CLASSIFICATION NOTES No. 31.1

STRENGTH ANALYSIS OF STRUCTURES IN BULK CARRIERS

JUNE 1999

DET N ORS KE VERIT AS Vcritasveien 1, N-1322 Hfl!vik, Norway Tel.: +47 67 57 99 00 Fax: +47 67 57 99 11 FOREWORD DET NORSKE VERJTAS is an autonomous and independent Foundation with the objective of safeguarding life, property and the environment at sea and ashore.

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Classification Notes

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© Det Norske Veritas AS .1999 Data processed and typeset by Division Technology and Products, Det Norske Veritas AS Printed in Norway by Det Norske Veritas AS 99-05-27 14:28 - Cn31-1.doc 6.99.2000 If at'rf pe1S011 suffers loss or damage which is proved to have been caused by any negligent act or omission of Del Norske Veritas, then Del Norske Veritas shall pay compensation 10 such person for his proved dirocl loss or damage. However, lhe compensation shall not exceed an amount equal lo ten limes the fee charged for Ille service in question, provided that the maximum compensa6on shall never exceed USO 2 million.

In this provision 'Del N(l(Ske Verilas' shall msan the Foundation Del Norske Verllas as well as all its subsidiaries, directors, officers, employees, agents and any other acting on behulf of Del Norske Ventas. CONTENTS

1. General ...... _ ...... 4 I. I Introduction ...... 4 I .2 Bulk Carriers ...... 4 1.3 Procedure ...... 5 1.4 Definitions ...... 6 2. Design Loads ...... 8 2.1 General ...... 8 2.2 Bulk cargo filling part of hold, (heavy cargo) ...... 8 2.3 Bulk cargo expanded to fill hold...... 8 3. Los ding Conditions ...... 9 3.1 General ...... 9 3.2 LCl: Specified maximum draught bulk cargo coru:litions with empty hold, seagoing ...... L1 3.3 LC2: Bulk cargo with empty holds "Rule minimum", seagoing ...... 11 3.4 LC3: Bulk cargo in two adjacent holds. seagoing ...... 11 3.5 LC4: Two or more adjacent empty holds, seagoing or harboar ...... 12 3.6 LC5: Bulk cargo with rilled hold, seagoing ...... 12 3.7 LC6: Water ballast in hold, (heavy ballast condition) adjacent hold empty, seagoing ...... 12 3.8 LC?: Water ballast in hold, (heavy ballast condition) adjacent hold empty, heeled condition, seagoing ...... 12 3.9 LC8: Cargo on deck, seagoing...... 12 3.10 LC9: Watertight bulkhead loading ...... 12 3.11 LCIO: Ballast in top wing tank, seagoing ...... 13 3. 12 LCl I: Ballast in top wing tank, heeled condition ...... 13 3. 13 LC12: Non homogeneous loading at reduced draught...... 13 4. Cargo H old Analysis ...... 13 4.1 General ...... 13 4.2 Model Extent ...... 14 4.3 Modelling of geometry ...... 14 4.4 Elements and Mesh Sizc ...... " ...... 15 4.5 Boundary Conditions ...... 18 4.6 Loading Conditions ...... 20 4.7 Presentation of input and results ...... : ...... 20 4.8 Evaluation of results and applicable acceptance criteria ...... 2 1 5. Local Structure Analysis ...... 24 5.1 General ...... 24 5.2 Stiffeners subject to large deformations ...... 24 5.3 Other fine mesh model s...... 25 5.4 Documentation and result presentation ...... 26 S.5 Acceptance Criteria ...... 26 6. Additional requirements con5idering fl ooding ...... ~...... , ...... 26 6.1 General ...... 26 6.2 Global Bending Moment and Shear Force Limitation ...... 26 6.3 Transverse Bulkhead Strength ...... 27 6.4 Diaphragm and shear plates in double bottom below bulkhead stool, considering flooding. Evaluation of the effectiveness ...... 27 6.5 Limit to Hold Loading, Considering Flooding ...... 28 7. Cargo Hold Load Limitations ...... 28 7.1 General ...... 28 7.2 Procedure for preparation of Local Strength Diagrams ...... 28 7.3 Local Tank Top Loading ...... 31 8. Wave Torsion induced Stresses in Crossdeck of Conventional Bulkcarriers... ~ ...... 33 8.1 General ...... 33 8.2 Stress of crossdeck...... 33 9. Shear force correction ...... 34 9.1 General ...... 34 9. 2 Definitions ...... 34 9.3 Rule Requirement ...... 35 9.4 Allowable Shear Force ...... 35 9.5 Corrected Shear Force ...... 35 Appendix A. Checklist for Finite .Element Analysis ...... 37 A. I Guidelines for use of checklist for FE analysis ...... 37 Appendix B. M odelling...... 39 B. l Beam modelling. general ...... 39 8.2 Transverse bulkhead structures ...... 45 B.3 Double bottom structure .., ...... 46 B.4 Top wing Lank I Deck structure ...... 49 B.5 Stiffness Properties of Transverse Bulkhead Elements, including effect of Lower Stool...... 49 B.6 Stress Analysis, general...... 51 B.7 Double bottom bending strength ...... S l B.8 Pipe tunnel strength ...... 5 L B.9 Strength of double bottom below transverse bulkhead stool...... 52 B.10 Shear strength of webs with cutouts ...... 54 B.11 Strength of transverse bulkhead ...... 54 B.12 Strength of main frames ...... 55

DET NORSKE VERITAS 4 Classification Notes No. 31.1

June 1999

1. General such vessels are employed will be influenced by a variety of factors, including the receivers' storage capacity, depth ot 1.1 Introduction water in the berth, regularity of the demand for the commodity and the financing of its purchase. This large 1.1.1 variety in demand and the variety in pattern of international The "Rules for Classification of Ships" require a direct trade has created a versatile world fleet of very varied structural analysis to be carried out in order to cope with the sizes. These may be categorised as follows: complexity in the loading of hulk carriers ::mil the: m11ny Handy-size bulkers: This is the most common size of bulk possible loading conditions. The scope for the analysis is to carriers with a of 25000-50000 tonnes and a verify that stresses in the girder structure are within specified draught less than 11.Sm. The handy-sized bulker is so called limits when the structure is loaded in accordance with the because her comparatively modest dimensions permit her to specified design load conditions. enter a considerable number of ports, world-wide. Such vessels are used in many trades in which the loading or 1.1.2 discharging port imposes a restriction upon the vessel's size, The structural analysis is generally related to primary or where the quantity of cargo to be transported requires only strength members of the midship region of bulk carriers a ship able to carry 50000 tonnes or less. arranged with double bottom and single or double side and without separate longitudinal bulkheads. However, additional bulkers: The trend is for each category of bulker calculations may have to be carried out for foremost and to increase in size, and some commentators now consider the aftmost holds as the hopper/top wing tunk construction larger handy-si:ted bulkers, in the 35000-50000 tonnes range, normally is changed significantly compared to the midship to be a separate category, the handy-max bulker. construction. bulkers: Larger than the handy-sized vessel is the Panamax , so named because she is designed to 1.1.3 the maximum dimensions (particularly the maximum Where in the text it is referred to the Rules, the references breadth) which can pass through the . The refer to the July 1998 edition of "Rules for Classification of limiting dimensions for canal transit are Loa 289.Sm, Ships". extreme breadth 32.2 m and maximum draught 12.04 m. The typical range is 50000-100000 tonnes. Panamax 1.1.4 bulkers arc extensively employed in the transport of large volume bulk cargoes such as coal. grain, bauxite and iron ore Any recognised calculation method or computer program the longhaul trades. may be applied provided the effects of bending, shear axial in and torsional deformations are considered when relevant. Cape-sized bulkers: Cape-siz.ed bulk carriers have dead weights in the range of 100000-180000 tonnes. While most 1.1.5 lie within the range of 100000-140000 tonnes, new-building Strength analysis carried out in accordance with the in recent years have been concentrated in the 140000- 160000 procedure outlined in the Note will normally be accepted as tonnes range. Cape-sized vessels, with loaded draughts basis for class approval. usually in excess of 17 m can be accepted fully laden at only a small number of ports world-wide and arc engaged in the "NAUTICUS HULL" is a computer program offered by longhaul iron ore and coal trades. The range of ports which DNV that is suitable for the calculations specified in this !hey visit is increased by the use of two port discharges, the Classification Note. ship being only part laden on reaching the second discharge port. 1.2 Bulk Carriers Very Large Bulk Carriers (VLBCs): VLBCs are bulkers 1.2.l greater than 180000 tonnes dead weight. These are mainly employed on the Brazil/Europe and the Australia/Japan Bulk carriers are ships designed primarily for the routes. A number of these largest vessels arc special types transportation of solid bulk cargoes. Such cargoes are such as ore carriers, ore/oil carriers and OBOs, vessels which generally uniform in composition, and are loaded directly will not be specially considered in this Classification Note. into the cargo space without any intermediate form of containment. The range of cargoes carried in bulk carriers is consjderable. Leading bulk cargoes in the world trade are 1.2.2 iron ore, coal, grain, bauxite/alumina and phosphate rock, Jn light of the variety both in cargoes, vessel size, hold along with substantial quantities of concentrates, petroleum arrangement and not least the trading routes, including multi coke, steel, ores, cement, sugar, quarts, salt, fertilisers, port loading and discharging it is evident that the masters and sulphur, scrap, aggregates and foreslry products. Further, the officers of such vessels, will be in great nec

DETNORSKE VERITAS Classification Notes No. 31.1 s

June 1999

Maximum allowable/minimum required mass in each A ship can be incorrectly block loaded without creating individual hold as a function of draught excessive hull girder shear forces or bending moments, Maximum allowable/minimum required mass in two (or so there is normally no evidence to warn the ship's more) adjacent holds. i.e. block loading as a function of officer that his loading may cause damage. draught. Adjacent hold loading (block loading) is likely to be Maximum allowable mass in each individual hold as a considered as a method of loading when several grades function of angle of repose in case the bulkhead has not of ore are to be loaded, or several consignments of cargo been designed for the cargo in question without filling carried, and has recently been used increasingly, for a restriction. third reason. Maximum allowable mass on deck and hatch cover loading. In order to cope with the above need for information a Allowable container loading anangement both in holds procedure for calculating the necessary cargo hold load and on deck/hatch cover. limitations is given in Chapter 7 of this Classification Note. Maximum allowable lank top pressure (steel coil loading). 1.3 Procedure Still water hcnding moment and shear force limitations. This classification note describes methods for performing calculations with respect to structural strength of bulk In paragraph 1.2.3 and 1.2.4 the most important local load carriers with conventional design. The calculations are based limitations and those most frequently not adhered to have on requirements given in DNV's Rules. For some vessels it been highlighted. is required that FEM analysis is carried out, while for other vessels beam analysis is acceptable. The flow chart in Figure 1.2.3 1.1 gives an overview of the applicable chapters depending In order to exemplify the need for information about on the method of calculation. 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. Finite Element Analysis Beam, 11nalyals

Many bulk carriers load iron ore in ports, which are Chapter 2. located within the tropical zone (Brazil, Australia, West Design loads Africa, India). When such vessels are loaded to tropical marks, and take only small quantities of bunkers, the Chapter 3. Load condi1ions total cargo tonnage carried will be substantially (5-10 per cent) larger than the standard loading shown in the

loading manual. In this situation each alternately loaded Chapter4. hold is likely to be overloaded by tonnage approaching Cargo hold anolyals Appendix 8. 5-10 per cent. Beam modelling general When a ship is asked to load two or more different Chapter 5. Local strvcture analysis 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 In longitudinal strength at each stage in the voyage. Chapter 6. these circumstances it is easy to decide to load an Flooding conditions excessive tonnage in one or several holds, if the maximum permitted tonnage is not prominently displayed and well known aboard ship. Chapter 7. Cargo hold load llmltattons

1.2.4 Chapter 8. In recent years there has hccn reported structural damages in Torsional stress calculatlons which there are reason to hclieve that incorrect adjacent hold Chapter 9. loading, (block loading), has caused such structural damages. Shear force correction The reason for such maloperation is not easy lo explain exactly, however, below we have indicated some arguments which should be sufficient lo justify the need for proper Figure 1.1 Flowchart of applicable chapters in this instruction for such load limitations. Classification Note depending of calculation method There are reasons to believe that the vast majority of ship operators and ships' personnel arc completely unaware that adjacent hold loading (block loading) can cause problems.

