stress of shell/plate elements in — — — — bottom plating inner bottom plating longitudinal girders cross deck cantilever beams — shear stresses of shell/plate elements in — — — — — — — — — — transverse floors longitudinal girders longitudinal girders below bulkhead stool stool diaphragms lower/upper stools top and bottom plating transverse bulkhead plating in way of ship side, (inner side if relevant) hopper and top wing tank and wing tank hopper plating, hopper girder and longitudinal bulkhead plating adjacent to transverse bulkhead web frames inside hopper and top wing tank and wing tank, mainframes, upper and lower bracket stringers inside double side and wing tank cross deck cantilever beams — axial stress of free flanges — deformations of supporting brackets for mainframes including longitudinals connected to these — deformation of supports for longitudinals subject to large relative deformation. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.4. Cargo Hold Analysis – Page 33 4.8 Evaluation of results and applicable acceptance criteria 4.8.1 In the following procedures for handling results and applying acceptance criteria are described. Acceptance criteria are in general given in the Rules for Classification of Ships Pt.3 Ch.1 Sec.12 and Pt.5 Ch.2 Sec.5. 4.8.2 Evaluation of results - Longitudinal stress: For buckling control the following longitudinal stresses may normally be considered: σ L = σ DB + σ S + σ W or σ LR = σ DB + σ S + σ WR σL = sum of longitudinal stresses based on wave bending moment with a probability of 10-8 of exceedance σLR = sum of longitudinal stresses based on wave bending moments with a probability of 10-4 of exceedance σDB = longitudinal girder bending stresses resulting from bending of large stiffened panels between transverse bulkheads, due to local load on an individual cargo hold. These stresses are often referred to as double bottom stresses, as they are typical for double bottom structures, and may be taken as results from the cargo hold analysis σS = longitudinal hull girder bending stresses defined as MS/Zi , where MS is the still water bending moment and Zi is the section modulus at the considered position (i) based on gross scantling. (No corrosion addition deducted). Maximum sagging or hogging moment to be applied as values for MS. MS is defined in the Rules for Classification of Ships Pt.3 Ch.1 Sec.5 and Pt.5 Ch.2 Sec.5 σW = longitudinal hull girder bending stresses caused by wave bending moment MW, which correspond to a probability of exceedance of 10-8. σW = MW/Zi . MW is defined in the Rules for Classification of Ships Pt.3 Ch.1 Sec.5 σWR = longitudinal hull girder bending stresses caused by reduced wave bending moment MWR, which corresponds to a probability level of exceedance of 10-4. MWR = 0.59 MW. Relevant stress components related to hull girder, girders, and stiffeners are defined in Fig.4-7. Fictitious longitudinal stresses may occur in the model due to assumptions made for the boundary conditions. These effects are due to “semi global bending” of the hull girder and a fictitious compression force when the middle hold is empty. When the longitudinal girder stresses are evaluated, typically for girders in double bottom, the magnitude of these effects should be considered as follows: — ordinary bulk carriers have longitudinal girders in the double bottom. It is advised that the fictitious compression force when the mid hold is empty is eliminated by applying boundary conditions as described in Table 4.1. As an alternative this may be done by manual corrections after the calculation — the effect of the “semi global bending” depends on the distance between the supports. For an ordinary bulk carrier, this effect may be significant and should be taken into consideration. Manual corrections should be done. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.4. Cargo Hold Analysis – Page 34 Upper deck N.A. σ al N.A. σ DB N.A. Hull Girder Bending Double Bottom Bending σ st Local Bending of Longitudinal Figure 4-7 Stresses identified as hull girder bending stresses, double bottom bending stresses and stiffener bending stresses, σal = σs + σw, see the Rules for Classification of Ships It should also be noted that the stiffener bending stress is not a part of the girder bending stresses. The magnitude of the stiffener bending stress included in the stress results depends on the mesh division and the element type that is used. This is shown in Fig.4-8 where the stiffener bending stress, as calculated by the FEmodel, is shown depending on the mesh size (valid for 4-noded shell elements). One element between floors results in zero stiffener bending. Two elements between floors result in a linear distribution with approximately zero bending in the middle of the elements. When a relatively fine mesh is used in the longitudinal direction the effect of stiffener bending stresses should be isolated from the girder bending stresses when buckling and stress level is checked for the plate flange. Figure 4-8 Normal stress caused by local load on the stiffener, depending on number of elements along the stiffener 4.8.3 Mean shear stress: The mean shear stress, τmean, is to be used for the capacity check of a plate. This may be defined as the shear force divided on the effective shear area. For results from finite element methods the mean shear stress may be taken as the average shear stress in elements located within the actual plate field, and corrected with a factor describing the actual shear area compared to the modelled shear area when this is relevant. For a plate field with n elements the following apply: i=n ( τi ⋅ Ai ) =1 τ mean = i---------------------------Aw Ai = effective shear area of element i τi = shear stress of element i DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.4. Cargo Hold Analysis – Page 35 Aw = effective shear area as of the real structure. To be taken in accordance with the Rules for Classification of Ships Pt.3 Ch.1 Sec.3. 4.8.4 Shear stress in the hull girder: It is not necessary to consider hull girder shear stresses in longitudinal bulkheads and ship side unless special boundary conditions as well as loads are applied. The shear strength of the hull girder may normally be evaluated in accordance with the Rules for Classification of Ships Pt.3 Ch.1 Sec.5. Detailed procedure for shear force correction is specified in Sec.9. 4.8.5 Buckling control and related acceptance criteria: Table 4-4 gives examples of areas to be checked for buckling and the applicable method and accept criteria. In case of any differences in the acceptance criteria given here compared with those given in the Rules for Classification of Ships, the latter shall apply. Table 4-4 Examples of areas to be checked and procedure to be used related to buckling control Item Remarks Buckling of girder plate flanges in: 1) Uniaxial buckling in transverse direction to be analysed based on mean transverse compressive stress with ψ = 1 and allowable usage factor, η = 0.8 — double bottom (including bottom and inner bottom) 2) Uniaxial buckling in longitudinal direction to be analysed according to the — side plating (including inner side Rules for Classification of Ships Pt.3 Ch.1 Sec.13 based on hull girder stress when relevant) σal = σS + σW. — deck 3) Bi-axial buckling to be analysed based on longitudinal stress and mean — longitudinal bulkhead transverse stress. When the longitudinal stresses are obtained from hull — hopper structure girder loads on a probability of exceedance of 10-4, usage factors ηx= ηy = — top wing tank structure 0.85 shall be used. For a probability of exceedance of 10-8, usage factors ηx — cross deck structure inc. stools = ηy = 1.0 shall be used. Buckling of girder plate flanges in: — plane transverse bulkhead — upper and lower stools and the web of these girders Buckling of cross tie Buckling of corrugated bulkheads Buckling of girder webs in: — — — — — — — — double bottom double side (when relevant) deck longitudinal bulkhead plane transverse bulkhead hopper tank topwing tank stools Comment: Mean transverse compressive stress is to be calculated from a group of elements representing one plate field between stiffeners. Longitudinal stresses are to be taken as described in 4.8.2. 1) Buckling to be analysed based on mean compressive stress with ψ = 1 and allowable usage factor, η = 0.8. 2) Bi-axial buckling to be checked when relevant. Comment: Mean compressive stress are to be calculated from a group of elements representing one plate field between stiffeners. 1) Buckling to be analysed based on axial stress with usage factor according to Rules, against column buckling, torsion buckling and web buckling. Note: Axial stress in cross tie may normally be taken as the stress at the mid height and at the mid span. The effective span of the cross tie may normally be taken as: Breadth of side tank – ½ Depth of both vertical girders 2) Buckling of local plate panels on cross ties to be checked according to buckling of girder webs with one or two plate flanges as appropriate. 3) Buckling of free flanges on the cross tie to be calculated according to Rules Pt.3 Ch.1 Sec.13 Buckling to be analysed based on mean compressive stress with kl = 5 (Pt.3 Ch.1 Sec.14) and allowable usage factor, η = 0.8. Buckling of girder webs with one plate flange: 1) Buckling to be calculated as for girder plate flanges 2) Buckling to be analysed based on mean shear stress with allowable usage factor, η = 0.85. 3) Bi-axial buckling with shear. Buckling of girder webs with two plate flanges: 4) Buckling to be analysed based on mean shear stress with allowable usage factor, η = 0.85. 5) Buckling caused by compression loads from sea and cargo, alternatively together with shear, to be checked when relevant. Comment: Mean shear stress to be taken as described in 4.8.3, representing one plate field between stiffeners. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.5. Local Structure Analysis – Page 36 4.8.6 Stress control and related acceptance criteria: Table 4-5 gives examples of areas where the stress level shall be controlled, together with the applicable method and accept criteria. In case of any differences in the acceptance criteria given here compared with those given in the Rules for Classification of Ships, the latter shall apply. Table 4-5 Examples of areas to be checked and procedure to be used related to control of nominal membrane stresses. All stresses in N/mm2 Item Stresses in longitudinal girders Stresses in transverse and vertical girders with two plate flanges (Double skin constructions) like: — Double bottom — Double side Stresses in transverse and vertical girders with one plate flange like: — Main frames — Side tank web frame — Stringer in wing tank — Deck partial girder — Cross tie — Top wing tank web frame — Hopper tank web frame Remarks 1) Allowable reduced longitudinal nominal stress, σ = 190 f1. Based on a probability of exceedance of 10-4. (Reduced longitudinal stress, σLR = σDB + σS + σWR < 190 f1, Ref 4.8.2) 2) Allowable mean shear stress τ = 90 f1 (sea) and τ = 100 f1 (harbour) for girders with one plate flange, and τ = 100 f1 (sea) and τ = 110 f1 (harbour) for girders with two plate flanges. Shear stress in way of openings not included in the calculation to be evaluated in terms of mean shear stress See 4.8.3. 1) Allowable nominal normal stress in flanges of girders σ = 160 f1 (sea) and σ = 180 f1 (harbour) in general. 2) Allowable mean shear stress of girder webs, τ = 100 f1 (sea) and 110 f1 (harbour). Shear stress in way of openings not included in the calculation to be evaluated in terms of mean shear stress See 4.8.3. 3) Allowable equivalent stress, σe = 180 f1 for seagoing conditions and σe = 200 f1 for harbour conditions. 1) Allowable nominal normal stress, σ = 160 f1 (sea) and σ = 180 f1 (harbour) in general. 2) Allowable mean shear stress τ = 90 f1 (sea) and 100 f1 (harbour). Shear stress in way of openings not included in the calculation to be evaluated in terms of mean shear stress See 4.8.3. 3) Allowable equivalent stress, σe = 180 f1 for seagoing conditions and σe = 200 f1 for harbour conditions. 4) Allowable nominal normal stress in flooded condition, σ = 220 f1 (Not applicable for mainframes). 5. Local Structure Analysis 5.1 General Local structure analysis may be used to analyse local nominal stresses in laterally loaded local stiffeners and their connecting brackets, subjected to relative deformations between supports. See Fig.5-1. The model and analysis described in the following are suitable for calculating: — nominal stresses in stiffeners — nominal stresses in longitudinals supporting main frames. These models may be included in the 3D cargo hold analysis model, or run separately as sub models with prescribed boundary deformations from a 3D-analysis. Local pressure loads must be applied to the local models. 5.2 Stiffeners subject to large deformations 5.2.1 General: Relative deformations between stiffener supports may give rise to high stresses in local areas. Typical areas to be considered are; — longitudinals in double bottom towards transverse bulkheads or partial girders — longitudinals connected to main frame supporting brackets. See Fig. 5-1. A method for the first example is shown in the following. For the other example, similar method applies. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.5. Local Structure Analysis – Page 37 Figure 5-1 Main frames, connecting brackets and longitudinals in bulk carriers 5.2.2 Model extent: In general, the model of a longitudinal in double bottom towards transverse bulkheads or partial girder is recommended to have the following extent: — The stiffener model shall extend to a stiffener support at least two frame spacings outside the area subject to the study. — The width of the model shall be at least ½ + ½ stiffener spacing. See Fig.5-3. Fig.5-2 shows the extent of a model of an inner bottom longitudinal and bottom longitudinal. Here the extent covering the full length is used for checking both sides of the unsymmetrical stools simultaneously. Figure 5-2 Extent of stiffener model for checking both sides of the unsymmetrical stool 5.2.3 Elements and element mesh: Normally three (3) 4-noded elements are to be used over the web height of the stiffeners. Corresponding sizes are to be used for the plate flange. The face plate shall normally be modelled with 2-noded beam elements. Effective flange in curved areas should however be represented properly. An example of a model as described is shown in Fig.5-3 and Fig.5-4. Generally, the element fineness along the stiffener shall be fine enough for providing a good aspect ratio of the elements. The two last elements towards the point of interest shall not be larger than 2% of the stiffener’s span length if the results are to be used directly. However, the elements may be up to 8% of the span length if extrapolation of the results towards the point of interest is carried out. A method for extrapolation is given in Ch.5.4. Figure 5-3 View of element model DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.5. Local Structure Analysis – Page 38 Figure 5-4 Acceptable element mesh. The size of elements does in this case require extrapolation of results towards the point of interest 5.2.4 Boundary conditions: If the model is run separately, prescribed displacements or forces are to be taken from the cargo hold analysis (or frame and girder analysis when relevant). These displacements or forces are to be applied to the boundaries of the local structure model in points where the results from the global model are representative. See Table 5-1. Table 5-1 Boundary conditions for model of longitudinals in double bottom Location Free edge of plate flanges forming the bottom, inner bottom and stool sides. Free edges of: Double bottom floors. Top of stool. Double bottom floors in line with stool. X D δx - Displacement δy - δz - θx X Rotation θy - θz X D D D D D D Restricted from displacement or rotation. Free. Displacements transferred from cargo tank model or frame and girder model. 5.3 Other fine mesh models Other fine mesh models may be made for the study of critical details. If the accept criteria are based on maximum allowable nominal stresses the modelling principles described above should be followed. 5.4 Documentation and result presentation When extrapolation of results is required, see 5.2.3, this shall normally be based on the results in the two last elements towards the point of interest. The results in the Gauss point in the middle of the element representing the flange of the longitudinal shall be used for the extrapolation. The extrapolation method is indicated in Fig.5-5. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.6. Additional Requirements Considering Flooding – Page 39 σ σ 2 σ 1 Figure 5-5 Extrapolation towards point of interest based on results in elements representing the flange Documentation and result presentation is to follow the principles given in Sec.4.7. The following stresses shall be given: a) Normal stresses and shear stresses of plate/membrane elements. b) Axial stress of truss/beam elements. 5.5 Acceptance Criteria Acceptance criteria for stress results from local structure analysis are given in the Rules for Classification of Ships Pt.3 Ch.1 Sec.12 and in Pt.5 Ch.2. 6. Additional Requirements Considering Flooding 6.1 General 6.1.1 Generally the Rules require that damage stability calculations are carried out to control that the ship has sufficient residual stability for given damage scenarios without reference to the ship’s actual loading conditions and without controlling the ships overall strength for such damage conditions. However, for vessels subject to the requirements as given in the Rules for Classification of Ships Pt.5 Ch.2 Sec.5 Table A3, the ships overall strength (hull girder shear and bending strength) are to be controlled for flooding of each cargo hold for all actual seagoing cargo and ballast conditions. I.e. the loading conditions given in the loading manual and those evaluated by the loading instrument only. The determination of the mass of water ingress should reflect the damaged waterline. A permeability of 0.3 for the volume occupied by cargo may be used. For the remaining flooded volume in the loaded hold and for empty holds a permeability of 0.95 to be used. For the loaded holds a permeability of 0.9 for the whole volume below the damaged waterline may be used as an alternative to the above. Realistic data for the cargo mass volume and density to be applied. 6.2 Global Bending Moment and Shear Force Limitation 6.2.1 Generally the maximum allowable still water bending moment in a flooded condition, MSf, is described by below formula, provided adequate uni-axial buckling capacity of the cross section is available. See the Rules for Classification of Ships Pt.3 Ch.1 Sec.13. M sf = 175 f 1 Z z – 0.8 M w Zz Mw = hull girder section modulus at the considered position = wave bending moment according to the Rules for Classification of Ships. When the hull girder capacity is fully utilised, the maximum allowable still water bending moment at the considered section, in flooded condition, MSf, is described by: M sf = M s + 0.2 M w DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.6. Additional Requirements Considering Flooding – Page 40 Ms = Allowable still water bending moment according to the Rules for Classification of Ships in intact condition. 6.2.2 It should be noted that there is only one limitation curve in a flooded condition, irrespective of possible reduced bending moment limits applied in an alternate intact condition. 6.2.3 The three typical bending moment limits are given in the illustration Fig.6-1 following. Max. allowable still water bending moment in flooded condition Max. allowable still water bending moment in intact condition Bending moment [tm] Possible reduced limit for bending moment in intact alternate condition Length LFP 20% of wave bending moment Figure 6-1 Typical bending moment limitation curves for intact and flooded conditions 6.2.4 The maximum allowable shear force capacity at the considered section in flooding condition, QSf , is described by: Q sf = Q s + 0.2 Q w QS QW = Allowable still water shear force according to the Rules for Classification of Ships in intact condition. See also 9.4. = Maximum vertical wave shear force according to the Rules for Classification of Ships. 6.3 Transverse Bulkhead Strength 6.3.1 Generally the Rules for Classification of Ships require that the strength of transverse bulkhead structure subjected to flooding loads have been controlled using a pressure head corresponding to the deepest equilibrium waterline in the damage condition, and pressure load from water alone only. 6.3.2 For vessels subject to the requirements as given in the Rules for Classification of Ships Pt.5 Ch.2 Sec.5 Table A3, the transverse bulkheads are to be checked according to Pt.5 Ch.2 Sec.8 D. The pressure loads in this case reflects the effect of mixed cargo and water. The following load cases may be applied: — water alone — filled cargo hold to deck at centre line with mass corresponding to the hold’s maximum allowable mass — cargo hold filled to a level corresponding to its maximum allowable mass and applying cargo density of 1.78 t/m3 — cargo hold filled to a level corresponding to its maximum allowable mass and applying cargo density of 3.0 t/m3. Flooding head shall be as required in above referred Rules. A most severe combination of angle of repose and cargo density should be applied for the case of filled cargo hold (ref. Sec.2.3). 6.3.3 It should be noted that the rule check program “Section Scantling” in the Nauticus Hull package may be used for checking corrugation girder, shedder and gusset plates, stool plating and stiffeners as relevant. However, diaphragm plates and in line shear plates inside double bottom is to be checked separately. Acceptable procedure is described in 6.4. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.6. Additional Requirements Considering Flooding – Page 41 6.4 Diaphragm and shear plates in double bottom below bulkhead stool, considering flooding (evaluation of the effectiveness) 6.4.1 The shear strength of diaphragm - and shear plates is to be checked with respect to the bending moment, MLS, from the lower stool as given by: p c, fl 2 ---------h LS ( Z le σ a, le 10 + QhLS ) 2 + p c, fu -------------------------------------------= --------------------------------------------------------- + 3 s1 –3 M LS Zle σa,le Q s1,hLS pc,fl pc,fu d1, hDB τf kNm ------------ m = as given in the Rules for Classification of Ships Pt.5 Ch.2 Sec.8 D303 = as given in the Rules for Classification of Ships Pt.5 Ch.2 Sec.10 D305 = as given in the Rules for Classification of Ships Pt.5 Ch.2 Sec.8 D209 = as given in the Rules for Classification of Ships Pt.5 Ch.2 Sec.8 D203 = pc,f as given in the Rules for Classification of Ships Pt.5 ch.2 Sec.8 D204 with h1 = d1 – hDB = pc,f as given in the Rules for Classification of Ships Pt.5 Ch.2 Sec.8 D204 with h1 = d1 – (hDB + hLS) = as given in the Rules for Classification of Ships Pt.5 Ch.2 Sec.8 D203 = σf ------3 σf = minimum upper yield stress. The shear moment capacity, Mt, of longitudinal double bottom girders and shear plates below the lower bulkhead stool, are within a load breadth of each longitudinal double bottom girder, bl, generally given by: M τ = M LS b l The shear moment capacity, Mt, may generally be determined as follows: Mτ = MτL + Mτs MτL = Mτs = l l s [ ( τ f ( t l a – 2 ) ( h DB – h oa ) + τ f ( t l f – 2 ) ( h DB – h of ) ) ] /2 n τf ( ts – 2 )ls hDB l n = number of effective shear plates including longitudinal double bottom girders within the load breadth bl. 6.4.2 For the determination of Mts, smaller size access holes in the shear plates within the length of the lower stool may generally be disregarded. Access holes etc. in shear plates and double bottom girder webs below the lower bulkhead stool are assumed to be arranged with effective edge stiffening. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.7. Cargo Hold Load Limitations – Page 42 Figure 6-2 Diaphragm and shear plates in double bottom below bulkhead stool and longitudinal girder 6.5 Limit to Hold Loading, Considering Flooding 6.5.1 Generally the Rules require that the strength of the double bottom construction is based on the most unfavourable loading conditions as given in the loading manual and the minimum loading as given in the Rules. The individual holds net loading (shear) and/or the most unfavourable combination of net loading and bending moment (buckling, longitudinals) will then decide the scantling. When first the extreme loadings have been checked they serve as basis for the Local Strength Diagrams giving the maximum allowable/minimum required mass as a function of the draught. See Sec.7 for further details. Typical for this approach is that it is based on intact loading only. 6.5.2 However, for vessels subjected to the requirements as given in the Rules for Classification of Ships Pt.5 Ch.2 Sec.5 Table A3, the double bottom shear strength are also to be checked for above loads in flooding condition. See the Rules for Classification of Ships Pt.5 Ch.2 Sec.8 E. It should be noted that the rule check program “Allowable Hold Loading” in the Nauticus Hull package may be used for this purpose. Further, the highest cargo density will give the strictest requirement and a cargo density of 3.0 t/m3 should generally serve as the extreme condition in combination with permeability of 0.3 for the volume occupied by the cargo. 7. Cargo Hold Load Limitations 7.1 General 7.1.1 The design loading conditions of the ship as defined in the loading manual, ref. Sec.3, (and also Rules Pt.5 Ch.2 Sec.5), refers to a given cargo mass and a given draught. These design loading conditions are, in addition to being used for scantling check, also utilised to define limits to the cargo mass of holds for other draughts. 7.1.2 Generally the allowable mass of cargo in a given hold or adjacent holds is related to the net loading on the double bottom of the considered hold(s). This implies that the allowable mass of cargo in the hold(s) will vary linearly with the buoyancy pressure acting on the bottom of the ship. 7.1.3 In any actual loading condition longitudinal hull girder bending moments and shear forces are to be within the limits defined in the loading manual/loading instrument. 7.2 Definitions MMAX MMIN MH MH, ADJ. = maximum allowable mass curve = minimum required mass curve = the actual cargo mass (t) in a cargo hold corresponding to a homogeneously loaded condition at maximum draught = sum of MH for the two adjacent holds DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.7. Cargo Hold Load Limitations – Page 43 MFULL = the cargo mass (t) in a cargo hold corresponding to cargo with virtual density (homogenous mass / hold cubic capacity = MH / VH = minimum 1.0 t/m3) filled to the top of the hatch coming. MFULL shall not be less than MH. MFULL, ADJ. = sum of MFULL for the two adjacent holds MHD = the maximum cargo mass (t) allowed to be carried in a cargo hold according to design alternative loading condition(s), i.e. specified in the loading manual, with specified holds empty = the maximum cargo mass (t) allowed to be carried in adjacent holds according to design MHD, ADJ. block loading conditions, i.e. specified in the loading manual, with cargo mass larger than MFULL, ADJ. VH = hold volume in m3 including volume of hatch T = maximum draught (m), i.e. scantling draught TA = draught (m) at mid-hold position of the cargo hold or the adjacent cargo holds in m associated with cargo mass = deepest ballast draught, usually heavy ballast draught THB l = length of the considered hold(s) in m, see Figure 7-1 b = mean breadth of the considered cargo hold(s) in m at the level of the top of the hopper tank, see Figure 7-1. In general, the above symbols are defined for a single cargo hold in seagoing conditions, unless clearly specified otherwise. When the symbols have a subscript of “adj.” and/or “harbour”, it means that they are defined for adjacent cargo holds and/or in harbour conditions. Figure 7-1 Definition of length and breadth to be used in calculation of local strength diagrams 7.3 Procedure for preparation of Hold Mass Diagrams 7.3.1 The procedures for determining limits to the loading of cargo hold(s), given in the following, are applicable for ships with class notation HC-A, HC-B, HC-C, HC-A No MP, HC-B No MP, HC-C No MP, and HC-B*. The procedures have been based on the assumption that the structure comply with class requirements for the ship’s design load conditions, but not necessarily utilising any strength margin, in particular at reduced draughts. In case such strength margins exist, the hold mass diagrams may alternatively be based on the stress response from the direct strength calculations reflecting the design mass and relevant draught. The limit to the mass of cargo in hold is primarily related to the shear response of the double-bottom floors and girders, and is largely given by the net pressure load exerted by cargo, other dead-weight and buoyancy on the double bottom structure. Ballast water in double bottom ballast tanks with in the extent of l times b as shown in Figure 7-1should be considered as a part of mass of cargo in hold(s). In the design stage, hold mass diagrams are prepared based on a preliminary loading manual. Very often the draught changes for the same loading condition in the final loading manual, which may make the condition unacceptable with respect to hold mass diagrams. It is therefore suggested to keep some margin in the hold mass diagrams. This may be achieved by round up of MH, MFull, MHD, etc. Examples of hold mass diagrams are shown in 7.4. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.7. Cargo Hold Load Limitations – Page 44 7.3.2 Single Hold Loading 7.3.2.1 Applicable for HC-B No MP and HC-C No MP Any cargo hold is: — to be capable of carrying MFULL at maximum draught (T) — to be capable of carrying minimum 50% of MH at maximum draught (T) — to be capable of being empty at deepest ballast draught (THB). The maximum allowable mass curve may be taken as: = MFULL − 1.025 l b (T − TA) = maximum MFULL The minimum required mass curve may be taken as the less of: MMAX = 1.025 l b (TA −THB) MMIN = 0.5 MH − 1.025 l b (T − TA) MMIN In harbour conditions, any cargo hold is: — to be capable of holding the maximum allowable seagoing mass at 67% of maximum draught (0.67 T) — to be capable of increasing the maximum allowable mass in a cargo hold at reduced draught during loading and unloading in harbour, by 15% of the maximum mass allowed at the maximum draught in sea-going condition, but shall not exceed the mass allowed at maximum draught in the sea-going condition. The minimum required mass may be reduced by the same amount. The maximum allowable mass curve (harbour) may be taken as the larger of: MMAX, harbour = MFULL − 1.025 l b (0.67T − TA) MMAX, harbour = MMAX + 0.15 MFULL = maximum MFULL The minimum required mass curve (harbour) may be taken as: MMIN, harbour = MMIN − 0.15 MFULL 7.3.2.2 Applicable for HC-A No MP only For ships where a specified reduced bending moment limit has been assigned for the condition with empty cargo holds at maximum draught, both limits, according to 7.3.2.1 and 7.3.2.2, to the mass of cargo in the holds should be included in the local strength diagram. If the vessel is loaded in between the two curves, the actual bending moment is not to be greater than the specified reduced bending moment. In addition to the requirements given in 7.3.2.1, any cargo hold is: — to be capable of carrying MHD + 0.1MH at maximum draught (T) (for ore holds) — to be capable of being empty at maximum draught (T). (for empty holds) For ore holds: The maximum allowable mass curve may be taken as: = MHD + 0.1 MH – 1.025 l b (T − TA) = maximum MHD The minimum required mass curve may be taken same as in 7.3.2.1. For empty holds: The maximum allowable mass curve may be taken same as in 7.3.2.1. The minimum required mass may be taken as: MMAX MMIN = 0 at T In harbour conditions, similar to the requirements given in 7.3.2.1: For ore holds: The maximum allowable mass curve (harbour) may be taken as the larger of: MMAX, harbour = MHD − 1.025 l b (0.67T − TA) MMAX, harbour = MMAX + 0.15 MHD = maximum MHD DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.7. Cargo Hold Load Limitations – Page 45 The minimum required mass curve (harbour) may be taken as: MMIN, harbour = MMIN − 0.15 MHD For empty holds: The maximum allowable mass curve (harbour) may be taken same as in 7.3.2.1. The minimum required mass curve (harbour) may be taken as: MMIN, harbour = MMIN − 0.15 MFULL 7.3.2.3 Applicable for HC-B and HC-C Any cargo hold is: — to be capable of carrying MFULL at 67% of maximum draught (0.67 T) — to be capable of being empty at 83% of maximum draught (0.83 T). The maximum allowable mass curve may be taken as: = MFULL − 1.025 l b (0.67 T − TA) = maximum MFULL The minimum required mass curve may be taken as: MMAX MMIN = 1.025 l b (TA − 0.83 T) In harbour conditions, any cargo hold is: — to be capable of increasing the maximum allowable mass in a cargo hold at reduced draught during loading and unloading in harbour, by 15% of the maximum mass allowed at the maximum draught in sea-going condition, but shall not exceed the mass allowed at maximum draught in the sea-going condition. The minimum required mass may be reduced by the same amount. The maximum allowable mass curve (harbour) may be taken as: MMAX, harbour = MMAX + 0.15 MFULL = maximum MFULL The minimum required mass curve (harbour) may be taken as: MMIN, harbour = MMIN − 0.15 MFULL 7.3.2.4 Applicable for HC-A only For ships where a specified reduced bending moment limit has been assigned for the condition with empty cargo holds at maximum draught, both limits, according to 7.3.2.3 and 7.3.2.4, to the mass of cargo in the holds should be included in the local strength diagram. If the vessel is loaded in between the two curves, the actual bending moment is not to be greater than the specified reduced bending moment. In addition to the requirements given in 7.3.2.3, any cargo hold is: — to be capable of carrying MHD + 0.1MH at maximum draught (T) (for ore holds) — to be capable of being empty at maximum draught (T) (for empty holds). For ore holds: The maximum allowable mass curve may be taken as: = MHD + 0.1 MH – 1.025 l b (T − TA) = maximum MHD The minimum required mass curve may be taken as same in 7.3.2.3. MMAX For empty holds: The maximum allowable mass curve may be taken as same in 7.3.2.3. The minimum required mass may be taken as: MMIN = 0 at T In harbour conditions, similar to the requirements given in 7.3.2.3: For ore holds: DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.7. Cargo Hold Load Limitations – Page 46 The maximum allowable mass curve (harbour) may be taken as the larger of: MMAX, harbour = MHD − 1.025 l b (0.67T − TA) MMAX, harbour = MMAX + 0.15 MHD = maximum MHD The minimum required mass curve (harbour) may be taken as: MMIN, harbour = MMIN − 0.15 MHD For empty holds: The maximum allowable mass curve (harbour) may be taken same as in 7.3.2.3. The minimum required mass curve (harbour) may be taken as: MMIN, harbour = MMIN − 0.15 MFULL 7.3.2.5 Applicable for HC-B* only Any cargo hold is: — to be capable of carrying 1.2 MFULL at 67% of maximum draught (0.67 T) — to be capable of being empty at maximum draught (T). The maximum allowable mass curve may be taken as: = 1.2 MFULL − 1.025 l b (0.67 T − TA) = maximum 1.2 MFULL The minimum required mass curve may be taken as: MMAX MMIN = 0 at T In harbour conditions, any cargo hold is: — to be capable of increasing the maximum allowable mass in a cargo hold at reduced draught during loading and unloading in harbour, by 15% of the maximum mass allowed at the maximum draught in sea-going condition, but shall not exceed the mass allowed at maximum draught in the sea-going condition. The minimum required mass may be reduced by the same amount. The maximum allowable mass curve (harbour) may be taken as: MMAX, harbour = MMAX + 0.18 MFULL = maximum 1.2 MFULL The minimum required mass curve (harbour) may be taken as: MMIN, harbour = MMIN − 0.18 MFULL 7.3.3 Adjacent Hold Loading 7.3.3.1 Applicable for HC-B No MP and HC-C No MP Any two adjacent cargo holds are: — to be capable of carrying MFULL, adj., at maximum draught (T) — to be capable of carrying minimum 0.5 MH, adj., at maximum draught (T) — to be capable of being empty at deepest ballast draught (THB). The maximum allowable mass curve may be taken as: MMAX, adj. = MFULL, adj. − 1.025 l b (T − TA) = maximum MFULL, adj. The minimum allowable mass curve may be taken as the less of: MMIN, adj. = 0.5MH,adj. − 1.025 l b (T − TA) MMIN, adj. = 1.025 l b (TA −THB) In harbour conditions, any two adjacent cargo holds are: — to be capable of carrying the MFULL, adj. at 67% of maximum draught (0.67 T) — to be capable of increasing the maximum allowable mass in a cargo hold at reduced draught during loading and unloading in harbour, by 15% of the maximum mass allowed at the maximum draught in sea-going DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.7. Cargo Hold Load Limitations – Page 47 condition, but shall not exceed the mass allowed at maximum draught in the sea-going condition. The minimum required mass may be reduced by the same amount. The maximum allowable mass curve (harbour) may be taken as the larger of: MMAX, harbour = MFULL, adj. − 1.025 l b (0.67T − TA) MMAX, harbour = MMAX + 0.15 MFULL, adj. = maximum MFULL, adj. The minimum required mass curve (harbour) may be taken as: MMIN, harbour = MMIN − 0.15 MFULL, adj. 7.3.3.2 Applicable for HC-A No MP only In addition to the requirements given in 7.3.3.1, any two adjacent cargo holds: — which according to a design loading condition may be loaded with the next holds empty, are to be capable of carrying 0.1 MH, adj. in addition to the maximum cargo load according to that design loading condition, MHD, adj., at maximum draught (T). The maximum allowable mass curve may be taken as the larger of: = MHD, adj. + 0.1 MH, adj. − 1.025 l b (T − TA) (only when MHD, adj. applicable) = maximum MHD, adj. The maximum allowable mass curve as given in 7.3.3.1. MMAX, adj. The minimum required mass curve may be taken same as in 7.3.3.1.In harbour conditions, similar to the requirements given in 7.3.3.1: The maximum allowable mass curve (harbour) may be taken as the larger of: MMAX, adj., harbour = MMAX, adj. + 0.15 MHD, adj. (only when MHD, adj. applicable) = maximum MHD, adj. The maximum allowable mass curve (harbour) as given in 7.3.3.1 The minimum required mass curve (harbour) may be taken as the less of: MMIN, harbour = MMIN − 0.15 MHD, adj. (only when MHD, adj. applicable) The minimum required mass curve (harbour) as given in 7.3.3.1. 7.3.3.3 Applicable for HC-B and HC-C Any two adjacent cargo holds are: — to be capable of carrying MFULL, adj., at 67% of maximum draught (0.67 T) — to be capable of being empty at 75% of maximum draught (0.75 T). The maximum allowable mass curve may be taken as: MMAX, adj. = MFULL, adj. − 1.025 l b (0.67 T − TA) = maximum MFULL, adj. The minimum allowable mass curve may be taken as: MMIN, adj. = 1.025 l b (TA − 0.75 T) In harbour conditions, any two adjacent cargo holds are: — to be capable of increasing the maximum allowable mass in a cargo hold at reduced draught during loading and unloading in harbour, by 15% of the maximum mass allowed at the maximum draught in sea-going condition, but shall not exceed the mass allowed at maximum draught in the sea-going condition. The minimum required mass may be reduced by the same amount. The maximum allowable mass curve (harbour) may be taken as: MMAX, harbour = MMAX + 0.15 MFULL, adj. = maximum MFULL, adj. The minimum required mass curve (harbour) may be taken as: MMIN, harbour = MMIN − 0.15 MFULL, adj. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.7. Cargo Hold Load Limitations – Page 48 7.3.3.4 Applicable for HC-A only In addition to the requirements given in 7.3.3.3, any two adjacent cargo holds: — which according to a design loading condition may be loaded with the next holds empty, are to be capable of carrying 0.1 MH, adj. in addition to the maximum cargo load according to that design loading condition, MHD, adj., at maximum draught (T). The maximum allowable mass curve may be taken as the larger of: MMAX, adj. = MHD, adj. + 0.1 MH, adj. − 1.025 l b (T − TA) (only when MHD, adj. applicable) = maximum MHD, adj. The maximum allowable mass curve as given in 7.3.3.3 The minimum required mass curve may be taken same as in 7.3.3.3. In harbour conditions, similar to the requirements given in 7.3.3.3: The maximum allowable mass curve (harbour) may be taken as the larger of: MMAX, adj., harbour =MMAX, adj. + 0.15 MHD, adj. (only when MHD, adj. applicable) = maximum MHD, adj. The maximum allowable mass curve (harbour) as given in 7.3.3.3 The minimum required mass curve (harbour) may be taken as the less of: MMIN, harbour = MMIN − 0.15 MHD, adj. (only when MHD, adj. applicable) The minimum required mass curve (harbour) as given in 7.3.3.3 7.3.3.5 Applicable for HC-B* only Any two adjacent cargo holds are: — to be capable of carrying 1.1 MFULL, adj. at 67% of maximum draught (0.67 T) — to be capable of being empty at 75% of maximum draught (0.75 T). The maximum allowable mass curve may be taken as: MMAX, adj. = 1.1 MFULL, adj. − 1.025 l b (0.67 T − TA) = maximum 1.1 MFULL, adj. The minimum allowable mass curve may be taken as: MMIN, adj. = 1.025 l b (TA − 0.75 T) In harbour conditions, any two adjacent cargo holds are: — to be capable of increasing the maximum allowable mass in a cargo hold at reduced draught during loading and unloading in harbour, by 15% of the maximum mass allowed at the maximum draught in sea-going condition, but shall not exceed the mass allowed at maximum draught in the sea-going condition. The minimum required mass may be reduced by the same amount. The maximum allowable mass curve (harbour) may be taken as: MMAX, adj., harbour =MMAX, adj. + 0.165 MFULL, adj. = maximum 1.1 MFULL, adj. The minimum required mass curve (harbour) may be taken as: MMIN, adj., harbour =MMIN, adj. − 0.165 MFULL, adj. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.7. Cargo Hold Load Limitations – Page 49 7.4 Hold mass diagrams 7.4.1 Single Hold Loading Applicable for HC-B No MP and HC-C No MP (Reference is made to 7.3.2.1 + LC5 and 6 in Chapter 3) Maximum seagoing curve: MMAX = = MFULL − 1.025 l b (T − TA) maximum MFULL Minimum seagoing curve (the less of): MMIN = MMIN = 1.025 l b (TA −THB) 0.5 MH − 1.025 l b (T − TA) Maximum harbour curve (the larger of): MMAX, harbour = MMAX, harbour = = MFULL − 1.025 l b (0.67 T − TA) MMAX + 0.15 MFULL maximum MFULL Minimum harbour curve: MMIN, harbour = MMIN − 0.15 MFULL Applicable for HC-A No MP - Ore Hold (Reference is made to7.3.2.2 + LC3, 5 and 6 in Chapter 3) Maximum seagoing curve: MMAX = = MHD + 0.1 MH − 1.025 l b (T − TA) maximum MHD Minimum seagoing curve (the less of): MMIN MMIN = = 1.025 l b (TA − THB) 0.5 MH − 1.025 l b (T − TA) Maximum harbour curve (the larger of): MMAX, harbour = MMAX, harbour = = MHD − 1.025 l b (0.67 T − TA) MMAX + 0.15MHD maximum MHD Minimum harbour curve: MMIN, harbour = MMIN − 0.15MHD DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.7. Cargo Hold Load Limitations – Page 50 Applicable for HC-A No MP – Empty Hold (Reference is made to 7.3.2.2 + LC3, 5 and 6 in Chapter 3) Maximum seagoing curve: MMAX = = MFULL − 1.025 l b (T − TA) maximum MFULL Minimum seagoing curve: MMIN = 0 at T Maximum harbour curve (the larger of): MMAX, harbour = MMAX, harbour = = MFULL − 1.025 l b (0.67 T − TA) MMAX + 0.15MFULL maximum MFULL Minimum harbour curve: MMIN, harbour = MMIN − 0.15 MFULL Applicable for HC-B and HC-C (Reference is made to 7.3.2.3 + LC1 and 2 in Chapter 3) Maximum seagoing curve: MMAX = = MFULL − 1.025 l b (0.67 T − TA) maximum MFULL Minimum seagoing curve: MMIN = 1.025 l b (TA − 0.83 T) Maximum harbour curve: MMAX, harbour = = MMAX + 0.15 ΜFULL maximum MFULL Minimum harbour curve: MMIN, harbour = MMIN − 0.15 MFULL DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.7. Cargo Hold Load Limitations – Page 51 Applicable for HC-A - Ore Hold (Reference is made to 7.3.2.4 + LC1, 2, 3 and 6 in Chapter 3) Maximum seagoing curve: MMAX = = MHD + 0.1 MH − 1.025 l b (T − TA) maximum MHD Minimum seagoing curve: MMIN = 1.025 l b (TA − 0.83 T) Maximum harbour curve (the larger of): MMAX, harbour = MMAX, harbour = = MHD − 1.025 l b (0.67 T − TA) MMAX + 0.15MHD maximum MHD Minimum harbour curve: MMIN, harbour = MMIN − 0.15 MHD Applicable for HC-A – Empty Hold (Reference is made to 7.3.2.4 + LC1, 2 and 3 in Chapter 3) Maximum seagoing curve: MMAX = = MFULL − 1.025 l b (0.67 T − TA) maximum MFULL Minimum seagoing curve: MMIN = 0 at T Maximum harbour curve: MMAX, harbour = = MMAX + 0.15 MFULL maximum MFULL Minimum harbour curve: MMIN, harbour = MMIN − 0.15 MFULL Applicable for HC-B* only (Reference is made to 7.3.2.5 + LC4 in Chapter 3) Maximum seagoing curve: MMAX = = 1.2 MFULL − 1.025 l b (0.67 T − TA) maximum 1.2 MFULL Minimum seagoing curve: MMIN = 0 at T Maximum harbour curve: MMAX, harbour = = MMAX + 0.18 MFULL maximum 1.2 MFULL Minimum harbour curve: MMIN, harbour = MMIN − 0.18 MFULL DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.7. Cargo Hold Load Limitations – Page 52 7.4.2 Adjacent Hold Loading Applicable for HC-B No MP and HC-C No MP (Reference is made to 7.3.3.1 + LC9 and 11 in Chapter 3) Maximum seagoing curve: MMAX, adj. = = MFULL, adj. − 1.025 l b (T − TA) maximum MFULL, adj. Minimum seagoing curve (the less of): MMIN, adj. = MMIN, adj. = 1.025 l b (TA − THB) 0.5MH, adj. - 1.025 l b (T − TA) Maximum harbour curve (the larger of): MMAX, adj., harbour = MMAX, adj., harbour = = MFULL, adj. − 1.025 l b (0.67 T − TA) MMAX, adj. + 0.15 MFULL, adj. maximum MFULL, adj. Minimum harbour curve: MMIN, adj., harbour = MMIN, adj. − 0.15 MFULL, adj. Applicable for HC-A No MP (Reference is made to 7.3.3.2 + LC8, 9 and 11 in Chapter 3) Maximum seagoing curve (the larger of): MHD, adj. + 0.1 MH, adj. − 1.025 l b (T − TA) maximum MHD, adj. (MHD, adj. is applicable only if design block loading condition specified in the loading manual) MMAX, adj. = = MMAX, adj. = = MFULL, adj. − 1.025 l b (T − TA) maximum MFULL, adj. Minimum seagoing curve (the less of): MMIN, adj. = MMIN, adj. = 1.025 l b (TA − THB) 0.5 MH, adj. − 1.025 l b (T − TA) Maximum harbour curve (the larger of): MMAX, adj. + 0.15 MHD, adj. maximum MHD, adj. (MHD, adj. is applicable only if design block loading condition specified in the loading manual) The larger of: MMAX, adj., harbour = = MMAX, adj. harbour = MMAX, adj. harbour = = MFULL, adj − 1.025 l b (0.67 T − TA) MMAX, adj. + 0.15 MFULL, adj maximum MFULL, adj. Minimum harbour curve (the less of): MMIN, adj. − 0.15 MHD, adj. (MHD, adj. is applicable only if design block loading condition specified in the loading manual) MMIN, adj., harbour = MMIN, adj., harbour = MMIN, adj. − 0.15 MFULL, adj. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.7. Cargo Hold Load Limitations – Page 53 Applicable for HC-B and HC-C (Reference is made to 7.3.3.3 + LC7 and 10 in Chapter 3) Maximum seagoing curve: MMAX, adj. = = MFULL, adj. − 1.025 l b (0.67 T − TA) maximum MFULL, adj. Minimum seagoing curve: MMIN, adj. = 1.025 l b (TA − 0.75 T) Maximum harbour curve: MMAX, adj., harbour = = MMAX, adj. + 0.15 MFULL, adj. maximum MFULL, adj. Minimum harbour curve: MMIN, adj., harbour = MMIN, adj. − 0.15 MFULL, adj. Applicable for HC-A (Reference is made to 7.3.3.4 + LC7, 8 and 10 in Chapter 3) Maximum seagoing curve (the larger of): MHD, adj. + 0.1 MH, adj. − 1.025 l b (T − TA) maximum MHD, adj. (MHD, adj. is applicable only if design block loading condition specified in the loading manual) MMAX, adj. = = MMAX, adj. = = MFULL, adj. − 1.025 l b (0.67 T − TA) maximum MFULL, adj. Minimum seagoing curve: MMIN, adj. = 1.025 l b (TA − 0.75 T) Maximum harbour curve (the larger of): MMAX, adj. + 0.15 MHD, adj. maximum MHD (MHD, adj. is applicable only if design block loading condition specified in the loading manual) MMAX, adj., harbour = = MMAX, adj. harbour = = MMAX, adj. + 0.15 MFULL, adj. maximum MFULL, adj. Minimum harbour curve (the less of): MMIN, adj. − 0.15 MHD, adj. (MHD, adj. is applicable only if design block loading condition specified in the loading manual) MMIN, adj., harbour = MMIN, adj., harbour = MMIN, adj. − 0.15 MFULL, adj. Applicable for HC-B* only (Reference is made to 7.3.3.5 + LC7 and 10 in Chapter 3) Maximum seagoing curves: MMAX, adj. = = 1.1 MFULL, adj. − 1.025 l b (0.67 T − TA) maximum 1.1 MFULL, adj. Minimum seagoing curves: MMIN, adj. = 1.025 l b (TA − 0.75 T) Maximum harbour curve: MMAX, adj., harbour = = MMAX, adj. + 0.165 MFULL, adj. maximum 1.1 MFULL, adj. Minimum harbour curve: MMIN, adj., harbour = MMIN, adj. − 0.165 MFULL, adj. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.7. Cargo Hold Load Limitations – Page 54 7.5 Local Tank Top Loading 7.5.1 Bulk Carriers are often designed to carry general cargo on inner bottom, e.g. steel coils, aluminium ingots etc., in addition to the normal homogeneous, alternate and block-loading mode. For that reason owners may have specified a maximum tank top pressure without specifying the purpose. If such tank top pressure is used as basis for calculating the maximum mass in the holds, see formula given in the Rules for Classification of Ships Pt.5 Ch.2 Sec.5 B100, this maximum mass may exceed the maximum mass applied for the different loading conditions in the loading manual. For the purpose of handling such cases the following procedure may be applied: 1) For girder strength control the hold maximum mass should reflect the extreme loading conditions as given in the loading manual. See Sec.3 in this Note. 2) Inner bottom plating and stiffeners are to be designed for the specified maximum tank top pressure. The latter assume that this pressure is greater than pressure caused by the cargo mass given in the loading manual. Regarding loading of slabs and ingots such cargoes is normally stowed on dunnage and the amount of such cargoes is rarely specified. However, if strength calculations or load limitations are requested, such strength calculations should be based on the actual footprint loading. If steel coil loading has been specified the requirement to thickness of inner bottom plating and stiffeners will be related to the mass, breadth, the number of tiers of steel coils and the number of dunnages arranged beneath each coil All above load limitations are to be clearly stated in the appendix to class certificate. 7.5.2 Local Scantlings of Inner Bottom Plating and Longitudinals for Steel Coil Loading The following procedure is an acceptable calculation method for verifying local scantlings of inner bottom plating and longitudinals for vessels intended to carry steel coils. Other equivalent methods will also be accepted as basis for approval. 7.5.2.1 Assumptions — Longitudinal stiffening is assumed with the coils stowed with the axis in the longitudinal direction. It should be noted that the method is not applicable for transverse stowage, which will be subject to special consideration. — The distance between two adjacent steel coils is a fraction (Cs) of the steel coil length. — The distance between two adjacent dunnages supporting a steel coil is the same. — The distance between the end of the steel coil and the nearest dunnage is half of the distance between two adjacent dunnages. — If plywood sheets are used instead of plank dunnages the point loads on the plate and longitudinal should be replaced by a line load. This effect may be approximated by specifying a large number of dunnages in the formulae. Cs lc lc 0.5 sd sd = lc / nd sd nd = number of dunnages Figure 7-2 Assumptions DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.7. Cargo Hold Load Limitations – Page 55 7.5.2.2 Calculation procedure This procedure is in general valid for the flat part of the inner bottom, for the hopper top plating forces must be recalculated at right angels to the plate, combining forces in accordance with the Rules Pt.3 Ch.1 Sec.4 C500. Inner bottom plating The thickness of the inner bottom plating (longitudinally stiffened) is not to be less than: t = K av Q K ⋅ Q-----------( ( 1.65 β – 2.3 ) k a – 6 β + 12.2 ) + t k f1 [mm] av 1.1 1 + ----- g = = vertical acceleration in centre of hold as given in the Rules for Classification of Ships Pt.3 Ch.1 Sec.4 = total force by steel coils on one plate field = Wn t np ---------------nd [t] W lf lc nt = = = = = = = = = = = = = = = mass of steel coil in t plate length in m length of coil in m number of tiers of steel coils 1.4 for a single tier of coils that are secured with a key coil number of dunnages per coil nd corrosion addition as given in the Rules for Classification of Ships Pt.3 Ch.1 Sec.2 tk f1 material factor as given in the Rules for Classification of Ships Pt.3 Ch.1 Sec.2 s spacing of inner bottom longitudinals in m. aspect ratio of plate field ka lf /s 3.0 max sd lc/nd Cs 0.2 in general, however Cs lc is not to be taken larger than 0.3 m number of patch loads acting on one plate field, the following assumption may be used, direct np calculation for a given arrangement will also be acceptable in general = > np = roundup {(lf - Cs lc (nc - 1))/sd} if (nd - 1) sd < lf - (1 + Cs) lc (nc - 1) => np = nc nd nc = number of coils on one plate field = roundup {lf / ((1 + Cs) lc)} = ratio of distance between outmost load point on plate and plate length. Unless calculated directly the following assumptions may be used: β = n p = 1 = > β = bd ⁄ lf when np > 1 => { ( n p – 1 )s d + C s lc ( nc – 1 ) } β = ------------------------------------------------------------------lf bd = breadth of dunnage in m Inner bottom longitudinals The section modulus of inner bottom longitudinals is not to be less than: Z ks 103 ks M wk /σall [cm3] 1.0 in general 0.65 for longitudinals with strut fitted at mid span corrosion addition as given in the Rules for Classification of Ships Pt.3 Ch.1 Sec.3 wk = = = = σall = 225 f 1 – 100 f 2b – 0.7 σ db 2 within 0.4 L (maximum 160 f 1 ) [N/mm ] DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.7. Cargo Hold Load Limitations – Page 56 f1 f2b σdb = 160 f1 within 0.1 L from the perpendiculars. Between specified regions the σ -value may be varied linearly = material factor as given in the Rules for Classification of Ships Pt.3 Ch.1 Sec.2 = stress factor bottom as given in the Rules for Classification of Ships Pt.3 Ch.1 Sec.6, utilising Stillwater Bending Moment as applicable for steel coil loading (Min 0.5 MSO). = mean double bottom stress (in homogenous loading condition) [N/mm2] = 20 f1 minimum The stiffener bending moment at the fixation is found by direct calculation for a given arrangement or according to the following simplified formulae. For one patch load, see Fig.7-3. 2 M = Pa ( l – a ) ⁄ l a l 2 = l/3 = Stiffener span as given in the Rules for Classification of Ships Pt.3 Sec.3 C100. a P M l Figure 7-3 One patch load For multiple patch loads, see Fig.7-4. 2 P ( Σa i ( l – a i ) ) M = -----------------------------------2 l sd a1 P P P M l Figure 7-4 Multiple patch loads P av l = = = = force on one dunnage in kN Wnt (9.81 + 0.5 · av)/nd vertical acceleration in centre of hold as given in the Rules for Classification of Ships Pt.3 Ch.1 Sec.4 stiffener span as given in the Rules for Classification of Ships Pt.3 Sec.3 C100 ai : a1 = sd / 2 = a1 + (i - 1) sd + Cs lc (round down {(i - 1) / nd}) ai for i = 2, 3, 4, 5 ... ... ... As long as ai < l End connections of longitudinals are to be evaluated according to the Rules for Classification of Ships Pt.3 Ch.1 Sec.12 C400. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.8. Wave Torsion Induced Stresses – Page 57 8. Wave Torsion Induced Stresses 8.1 General 8.1.1 For bulk carriers of conventional type, the tensional stiffness of the hull is mainly related to the effective St Venants' moment of inertia of the hull, which is greatly increased, compared to that of the typically open ship. Consequently, wave torsion induced stresses are in general not necessarily to be considered. 