DET N ORSKE VERITAS 6 Classification Notes No. 31.1

June 1999

The chapters are briefly described in the following: 1.4 Definitions

Chapter 2. Design Loads, gives description or references to 1.4.1 the applicable local loads, like sea pressure and pressure Symbols not mentioned in the following list are given in from cargo. connection with relevant formulae. The general symbols may he repeated when additional definition is found necessary in Chapter 3. Loading Conditions, gives a description of connection with specific formulae. applicable loading conditions. The conditions described in detail here are normally covering all relevant conditions for a L = Ruic length in m. * typical bulk carrier design. Some conditions represent the Rule minimum loading while others represent the extreme B = Rule moulded breadth in m. * loading conditions as defined in the loading manual. Steel coil loading and container loading are to be evaluated D = Moulded depth in m • separately. T = Mean moulded summer draught in m. * Chapter 4. Cargo Hold Analysis, gives a description of an acceptable procedure for Finite Element Analysis for bulk Cu = Block coefficient. * carriers. It is here focused on extent of model, the structure that shall be included, boundary conditions, mesh topology v = Maximum service speed in knots on draught T. and results that shall be evaluated. h = Cargo or ballast head in m. Chapter 5. Local Structure Analysis gives a description of Height of double bottom in m. how to perform Finite Element Analysis of local structures of hdb = bulk carriers. E = Modulus of elasticity= 2.06"105 N/mm2 for :;tee!. Chapter 6. Flooding Conditions, gives a description of additional requirements for vessels where this is applicable. g,, Acceleration of gravity. g., = 9.81 m/ These requirements ascribe from unified rules given by = IACS (International Association of Classification Societies) Cw = Wave coefficient. ** and are applicable lO hulk carriers above 150 meters carrying 2 heavy cargoes. a. = combined vertical acceleration in m/s • **

2 Chapter 7. Cargo Hold Limitations, gives a procedure for at = combined transverse acceleration in mls • ** preparation of local load diagrams for individual holds and f

Chapter 8. Wave Torsion induced Bending Stresses in * For details see the Rules Pt.3 Ch. I Sec.I Crossdeck of Conventional Bulkcarriers, gives a method to calculate torsion induced bending stresses. ** For details see the Rules Pt.3 Ch. l Sec.4 B

Chapter 9. Shear force correction, describes the method and p , Puc, o = as given in the Rules Pt.5 Ch.2 Sec.5 BI 00. background for shear force corrections. 1.4.2 Appendix. A, Checklist for FE Analysis, gives checklists related to modelling of Finite Element Models. The The structural terminology adopted in this Note is illustrated checklists are suitable tor verification of the model. in Fig. l .2, showing a typical structural arrangement of a hulk carrier in the midship area . 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 other types of bulk carriers, similar procedures should be followed. For open type bulk carriers, it is advised that additional calculations are carried out for the purpose of investigating the torsional effect of the structural elements.

DET NORSKE VERITAS Classification Notes No. 31.l 7

June 1999

Top wing tank vrebframe ,______Top wing tank pinllng Top wing vertical slrake tank Side longitudinal

Sido plating CARGO HOLD

Slde longitudnal Hopper side webframe

Bllgo \ longltudinol

Ooullle botlom Bil119 floor plating

Shedder plate

Cross deck structure - Hatch end coaming

Cross deck structure transverse beam

Cross deck structure cantilever beam ,.....---CorNgated transverse bulkhead

Lower stool diaphragm

-1-+--+--Double bottom 0 0 longitudinal girder

Figure 1.2 Typical nomenclature for bulk carrier sections in way of cargo hold and transverse bulkhead

DET NORSKE VERITAS 8 Classification Notes No. 31.1

June 1999

2. Design Loads

2.1 General 0,14 b, 2.1.1 Design pressure loads applied in direct calculations 0,3 H representing external sea pressure, liquid in tanks and cargo I in holds, are to be taken as given in the Rules Pt.3 Ch.I Sec.13. L1>ads from cargo in holds are further specified in 2.2-2.3 in the fo llowing.

2.2 Bulk cargo filling part of hold, (heavy cargo).

2.2.1 Design pressure: The design lateral pressures with bulk cargo in hold are in accordance with Rules Pt.3 Ch.1 Sec.13 to be taken as:

= Angle between panel in question and the horizontal plane in degrees. Figure 2.1 Cargo distribution filling part of cargo hold

= Angle of repose. In general to be taken as 20 2.2.2 degrees for light bulk cargo (grain etc.), 25 Shear load: A design shear load, Ps• has been added in order degrees for cement cargo (associated cargo 3 to obtain the correct total downward force in way of sloping density 1.35t/m ) and 35 degrees for heavy bulk elements i.e. transverse bulkhead :.tools and hopper tank cargo. construction, corresponding to the cargo mass, see also Fig.2.2. The shear load, Ps acting on sloping parts of Assumed level of cargo surface in hold, ref. = bulkheads is to be taken as: Rules Pt.5 Ch.2 Sec.5, see also Fig.2.1. To be taken as 0.3H + 0.14 br within 60% of the ho Id (I- K) he 2 length and breadth, and linearly reduced to a Ps = p (g +0.5av) (kN/m ) . 0 tan ex level 0.3H at hold sides and to 0.3 H + 0.07 brat transverse bulkheads. p , ex, K , he = as given in 2.2.1. H = Height of hold (including hatchway) above plane part of inner bottom in m.

= Breadth of hold in mat level 0.3H above inner bottom at hold midlength.

3 p = MttNHR· Assumed cargo density in t/m

M11 = Mass of cargo in hold, in (t), in accordance with the Rules Pt.5 Ch.2 Sec.5.

V HR = Defines volume of cargo hold below the level of he. To be taken as Vo.3H+O. l0267b/lh for regularly shaped cargo holds. For irregularly Figure 2.2 Cargo shear load on sloping elements shaped holds, V HR may be specially considered. 2.3 Bulk cargo expanded to fill hold V = Volume of hold in m3 below level 0.3H above 0311 2.3.1 inner bottom. Design pressure: The below pressure distribution assumes lh = Length of hold above lower .stool in m, that the hold is filled completely up to the top of hatch measured to the middle of corrugation depth. coaming with bulk cargo. The mass in the hold is then See also Fig. 2.1. expanded giving a different definition of p compared with Chapter 2.2 . The design lateral pressures are to be taken as:

DET NORSKE V ERITAS Classification Notes No. 31.1 9

June 1999

2 p = p (g + 0.5 a,,) K he (Kn/m ). 0 3. Loading Conditions K = As defined in 2.2.l 3.1 General he = Vertical distance in m from the load point to the 3.1.1 highest point of the hold including hatchway in In Table 1, applicable loading conditions given in the Rules general. For sloping hopper, lower stool, Pt.5 Ch.2 Sec.5 arc listed with indications regarding their bulkhead and shipside plating the distance may be applicability with respect to typical class notations, structural measured to the deck level only, unless the hatch part and analysis. coaming is in line with or close to Lhe panel considered. (Note that sloping hopper, lower These conditions are normally coveri ng all relevant loading stool, bulkhead and shipside may be taken to be conditions for a typical bulk carrier design. These conditions close to the hatch coaming when it is Jess than 10 also cover the Rule "minimum condition" in which the degrees out of line from the vertical when intention is to ensure sufficient flexibility of the vessel, measured from the deck, see also Pig. 2.3.) independent of the specified loading conditions. The Pressure on overhang structure like sloping specified loading conditions for the vessel in question may topwing tank and upper stool may be disregarded. however contain conditions not represented in Table 1, such as steel coils, containers, lumber etc. It is therefore of p 3 = MNH. "Expanded" cargo density in Um . outmost importance that the loading manual is carefully reviewed prior to defining the final design conditions. M = Mass of cargo in hold (t). Defined as the mass, according to the loading manual, combined with The structure in the loaded hold as well as in the empty holds the corresponding angle of repose that gives the are to he evaluated for all the relevant loading conditions. largest nominal lateral pressure on the bulkhead. This is expressed by the largest effective lateral 3.1.2 mass, Mn, where ME= Mtan2(45-0.5o). ME is not to be less than 0.43 V H, which correspond to a Flooding conditions applicable for vessels as described in l.3 cargo dern;ity of 0.88 t/m3 and an angle of repose Procedure, arc separately described in chapter 6. The of20 deg. Ref Rules Pt.5 Ch.2 Sec.5 structure is in general not dimensioned by direct calculations for such conditions. 3 VH = Cargo hold volume including hatch in m .

:i ; ~ 1\ ..: l : ~ n h ...... ;_...... \ .! 10• ',. ' . i' "\ . "

Load ponls

Figure 2.3 Design load pressure height for cargo bulkhead

2.3.2 Design shear load: The de.sign shear load, Ps, described in 2.2.2, is to be applied for sloping parts of bulkheads.

DET NORSKE VERITAS 10 Classifieation Notes No. 31.1

June 1999

Table 1 Applicable loading conditions for bulk carriers

LC Description Class notation Application Illustration Specified full draught Bulk Carrier HC/E Double bottom 1 condition with empty hold, Bulk Carrier HC/EA structure and ~T sea:;::cinJ:: mainframc3 ~ Bulk Carrier Douhle bottom Bulk cargo with empty holds Bulk Carrier HC structure and 2 "Rule minimum", seagoing --=-0.BT Bulk Carrier HCIE mainframes 0.6 T Bulk Carrier HC/EA ~rDi Bulk Carrier Transverse Bulk Carrier HC bulkhead, Bulk cargo in two adjacent 3 Bulk Carrier HCIE transverse deck and holds, seagoing Bulk Carrier HC/EA double bottom ~' siren 2th Bulk Carrier Transverse - Bulk Carrier HC bulkhead, Two or more adjacent empty 4 Bulk Carrier HC/E transverse deck and holds, seagoing or harhour Bulk Carrier HC/EA double bouom m'~ DJ strength Bulk Carrier Transverse Bulk cargo with filled hold, Bulk Carrier HC bulkhead lateral 5 seagoing Bulk Carrier HC/E strength ., Bulk Carrier HC/EA IJ Bulk Carrier Transverse Water ballast in hold, heavy Bulk Carrier HC bulkhead, top wing 6 ballast condition, adjacent -- IJ Bulk Carrier HC/E tank hold empty, seagoing - ~Ii~~' Bulk Carrier HC/EA Water ballast in hold, heavy Bulk Carrier Top wing tank and ballast condition, adjacent Bulk Carrier HC hopper tank girders 7 ~~2 hold empty, heeled Bulk Carrier HC/E ~~2 T,,/0. 45 T condition, seagoing Bulk Carrier HC/EA Bulk Carrier Top wing tank, Bulk Carrier HC cross deck 8 Cargo on deck, seagoing Bulk Carrier HC/E cantilevers, hatch Bulk Carrier HC/EA end and side coamings r:Ll' LIJ Bulk Carrier Transverse Bulk Carrier HC hulkhead lateral 9 Watertight bulkhead loading Bulk Carrier HCIE strength Bulk Carrier HC/EA IJ Bulk Carrier Top wing tank --'·· Ballast in lop wing tank, Bulk Carrier HC construction 10 seagoing Bulk Carrier HC/E Bulk Carrier HC/EA 0 - '-~ Bulk Carrier Top wing tank Ballast in top wing tank , Bulk Carrier HC construction 11 heeled condition Bulk Carrier HC/E Bulk Carrier HC/EA ~~- OJ Bulk Carrier HC Transverse Bulk Carrier HC/E bulkhead, Non-homogeneous loading 12 Bulk Carrier HC/EA transverse deck and at reduced draught double bottom strength ~ '~ -

DET NORSKE VERlTAS Classification Notes No. 31.1 11

June 1999

3.2 LCt: Specified maximum draught bulk cargo 3.3.2 conditions with empty hold, seagoing Cargo pressure is to be taken as given in Chapter 2.2 with cargo mass, Mn. assumed in the loaded hold defined as 3.2.l follows: This condition is applicable for bulk carriers with the class notations Bulk Carrier HCIE or Bulk Carrier HCIEA, and MH = kp D<.: VH(t) represent typical "ore" loading conditions. The loading condition shall be in accordance with the specified loading k :::: 1.0 for Bulk Carrier condition with empty cargo hold at maximum draught. I.e. 1.25 for Bulk Carrier HC and Bulk Carrier the loading manual should normally contain loading = HC/E condition reflecting alternate loading with maximum cargo deadweight on maximum draught and without any ballast. = 1.50 for Bulk Carrier HC/EA For class notation Bulk Carrier HC/E this is mandatory while for Bulk Carrier HC/EA it may be considered non­ p vc: = (Ship cargo deadweight capacity) I (total cargo mandatory. For Bulk Carrier HC/EA vessels, without any 3 hold volume), (tlm ) specified combination of empty holds, LCl will be similar to LC2. = 0.7 minimum 3 This loading condition is generally applied for the strength VH = cargo hold volume including hatchway in m . evaluation of the double bottom structure. However, it may also be decisive for the mainframe ends, if rotation of hopper/top wing tank eonsu·uction becomes significant. It 3.3.3 should be noted that for vessels with clearly defined combinations of empty holds on maximum draught, i.e. Sea pressures load is to be taken as given in Chapter 2.1. The alternate loading, the double bottom strength may be draught is to be taken as 0.6 T for Bulk Carrier, 0.8 T for evaluated with basis in a reduced still water bending· Bulk Carrier HC and Bulk Carrier HC/E and 1.0 T for Bulk moment. Ref. is made to Pt.5 Ch.2 Sec.5 C. Carrier HC/EA. The double bottom strength shall be evaluated with basis in full still water bending moments. 3.2.2 3.4 LC3: Bulk cargo in two adjacent holds, The bulk cargo pressure loads are to be taken with cargo mass in hold MH, in accordance with the specified loading seagoing condition(s). Nole that any fuel oil specified for the double 3.4.1 bottom tank below the loaded cargo hold should be included in the consideration. Cargo pressure to be in accordance with This condition is applicable for bulk carriers with class Chapter 2.2. notations Bulk Carrier, Bulk Carrier HC, Bulk Carrier HC/E and Bulk Carrier HC/EA, and is generally to be applied as a "minimum" condition for any two adjacent cargo holds. 3.2.3 The sea pressure load is to be in accordance with 2.1 at For bulk carriers where loading conditions with two adjacent maximum draught, T. holds have been specified with net load on the double bottom construction exceeding the "rule minimum", LC12 are to be 3.3 LC2: Bulk cargo with empty holds "Rule considered. The remaining "two adjacent holds" are to be checked as for the "minimum" condition as described below. minimum", seagoing 3.3.1 The condition may be decisive for the compression strength of the transverse deck ~tructure between hatches and for the This condition is applicable for bulk carriers with the class shear strength of the transverse bulkheads at the shipside. notations, Bulk Carrier, Bulk Carrier HC, Bulk Carrier HC/E or Bulk Carrier HC/EA, and is generally applied for the · 3.4.2 double bottom strncture such that any single hold is assumed filled with heavy cargo with adjacent cargo hold empty. This The bulk cargo pressure loads are to be taken as given in loading condition represent the "Rule minimum" and is Chapter 2.2. Both cargo holds are assumed filled with cargo intended to give the vessel sufficient flexibility, realising that with a mass, MH, defined as: "ore" holds may be empty and "empty" hold may be loaded.

If the loading manual contain loading conditions representing a higher net load on the double bottom construction than the k = 1.0 minimum for Bulk Carrier "Rule minimum", for holds other than "ore" holds, LC2 shall be adjusted to comply with these conditions for the actual = 1.125 mimimum for Bui k Carrier HC and Bulk holds. The remaining holds shall comply with the "Rule Carrier HC/E minimum" requirements. = 1.25 minimum for Bulk Carrier HC/EA

DET NORSKE VERITAS 12 Classification Notes No. 31.l

June 1999

Poc = (Ship cargo dead weight capacity) I (total cargo 3.7.2 3 hold volume), (t/m ) Water ballast tanks below the ballast hold may normally be assumed filled. Top wing ballast tank adjacent to the ballast = 0.7 minimum hold shall be empty for checking the strength of the top wing tank construction. = cargo hold volume including hatchway in m3 3.7.3 The sea pressure loads fire to he tflkem in accord!•!!'.'<:'· w!th ...... ,., .....> 2.1. reflecting the actual vy ballast draught, T li.B· If data Sea pressure load is to be taken as given in Chapter 2.1. The for the ballast draught are not available, the draught may be draught is to be taken as maximum draught, T. taken as 0.45 T. Load from ballast pressure acting on the hatch cover shall be included as appropriate. 3.5 LC4: Two or more adjacent empty holds, seagoing or harbour 3.8 LC7: Water ballast in bold, (heavy ballast condition) adjacent hold empty, heeled condition, 3.5.J seagoing In case the loading manual is specifying two or more 3.8.1 adjacent holds empty at a specified draught, TAL'T• exceeding the hca vy ballast draught, T HB• this condition should be This condition is generally applicable for the top wing tank considered. Typical loading conditions are those representing structure adjacent to the ballast hold, side structure and local multiport conditions. The sea pressure should reflect whether scantlings of the transverse bulkhead. this is a sea going or harbour condition whichever is relevant. 3.8.2 This condition may be decisive for the longitudinal girders in double bottom and for the tensile strength of the cross deck The draught is to be as given in 3.7 and sea pressure as given construction and the bulkhead shear strength. in 2.1. Internal pressure from ballast is to be taken as described in Rules Pt.3 Ch. I Sec.13 as for liquid in tanks, This condition may be used as basis for specifying the heeled condition. Load from ballast pressure acting on the minimum required mass in two adjacent holds when hatch cover shall be included as appropriate. Top wing approaching maximum draught which are to be specified in ballast tank adjacent to the ballast hold shall be empty for the local load diagrams. See chapter 7 covering "Allowable checking the strength of the top wing tank construction. Hold Load Limits". If such draught has not been specified it is proposed to use maximum draught as basis in order to 3.9 LCS: Cargo on deck, seagoing estimate a draught corresponding to the bulkhead and or cross deck strength capacity. 3.9.1 This condition is applicable for bulk carriers with a dislinct 3.6 LCS: Bulk cargo w;th filled bold, seagoing top wing tank arrangement, where a deck cargo loading capacity has been specified. 3.6.1 3.9.2 This load condition is applicable for the transverse bulkhead structure including stool diaphragm plates and in-line shear Forces due to specified cargo load on hatches should be plates inside double bottom and for local design of the included in the consideration. Ref. Rules Pt.3 Ch.1 Sec.4 C. hopper tank. 3.9.3 3.6.2 The external sea pressure load is to be in accordance with 2 .1 at maximum draught, T. It should be noted that any The cargo pressure load is to be taken according to Chapter combination of sea pressure and deck load is not considered 2.3 and the sea pressure to be taken according to Chapter 2.1. necessary provided appropriate limitation is explicitly given The draught to be taken as maximum draught, T. in appendix to Classification Certificate. Ref.Pt.3 Ch.1 Sec. 4 C400. 3.7 LC6: Water ballast in hold, (heavy ballast condition) adjacent hold empty, seagoing 3.10 LC9: Watertight bulkhead loading

3.7.l 3.10.1 This condition shall be considered if ballast in holds has been This loading condition is intended to ensure that the specified for the vessel. The condition may be decisive for watertight subdivision is maintained in case of an emergency the transverse bulkhead, hopper and top wing tank structures. flooding and is applicable for watertight bulkhead structures For bulk carriers without the HC/E or HC/EA class notations, including stool diaphragm plates and in-line shear plates the condition may jn addition be decisive for the double inside double bottom. However, this condition is not bottom structure of the ballast hold. applicable for vertical corrugated bulkheads being built in compliance with the requirements as given in Pt. 5 Ch. 2 Sec. 10 D (IACS Unified Requirements {URS18))

DET NORS KE VERITAS Classification Notes No. 31.1 13

June 1999

Internal pressure load is to be according to the Rules, Pt.3 4. Cargo Hold Analysis Ch.I Scc.9 B, with filling of the hold up to the damaged . 4.1 General 3.10.2 4.1.l The external pressure may be taken at a draught equal to the Thi::; chapter gives guidance on how to perform finite damaged waterline, ToAM· Further design criteria are given in element calculations for the girder system within the midship the Rules, Pt.3 Ch. l Sec.9. area of bulk carriers.

3.11 LCJ 0: Ballast in top wing tank, seagoing 4.1.2 In general the finite element model shall provide results 3.11.1 suitable for evaluating the strength of the girder system and This condition is applicable for bulk carriers with top wing for performing buckling analysis or plate tlanges and girder tanks. The intention with this condition is to check the webs. This may be done hy using a 3D finite element model topwing tank structure only. Consequently, application of a of the midship area. Several approaches may be applied; realistic pressure distribution on the double bottom ranging from a detailed 3D-model of the cargo holds lo a construction is not necessary. coarse mesh 30-model, supported by finer mesh submodels. 3.11.2 Coarse mesh models can be used for calculating deformations and stresses typically suited for buckling The internal pressure shall he applied in the top wing tank control. The deformations may be applied as boundary and arc to be taken in accordance with 2.1. The sea pressure conditions on submodels for finding the stress level in more loads may correspond to the heavy ballast draught, Tns. when detail. considered relevant or disregarded of reasons as mentioned in 3.ll.l. The same principles may normally he used on structures outside the midship area but within the cargo area, provided 3.12 LCll: Ballast in top wing tank, heeled special precautions are taken regarding model extent and boundary conditions. condition 3.12.1 4.1.3 The condition is similar to condition LClO with modified Figure 4.1 shows a typical 3D-model of a conventional bulk internal and external pressure loads. carrier. Whichever approach is used, the model or set of models applied shall give a proper presentation of the 3.12.2 following structure:

The internal pressure is to he taken according to the Rules Typical web frames in hopper and top wing tanks, Pt.3.Ch. l Sec.13 as for liquid in tanks in heeled condition. including floors and mainframes at midhold in midship The sea pressure loads may correspond to the heavy ballast area draught, T HB. when considered relevant or disregarded of reasons as mentioned in 3 .11. l Typical corrugation section of transverse bulkhead with connection lo upper and lower stool Transverse section in way of pipe duct in line with the 3.l 3 LC12: Non homogeneous loading at reduced lower transverse bulkhead stool side draught Typical longitudinal girder in double bottom. 3.13.t In the model description and examples given in the following Special non-homogeneous loading condition given in the all these structures arc induded in one 3D-model of the Loading Manual, i.e. with heavy cargo in a limited number cargo hold for evaluating the results in these areas directly. of cargo holds at a reduced draught may have to be This implies that the "cargo hold analysis" and "frame and considered. Typical loading is multiport conditions. The girder analysis", in the Rules Pt.3 Ch. l Sec.13, arc combined principle will be the same as for LC3, or LCl if this condition represent a single loaded hold with adjacent holds into one model. empty, except that the draught is reduced. 4.1.4 3.13.2 In addition, analyses of local structure can be made for determining the detailed stress level in stiffeners subject to The bulk cargo pressure loads are to be lakcn as given in 2.2. large relative support deflections. Such analyses ure The cargo mass, M11, is to be taken from specified conditions for each of the holds considered. described in Chapter 5 "Local structure analysis". It is emphasised that this represents one acceptable approach 3.13.3 for performing such calculations, and that alternative Sea pressure load is to be taken as given in Chapter 2.1. The methods may be equally applicable. draught is to be taken as the actual mean draught, T ACT·

DET NORSKE VERITAS 14 Classification Notes No. 31.1

June 1999

4.3 Modelling of geometry

4.3.1 General model idea/isatio11: All main longitudinal and transverse geometry shall be included in the model. The scantlings shall, according lo DNV Rules, be modelled with reduced scantlings; i.e. corrosion addition according to the Rules shall be deducted from the actual scantlings.

When reduced effectivity of curved flanges are not represented by the model formulation iL-:elf, 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 Pt.3 Ch. I Scc.3. Typical structures arc:

• Curved plate flanges (e.g. bilge plating) Figure 4.1 Example of a 3D-model of an ordinary bulk • Curved face plates on hopper tank web frame and Lop wing tank web frame. carrier

4.2 Model Extent Half thicknesses shall be applied on plat.cs in symmetry planes on the boundaries of the model. 4.2.1 Ge11eral: The extent of the model docs in general depend on 4.3.2 Girders the structure and the loading conditions, and whether these Free flanges ofgirders sllall be includetl in the model: are symmetric in the longitudinal and transverse direction. In ship structures, openings in the girder webs will be present for access and pipe penetrations. If such cut-outs affect the The extent of the recommended model extent is visualized overall force distribution or stiffness of the girder, the cut-out in Table 4.1. shall be reflected in the model. This may be done by either; reducing the thickness according to the formula below or by 4.2.2 geometrical modelling of the cut-out The mean girder web thickness may for the first approach be taken as follows: Tram;ver~·e extent: Normally the structure is symmetric in the transverse direction while the load pattern in the heeled condition, LC7, is not symmetric. This implies that a full breadth model should be made:

For vessels without symmetry about centreline with re:,pect linaa11 to structure or loads, the analysis model amidships should / comprise full breadth of the model. I.,, h \... _.)" However, even for the heeled condition a half breadth model I may be satisfactory if due concern is shown to boundary I.,., conditions and their influence of the results in the structure. In the examples in the following. a full breadth model is applied. Figure 4.2 Mean girder web thickness h-hco 4.Z.3 tmeon =---·tw h. rco Longitt1dinal extent: Often the transverse bulkhead with upper and lower stools stool are not symmetric in the where: longitudinal direction. In order to represent this correctly the model must have an extent including onefall lenglh cargo lw = web thickness hold: 12 co fco = I+ For vessels without symmetry about the transverse bulkhead. 2.6{h - hco)2 the analysis model amidships should comprise two hold lengths (112 + 1 + 112). lco = length of cut-out For vessels with symmetry about the transverse bulkhead, the hco = height of cut-out model may be limited to 112 +Yi hold models. h = height of girder web

DET NORSKE VERITAS Classification Notes No. 31.l 15

June 1999

When rco is larger than l.2, (r0,. > 1.2 ), it is advised that the The calculated response for designs without such brackets cut-out is included in the model in one of the two ways given should however be adjusted to represent the reduced efficiency of the web. Alternatively, a model with a fine above. When r00 is larger than 2, (r00 > 2 ), it is advised that the cut out is geometrically included in the model. element mesh, or a separate evaluation, may be used.

Smaller openings for access and piping may be ignored. 4.3.5 However, when such openings are ignored this must be Mainframes, supporting brackets anti connected considered when evaluating the results ref. Chapter 4.8.2. longitudinals: The cargo hold model shall give a proper representation of deflection of mainframes. In order to 4.3.3 achieve this, the mainframes, the supporting brackets in the Stiffeners: Continuos stiffeners oriented in the direction of hopper tank and top wing tank and the connected the girders contributes to the overall bending stiffness of the longitudinals must be represented in the model. A practical girders and shall he included in the model in such a way that approach is to include all the mainframes in the model. In the bending stiffness of the girder is correctly modelled. order to evaluate the mainframes, supporting bracket and connected Jongitudinals, in detail, a fine mesh model must be Non-continuos stiffeners may be included in the model as made. beam element with reduced effectivity. Sectional area of such stiffeners may be calculated as follows: 4.3.6 Sniped at both ends 30 % of actual area Hatch coamings, hatch corners and /latches: The hatch coamings shall be included in the model. When it is Sniped al one end 70 % of actual area necessary to evaluate the scrcngth of hatch corners a separate fine meshed model must be made. Hatch covers shall nol be Connected at both ends 100 % of actual area 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 Stiffeners on girders perpendicular to the flanges may be caused by global hull girder forces. In such cases these forces included in the model when considered important, must be applied to the model. alternatively by transferring them to the nearest nodes instead of introducing additional nodes. Buckling stiffeners considered less important for the stress distribution, as sniped 4.4 Elements and Mesh Size buckling stiffeners, may be ignored. 4.4.1 Genera/:The performance of the model is closely linked to 4.3.4 the type-, shape- and aspect ratio of elements, and the mesh Corrugatetl hulk/lead and stools: Corrugated bulkheads topology that is used. The mesh described here is adequate shall be included in the model. Slanted plates (shedder for representing the cargo hold model and frame and girder plates) shall, if present, be included in the model as they model as defined in the Rules Pt.3 Ch. I Sec. l 3. The transfer loads from the flange of the corrugations to the following guidance on mesh size etc. is based on the opposite side of the stool. assumption that 4-noded shell or membrane elements in combination with 2-noded beam or truss elements are used. Normally it is difficult to match the mesh from the corrugations directly with the mesh from the stool, so a Higher order elements such as 8-noded or 6-noded elements practical approach is to adjust the mesh of the stools in to the with a coarser mesh than described below may be used corrugations. The corrugations will then have their true provided that the structure and the load distribution are geometrical shape. properly described.