8.1.2 For ships with large deck openings (total width of hatch openings in one transverse section exceeding 65% of the ship's breadth or length of hatch opening exceeding 75% of hold length), for example, open hatch bulk carriers, the wave torsion induced stresses shall be considered. An acceptable procedure is specified in Classification Note. 31.7 Strength Analysis of Hull Structures in Container ships (CN31.7). All calculation/ analysis specified in the CN31.7 should be carried out depending on ship’s size, except the cargo hold analysis which may be waived. If such kind of ships are designed with asymmetrical (to ship’s centre line) loading conditions, for example container loading conditions, hull girder still water torsion moment limitations shall be specified in the loading manual and shall envelope all asymmetrical loading conditions. When evaluating torsion induced stress, the still water torsion moment shall be also included. 9. Shear Force Correction 9.1 General 9.1.1 For ships with several shear carrying elements such as single/double side, longitudinal bulkhead and longitudinal bottom girders, the nominal shear force distribution among those elements may normally be decided based on “Shear Flow Calculation”. The typical shear force distribution factors for the main shear carrying members of the hull, for various type of the vessel can be found from the Table D1 of the Rules for Classification of Ships Pt.3 Ch.1 Sec.5. However, for ships covered by this Classification Note, the actual shear force distribution of the ship side structure for various loading conditions will be different from those calculated by “Shear Flow Calculation”, where the 3-D effect of the load distribution on bottom structure is not considered. Therefore, for a correct shear strength evaluation, the corrected shear force has to be calculated taking into account the local load distribution. Rules Pt.3 Ch.1 Sec.5 D200 and D300 describe the principle of this shear force correction for bulk carriers. This part of the note will provide the background and/or additional information to the Rules. 9.2 Definitions 9.2.1 Symbols IN SN Qs ΔQs Qw Φ t τ = moment of inertia in cm4 about the transverse neutral axis = first moment of area in cm³ of the longitudinal material above or below the horizontal neutral axis, taken about this axis = conventional (not corrected distribution of local load in hold(s)) stillwater shear force in kN = shear force correction in kN due to distribution of local loads in hold(s) = rule wave shear force in kN as given in the Rules for Classification of Ships Pt.3 Ch.1 Sec.5 B200 = shear force distribution factor for the effective longitudinal shear carrying elements in the hull girder (side, inner side and longitudinal bulkhead). = thickness of effective longitudinal shear carrying element, in mm. = allowable shear stress, the lesser of (110 f1 and 0.9τcr (buckling stress)), in N/mm2. 9.3 Rule Requirement 9.3.1 The rule requirement to thickness of ship side or double side as given in Pt.3 Ch.1 Sec.5 D103 of the Rules may be reformulated as follows: QS ± 0 .5 tτ I N ΔQS ≤ − QW Φ Φ ⋅ 100 S N The right hand side of the equation may be considered to express the still water shear force capacity (Qallowable) of the hull in way of the considered section. The method for establishing allowable shear force curves is described in Sec.9.4. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.9. Shear Force Correction – Page 58 The left hand side express the actual “Corrected Shear Force” which could be further simplified into Qs ± (KPc) The procedure to determine (KPc) is described in Sec.9.5. For bulk carriers with single side or double side construction, corrected shear force for all seagoing conditions, harbour conditions and flooded cases if applicable should be checked within the allowable shear force. The hull girder shear strength should always be checked for areas around engine room forward bulkhead, where many hull structures in cargo hold region normally terminate and hull girder shear capacity normally decreases. 9.4 Allowable Shear Force 9.4.1 Seagoing condition The allowable shear force Qallowable shall be calculated based on shear flow. Nauticus Hull Section Scantling is a tool used for this purpose. With reference to the formula above the allowable still water shear force can be expressed as follows Qallowable + QW = tτ I N Φ ⋅ 100 S N In Nauticus Hull, the shear flow q (N/mm) is calculated based on 1N vertical force and therefore satisfy the equation below for each plate panel in side/inner side and longitudinal bulkhead. 1= q ⋅10 I N Φ SN Comparing the two equation above, Qallowable + QW = tτ (kN) q ⋅ 1000 Obviously, Qallowable based on side plating is decided by minimum of tτ of all plate panels on side, q ⋅ 1000 tτ Qallowable , side = − QW q ⋅ 1000 min, side Qallowable based on inner side or longitudinal bulkhead plating may be calculated similarly. Therefore, Qallowable is Qallowable = Qallowable , side for single skin bulk carrier, Qallowable = min(Qallowable , side , Qallowable ,innerside ) for double skin bulk carrier, In general, allowable shear force should be calculated based on shear flow calculations carried out at all frames where scantling of plating is changed in side, inner side or longitudinal bulkhead. However, the procedure as following may be acceptable as a simplification, — In the parallel midship area, shear flow calculation should be carried out at transverse bulkheads. For the area in between any two transverse bulkheads, the allowable shear force may be based on the larger shear flow q at transverse bulkheads and the actual plating scantling in the area. — Outside the parallel midship area, shear flow calculation should be carried out at transverse bulkheads. The cross section where the hull shape starts to change from parallel midship area is considered similar as a transverse bulkhead. For the area in between any two transverse bulkheads, the allowable shear force may be based on the shear flow q (assumed as linearly varied in between the two transverse bulkheads) and the actual plating scantling in the area. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.9. Shear Force Correction – Page 59 9.4.2 Harbour condition The allowable still water shear force in harbour conditions will be obtained according to the same formula and principles as given in 9.4.1 except that the wave shear force, QW, is reduced to 50% for the sections in question. 9.4.3 Flooded cases The allowable still water shear force in flooded cases will be obtained according to the same formula and principles as given in 9.4.1 except that the wave shear force, QW, is reduced to 80% for the sections in question. 9.5 Corrected Shear Force 9.5.1 General With reference to the formula in 9.3 the corrected shear force, QS,C, can be expressed as follows QS,C = QS ± (KPC) QS is the uncorrected shear force or the shear force normally found in the loading manual (nominal shear force). The sign convention for QS and QS,C is as described in the Rules for Classification of Ships Pt.3 Ch.1 Sec.5 B100 (weight of hull aft of considered section exceeding buoyancy → positive), “ + “ applies for the corrected shear force at fore end of the hold, and “-“ applies to the corrected shear force at aft end of the hold. The shear force correction, (KPC), will be further described below for typical bulk carrier construction, i.e. with single and double side. The calculated (KPC)-value should be considered in connection with the peak values of the conventional shear force curve at the transverse cargo hold bulkheads. 9.5.2 Bulk Carriers, single/double side construction The correction, (KPC), to the nominal shear force may be expressed as follows: absolute value of (CP(PH + Σ(KNPN)) – CDT1) cargo or ballast in (t) for the hold in question bunker or ballast (t) in double bottom tank no. N (port and starboard) situated below considered hold draught in m at the middle of hold load correction factor in kN/t buoyancy correction factor in kN/m (VH A’N)/(H AN A’B) to be calculated for each filled tank height of hold in m volume of hold in m³ horizontal cross-sectional area (m²) (port and starboard) at level of inner bottom tank N horizontal cross-sectional area (m²) (port and starboard) at level of inner bottom of that part of the double bottom tank no. N which is situated within the length of the considered hold A’B = sum of all A’N. For practical purposes CP and CD may be taken as constants independent of cargo filling height and draught respectively. The following values may be used: (KPC) = PH = PN = = T1 CP = CD = KN = H = VH = AN = A’N = CP CD C BDB LH = = = = = (9.81 C BDB LH H)/VH (kN/t) 10 C BDB LH (kN/m) B/(2.2 (B + LH)) (for conventional designs) breadth of the flat part of the double bottom in m, see Fig. 9-2 length of hold in m see Fig. 9-1. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.9. Shear Force Correction – Page 60 LH A’B A’N A’N AN AN Figure 9-1 Longitudinal section BDB AN , A’N , A’B (pipe duct to be deducted) Figure 9-2 Transverse section For bulk carriers with single side or double side construction, the double bottom girders always transfer parts of net load applied on the double bottom structure directly to transverse bulkheads. Therefore the load transferred by single side or double side structure are decreased. Consequently the corrected shear force curve in each cargo hold should always have smaller absolute slope ratio comparing to nominal shear force. Following the above principle, the (KPC) should be added to or deducted from the peak values of the nominal shear force curve at transverse bulkheads in each cargo hold. It should be also noted that (KPC) due to net loads in fore peak tank and engine room are normally neglected. See Figure 9-3 and 9-4 for examples of nominal and corrected shear force for an alternative loading condition and a heavy ballast loading condition respectively. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Sec.9. Shear Force Correction – Page 61 Figure 9-3 Nominal and corrected shear force for an alternative loading condition Figure 9-4 Nominal and corrected shear force for a heavy ballast loading condition DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Appendix A Checklist for Finite Element Analysis – Page 62 Appendix A Checklist for Finite Element Analysis A.1 Guidelines for use of checklist for FE analysis A.1.1 The checklist is developed as an aid to ensure a satisfactory level of technical quality of work for analysis performed by the FE method. The checklist may also function as guidance for the process of completing FE analysis. It is recommended that the checklist is used for self-checking by the one performing the analysis, and preferably by those performing independent verification. A.1.2 The control may be further adapted to the computer program used in the analysis. In general the following main items should be checked: — — — — — geometry and element mesh stiffness properties boundary conditions loads and pressures stresses and reaction forces. CHECKLIST FOR GEOMETRY, MESH AND ELEMENT PROPERTIES STRUCTURAL PART: Reference drawings: Directory: Input and model file names: FEM file name: Units (have been checked): Controlled by / date: Length: [mm] Mass: [t] Time: [s] Force: [N] Pressure: [N/mm2] Constants (have been checked): Gravity: 9810 [mm/s2] -9 Density (steel): 7.85 E 10 [t/mm3] 5 Young's mod.: 2.1 E 10 [N/mm2] Thermal exp. coeff.: 0.0 Poisson's ratio: 0.3 Scantlings: Net scantlings applied/ not applied Check of nodes: Spot checks of co-ordinates for key-nodes and nodes at border lines have been performed. Check of elements: Elements have been checked for having correct material. Elements have been checked for having correct thickness (membrane/shell) or cross section properties (truss/beam). Truss/beam elements have been checked for having correct eccentricity. Free flange sectional area has been checked for efficiency of curved flanges. Secondary elements (buckling stiffeners) been checked for having correct efficiency according to end connection (sniped/welded). Boundary conditions: The boundary conditions given (fixations) have been checked. Spring constants calculated according to prevailing Class Note used / not used Loads: Load directions are found to be correct DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Appendix A Checklist for Finite Element Analysis – Page 63 Plots: Plots of element mesh with thickness (colour plots or by numerical value on elements) and boundary conditions are submitted with the checklists. There is conformance between drawings and plots. Structural part accepted: date:__________ _________________________ sign. CHECKLIST FOR LOADS Structural part: Loads: Hand calculations or other program calculation for each basic load case are compared with the results from data check performed by the solver. Load directions are found to be correct The sum of loads from data check are checked Superelements are/are not mirrored or rotated. Loads are checked for mirrored and rotated superelements. Prints with data check of all loadcases is submitted with the checklists Controlled by / date: Loads and load application are accepted: date:__________ _________________________ Sign. CHECKLIST FOR LOAD COMBINATIONS AND RESULTS PRESENTATION STRUCTURAL PART: Controlled by / date: Plots: Plots of structural part with deformed shape in proper scale are submitted with the checklists. Plots of transverse membrane stresses of shell elements for relevant structural parts are submitted with the checklists (contour plots and/or plots with numerical values). Plots of shear stresses for relevant structural parts are submitted with the checklists (contour plots and/or plots with numerical values). Plots of in plane stresses for relevant structural parts are submitted with the checklists (contour plots and/or plots with numerical values). Plots of equivalent (von-Mises) stresses for relevant structural parts are submitted with the checklists (contour plots and/or plots with numerical values). Plots of axial stress of free flange for relevant structural parts are submitted with the checklists (contour plots and/or plots with numerical values). Stresses / forces: Spot checks of the calculated stresses have been compared to values calculated by simplified methods. Plots have been used to identify peak stresses. Cross sectional forces and moments have been checked with simplified methods. Code checks / acceptance criteria: Yield check of main structure performed based on relevant load cases and stresses. Hull girder stresses added/not added manually. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Appendix A Checklist for Finite Element Analysis – Page 64 Yield check of secondary structure performed based on relevant load cases and stresses. Local bending has been taken into account. Buckling check of transverse elements performed based on relevant load cases and stresses. Buckling check of longitudinal elements performed based on relevant load cases and stresses. Hull girder stresses added/not added manually. Fatigue check performed based on relevant load cases, stresses and available stress concentration factors. Analysis accepted date:__________ _________________________ DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Appendix B Beam Modelling – Page 65 Appendix B Beam Modelling B.1 Beam modelling, general B.1.1 The 2-dimensional beam models, which may be applied for conventional bulk carriers, are as follows: a) Transverse bulkhead structure, which is modelled as a framework model subjected to in plane loading, see B.2. b) Double bottom structure, which is modelled as a grillage model, subjected to lateral loading, see B.3. Note that this calculation may utilise stiffness data and loads as calculated for the transverse bulkhead calculation mentioned under a) above. Alternatively, load and stiffness data for the bulkhead may be based on approximate formulae. c) Top wing tank structure, which for ships without specified deck cargo, is calculated by a framework model of the top wing tank web frame subjected to in plane loading, see B.4. B.1.2 Three-dimensional modelling may be applied instead of some or all of the 2-dimensional models referred above. It may be mentioned that 3-dimensional modelling for the double bottom structure may be utilised for improved description of the hopper and main frame region of conventional bulk carriers. B.1.3 Three-dimensional models representing the total cargo hold structure of one or more cargo holds, should preferably be carried out as finite element models. B.1.4 The symbols used in model sketches are described in Fig.B-1. B.1.5 For the formulae given in this section, consistent units are assumed used. The actual units to be applied, however, may depend on the structural analysis program used in each case. B.1.6 The models should represent the “net” structure; i.e. the corrosion additions as specified in the Rules for Classification of Ships Pt.3 Ch.1 Sec.2 are to be deducted from the given scantlings. B.1.7 Beam- and bar elements representing the stiffness of flanges are generally to be adjusted for effective width in accordance with the Rules for Classification of Ships Pt.3 Ch.1 Sec.3 C400. For grillage type double skin structures, however, such as double bottoms stiffened by floors and longitudinal girders, full flange effectivity may normally be assumed for the elements representing the girders of the grillage. B.1.8 The increased stiffness of girder elements with bracketed ends is to be properly taken into account by the modelling. The rigid length of beam elements in way of bracket regions, lr, may normally be taken as: lr d lτ = = = = = l – d – lτ, see also Fig.B-2 0, minimum as given in Fig.B-2 represents the shear induced bending flexibility of the bracket 0 in general 2.6I ---------- I A t = A t if considered element is ⊥ to all other elements representing the bracket region, and the lτ of these elements are taken = zero. = moment of inertia of considered girder element = area of the bracket region including adjacent girder webs = thickness (mean) of bracket and adjacent girder webs. B.1.9 The additional girder bending flexibility associated with the shear deformation of girder webs in nonbracketed corners and corners with limited size softening brackets only should normally be included in the models as applicable. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Appendix B Beam Modelling – Page 66 The bilge region of transverse girders of open type bulk carriers and longitudinal double bottom girders supporting transverse bulkhead represent typical cases where the web shear deformation of the corner region may be of significance to the total girder bending response, see also Fig.B-3. The additional flexibility may be included in the model by introducing a rotational spring, KRC, between the vertical bulkhead elements and the attached nodes in the double bottom, or alternatively by introducing beam elements of a short length, l, and with cross-sectional moment of inertia, I, as given by the following expressions: KRC = b1 b2 t G b b tlG 1 2 I = ------------------------- E B.1.10 It is important to use a short element with above properties as this approach assumes constant moment over the element length. The modelling shall generally take into consideration relevant effects due to variation in element web height over its length as applicable. Unless special beam elements with varying web height are available, members with varying height should preferably be represented by a grid as shown in Fig.B-4, which shows a typical bulkhead lower stools. The proposed meshes are appropriate for stools, which are stiffened by diaphragm plates with varying sized lightening holes. The purpose of the horizontal system lines is to connect the elements representing the stool side plating and stiffeners (flange effect) with the elements representing the web plating of the stool to form an integrated structural system. The horizontal elements should be made rigid compared to the vertical elements representing the web plating, but should not have excessive shear area and moment of inertia (in order to avoid numerical problems in the solution process). The necessary number of rigid horizontal elements depends on the shape of the structure. Normally, however, 4-5 horizontal elements as indicated in Fig.B-4 should be enough for a satisfactory model representation. B.1.11 In simplified two-dimensional modelling, possible three-dimensional effects caused by supporting girders etc. are normally represented by springs. The spring stiffness, KG, of axial springs representing supporting girders may normally be given by the following formula: c 1 EIs m K G = -----------------------------c2 I 4 l 1 + ----------- 2 l A s l I As sm c1 c2 = = = = = = = = supporting girder span. moment of inertia of the supporting girder shear area of supporting girder model breadth 76.8 for simple end condition for supporting girder 384 for fixed end condition for supporting girder 50 for simple support condition for supporting girder 250 for fixed end condition for supporting girder. B.1.12 In beam models the torsional stiffness of box structures is normally represented by beam element torsional stiffness, and in case of three-dimensional modelling sometimes by shear elements representing the various panels constituting the box structure. Typical examples where shear elements have been used are shown in Fig.B-7, while a conventional beam element torsional stiffness has been applied in Fig.B-8. The torsional moment of inertia, IT, of a torsion box may generally be determined according to the following formula, see also Fig.B-5. m IT m ti si (Σ rs) i=1 i i = --------------------------si m Σ i = 1 --ti 2 = no. of panels of which the torsion box is composed = thickness of panel no. i = breadth of panel no. i DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Appendix B Beam Modelling – Page 67 ri = distance from panel no. i to the centre of rotation for the torsion box. Note the centre of rotation must be determined with due regard to the restraining effect of major supporting panels (such as ship side and double bottom) of the box structure. B.1.13 In two-dimensional modelling, the three-dimensional effect of supporting torsion boxes is normally represented by rotational springs or by axial springs representing the stiffness of the various panels of the box. The spring stiffness, KT, of a rotational spring representing a supporting torsion box is normally given by the following expression: 8Gs m I T K T = ------------------2 l sm l IT = breadth l assumed for two-dimensional model = length of torsion box between supports = as given in B.1.12. B.1.14 The rotational restraint by torsion boxes (e.g. top wing tank) may be represented by axial springs as indicated in Fig.B-6. The stiffness of the axial spring(s) is generally given by the following formula: 4Gtbs m K s = ------------------2 l l b t sm = = = = length of torsion box between supports breadth of panel represented by spring considered thickness of panel breadth assumed for two-dimensional model. In case the axial spring direction may not be correctly defined in the program applied, the spring should be replaced by an area element of the equivalent cross-sectional area and extending in the desired spring direction to a fixed support. The cross-sectional area, A, of the area element is generally given by: Ks l A = -------E l = length of element ELEMENTS BETWEEN NODES RIGID END OF ELEMENTS RIGID ELEMENTS ELEMENT HINGED AT NODE FIXED NODE NODE WITH FIXED IN PLANE ROTATION AND X-MOVEMENT, FREE Y-MOVEMENT NODE WITH FIXED X- AND Y-MOVEMENT, FREE IN PLANE ROTATION NODE WITH FIXED Y-MOVEMENT FREE IN PLANE ROTATION AND X-MOVEMENT NODE WITH LINEAR IN PLANE RESTRAINT (LINEAR SPRING) NODE WITH ROTATIONAL IN PLANE RESTRAINT (ROTATIONAL SPRING) Y X Figure B-1 Symbols DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Appendix B Beam Modelling – Page 68 l l lr lr I I ho h b ho ho r (a) ho (b) d , d b r 1.0 0.9 0.8 0.7 0.6 (b) 0.5 0.4 (a) 0.3 0 0.5 1.0 1.5 2.0 h , r ho h ° Figure B-2 Rigid end lengths of beam elements Double bottom b2 KRC t b1 Figure B-3 Nonbracketed corner model DET NORSKE VERITAS AS I l Classification Notes - No. 31.1, December 2012 Appendix B Beam Modelling – Page 69 Flange Web Figure B-4 Element mesh representing tapering member (bulkhead stool) s1 Centre of rotation r1 r2 s2 r3 s3 Figure B-5 Torsional stiffness of box structure KS b t b KS Figure B-6 Spring modelling of supporting panels of torsion boxes DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Appendix B Beam Modelling – Page 70 Figure B-7 3-D beam element model covering double bottom structure, hopper region represented by shear panels, bulkhead and deck between hatch structure. Lumped main frames Figure B-8 3D beam element model covering double bottom structure, hopper region, bulkhead and deck between holds. Lumped main frames B.2 Transverse bulkhead structures B.2.1 The transverse bulkhead is normally modelled as a two-dimensional structure. In such case the model normally represents the corrugation at centreline. Three-dimensional modelling including also the deck structure may be advisable in order to determine the variation in the support stresses of the bulkhead corrugation at the lower and upper stool over the breadth of the hold, or for instance to represent special load conditions including such as the moment exerted by a crane pedestal and or deck loads. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Appendix B Beam Modelling – Page 71 B.2.2 Fig.B-9 shows a sketch of a typical transverse bulkhead design and the corresponding two-dimensional beam model. For calculation of the watertight bulkhead loading, LC17, the fixed support condition should generally be assumed at the lower bulkhead support at the inner bottom. For consideration of bulkhead strength for cargo load as given by load case LC12, the rotational displacement obtained for the double bottom calculation should be applied at the lower bulkhead support. B.2.3 The element mesh pattern of the stool should generally be made in accordance with B.1.10. Note that in the regions where each stool side is supported by separate webs, the sloping system lines should represent the complete stiffness of the webs including the plate flanges. B.2.4 As indicated in Fig.B-9, it is normally sufficient to represent the bulkhead support at the deck by a simply supported node. Note, however, that the deck support should in principle be positioned in the shear centre position of the crossdeck structure, which in cases with a high hatch end coamings or a large upper stool tends to be below the deck level. If the shear centre position of the crossdeck is not known, a support position at deck level is generally acceptable. It should be noted that when an upper stool has been arranged, the torsional stiffness of the stool structure may be included as a rotational spring, KT, as given in B.1.13, see also Fig.B-10. The support by the hatch end coamings and transverse beam may be represented as axial springs as indicated in Fig.B-10, KD, which according to B.1.11 for the corrugation at centreline (assuming simple support at the hatch side coaming) may be expressed as: 77EIs m K D = ---------------------------------4 50 I b 1 1 + ------------- 2 b 1 A S b1 I AS sm = = = = hatchway breadth moment of inertia of hatch end coaming about horizontal axis vertical shear area of hatch end coaming model breadth. B.2.5 The two-dimensional bulkhead model is normally taken at the ships' centreline. The required model breadth will depend on the actual design in each case. It may be convenient to choose the breadth corresponding to the longitudinal bottom girder spacing. Note that the stiffness of corrugated bulkhead above the stool is in this case to be taken as a multiple of the stiffness of one corrugation. B.2.6 The bulkhead calculation may be utilised in order to determine stiffness- and force data for the bulkhead to be applied for the double bottom grillage