Diaphragms in the stools and vertical stiffeners on the stool In general the mesh size should be decided on the basis of side plating are to be included in the model. proper stiffness representation and load distribution of tank and sea pressure on shell- or membrane elements. It is proposed to use one or two 4-noded element over the depth of the corrugation web. This model formulation gives a 4.4.2 good representation of the response of the corrugated bulkhead provided supporting brackets ~e fitted in line with Plating: 4-noded shell or membrane elements may be used in the corrugations. Modelling of these brackets do normally connection with mesh size as described below. 3-noded shell not change the load transfer from the corrugations to the or membrane elements with constant strain shall normally stool significantly as the vertical flanges are well supported not be used. It may however be used to a limited extent for by the vertical or slanted stool plate. Such brackets do avoiding poor mesh transitions. 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.

DET NORSKE VERITAS 16 Classification Notes No. 31.1

June 1999

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 shouid be minimum chree eiemcms over che height of girders. The mesh should in general and as far as practical follow the stiffener system on the girder. See Figure 4.3 • One, two or three elements between transverse girders. By using three elements it normally matches with

Figure 4.5 Mesh on transverse web frame in hopper tank

Figure 4.3 Mesh on transverse webframe

Figure 4.6 Mesh on corrugated transverse bulkhead

DET NORSKE VERITAS GUIDELINES AND CLASSIF1CATION NOTES !I AS OF lST JULY 1999

-VOLUME 1 GUIDELINES (l) Design and Classification of Roll on/Roll off Ships ...... May 1980 (2) Prevention of Hannful Vibration in Ships ...... July 1983 (3) Internal Conlrol Mobile Offshore Units (Owners' Conlrol System) September 1983 (4) Stahility Documentalion for Mobile Offshore Units - Class and Slalulory Services November 1986 5 Recommended Content of Information on Damage Conlrol in Dry Cargo Ships November 1997 (6) Condition Asscssmenl Program ...... September 1991 (7) Safety and Quality Management Guidelines .. . May 1992 8 Corrosion Protection of Ships ...... July 1996 9 Advisory Service Condition Survey Programme . July 1993 10 DNV Recommended Reporting Principles for Ultrasonic Thickness Measurement of Hull Structures September 1993 11 Renewal Survey, Survey Planning ...... September 1993 12 Crew Manning Offices, System Development . September 1996 13 Interference between Trawl Gear and Pipelines Sept~mbcr 1997 14 Frc.c Spanning Pipelines ...... June 1998

) CLASSIFICATION NOTES 4 .1 Guidance Manual for Inspection and Repair of Bronze Propellers . . . . . October 1992 4.2 Guidance Manual for Inspection and Repair of Steel Propellers ...... October 1992 6. Fire Test of Components Intended for Use in Piping Systems on Board Ships . . May 1980 (reprint of 1975) 6.1 Fire Test Methods for Plastic Pipes, Joints and Fittings January 1987 7. Ultrasonic Inspection of Weld Connections ...... May 1980 (reprint of Nov. 1978) 10. l Alternative Survey Arrangements for Machinery and Automation Systems Ships and Mobile Offshore Units...... '. January 1999 13. Erosion and Corrosion in Piping Systems for Sea Water . . May 1980 (reprint of Jan. 1979) 14. Instrumcntalion and Automation, Computer Based Systems May 1991 20.J Stability Documenlation - Ships Newbuildings .. . , . Pebruary 1990 20.2 Lightweight Determination - Ships ( and Lightweight Survey) February 1990 20.3 Systems for Stability Control of Mobile Offshore Units in Operation Tentative Guidance for Acceptance ...... December 1995 21.1 Approval and Certification of the Software of Loading Computer Systems June 1998

VOLUME2 CLASSIFICATION NOTES 30.I Buckling Strength Analysis ...... July 1995 ) 30.2 Fatigue Strength Analysis for Mobile Offshore Units ...... August 1984 30.3 Buckling Criteria of LNG Spherical Cargo Tank Containment Systems - Skirt and Sphere December 1997 30.4 Foundalions ...... February 1992 30.5 Enviroruncntal Conditions and Environmental Loads March 1991 30.6 Structural Reliability Analysis of Marine Structures July 1992 30.7 Fatigue Assessment of Ship Structures ...... September 1998 30.8 Strength Analysis of Hull Structures in High Speed and Light Craft August 1996 31.l Strength Analysis of Hull Structurei> in Bulk Carriers June 1999 31.2 Slrength Analysis of Hull Slructurcs in Roll on/Roll off Ships May 1980 31.3 Strength Analysis of Hull Structures in Tankers ...... January 1999 31.4 Strength Analysis of Main Structures of Column Stabili:r.ed Units (Semisubmcrsible Platforms) September 1987 31.5 Strength Analysis of Main Structures of Self-Elevating Units February 1992 32.1 Strength Analysis of Rudder Arrangements .. . .. January 1984 32.2 Strength Analys is of Container Securing Arrangements July 1983 41.2 Calculation of Gear Rating for Marine TransmissionH July 1993 41.3 Calculation of Crankshafts for Diesel Engines July 1988 42.1 Dual Fuel Arrangement for Diesel Engines with High Pressure Gas Injection January 1999 45.l Electromagnetic Compatibility ...... December 1995

DET NORSKE VERITAS Veritasvcicn 1, N-1322 H0vik, Norway Tel.: +47 67 57 99 00 Fax: + 47 67 57 99 11

Issue: July 1999 - 3000

GUIDELINES AND CLASSIFICATION NOTES AS OF lST JULY 1999

VOLUME 1 GUIDELINES (1) Design and Classification of Roll on/Roll off Ships ...... May 1980 (2) Prevention of Harmful Vibration in Ships ...... July 1983 (3) Internal Control Mobile Offshore Units (Owners' Control System) September 1983 (4) Stability Documentation for Mobile Offshore Units - Class and Statutory Services November 1986 5 Recommended Content of Information on Damage Control in Dry Cargo Ships November 1997 (6) Condition Assessment Program ...... September 1991 (7) Safety and Quality Management Guidelines . . . May 1992 8 Corrosion Protection of Ships ...... July 1996 9 Advisory Service Condition Survey Programme . July 1993 10 DNV Recommended Reporting Principles for Ultrasonic Thickness Measurement of Hull Structures September 1993 ) 11 Renewal Survey, Survey Planning ...... September 1993 12 Crew Manning Offices, System Development . September 1996 13 Interference between Trawl Gear and Pipelines September 1997 14 Free Spanning Pipelines ...... June 1998 CLASSIFICATION NOTES 4.1 Guidance Manual for Inspection and Repair of Bronze Propellers . . . . . October 1992 4.2 Guidance Manual for Inspection and Repair of Steel Propellers ...... October 1992 6. Fire Test of Components Intended for Use in Piping Systems on Board Ships . . Mar 19so (reprint o 1975) 6.1 Fire Test Methods for Plastic PipeR, Joints and Fittings January 1987 7. Ultrasonic Inspection of Welti Connections ...... May 1980 (reprint of Nov. 1978) 10.1 Alternative Survey Arrangements for Machinery and Automation Systems Ships and Mobile Offahore Units...... '. . .. . January 1999 13. Erosion and Corrosion in Piping Systems for Sea Water May 1980 (reprint of Jan. 1979) 14. Instrumentation and Automation, Computer Based Systems May 1991 20. l Stability Documentation - Ships Newbuildings . . . . . February 1990 20.2 Lightweight Dctenninalion - Ships (Inclining Test and Lightweight Survey) February 1990 20.3 Systems for Stability Control of Mobile Offshore Units in Operation Tentative Guidance for Acceptance ...... December 1995 21. l Approval and Certification o f the Software of Loading Computer Systems June 1998

VOLUME2 CLASSIFICATION NOTES 30.1 Buckling Strength Analysis ...... July 1995 ) 30.2 Fatigue Strength AnalysiR for Mobile Offshore Units ...... August 1984 30.3 Buckling Criteria of LNG Spherical Cargo Tank Containment Systems - Skirt and Sphere December 1997 30.4 Foundations ...... February 1992 30.5 Environmental Conditions and Environmental Loads March 1991 30.6 Slructural Reliability Analysis of Marine Structures July 1992 30.7 Fatigue Assessment of Ship Structures ...... September 1998 30.8 Strength Analysis of Hull Structures in High Speed and Light Craft August 1996 31.1 Strength Analysis of Hull Structures in Bulle Carriers June 1999 31.2 Strength Analysis of Hull Structures in Roll on/Roll off Ships May 1980 31.3 Strength Analysis of Hull Structures in Tankers ...... January 1999 31 .4 Strength Analysis of Main Structures of Column Slabili1.ed Units (Scmisubmersible Platforms) September 1987 31.5 Strength Analysis of Main Structures of Self-Elevating Units February 1992 32.1 Slrenglh Analysis of Rudder Arrangements . . . . . January 1984 32.2 Strength Analysis of Container Securing ArrangcrnentR July 1983 41.2 Calculation of Gear Rating for Marine Transmissions July 1993 41.3 Calculation of Crankshafts for Diesel Engine!! July 1988 42.1 Dual Fuel Arrangement for Diesel Engines with High Pressure Gas Injection January 1999 45.1 Electromagnetic Compalihility ...... December 1995

DET NORSKE VERITAS Vcritasvcicn l, N-1322 Hevik, Norway Tel.: +47 67 57 99 00 Fax: + 47 67 57 99 11

Issue: July 1999 - 3000 \ Classification Notes No. 31.l 17

June 1999

4.4.3 Lo11git11dinals and stiffeners: Longitudinals and other continuos 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 give the corrccl section modulus for double and single skin structures. However, axial area and shear area of such stiffeners should only represent the profile without the plale flange.

Low&r slool

Beam element

Beam element "Overlap"

Figure 4. 7 Overlap of beam elements and shell elements Special auention 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 Sec Figure 4.7.

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 Oanges are to be represented with their true effeclivily in the model.

Stiffeners inside stools may in general be represented by beam elements or alternatively by shell or membrane elements.

DET NORSKE VERITAS 18 Classification Nates No. 31. l

June 1999

4.5 Boundary Conditions Alternatively, verlical forces applied in the same intersections may be applie

Table 4.1 Boundary conditions for an orderinary bulk carrier with unsymmetrical stool structure

Location Displacement Rotation

ox oy 5z 0x 0y 6z Plane A L x x Plane B x x x Line C s Point a x Point c

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 for(;e

DET NORSKE V ERITAS Classification Notes No. 31.1 19

June 1999

4.5.2 Boundary conditions for the application of hull in the middle of the model. Some modifications to the size of girder loads this bending moment are however necessary. The When hull girder loads, i.e. bending moment and shear background for this is that the allowable hull girder bending force.'!, arc intended applied to the model, it is adviccd that momcnl (Ms + Mw) is based on gross scantlings. The FEM such loads arc applied as separate load cases with separate model is based on net scantlings (gross scantling reduced by boundary conditions. The resulting stresses may then be tk). It is therefore necessary to reduce Lhe Hull girder bending manually superimposed to the relevant stresses from the moment by a factor of Zmod I Zgcos.- Where Zrnod is the hull local load model. The described boundary conditions and girder section modulus as modelled (i.e gross scantling load application are summarised in Table 4.2 and Table 4.3 reduced by the corrosion addition, tk) and Zgross• the hull girder section modulus hascd on actual scantlings. In Bending moment - boundary conditions: One end should be addition to this bending moment the local loads will also set restricted as shown in Table 4.2. The other end .should be up a "semi-glohal hull girder bending moment" that may be kept plane and the displacements or the plane should be as a compensated for when applying the bending momcnc. (It is rigid body. The latter is necessary to apply the hull girder advised that the loads arc adjusted to match the acceptance bending moment. In order to keep the nodes in one plane criteria and not the opposite.) they arc lo be linearly dependent of each other as a rigid body. The magnitude of the force pair will be as follows:

Symmetry conditions along the centreline of the model are to P=~ be applied for models covering a half breadth of the ship. h

Application ofhull girder bending moment: ln general a Where bending moment shall be applied to the end of the model. The bending moment at the end may be applied as a force F = Magnitude of force at points in deck and bottom pair acting in the opposite direction applied at two points. M Modified bending moment as described above The points should be positioned vertically above each other = with one point in the deck and one point in bottom. The size h = Height from base line to point in deck of the bending moment shall be such that the vertical hull girder bending moment, as described in the rules, is achieved

Table 4.2 Boundary conditions for bulk carrier cargo hold analysis when hull girder be~ding moments are applied f,ocation Di.~placement Rotation

ox Oy & Ox 8y 8z Plane A L L L L L L Plane B x x x x x x Centreline (when x x x applicable)

Point a,b F•. b X Fixed. L Rigid body linearly dependent. F,,h Force according to the above. Forces acting in opposite direction at point a and b. ·

DET NORSKE VERITAS 20 Classification Notes No. 31.1

June 1999

Shear force - boundary conditions: The boundary conditions Application ofshear forces: The shear forces are to be are given in Table 4.3. Synunetrieal boundary conditions are applied at the outer shell at the ends of the model (Line C to be applied at ends. Symmetry conditions along the and F). The shear forces are to be applied as vertical line cenlreline of the model are to be applied for models covering loads. The forces are to be distributed according to a shear a half breadth of the ship. For models covering the full tlow calculation with the forces acting in opposite directions breadth of the ship the model mu.st be fixed in the transverse ut the two ends as shown in Table 4.3. The magnitude of the direction at the intersections between the transverse bulkhead shear force shall be such that the maximum allowable shear and the longitudinal centerline girder at inner bottom. fo rce is achieved within the model. Springs shall be applied at one end.

Table 4.3 Boundary conditions for bulk carrier cargo hold analysis when global shear forces arc applied

Location Displacement Rotation

OX oy (jz Bx By 8z Plane A x x x Plane B x x x Centre line (when x x x applicabl e) LlneC S , F. Line P P. X Pixed. S Springs Fv Vertical forces acting in opposite directions at lhe ends

4.6 Loading Conditions 4.7 Presentation of input and results 4.6.1 4.7.l Ge11eral: Normall y the basic loading conditions as described The requirements given in DNV Rules Pt3 Ch. l Scc.13 in Pt.5 Ch.2 of the Rules, shall be considered. These loading regarding proper documentation of the model shall be conditions are further elaborated in Chapter 3 of this followed. A practical guidance is given in the following. In Classification Note. For some bulk carriers, depending on the appendix A, examples of checklists for internal verification length, class notations and arrangement of bottom of FEM analyses are given. longitudinal girders, additional loading condition as dc:.cribed in 4.6.2 may be necessary for the estimation of the 4.7.2 fatigue life of the longitudinal strength elements. Presentation of input data: A reference to the set of The loading should be applied in the form of lateral pressure drawings the model is mcanl to represent .should be given. on shell elements, (or line loads on membrane elements). The modelled geometry is to be documented, preferably as Alternative load application may be specially considered. an extract directly from the generated model. The following input shall be reflected:

4.6.2 • Plate thickness Fatigue loads: For vessels subject to the class notation • Free tlange sectional area considering efficiency of NAUTICUS(Newbuilding), ref. Rules Pt.5 Ch 2 Sec 5A, curved flanges fatigue strength assessment are in general to be carried out • Beam section properties for end structures of longitudinals in bottom, inner bottom, • Boundary conditions side, inner side and deck in the midship area. For that • Load cases purpo.se any deformation of the said longitudinals caused by relative deformation hy the Sllpporting strength members may have to he calculated. However, for conventional bulk 4.7.3 carrier design the large number of bouom longitudinal Presentation ofresults: The stress presentation should he girders will normally result in relative deformations not based on element membrane stresses or gauss membrane having any significant etlcct on the fatigue life and may thus stresses at the middle of element thickness, excluding plate be ignored. bending stress, in the form of iso-stress contours in general. Numerical values should also be presented for highly It is emphasized that such deformations are to reflect stressed areas (e.g. areas where stress exceeds 60% of dynamic loading only. The dynamic pre.ssure loads are to be allowable limits or areas in way of openings not included in calculated according the Classification Note 30.7 "Fatigue the model). Assessment of Ship Structure" .

DET NORSKB VERITAS Classification Notes No. 31.l 21

June 1999

The following should be presented: where :

• Deformed shapes = Sum of longitudinal stresses based on wave 8 • Transverse membrane stress of shell/plate elements in bending moment with a probability of lff of Bottom plating cxceedance. Inner bottom plating Sum of longitudinal stresses based on wave Cross deck/upper stool plating bending moments with a probability of I 0-4 of Hopper tank plating exceedance. Top wing tank bottom plating

Transverse floors and hopper and top wing tank weh

DET NORSKE VERITAS 22 Classification Notes No. 31.1

June 1999

Upper deck

./;;i;i;_~~=---1 N.Ar·-£-·-·i NAf-·-·-<»1£---·--C Hull Girder Bending Double Bottom Bending Local Bending of Longitudinal

Figure 4.8 Stresses identified as hull girder bending stresses, double bottom bending stresses and stiffener bending stresses,

calculated by the FE-model, is shown depending on the mesh 4.8.3 size (valid for 4-noded shell elements). One element between floors results in zero stiffener bending .. Two clements Mean shear stress: The mean shear stress, "tmean. is to be between floors result in a linear distribution with used for the capacity check of a plate. This may he defined as approximately zero bendjng in the middle of the elements. the shear force divided on the effective shear area. For When a relatively fine mesh is used in the longitudinal results from finite element methods the mean shear stress direction the effect of stiffener bending stresses should be may be taken as the average shear stress in elements located isolated from the girder bending stresses when buckling and within the actual plate field, and corrected with a factor stress level is checked for the plate flange. · 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 L,(r1 ·Ai) j o:J •mellll

Where

Ai = effective shear area of clement i.

t; = shear stress of element i.

Figure 4.9 Normal stress caused by local load on the Aw = effective shear area as of the real structure. To be stiffener, depending on number of elements along.the taken in accordance with DNV Rules Pt.3 Ch.1 stiffener Sec.3

DET NORSKB YERITAS Classification Notes No. 31.1 23

June 1999

4.8.4 4.8.5 Shear stress i11 the hull girder: It is not necessary to Buckling control and related acceptance criteria: Table 4.3 consider hull girder shear stresses in longitudinal bulkheads gives examples of areas to be checked for buckling and the and ship side unless special boundary conditions as well as applicable melhod and accept criteria. In case of any loads are applied. The sJ1ear strength of the hull girder may differences in the acceptance criteria given here compared normally be evaluated in accordance with the Rules Pt.3 with those given in the Rules for Ships, the latter shall apply. Ch.1 Sec.5.

Table4.3 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 'I' = I and allowable usage factor, ri =0.8 • Double bottom (including 2) Uniaxial buckling in longitudinal direction to be analysed according to Sec.14 based on hull bottom and inner bottom) girder stress 0-.1=O's+ O'w. • Side plating ( including inner 3) Bi-axial buckling to be analysed based on longitudinal stress and mean transverse stress. When the longitudinal stresses arc obtained from hull girder loads on a probability of side when relevant) 4 • Deck exceedance of 10' , usage factors 1i.=fly=0.8S shall be used. For a probability of exceedancc of factors shall be used. • Hopper struclure 10-8, usage 1i.=iiy= 1.0 • Top wing tank structure • Cross deck structure inc. stools Comment: Mean transverse compressive stress is to be calculated from a group of elements representing one plate field between stiffeners. Longitudinal stress al"e to be taken as described in 4.8.2

Buckling of girder plate Oanges in: 1) Buckling to be analysed hased on mean compressive stress with '\jl = l and allowable usage factor, ri=0.8. • Upper and lower stools and the 2) Bi-axial buckling to be checked when relevant. web of these girders

Comment: Mean compressive stress arc to be calculated from a group of elements representing one plate field between stiffeners

Buckling of corrugated bulkheads I. Buckling to be analysed based on mean compl"essive stress with k1 = 5 (Pt.3 Ch.I Sec.14) and allowable usage factor, ri=-0.8.

Buckling of girder webs in: Buckling ofgirder webs with one plate flange: I) Buckling to be calculated as for girder plate flanges • Double bottom 2) Buckling to be analysed based on mean shear stress with allowable usage factor, T)=0.85. • Double side (when relevant) 3) Bi-axial buckling with shear. • Deck • Hopper tank Buckling ofgirder webs with two plate flanges: • Topwing tank 1) Buckling to be analysed based on mean shear stress with allowable usage factor, ri=0.85. • Stools 2) Buckling caused by compression loads from sea and cargo, allematively together with shear, to be checked when relevant.

Comment: Mean shear stress to be laken as described in 4.8.3, representing one plate field between stiffeners.

DET NORSKE VBRITAS 24 Classification Notes No. 31.1

June 1999

4.8.6 Stress control and related accepta11ce criteria: Table 4.4 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, the latter shall apply.

Table 4.4 Examples of areas to be checked and procedure to be used related to control of nominal membrane stresses. All stresses in N/mm2

Item Remarks

Stresses in longiludinal girders 1) Allowable reduced longitudinal nominal stress, a= J90f 1• Based on a probability Qf exceedance of 4 10· , (Reduced longitudinal stress, O'LR = cr0 a +O's+ 0\vR < 190 fr, Ref 4.8.2) 2) Allowable mean shear stress 't =90f 1 (sea) and 't =100f1 (harbour) for girders with one plale flange, and 't = 100f1 (sea) and 't = 11Of 1 (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 Ref. 4.!U.

Stresses in transverse and 1) Allowable nominal normal stress in flanges of girders O' = 160f1 (sea) and o:: 180f1 (harhour) in vertical girders with two plate general. flanges (Double skin 2) Allowable mean shear stress of girder webs, t 100f (sea) and 1 I Of {harbour). Shear stress in way constructions) like: = 1 1 of openings nut included in the calculation to be evaluated in terms of mean shear stress Ref. 4.8.3. Double bottom • 3) Allowable equivalent stress, 0'0 =180f 1 for seagoing conditions and O'e =20 0f1 for harbour • Double side conditions.

Stresses in transverse and 1) Allowable nominal normal stress, cr = 160f1 (sea) and o = 180f1 (harbour) in general vertical girders with one plate 2) Allowable mean shear stress 't' =90f 1 (sea) and 100f (harbour). Shear stress in way of openings not flange (Single skin 1 included in the calculation to be evaluated in terms of mean shear stres~ Ref. 4.8.3. constructions) like: 3) Allowable cqui valent stress, o~ = 180f1 for seagoing conditions and 0'0 = 200f1 for harbour conditions Main frames • 4) Allowable nominal normal stress in flooded condition, o:: 220f1 {Not applicable for mainframes) • Top wing tank web frame • Hopper tank web frame

be considered are, longitudinals in double bottom towards 5. Local Structm·e Analysis transverse bulkheads or partial girders, and longitudinals connected to main frame supporting brackets. A method for 5.1 General the first example is shown in the following. 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 Figure 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 30 cargo hold analysis model, or run separately as submodels with prescribed boundary deformations from a 30-analysis. Local pressure loads must be applied to the local models. Figure 5.t Main frames, connecting brackets and 5.2 Stiffeners subject to large deformations lon2itudinals

5.2.1 General: Relative deformations between stiffener supports may give rise to high stresses in local areas. Typical areas to

DET NORSKE VERITAS Classification Notes No. 31.1 25

June 1999

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 Y:z + 'h stiffener spacing. See Figure 5.3.

Figure 5.2 shows the extent of a model of an inner bottom longitudinal and hottom longitudinal. Herc the extent covering the full length is used for checking both sides of the unsymmetrical stools simoultanously.

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 Figure 5.2 Extent of stiffener model for checking both sides cargo hold analysis (or frame and girder analysis when of the unsymmetrical stool relevant). These displacements or forces arc to be applied to the boundaries of the local structure model in points where 5.2.3 the results from the global model are representative. See Tahlc 5. l. Elements and element mesh: Normally three (3) 4-noded elements arc to be used over the web height of the stiffeners. Corresponding sizes are to be used for the plate flange. The Table 5.1 Boundary conditions for model of longitudinals in double bottom face plate shall normally be modelled with 2-no

5.3 Other fine mesh models. Other fine mesh models may be made for Che study of critical details. If the accept criteria are based on maximum allowable nominal stresses the modelling principles described above should be followed.

Figure 5.3 View of element model

DET NORSKE VERITAS 26 Classification Notes No. 31.1

June 1999

5.4 Documentation and result presentation the remaining flooded volume in the loaded hold and for empty holds a permeability of 0.95 to be used. For the loaded When extrapolation of results is required, ref. 5.2.3, this shall holds a permeability of 0.9 for the whole volume below the normally be based on the results in the two last elements damaged waterline may be used as an alternative to the towards the point of interest. The results in the Gauss point above. Realistic data for the cargo mass volume and density in the middle of the element representing the flange of the to be applied. longitudinal shall be used for the extrapolation. The extrapolation method is indicated in Figure 5.5. ~? r!lnhol n .. n,.Hnn 1\11,...... ,.,.nt .. .,..:1 ~s...... lT~ ...... -·- _ .. "" ...... -· --·... -···e ·~ ---···-~4. ... -··- ...... -...... , .. _..,. Limitation 6.2.1 Generally the maximum allowable still water bending moment in a flooded condition, Msr, is described by below formula, provided adequate uni-axial buckling capacity of the cross section is available. Ref. Rules Pt.3 Ch. l Sec.14.