calculation. In this case the supporting moment at the lower support, MBB, may be applied in the double bottom grillage calculation as a moment, MBS, per double bottom girder as follows: M BB s g M BS = ----------------sm sg = effective breadth of the double bottom side girder considered = model breadth of bulkhead model. sm The rotational constraining stiffness exerted by the bulkhead on the double bottom may be determined by subjecting the lower bulkhead support to a rotational displacement, φ, as a separate load case. The rotation spring stiffness exerted by the bulkhead is then determined from the calculated supporting moment, M, by the formula: Ms g K RB = ---------φ sm B.2.7 If three-dimensional modelling is used, the transverse bulkhead model should be joined to the double bottom DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Appendix B Beam Modelling – Page 72 grillage model described in B.3 following. In such case short bending elements representing the shear flexibility of longitudinal double bottom girders below the bulkhead (stool) should be considered introduced as described in principle in B.1.9. Crossdeck shear centre Figure B-9 Two-dimensional mesh of bulkhead structure KD KD KD KD KT Figure B-10 Spring support by hatch end coamings B.3 Double bottom structure B.3.1 The double bottom structure is normally modelled as a grillage or as a part of a three-dimensional model covering the hopper and/or the transverse bulkhead and deck, in addition to the double bottom structure. Three-dimensional modelling is preferable, and should generally be used for the hopper region unless the hopper tank is small. Similarly the inclusion of the transverse bulkhead structure into the double bottom model may be important for the correct assessment of shear forces in double bottom longitudinal girders and for the bulkhead member shear and bending response. B.3.2 Fig.B-11 shows a typical double bottom grillage element mesh with the hopper tank modelled as a three dimensional structure. The model is to extend athwartships from the ship side to the centreline, where symmetry is assumed for relevant load conditions. In the longitudinal direction the model should extend at least from the middle of one hold to the middle of the adjacent hold. Symmetry is assumed at both model ends. In cases where the considered holds are unsymmetrical, due to an unsymmetrical lower stool, or due to an DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Appendix B Beam Modelling – Page 73 unsymmetrical floor arrangement, an increased model length extending over one complete hold and two half hold lengths should be considered. Alternatively, if a model extending over 2 half hold lengths is used, care should be exerted to ensure that longitudinal double bottom girders are modelled with their true effective span length between bulkhead corrugations. This may be obtained by modelling the bulkhead lower stool as an equivalent symmetrical structure, or by rearranging the floor spacing such that the midspan position is located at a floor or midway between two floors. The vertical model support(s) is generally assumed at the transverse bulkhead(s) in the shear centre position of the half cross-section of the hull. The shear centre position of the half cross-section may be determined by a shear flow analysis. For bulk carriers of conventional arrangement the distance of the support position outside of the side shell, ys, is given approximately by the following expression: B – b1 y s = --------------16 b1 = breadth of hatch opening (m) For open type double skin bulk carriers, the support point may be assumed at the mid-breadth of the wing tank. B.3.3 The beam elements representing floors extending from centreline to the hopper side and longitudinal double bottom girders should have a torsional moment of inertia, IT, equal to: 2 bh I T = ----------------1 1 ------ + ---t ib t b b h tib tb = = = = member flange breadth (assuming 100% effective flange breadth, see B.1.7 above web height thickness of bottom plating thickness of inner bottom plating. B.3.4 The shear stiffness of double bottom girder elements is in general to be reduced for girders with large web openings. For normal arrangement of access and lightening holes a factor of 0.8 may be suitable. B.3.5 Adjacent floor elements of the grillage model are assumed to be separated halfway between floors. The floors in line with stool sides have not been included in the model. B.3.6 Transverse elements in way of pipe tunnels with separate bottom and inner bottom stiffening may be modelled as the other floor elements, except for the effective shear area, AS, which should be taken as: 2.6 A S = -----------------------------2 l - ---------2.6----------+ 12ΣI ΣA S l ΣI ΣAS = span of transverse stiffeners in pipe tunnel = sum of moments of inertia of bottom and inner bottom transverse stiffeners within the floor flange breadth. = sum of shear areas of bottom and inner bottom transverse stiffeners within the floor flange breadth. B.3.7 The transverse bulkhead elements should represent the shear and bending stiffness of the bulkhead and the torsional stiffness of the lower stool and that part of the inner bottom below and adjacent to the stool which is not represented by the neighbouring floor elements. The cross-sectional properties of the transverse bulkhead elements should generally be based on an assumed effective flange width for bottom, inner bottom and deck which does not exceed 20% of the vessel breadth. For corrugated bulkheads with a lower stool structure, the element moment of inertia and shear area of the transverse bulkhead may be determined according to B.5.4. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Appendix B Beam Modelling – Page 74 The torsional moment of inertia, IT, of the bulkhead elements representing the lower stool should (in agreement with B.1.12) be determined according to the following formula, see also Fig.B-12. 6 2 ( Σi = 1 ri si ) I T = ----------------------------si 6 Σ i = 1 --ti B.3.8 Adjacent longitudinal double bottom elements are assumed to be separated halfway between the girder webs. The sloping hopper side plate and the bottom plating outside of the hopper side girder should be disregarded when the hopper side girder element cross-sectional properties are determined. The bending stiffness contribution of the bottom-and inner bottom longitudinals may be included by increasing the longitudinal girder web thickness as follows: h u + h n 2 3 ( A N + A U ) 1 – ----------------- h db Δt w = -----------------------------------------------------------------h db AN = sum of net cross-sectional area of bottom longitudinals within flange breadth of girder (corrosion margin deducted) AU = sum of net cross-sectional area of inner bottom longitudinals within flange breadth of girder (corrosion margin deducted) = distance from bottom plating to neutral axis of bottom longitudinals (plate flange disregarded) hn hu = distance from inner bottom plating to neutral axis of inner bottom longitudinals (plate flange disregarded). The correct effective shear area for the girder is obtained by multiplying the element shear effectivity factor (if available) by: tw -------------------t w + Δt w B.3.9 For the elements representing the ship side and hopper region, an element with bending and shear stiffness in accordance with the half hull girder cross-section may be used. The torsional moment of inertia of the hopper tank, IT, should be determined in accordance with B.1.12. B.3.10 The stiffness and load effects from the side frames acting on the double bottom structure may be represented by rotational springs and nodal forces and moments described for the nodes representing the hopper webs at the hopper top. B.3.11 In general, a 3-dimensional modelling of the web frames of hopper region should be applied. The torsional stiffness of the hopper tank should then be represented by shear elements (elements with large bending rigidity) with shear area equal to the cross-sectional area of the hopper side plate. The local axis of these elements should be defined in the plane of the hopper side. B.3.12 The rotational spring stiffness representing the transverse bulkhead, KRB, in accordance with B.2.6, may for each longitudinal girder be determined from the transverse bulkhead calculation. B.3.13 The moment and the forces are to be applied for each longitudinal girder due to the lateral pressure by cargo on the transverse bulkhead may be determined from the transverse bulkhead calculation. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Appendix B Beam Modelling – Page 75 Transverse section Girder model Longitudinal section Floor models ys Figure B-11 Double bottom grillage element mesh s2 t2 s1 s3 t1 t3 r2 s6 s4 t6 r6 t4 r1 r3 r5 t5 s5 Figure B-12 Lower stool torsional moment of inertia DET NORSKE VERITAS AS r4 Classification Notes - No. 31.1, December 2012 Appendix B Beam Modelling – Page 76 B.4 Top wing tank / Deck structure B.4.1 The top wing tank web frame structure is in some cases analysed as a two-dimensional structure where the closed cell torsional supporting stiffness of the top wing tank between transverse bulkheads is modelled as springs. In other cases a three-dimensional model covering the deck structure and sometimes also the main frames and the transverse bulkhead should preferably be used. B.4.2 The two-dimensional modelling assumes that every web frame within one hold length is subjected to the same loading, and that the supporting stiffness of the top wing tank may be reliably defined in terms of axial spring supports as given in B.1.14. This modelling assumption is normally suitable when calculating the load cases LC15 and LC16 with ballast in the top wing tank. For the load cases LC13 and LC14 with ballast in hold the boundary assumption for the axial spring supports for the two-dimensional model of the top wing tank web frame must be specially considered due to the constraining effect of the transverse bulkhead load. A two-dimensional model based on an assumed support at the hatch end coamings may, however, be used provided the hatch end coamings are connected by effective bracket structures to the transverse bulkhead upper stool. B.4.3 The two-dimensional modelling may be less well suited for bulkcarrier designs intended for cargo on deck and hatch where the hatch cover load is supported on the hatch end coaming structure, and in particular if the deck structure between hatches is also utilised for support of a deck crane pedestal. The two-dimensional model may also be insufficient when calculating the load cases LC13 and LC14 considering ballast in the ballast hold. In these cases it is advised that the deck structure including top wing tank is modelled as a three-dimensional structure. B.4.4 In addition, the two-dimensional modelling may be insufficient in such cases where the hull girder bending gives rise to significant local bending and/or shear stresses in longitudinal deck members. Important in such respect could be designs where high hatch side coamings are combined with deep hatch side coaming girder brackets at transverse bulkheads for effective support of deck cargo loads etc. B.4.5 Three-dimensional models of the top wing tank and deck structure should normally extend over minimum two half cargo hold lengths, and from the ship side to the centreline. The model should in addition include the side main frames and the transverse bulkhead structure at least as supporting springs. A finite element model is generally preferable, but beam formulations may also be utilised. When a beam model is used, it is important that the torsional stiffness of supporting panels of the top wing tank and bulkhead upper stool are properly included in the model in terms of element torsional moment of inertia as given in B.1.12 or by shear elements. B.5 Stiffness Properties of Transverse Bulkhead Elements, including effect of Lower Stool B.5.1 The following gives an approximate formula for the determination of cross-sectional data for transverse corrugated bulkheads including the effect of the lower stool structure. B.5.2 For the corrugated part, the cross-sectional moment of inertia, IB, and the effective shear area, AB, may be obtained as follows: 2 AD AL I B = H --------------------AD + AL Hb s A B = t c --------bc AD AL H tc bs bc = = = = = = cross-sectional area of deck part cross-sectional area of lower stool and bottom part distance between neutral axis of deck part and lower stool and bottom part mean thickness of bulkhead corrugation breadth of corrugation breadth of corrugation measured along the corrugation profile. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Appendix B Beam Modelling – Page 77 B.5.3 For the stool and bottom part, see Fig.B-13, the cross-sectional properties, IS and AS, should be determined as normal. Based on the above, a correction factor, K, may be determined by the formula: 100I B I S 1 + -------------- 2 AB B K = 1 + ----------------------------------100I S I B 1 + -------------- 2 AS B B.5.4 By applying this factor, the cross-sectional moment of inertia, I, and shear area, A, of the transverse bulkhead as a whole are calculated to: I = K IB A = K AB B.5.5 The normal stress in the upper deck, σD, due to the bulkhead bending may be determined according to the following formula: M BHD σ D = -----------------K H AD B.5.6 Similarly the normal stress in the lower stool, σls, due to the bulkhead bending may be determined according to the following formula: M BHD 1 ks ( K – 1 ) - ------------ + ---------------------- σ l s = -------------- Z LS K HA L ZLS ks = section modulus of lower stool with respect to position considered = 1.0 for position below neutral axis of lower stool and bottom part = -1.0 for position above neutral axis of lower stool and bottom part. AD AD NEUTRAL AXIS, DECK bc bs H tc IS , AS , A L NEUTRAL AXIS LOWER STOOL AND BOTTOM PART 0.2 B (max) Figure B-13 Bulkhead double bottom grillage element definition DET NORSKE VERITAS AS AL Classification Notes - No. 31.1, December 2012 Appendix B Beam Modelling – Page 78 B.6 Stress Analysis, general B.6.1 The analysis procedures described in the following refer to beam calculations carried out in accordance with B.1-B.4. B.6.2 The described stress analyses generally refer to allowable stress limits given in the Rules. In addition compressive normal stresses and shear stresses shall be considered with respect to buckling in accordance with Pt.3 Ch.1 Sec.14 of the Rules for Classification of Ships, also for cases where no special reference to buckling control has been included in the text following. B.6.3 In the following calculated forces and moments are assumed given in N and Nmm, and material scantlings referred in formulae are assumed to be net scantlings, i.e. corrosion additions as stated in the Rules for Classification of Ships Pt.3 Ch.1 Sec.2 D400 deducted. B.7 Double bottom bending strength B.7.1 Allowable normal girder stresses as given in the Rules for Classification of Ships Pt.3 Ch.1 Sec.13 B400 and buckling requirements given in Pt.3 Ch.1 Sec.14 B200 and B400 are generally to be complied with. For the sum of longitudinal normal stress due to hull girder bending and longitudinal double bottom stress in nonhomogeneous loading conditions (Rule allowable stress = 190 f1 (N⁄mm2), the still water hull girder stress may generally be based on the mean still water bending moment value, MSM, which for the middle of hold position is given by: M S1 + M S2 M SM = ---------------------------2 MS1, MS2 denote still water hull girder bending moments calculated for the aft and forward transverse bulkhead positions of the cargo hold for the loading condition being considered. B.7.2 The transverse axial force of the double bottom structure due to external sea pressure on the sides need not be considered when the bottom panel is evaluated with respect to biaxial buckling in accordance with Pt.3 Ch.1 Sec.14B of the Rules, provided the inner bottom structure is able to effectively support the external sea pressure load. B.8 Pipe tunnel strength B.8.1 The modelling technique applied normally reflects the transverse stiffness of the combined bottom and inner bottom structure in the pipe tunnel. Consequently, special stress analysis will be required to determine the local stress response. B.8.2 The shear area of the pipe tunnel transverse members may normally be expressed as follows: Inner bottom transverse member: 2F ( 1 – k ) + 1000p i sl τ = --------------------------------------------------200A I ( N ⁄ mm ) 2Fk + 1000p e sl τ = -------------------------------------200A E ( N ⁄ mm ) 2 Bottom transverse member: F 2 = mean calculated shear force (N) in floor in way of pipe tunnel. ( F + F )s 1 2 = ------------------------- 2s f DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Appendix B Beam Modelling – Page 79 = 0 for pipe tunnels in the ships' centreline k I E = -------------- IE + II s = spacing in m of transverse stiffening members of in pipe tunnel = mean spacing in m of double bottom floors in way of the considered transverse tunnel members sf l = span of transverse pipe tunnel members in m. IE, II denote moment of inertia of stiffeners including plate flange in cm4. AE, AI denote shear area of stiffeners in cm2. Other symbols are illustrated in Fig.B-14. Note the allowable shear stress is to be taken according to the Rules for Classification of Ships Pt3 Ch.1 Sec.13 D400 (= 90 f1 N/mm2). B.8.3 The total normal stress of pipe tunnel transverse members may normally be determined according to the following formula: Inner bottom transverse member: 2 3 Fl ( 1 – k -) p-------------------i sl 10 --------------------+ σ ib ( h db – 2 h ) 2 2 12 ib σ = -------------------------------------------------- + -----------------------------------( N/mm ) h db Zi Bottom transverse member: 2 3 p e sl 10 Flk -------- + -------------------- σ (h – 2 ) 2 2 12 b db hb - ( N/mm ) σ = ------------------------------------- + --------------------------------h db Ze F,l,s = as given in B.8.2 σib = transverse stress (N/mm2) in inner bottom in way of pipe tunnel according to double bottom calculation σb = transverse stress (N/mm2) in bottom in way of pipe tunnel according to double bottom calculation hib = height in m of transverse inner bottom pipe tunnel member hb = height in m of transverse bottom pipe tunnel member hdb = height of double bottom at pipe tunnel in m = internal pressure from cargo as given in the Rules for Classification of Ships Pt.3 Ch.1 Sec.4 C400 pi for the load case considered = external lateral sea pressure according to the load case considered pe Ze, Zi = section modulus of pipe tunnel members (cm3). Other symbols are defined under B.8.2 and in Fig.B-14. Note the allowable normal stress is to be taken according to the Rules for Classification of Ships Pt.3 Ch.1 Sec.13 B400 (= 160 f1 N/mm2 in general). DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Appendix B Beam Modelling – Page 80 l h ib , I i , A i , Zi STRUCTURAL DESIGN hb , I e, A e , Ze pi F F 2 DISTR. PRESSURES 1 FORCES pe Figure B-14 Analysis of pipe tunnel transverse members B.9 Strength of double bottom below transverse bulkhead stool B.9.1 When vertically corrugated transverse bulkheads are subjected to lateral load, large support forces, PF, occurs by the bulkhead bending at the lower stool side or the corrugation flange (if no lower stool is fitted) attachment to the double bottom as illustrated in Fig.B-15. The force, PF, may be determined from the calculated bending moment of the transverse bulkhead at the inner bottom, MB (Nmm), as follows: MB P F = -------bs (N) bs = breadth (mm) of stool at inner bottom. For wide stools the force PF will be balanced by the shear forces, FS1 and FS2, in the adjoining longitudinal bottom girder. For narrow stools the vertical stool side force may become very large giving rise to high shear stress in the web area below the stool. The nominal shear stress in the web may normally be determined as the larger of: τ P = ---------------100A S Pb s = -----------------------100h A db P h 2 ( N ⁄ mm ) = ( 2P – ( F + F ) ) ⁄ 2 (N) F S1 S2 = the (vertical) shear area of the longitudinal girder below stool in cm = 10 t(hdb – hl) AH = the (horizontal) shear area of the longitudinal girder below the stool in cm2. = 10 t(bs – bl) hdb = as given in B.8.3 = breadth in m of lightening hole arranged in double bottom girder below stool hl = breadth in m of lightening hole arranged in double bottom girder below stool bl t = thickness of longitudinal double bottom girder below stool in mm. FS1 and FS2 denote shear forces (N) of the longitudnal girder at the bulkhead stool, taken from the double bottom grillage calculation. The allowable nominal shear stress is to be taken in accordance with the Rules for Classification of Ships Pt.3 Ch.1 Sec.13 B400 (= 100 f1 N/mm2). AS DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Appendix B Beam Modelling – Page 81 B.9.2 Where the floors below the stool side are discontinuous, e.g. at pipe tunnels, large stress concentrations may occur when the normal force, P, is transmitted from the stool to the double bottom. With reference to Fig.B-16, the nominal normal stress of the stool side, σ, at inner bottom may be calculated to: ( 3b – b e )P σ = ------------------------2b b e t s P = force (N) transmitted between stool side and double bottom in way of the longitudinal girder considered = b 2 ( N ⁄ mm ) bs tw P F 1 – ---------- 6t s b (N) = breadth of stool side in mm corresponding to longitudinal girder b +b 1 2 = ---------------- 2 be ts tw PF = = = = effective breadth considering continuity thickness of stool side plating in mm thickness of diaphragm plate in stool in line with considered longitudinal double bottom girder as given in B.9.1. The allowable normal stress may be taken in accordance with the Rules for Classification of Ships Pt.3 Ch.1 Sec.13 B400 (= 160 f1 N/mm2). The nominal shear stress, τ, at the intersection between floor and longitudinal girder may be calculated to: PF τ = --------------------------------------100 ( A S1 + A S2 ) 2 ( N ⁄ mm ) AS1, AS2 denotes shear areas as indicated in Fig.B-16. The allowable nominal shear stress may be taken in accordance with the Rules for Classification of Ships Pt.3 Ch.1 Sec.13 B400 (= 90 f1 N/mm2). hl hdb bl bs PF FS1 PF FS2 Figure B-15 Stress analysis of longitudinal web below transverse bulkhead (stool) DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Appendix B Beam Modelling – Page 82 b2 b1 b= b1 + b 2 2 STRUCTURAL DESIGN P be 30 o EFFECTIVE BREADTH AT INNER BOTTOM AS2 EFFECTIVE SHEAR AREA AS1 Figure B-16 Stress analysis of floors below stool sides in way of double bottom tunnel B.10 Shear strength of webs with cutouts B.10.1 The nominal shear stress, τ, in webs in way of scalops and holes may in general calculated as: FS τ = ------------------100hA S 2 ( N ⁄ mm ) = calculated shear force in N at section considered. FS The allowable nominal shear stress for double bottom webs is to be taken in accordance with the Rules for Classification of Ships Pt.3 Ch.1 Sec.13 B400 (= 100 f1 N/mm2). B.10.2 For floor panels, a section parallel to the element axis may be decisive for the design shear stress. With reference to Fig.B-17 the nominal shear stress for the horizontal sections at neutral axis and at bottom / resp. inner bottom may be calculated according to the following formulae: τ = nominal shear stress between stiffeners at neutral axis sF S = ---------------------------- τ 100h db A S1 2 ( N ⁄ mm ) = nominal shear stress between stiffeners at bottom (or at inner bottom) 0.9sF S = --------------------------- 100h db A S2 2 ( N ⁄ mm ) The allowable nominal shear stress is to be taken as given in B.10.1. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Appendix B Beam Modelling – Page 83 AS1 hdb s AS2 CRITICAL HORIZONTAL SECTIONS OF SHEAR STRUCTURAL DESIGN Figure B-17 Shear stress analysis of girder webs with cutouts B.11 Strength of transverse bulkhead B.11.1 The shear connection of the transverse bulkhead structure to the side shell, and compressive / tensile stresses in the transverse deck structure are matters of importance when the overall strength of the transverse bulkhead is evaluated. Both are of particular interest when the bulkhead is of the vertically corrugated type, and when special load conditions with two adjacent holds empty on a large draught or with two adjacent holds loaded (combined with one or more of remaining holds empty) have been specified. Such load conditions have been calculated with respect to the double bottom strength as described in the following. The consideration of the bulkhead strength with respect to these load cases may therefore be based on the double bottom calculation results. B.11.2 The nominal shear stress of transverse bulkheads (above the lower stool) is generally given by: F BHD τ = ---------------------------------------------------100K ( D – h db – h s )t e 2 ( N ⁄ mm ) FBHD = maximum calculated shear force in the transverse bulkhead at the section considered according to the double bottom (or quivalent) calculation, see B1-B.4 K = as given in B.5 = height of lower stool (m) hs = effective thickness of bulkhead plating te = thickness of corrugation in way of corrugated part of bulkhead = for diaphragm plate fitted in top wing tank in line with bulkhead corrugation t(h – h ) t l--------------------ht t = plate thickness of diaphragm plate in the top wing tank. ht = height of top wing tank in way of considered section = height of lightening holes in diaphragm plate in way of considered section. hl The allowable nominal shear stress is to be taken in accordance with the Rules for Classification of Ships Pt.3 Ch.1 Sec.13 B 400 (= 90 f1 N/mm2). Within the top wing tank (above the top wing tank bottom), the nominal shear stress as calculated according to the above formula may generally be reduced by a factor = 1.5, by consideration of the partial support exerted by the top wing tank bottom panel. B.11.3 The strength of the bulkhead corrugation in way of its attachment to the lower stool shall generally be considered in accordance with the Rules for Classification of Ships Pt.3 Ch.1 Sec.9 C 305. For stools with sloping stool top plate note in addition that the bending moment applicable for the control of stresses in way of the attachment of the corrugation to the stool need generally only be related to the bending moment at the level of the top of the sloped stool top plate. DET NORSKE VERITAS AS Classification Notes - No. 31.1, December 2012 Appendix B Beam Modelling – Page 84 B.11.4 The stress of the stool side plate at the attachment to the bulkhead corrugation may generally be determined based on the following formula: σ corr t corr σ stool = -------------------------t stool cos β σcorr = nominal bending stress in bulkhead corrugation at attachment to stool tcorr = thickness of bulkhead corrugation, corrosion margin tk deducted tstool = thickness of stool side plate, corrosion addition tk deducted β = angle of stool side plate with the vertical. Generally the σstool should not exceed 1.2 σ, where σ denotes the allowable stress given in the Rules for Classification of Ships Pt.3 Ch.1 Sec.9 C 302. B.12 Strength of main frames B.12.1 Generally the main frames of bulkcarriers are to comply with section modulus requirements as given in the Rules for Classification of Ships Pt.5 Ch.2 Sec.10 B. For ships with long cargo holds, the main frames will normally be subjected to considerable prescribed deformation caused by the rotational deformation of the hopper and top wing tanks. Such prescribed deformation occurs in particular for the empty holds and the ore holds in bulkcarriers in the alternate loading condition and for the condition with ballast cargo hold filled. B.12.2 Main frames subjected to prescribed deformations shall comply with the allowable stress given in Pt.3 Ch.1 Sec.13 B400. The occurring stresses may be determined by including the main frames in the double bottomor wing tank models described in B.1-B.4, or by separate direct calculation. DET NORSKE VERITAS AS