Where:

= Hull girder section modulus at the considered position. Figure 5.5 Extrapolation towards point of interest based on results in elements representing the flange Mw = Wave bending moment according to DNV Rules. Documentation and result presentation is to follow the principles given in chapter 4.7. When the hull girder capacity is fully utilised, the maximum The following stresses shall be given. allowable still water bending moment at the considered section, in flooded condition, Msr. is described by: a) Normal stresses and shear stresses of plate/membrane elements. Msr =Ms + 0.2 Mw b) Axial stress of truss/beam elements. Where: 5.5 Acceptance Criteria M.~ = Allowable .still water bending moment Acceptance criteria for stress results from local structure according to DNV Rules in intact condition. analysis arc given in the Rules Pt.3 Ch:1 Sec.13 and in Pt.5 Ch.2. 6.2.2 It should be noted that there is only one limitation curve in a 6. Additional requirements considering t1ooded condition, irrespective of possible reduced bending moment limits applied in an alternate intact condition. flooding 6.2.3 6.1 General The three typical bending moment limits arc given in the 6.1.1 illustration figure 6.1 following. Gcneral.ly the Rules require that damage stability calculations 1 are earned out to control that the ship has sufficient residual

stability for given damage scenarios without reference to the • Max allowable ~lill w~t~r bending ship's actual loading conditions and without controlling the 1'1omenr in ll-0od&d cohdillon • Mu. •kMJ.tie. 1tll wats bending ships overall strength for such damage conditions. IHom«\l in infacl Condition • - r.ducod lnU ... beQdr.g mmweol i\ in1ad &lletna~ ciondltot't However, for vessels subject to the requirements as given in Pt.5 Ch.2 Sec.5 A I 02 Table l , the ships overall strength (hull girder shear and bending strength) are to be controlled for tlooding of each cargo hold for all actual seagoing cargo and ballast conditions. I.e. the loading conditions given in the '\______J:J"" ---20% ol wave bending momen• loading manual and those evaluated by the loading in.strument only. The determination of the mass of water ingress should reflect the damaged waterline. A permeability Figure 6.1 Typical bending moment limitation curves for of 0.3 for the volume occupied by cargo may be used. For intact and flooded conditions

DETNORSKE VERITAS Classification Notes No. 31.1 27

June 1999

6.2.4 6.4 Diaphragm and shear plates in double bottom The maximum allowable shear force capacity at the below bulkhead stool, considering flooding. considered section in flooding condition, Qsr, is described Evaluation of the effectiveness. by: 6.4.1 The shear strength of diaphragm - and shear plates is to be checked with respect to the bending moment, MLS, from the Where: lower stool as given by:

Allowable still water shear force according to 3 = (Z1e On.te 10- +Q ,s) + hf_., DNV Rules in intact condition. Ref. also 9.4. (kNm) St 3(Pc.(f + P~fu) Qw = Maximum vertical wave shear force according to DNV Rules Z1e = as given in the Rules Pt.5 Ch.2 Sec. 10 0303 6.3 Transverse Bulkhead Strength cr.,,e = as given in the Rules Pt.5 Ch.2 Sec. 10 0305 6.3.l = as given in lhe Rules Pt.5 Ch.2 sec. 10 0209 Generally the Rules require that the strength of transverse Q bulkhead structure subjected to flooding loads have been S1, hLs as given in the Rules Pt.5 Ch.2 sec. JO 0203 controlled using a pressure head corresponding to the deepest = equilibrium waterline in the damage condition, and pressure Pc. 11 = Pc.r as given in the Rules Pt.5 ch.2 Sec. 10 load from water alone only. 0 204 with h1 =d 1 - hoe

6.3.2 Pc,fu = Pc,r as given in the Rules Pt.5 Ch.2 Sec. JO 0204 with h1 d1 - (hon + hLs) For vessels subject to the requirements as given in the Rules = Pt.5 Ch.2 Sec.5 A102 Tahle Al, the transverse bulkheads are d1 ,hoa as given in the Rules Pt. 5 Ch. 2 sec. 10 0203. lo be checked according to Pt.5 Ch.2 Sec.10 D. The pressure = loads in this case reflects the effect of mixed cargo and ~ water. 'tr = l3 The following loadcases may be applied: crr = minimum upper yield stress water alone filled cargo hold to deck at side with mass corresponding to the hold's maximum allowable mass The shear moment capacity, M1, of longitudinal double bottom girders and shear plates below the lower bulkhead cargo hold filled to a level corresponding to its max. 3 stool, are within a load breadth of each longitudinal double allowable mass and applying cargo density of 1.78 t/m bottom girder, b , generally given by: cargo hold filled to a level co rre~'P onding to its max. 1 allowable mass and applying cargo density of3.0 t/m3

Flooding head to be as required in above referred Rules and The shear moµient capacity, M~, may generally be an angle of repose of 35 degrees may be applied. determined as follows:

6.3.3 Mi: =M'tL +Mi:s 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 a:; relevant. However, diaphragm n plates and in line shear plate:; inside double bottom is to be M,, = L 'tf (t, - 2) /5 h08 checked separately. Acceptahlc procedure is described in 6.4. I n = number of effective shear plates including longitudinal double bottom girders within the load breadth b1.

6.4.2 For the determination of Mu, smaller size access holes in the shear plates within the length of the lower stool may generally be disregarded.

DET NORSKE VERITAS 28 Classification Notes No. 31.1

June 1999

Access holes etc. in shear plates and double bottom girder 7. Cargo Hold Load Limitations webs below the lower bulkhead stool are assumed to be arranged with effective edge stiffening. 7.1 General

7.1.1 The design load conditions of the ship as defined in the loading manual, ref. 3.2, and normally also reflecting class nf"r" •~ ~ n ' - _ ... ·-·-· ., ·-·· ...... > ... - ... -& ... ~· .... w given draught. These design conditions are, in addition to being used for scantling check, also utilised to define limits ts to the cargo mass of holds for other draughts. t,. CB- t,f CB- hoa hof 0 7.1.2 Generally the allowable mass of cargo in a given hold is related to the net loading on the double bottom of the considered hold. This implies that the allowable mass of cargo in the hold will vary linearly with the buoyancy Figure 6.2 Diaphragm and shear plates in double bottom pressure acting on the bottom of the ship. Typical Local below bulkhead stool and longitudinal girder Strength Diagrams for the allowable mass of cargo of a cargo hold are shown in Fig. 7.2.1. 6.5 Limit to Hold Loading, Considering Flooding With reference to 3.4 the Rules also specify minimum limits 6.S.I to the mass of cat"go in any two adjacent cargo holds at Generally the Rules require that the strength of the double maximum draught. The limit to the mass of car

7.2.1 6.S.2 The procedures fur determining limits to the loading of cargo However, for vessels subjected to the requirements as given holds given in the following are applicable for ships with in Pt.5 Ch.2 Sec.5 Table A I, the double bottom shear additional class notation HC, HC/E or HC/EA, but may also stren~~ are also to be checked for above loads in flooding be considered bulk carriers without such additional class cond1t10n. Ref. Pt. 5 Ch. 2 Sec.10 subsection E. It should be for notation. The procedures have been based on the assumption ?oted that the rule check program "Allowable Hold Loading" that the structure comply with class requirements for the m the NAUTICUS HULL package may be used for this purpose. ship's design load conditions but not necessarily utilising any strength margin. in particular at reduced draughts. In case Further, the highest cargo density will give the strictest such strength margin(s) exist, the local strength diagrams requirement and a cargo density of 3.0 t/m3 should generally may alternatively be based on the stress response from the serve as the extreme condition in combination with direct strength calculations reflecting the design mass and permeability of 0.3 for the volume occupied by the cargo. relevant draught.

7.2.2 It should be noted that the local strength diagrams generally do not apply for the carriage of ballast in the ballast hold.

DET NORSKE VERITAS Classification Notes No. 31.l 29

June 1999

7.2.3 = hold volume in m3 including volume of hatch Limit to mass ofcargo in cargo hold: The limit to the mass hold volume in rn3 to deck level of cargo in hold is primarily related to the shear response of = the double bottom floors and girders, and is largely given by = hold height from inner bottom to deck al centre the net pressure load exerted by cargo, other deadweight and line buoyancy on the double bottom structure.

For seagoing cargo conditions the maximum allowable mass For ships with notation HOLDS ...... EMPTY, where a of cargo, M, in tonnes at draught TA in a given cargo hold reduced bending moment limit has been assigned for the and in the associated double bottom tank(s), may generally condition(s) with empty cargo hold(s) at maximum draught, be taken as the larger ofM1 and M2, which are given as both limits to the mass of cargo in the loaded hold(s) should follows: be included in the local strength diagrams.

The higher allowable mass limit may then only be applied if the still water bending moments within the considered loaded MR maximum hold and the adjacent empty hold(s) do not exceed the reduced still water bending moment limits. For intermediate = Mo+ 1,025 An (TA-To+aT) still water bending moment values (hctwccn the two bending = Mo maximum moment limits), the allowable mass of cargo in the loaded ore hold may be taken as: = Rule minimum limit for allowable mass of cargo in hold M Maximum calculated still water bending = l,00Pdc V11 if no additional class notation Msc = moment within the length of the considered = 1,25Pc1c V H for additional class notations HC and hold and adjacent empty cargo hold(s). HC/E = Allowable still water bending moment at the = l,50Pt1c Vu for additional class notation HCfEA location of Msc:-

= the homogeneous bulk cargo density in tonnes = Allowable reduced still water bending pcrm3 moment at the location of Msc·

= cargo density required to fill all cargo holds with vessel at maximum draught The maximum allowable mass in tonnes of a cargo hold and the associated double bottom tank(s), MH, in harbour = Rule draught in m associated with cargo mass condition may generally be taken as: MR. MH = 1,15 M = 0,6 T if no additional class notation = Mcmax), maximum = 0,8 T for additional class notations HC and HC/E

= 1,0 T for additional class notation HCIEA For all cargo ~olds of bulk carriers with no additional class notation, with additional class notation HC, and for the Mo = specified maximum muss of cargo in hold, e.g. loaded holds of the alternate condition(s) in bulk carriers for loaded holds in the specified empty hold with additional class notation HC/E, the required minimum condition. mass of cargo, MM. in tonnes in seagoing conditions is given by: T = vessel scantling draught in m

= vessel draught in m associated with cargo mass M0 , normally = scantling draught = 0. minimum

For the empty holds of ships with additional class notation = trim allowance HC/E where a reduced still water bending moment limit has been specified for the alternate load condition, the required = I xn - o,oos u2I minimum mass of cargo, MM, in tonnes in seagoing = distance from A.P to middle of considered hold conditions is given by:

DET NORSKE VERITAS 30 Classification Notes No. 31.l

June 1999

MM = 1,025 AH (TA -T + (T-TR) (Msc - MsR) I (MsF­ MR = Rule minimum limit for allowable mass of cargo MsR)) in the considered adjacent holds

MM may be taken = 0 for all values less than = undefined if no additional class notation 1,025 A 11 (TA - T 0 I 5 = l, 125 Pde V ti for additional class notations HC and HC/E

o ...... i...;~ ...... : ...... ,...,.fA.:+; ..... - .... 1 ...... -.-..f .... ,; ...... ur Ul"'IC ..... H Ul"'ICA A VA ~uaat" 11V&.C.UIVJI I IV) I'"°'''- \Jl I t'io;lt.-'"' no minimum mass of cargo is required for any cargo hold in harbour condilions, i.e. any cargo hold may be empty at = length of the considered adjacent holds in m. See maximum draught. For bulk carriers without additional class Fig. 7.1. notation the minimum mass of cargo, MMH· of any hold in harbour condition is given by: b = mean breadth of Che two considered cargo holds in m at the level of the top of the hopper tank. See MMll = l,025 AH (TA -TR)/ 1,2 fig. 7.1.

= 0. Minimum Mo = specified maximum mass of cargo of the considered adjacent holds. 7.2.4 Limit to muss ofcargo in two adjacent cargo lio/ds: The The maximum allowable mass in tonnes of a cargo hold and limit to the mass of cargo in two adjacent holds is primarily the associated double bottom tank(s), Mrn, in harbour related to the shear response of the transverse bulkhead at its condition may generally be taken as: attachment to the side structure, and to the normal stress response of the cross deck structure (mainly) at centre line. McH = 1,15 Mc Both responses arc governed by the net vertical force exerted by weight of cargo and other deadweight (mass in double = MccmaJ()t tnaxirnum side tanks excluded) and by the vertical buoyancy force within the considered hold lengths. Note that the formulas given in the following do not apply for conditions where the Unless a direct calculation of the bulkhead strength in the mass considered include ballast water carried in a ballast two adjacent hold empty condition is carried out, the hold. required minimum mass of cargo, McM• in tonnes of adjacent cargo holds in seagoing conditions may be taken as: 7.2.5 McM For seagoing conditions the allowable combined mass of cargo, Mc, in tonnes at draught TA, of two adjacent cargo = 0 minimum holds may generally be taken as the larger of Mc 1 and Mc2. which are given as follows: = The largest design ballast draught in m.

The required minimum mass of cargo, McMH• in tonnes of = MR maximum adjacent cargo holds in harbour conditions is given by:

McMH

= Mo maximum

DETNORSKE VERITAS Classification Notes No. 31.l 31

June 1999

b b

Figure 7.1 Definition of length and breadth to be used in calculation of local strength diagrams

7.3 Local Tank Top Loading Regarding loading of slabs and ingots such cargoes is normally stowed on dunnage and the amount of such cargoes 7.3.l is rarely specified. However, if strength calculations or load limitations are requested, such strength calculalions should Bulk Carriers are often designed to carry general cargo on be based on the actual footprint loading. inner bottom, e.g. steel coils, aluminum ingots etc.. in addition to the normal homogeneous, alternate and block­ If steel coil loading has been specified the requirement to loading mode. For that reason owners may have specified a thickness of inner bottom plating and stiffeners will be maximum tank top pressure without specifying the purpose. related to the mass, breadth, the number of tiers of steel coils If such tank top press.ure is used as basis for calculating the and the number of dunnages arranged beneath each coil. maximum mass in the holds, ref. formula given in Pt.5 Ch.2 Sec.5 A200, lhis maximum mass may exceed the maximum All above load limitations are to be clearly stated in the mass applied for the different loading conditions in the appendix to class certificate. loading manual.

For the purpose of handling such cases the following procedure may be applied:

1) For girder strength control lhc hold maximum mass should rel1ect the extreme loading conditions as given in the loading manual. Ref. Chapter 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.

DET NORSKE VERITAS 32 Classification Notes No. 31.1

June 1999

HC/E (ore hold) M Not allowable The upper line is the limitation when the hold is loaded with ore M0 and a reduced allowable still water bending moment has been assigned.

Allowable

Not aaowable The lower limitation cover the limitation when the hold is loaded with rule minimum mass MR O.ST T and combined with full rule still water bending Seagoing moment. Harbour

HC/E (empty hold) M Not allowable Typical local strength diagram for an empty hold. ------·

O.ST T Seagoing

Harbour

HC and HC/E (two adjacent holds) M Typical local strcnglh diagram for two adjacent holds.

Allowable

Not allowable

T Seagoing

Harbour

Figure 7.2 Typical local strength diagram

DETNORSKE VERITAS Classification Notes- No. 31.1 33

June 1999

8. Wave Torsion induced Stresses in ft = 2 lso b1 (I + a.1) Crossdeck of Conventional Bulkcarriers. 2 Iso b1 (I + «1) +ten h (1 + a.1)

8.1 General G = material shear modulus.

8.1.l lco = (mean) moment of inertia of crossdeck about vertical axis. The hatch end coaming and For bulkcarriers of conventional type, the torsional stiffness hatch end beam may generally be included of the hull is mainly related to the effective St Venants' in the inertia calculation. moment of inertia of the hull, which is great! y increased compared to that of the typically open ship, as a consequence lso = moment of inertia of upper deck outside of of the rigid cross deck structure. hatches about vertical axis. The hatch side coaming, top wing tank plating vertical 8.1.2 i-;trake and ship side within the half height of The torsional deformation of a hull structure with large hatch the to wing tank may be included in the openings is primarily characteri1.cd hy an in plane inertia calculations. deformation of the deck, giving rise to large horizontal shear thickness of upper deck plating at side. forces and bending moments in the crossdeck structures. Is = y = distance from centreline to considered 8.2 Stress of crossdeck section on crossdeck. 8.2.l Zs = position of shear center below base line of The normal stress, cr, of the crossdeck structure shoulo hull cross-section including the St. Venant's generally be considered for critical sections within the stiffness effect of the crossdcck. For a breadth of the hatch opening. It is generally determined conventional bulk carrier the shear center according to the following formula: may as a first approximation be assumed located 0.1 B below the base line. 2 0 oo + crr (N/mm ) . Zco = section modulus of crossdeck about vertical OD = normal stress in crossdeck due to load case axis with respect to considered section. caused by maximum vertical bending of 12Eico bulkhead at the position considered. Ref. Clr = load case LCl, LC3, LC4 or LC12 as bf 0 Aco applicable. Alternatively, as calculated according to B.5.5 of B.5 for maximum

O"T torsional induced stress in crossdeck at section considered. Alternatively, as = unit warping of the deck at the hatch side calculated according to 8.2.2 for c<~aming according to shear flow analysis of conventional bulkcarriers. hull cross-section.

Aco horiwntal shear area of crossdeck, generally 8.2.2 = deck plating only. For a conventional bulkcarrier, the bending stress of crossdeck induced by the torsional deformation, err. may be Aso = horizontal shear area of upper deck plating related to the rate of twist of the hull, r , by the following outside of hatches. equation:

OT = ± 12f1 EI~ (z, +D) (l+ow)y 4'~ For further definition of terms, see Fig. 8.1 ZcobfO+o.1)

B = vessel breadth D = vessel depth. E = material elastic modulus.

DETNORSKE VERITAS 34 Classification Notes No. 31.1

June 1999

8.2.3 9. Shear force correction The wave torsion induced shear response in the cross deck should generally be considered in combination with the shear 9.1 General stress response due to lateral bulkhead loading and still water torsion loading as applicable. The wave torsion induced 9.1.1 shear stress in cross decks may in addition have to be For ships with several shear carrying elements such as considered with respect to the fatigue life in way of stress single/double side and longitudinal bottom girders, the concentration areas such as acces.'\ openine1;. Th~ sh~ar nominal shear force rlistrihntion :imone th()~i>. Fcl~mi:>D~~ !TI!!)' stress, tT , in the crossdeck induced by the torsional normally be decided based on "Shear Flow Calculation". The deformation may be related to the rate of twist by the typical shear force distribution factors for the main shear following equation: carrying members of the hull, for various type of the vessel can be found from the Table DI of the Rules Pt.3 Ch. I 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 8.2.4 calculated by "Shear Flow Calculation", where the 3-D effect of the load distribution on bottom structure is not considered. The rate of twist of the hull, 4>1- , is related conscrvati vel y to Therefore, for a correct shear strength evaluation, the the hull girder torsional moment, MT, hy the following corrected shear force has to he calculated taking into account equation: the local load distribution. The Rule Pt.3 Ch. I Sec.5 0200 describe the principle of this shear force correction. = ~ Ro This part of the note will provide the hackground and/or additional information to the Rules. k = fraction of the torsional moment that is supported through St. Venant's response of the model. 9.2 Definitions = 0.8 by the order of magnitude when related to the 9.2.t Symbols maximum wave torsional moment for 4 conventional bulk carriers) IN = moment of inertia in cm about the transverse neutral axis Ro = 24 f, E Ico (Zs +D)(l+ow)B D = first moment of area in cm1 of the bf lb(l+«,) longitudinal material above or below the horizontal neutral axis, taken about this MT = maximum value for the wave torsional moment as axis given in the Rules Pt.3 Ch. l Sec.5 B206 at 8 IN/SN = refer to neutral axis and is calculated in probability_of_exceedance_10· . (Note if the water the program "Section Scantlings" or may plane area coefficient, Cswp, of the vessel is not be taken as 900 known for the determination of MT, the calculated value may generally he based on an assumed Qs conventional (not corrected distribution of value for Cswr =0.9.) local load in hold(s)) stillwater shear force in kN For definition of remaining terms it is referred to 8.2.2. = shear force correction due to distribution of local loads in hold(s) Qw = rule wave shear force in kN as given in SHIP SIDE Pt.3 Ch.1 Sec.5 B200 h lsD Asp = shear force distribution factor for the leo effective longitudinal shear carrying Arn elements in the hull girder, see Pt.3 Ch. l Sec. 5 0103 = thickness of effective longitudinal shear carrying element

SHIP SIDE = allowable shear stress, the lesser of {l 10f1 and 0.9tc,(buckling stress))

Figure 8.1 Bulk carrier deck I hatch arrangement

DET NORSKE VERITAS Classification Notes- No. 31.1 35

June 1999

9.3 Rule Requirement are the thickness of the ship side as indicated in Figure 9.1 9.3.l The rule requirement to thickness of ship side or double side are situated above D/2 for the ship. Due to the as given in Pt.3 Ch.1 Sec.5 Dl03 of the Rules may be reduction in shear stress value when moving above reformulated as follows: D/2, the plate thickness above D/2 may be corrected as shown below.

Q ± 0.5 !J.Q =-t_'t_.!N__Q SN w - t i s cp s cp 100 ti.wrr - 0 I 0.9 + - · - (0.5D - y) 0.5D The right hand side of the equation may be considered to express the still water shear force capacity ( Q.uowabte) of the y = vertical distance from 012, see Fig. 9.1 hull in way of the considered section. The method for establishing allowable shear force curves is described in chapter 9.4. Double side Bulk Carrier:

The left hand side express the actual "Corrected Shear The thickness to be used in

9.4.l Seagoing condition 9.4.2 Harbour condition With reference to the formula above the allowable still water The allowable still water shear force in harbour conditions shear force can be expressed as follows will be obtained according to the same formula and principles as given in 9.4.l except that the wave shear force, Qw. is reduced to 50% for the sections in question. where 9.5 Corrected Shear Force 9.5.1 General t, is the smallest thickness as described in the text below. Other symbols are as given in 9.2. With reference to the formula in 9.3 the corrected shear force, Qs.c , can be expressed as follows In the following a description is gi vcn for deciding the thickness, t, to be used in the above formula. Qs,c = Qs ± (KPc)

SITengt!iened Area where • I --.----..---.-----,.--...,....., Deck I = is the uncorrected shear force or the shear force +- l I Loworcrnlof10pwif1Atank pl•li•A normally found in the loading manual. The sign Y 1: : !: ; Pia~ Scam convention for Qs and Qs.c is as described in our rules Pt. 3 Ch. I Sec .5 B 100 (weight of hull aft of Of.! -!---··-·····-+ · · 1-- '!..... Upp

Figure 9.1 Ship side/double side at the intersection with The shear force correction, (KPc), will be further described transverse bulkhead below for typical Bulk Carrier construction, i.e. single and double side construction.

The calculated (KPc)-value should be considered in With reference to Fig. 9.1 the thickness, l, used in the connection with the peak values of the conventional shear formula for Q.uowable is to be taken as follows: force curve at the transverse cargo hold bulkheads. Single side Bulk Carrier: 9.5.2 Bulk Carriers, single/double side construction The correction, (KPc), to the nominal .shear force may be expressed as follows: where

DET NORSKE VERITAS 36 Classification Notes No. 31.l

June 1999

(KPc) = Cp(PH + l:(I<.NPN))-CoT1 The (KPc)-value is always to be deducted from the peak- values of the conventional shear force curve in way of loaded PH = cargo or ballast in (t) for the hold in hold between empty holds or empty hold between loaded question holds.

bunker or ballast (t) in double bouom tank PN = For practical purposes Cr and C0 may be taken as constants no. N (port and starboard) situated below independent of cargo filling height and draught respectively. considered hold The following values may be used: = draught in m at the middle of hold cl' (9.81 C Boa LH H)NH (kN/t) Cp = load correction factor in kN/t ell 10 C Bn.s Ln (kN/m) Co = buoyancy correction factor in kN/m

0 B/(2.2 (B + LH)) (for conventional de.signs) 0 c = KN = (VH A N)/(H AN A a) to he calculated for each fill ed tank Bos = breadth of the flat part of the double hottom inm. H = height of hold in m = length of hold in m. Vn :;:: volume of hold in m3

AN :::: horizontal cross-sectional area (m2) (port and starboard) at level of inner bottom tank N

A'N = horizontal cross-sectional aTea (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

As = sum of all A'N

DETNORSKE VERITAS Classification Notes- No. 31.1 37

June 1999

Appendix A. Checklist for Finite Element A.1.2 Analysis The control may be further adapted to the computer program used in the analysis. In general the following main items A.1 Guidelines for use of checklist for FE analysis should be checked: A.1.1 • Geometry and element mesh The checklist is developed as an aid to ensure a satisfactory • Stiffness properties level of technical quality of work for analysis performed by • Boundary conditions the FE method. The checklist may also function as guidance • Loads and pressures for the process of completing FE analysis. • Stresses and reaction forces It is recommended that the checklist is used for self-checking by the one performing the analysis, and preferably by those performing independent verification. CHECKLIST FOR GEOMETRY, MESH AND ELE:tvlENT PROPERTIES STRUCTURAL PART: Reference drawings: Directory: Input and model file names: FEM file name: Units (have been checked): Controlled by I date: Length: [mm] Mass: [l] Time: [s] Force: [NJ 2 Pressure: [N/mm ] Constants (have been checked): 2 Gravity: 9810 [mm/s ] 9 3 Density (steel): 7.85E l0" [l/mm 5 ! Young's mod.: 2. IEJ0 [N/m m] Thennal exp. cocff.: 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 tines have been performed. Check of elements: Elements have heen checked for having correct material. Elements have been checked for having correct thickness (membrane/shell) or cross section properties (tru.ss/beam). Truss/beam clements have been checked for having correct eccentricity. Pree 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 I not used Loads: Load directions are found to be correct Plotc;: Pio ls of element mesh with thickness (colour plots or by numerical value on elements) and boundary conditions arc submitted with the checklists. There is confonnance between drawings and plots.

Strnctural part accepted: date: - --- sign.

DET NORSKE VERITAS 38 Classification Notes No. 31.1

June 1999

CHECKLIST FOR LOADS

Structural part: Controlled by I date:

Loads: Hand calculations or other program calculation for each basic load ca~e are cvn1prucd w·iih l1:.c 1Quii:. l1v1u J uia L-itet.,;k JJCI lut u1cU Uy d1e :suive1. Load directions are found to be correct The sum of loads from datacheck are checked Superelcments are/are not mirrored or rotated. Loads arc checked for mirrored and rotated superelements. Prints with datacheck of all loadcases is submitted with the checklists

Loads and load application are accepted: date:_ ___ sign.

CHECKLIST FOR LOAD COMBINATIONS AND RESULTS PRESENTATION

STRUCTURAL PART: Controlled hy I date:

Plots: Plots of structural part with deformed shape in proper scale arc submitted with the checklists. Plots of transverse membrane stresses of shell elements for relevant structural parts are submitted with the checklists (conto ur 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 suhmilled 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). Plols of axial stress of free flange for relevant structural parts are submitted with the checklists (contour plots and/or plots with numerical values). Stresses I 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 I acceptance criteria: Yield check of main structure performed based on relevant load cases and stresses. Hull girder stresses aQQ~dlllQ1 added manually. Yie ld check of secondary structure performed based on relevant load cases and stresses. Local bending has been taken into account Buckling check of transverse clements performed based on relevant load cases and stresse.~ . Buckling check of longitudinal elements perfonned 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 Classification Notes- No. 31.1 39

June 1999

For grillage type double skin structures, however, such as Appendix B. Beam Modelling double bottoms stiffened by tloors and longitudinal girders, full flange effectivity may normally be assumed for the B.l Beam modelling, general. elements representing the girders of the grill age.

B.1.1 B.1.8 The 2-dimcnsional beam models, which may be applied for The increased stiffness of girder elements with bracketed conventional bulk carriers, are as follows: ends is to be properly taken into account by the modelling. The rigid length of beam elements in way of bracket regions. a) Transverse bulkhead structure, which is modelled as a l" may normally be taken as: framework model subjected to in plane loading, ref. B.2. b) Douhle bottom structure, which is modelled as a grillagc l, :::: l-d-/t, see also Fig.B.2. model, subjected to lateral loading, ref. B.3. Note that this calculation may utilise stiffness data and loads as = 0, minimum. calculated for the transverse bulkhead calculation mentioned under a) above. Alternatively, load and d = as given in Fig. B.2. stiffness data for the bulkhead may be based on approximate formulae. It = represents the shear induced bending flexibility of e) Top wing tank structure, which for ships wi

DET NORSKE VERITAS 40 Classification Notes No. 31.1

June 1999

B.1.10 B.1.12 It is important to use a short element with above properties as In beam models the torsional stiffness of box structures is this approach assumes constant moment over the clement normally represented by beam clement torsional stiffness, length. The modelling shall generally take into consideration and in case of three-dimensional modelling sometimes by relevant effects due to variation in element web height over shear elements representing the various panels constituting its length as applicable. Unless special beam elements with Lhe box structure. Typical examples where shear elements varying web height are available, members with varying have been used arc shown in Fig. B.7(a), while a iu::i~ii siiuuiJ preforabiy b~ represeme

Fig. B.4 1 which shows a typical bulkhead lower stools. applied in Fig. B.7(b).

The proposed meshes are appropriate for stools, which are The torsional moment of inertia, IT, of a torsion box may stiffened by diaphragm plates with varying sized lightening generally be determined according to the following formula, holes. The purpose of the horizontal system lines is to see also Fig. B.5. connect the elements representing the stool side plating and stiffeners (flange effect) with the clements representing the web plating of the stool to form an integrated structural system. The horizontal clements should be made rigid compared to the vertical clements representing the web plating, but should no t have excessive .shear area and moment of inertia (in order to avoid numerical problems in m = no. of panels of which the torsion box is the solution process). composed.

The necessary number of rigid horizontal elements depends l; = thickness of panel no. i. on the shape of the structure. Normally, however, 4-5 horizontal clements as indicated in Fig. B.4 should be S; = breadth of panel no. i. enough for a salisfactory model representation. r1 = distance from panel no. i to the centre of rotation for the torsion box. Note the centre ofrotation B.1.11 must be determined with due regard to the In simplified two-dimensional modelling, possible thrcc­ restraining effect of major supporting panels dimensional effects caused by supporting girders etc. arc (such as ship side and double bottom) of the oox normally represented by springs. structure.

The spring stiffness, Kc;, of axial springs representing B.1.13 supporting girders may normaily be given by the following formula: In two-dimensional modelling, the three-dimensional effect of supporting torsion boxes is normally represented by K _ Eis,ll rotational springs or by axial springs representing the G- /4(]+ ~ ) stiffness of the various panels of the box. f2 As The spring stitlncss, KT, of a rotational spring representing a .supp

As = shear area of supporting girder.

= model breadth. = breadth assumed for two-dirnen.i;ional model. = length of torsion box between supports. Ct = 76.8 for simple end condition for supporting l girder. = as given in B.1.l2 = 384 for fixed end condition for supporting girder. B.1.14 The rotational restraint by torsion boxes (e.g. top wing tank) = 50 for simple support condition for supporting may be represented by axial springs as indicated in Fig. B.6. girder. The stiffness of the axial spring(s) is generally given by the = 250 for fixed end condition for supporting following formula: girder. K _ 4G l bsm s - z2

DET NORSK.E VERJTAS Classification Notes- No. 31.1 41

June 1999 l = length of torsion box between supports. b = breadth of panel represented by spring considered. t = thickness of panel. s,.. = 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 equi vafent 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:

A= Ks/ E l = length of area clement.

RIGID END OF ELEMENTS

RIGID lll.EMENTS

- --II>-" ELEMENTHIN(lEDATNODE

flXl!DNOOU

------<~ NOOE wrm FIXED JN PLANE ROTATION AND X-MOVEMEl'IT, FREE Y-MOVEMEl'IT

NODfl WlTII FIXED X· ANDY-MOVEMENT, ~­ PREil iN l'l.ANE ROTATION

NODE WlTI\ f'IXflD Y-MOVEMl!NT ~- FREll 1N PLANE ROTA TION A ND X-MOVEMflNT ~ l«lOO Willi LINEAR JN PLANS RESTI\Alf'/'r

NODE WlTI\ ROTATIONAL IN 1'1.ANE R6S1'RAIITT -----+~ (ROTATIONAL SPRING) vf_ x

Figure B.1 Symbols

DET NORSKE VERITAS 4:2 Classification Notes No. 31.1

June 1999

. ~ b ~ ! (a) (b)

_d. • .d b r 1.0 ~ \I"'- 0.9 "- \ " ['... I\. ~ 0.8 '\ ('\.. "t'--- '\ I'\. r----. r-.... 0.7 '\ .... __ I'\ --- r-- ~r-. r-- 0.6 ""' ~-- ~ r- ...._ - (b) 0.5 '~ I'.. ~ !"---.. '- ~-. 0.4 -r--r-- --r-r-. __ 0.3 (a) 0 0.5 1.0 1.5 2.0 h r I\;' ~

Figure B.2 Rigid end lengths of beam elements

r--./\...-

Double bottom .0. ~ b t l ', 2

Figure B.3 Nonbracketed corner model

DET NORS KE VERITAS Classification Notes· No. 31.t 43

June 1999

Centre of rotation

Figure B.5 Torsional stiffness of box structure

Figure B.4 Element mesh representing tapering member (bulkhead stool)

Figure B.6 Spring modelling of supporting panels of torsion boxes

DET NORSKE VERITAS 44 Classification Notes No. 31.1

June 1999

• t l l

Figure 8.7 (a)

3-D beam element model covering double bottom structure, hopper region represented by shear panels, bulkhead and deck between hatch structure. Lumped main frames

(h)

3D beam element model covering double bottom structure, bopper region, bulkhead and deck between holds. Lumped main frames

DET NORSKE VERITAS Classification Notes- No. 31.l 45

June 1999

B.2 Transverse bulkhead structures. moment of inertia of hatch end coaming about horizontal axis. B.2.1 As vertical shear area of hatch end coaming. The transverse bulkhead is normally modelled as a two­ dimensional structure. In such case the model normally Sm = model breadth. 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 B.2.5 the bulkhead corrugation at the lower and upper stool over The two-dimensional bulkhead model is normally taken at the breadth of the hold, or for instance to represent special the ships' centreline. The required model breadth will depend load conditions including such as the moment exerted by a on the actual design in each case. It may be convenient to crane pedestal and or deck loads. 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 B.2.2 stiffness of one corrugation. Pig. B.8 shows a sketch of a typical transverse bulkhead design and the corresponding two-dimensional beam model. B.2.6 For calculation of the wate1tight bulkhead loading, LC9, the fixed support condition should generally be assumed at the The bulkhead calculation may be utilised in order to lower bulkhead support at the inner bottom. For determine stiffness- and force data for the bulkhead to be consideration of bulkhead strength for cargo load as given by applied for the double bottom grillage calculation. load case LC5, the rotational displacement obtained for the double bottom calculation should be applied at the lower In this case the .supporting moment al the lower support, bulkhead support. Mee. may be applied in the double bottom grillage calculation as a moment, M 11s, per douhle hollom girder as follows: B.2.3 The clement mesh pattern of the stool should generally be Mes:::: MBBSg made in accordance with B.1.10. Note that in the regions Sm where each stool side is supported by separate webs, the sloping system lines should represent the complete s!iffncss s g == effective breadth of the double bottom side of the webs including the plate flanges. girder considered.

B.2.4 ::: model breadth of bulkhead model. As indicated in Fig. B.8, it is normally sufficient to represent the bulkhead support at the deck by a simply supported node. The rotational constraining stiffness exerted by the bulkhead Note, however, that lhe deck suppo1t should in principle be on the double bottom may be determined by subjecting the positioned in the shear centre position of the erossdeck lower bulkhead support to a rotational displacement, ¢ , as a structure, which in cases with a high hatch end coamings or a separate load case. The rotation spring stiffness exerted by large upper stool tends to be below the deck level. If the the bulkhead is then determined from the calculated shear centre position of the crossdcck is not known, a support supporting moment, M, by the formula: position at deck level is generally acceptable. Ms It should be noted that when an upper stool has hcen KRn ;;--g arranged, the torsional stiffness of the stool structure may be = 77Elsm

4 b1 [ 1 +.lQ!_Jbf As b1 = hatchway breadth.

DET NORSKE VERITAS 46 Classification Notes No. 31.1

June 1999

In the longitudinal direction the model should extend at least from the middle of one hold to the middle of the adjacent Crossdack snaar centre ~ 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 unsymmetrical floor arrangement, an increased model length extending over one complete hold and two half hold lengths should be considered. Aiternativeiy, ii a model extendmg over 'L halt hold !cng

The vertical model support(s) is generally assumed at the transverse bulkhcad(s) in the shear centre position of the half Figure B.8 Two-dimensional mesh of bulkhead structure 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-b Ys'"' --·1 16

b, = breadth of hatch opening (m). ~K~o~-c=:;::~=>-~~4 Ko For open type double skin bulk carriers, the support point may be assumed at the mid-breadth of the wing tank.

B.3.3 Figure B.9 Spring support by hatch end coamings The beam clements representing floors extending from centreline to the hopper side and longitudinal double bottom B.3 Double bottom structure. girders should have a torsional moment of inertia, IT, equal to: B.3.1 2 The double bottom structure is normally modelled as a b h IT = 1 1 grillage or as a part of a three-dimensional model covering -+­ the hopper and/or the transverse bulkhead and deck, in lib tb addition to the double bottom structure. b = member flange breadth (assuming 100 % Three-dimensional modelling is preferable, and should effective flange breadth, ref. B.1.7 above. generally be used for the hopper region unless the hopper tank is small. Similarly the inclusion of the transverse h = web height. bulkhead structure into the double bottom model may be important for the correct assessment of shear forces in double t;b = thickness of bottom plating. bottom longitudinal girders and for the bulkhead member thickness of inner bottom plating. shear and bending response. tb =

B.3.2 B.3.4 The shear stiffness of double bottom girder elements is in Fig. B .10 shows a typical double bottom grillage element general to be reduced for girders with large web openings. mesh with the hopper tank modelled as a three dimensional For normal of access and lightening holes a structure. The model is to extend athwartships from the ship arrangemenl factor of 0.8 may be suitable. side to the centreline, where symmetry is assumed for relevant load conditions.

DET NORSKE VERITAS Classification Notes- No. 31.1 47

June 1999

B.3.5 The bending stiffness contribution of the bottom-and inner bottom longitudinals may be included by increasing the Adjacent floor elements of the grillage model are assumed to be separated halfway between floors. The lloors in line with longitudinal girder web thickness as follows: 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 clements, except for Lhc effective shear area, As, AN = sum of net cross-sectional area of houom which should be taken as: longitudinals within flange breadth of girder (corrosion margin deducted). A ___2_.6 __ s - ,2 2.6 J\ll = sum or net cross-sectional area of inner bottom - - +-- 1011gitudinals within flange breadth of girder 12Ll LAs (corrosion margin deducted). l = span of transverse stiffeners in pipe tunnel. h0 = distance from bottom plating to neutral axis of bottom longitudinals (plate flange disregarded). = sum of moments of inertia of bottom and inner bottom transverse stiffeners within Lhc floor hu = distance from inner bottom plating to neutral nange breadth. axis of inner bottom longitudinals (plate flange disregarded}. LAs = sum of shear areas of bottom and inner bottom transverse stiffeners within the floor flange breadth. The correct effective shear area for the girder is obtained by multiplying the element shear effectivity factor (if available) hy: B.3.7

The transverse bulkhead clements should represent the shear lw 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 tloor elements. B.3.9 For the elements representing the ship side and hopper The cross-sectional properties of the transverse bulkhead region, an element with bending and shear stiffness in clements should generally be based on an assumed effective accordance with the half hull girder cross-section may be flange width for bottom, inner boltom and deck which docs used. The torsional moment of inertia of the hopper tank, h. not exceed 20 % of the vessel breadth. For corrugated should be determined in accordance with B.1.12. bulkheads with a lower stool structure, lhc element moment of inertia and shear area of the transverse bulkhead may be B.3.10 determined according to B.5.4. The stiffness and load effects from the side frames acting on The torsional moment of inertia, IT. of the bulkhead elements the double botlom structure may be represented by rotational representing the lower stool should (in agreement with springs and nodal forces and moments described for the B.1.12) be detcm1ined according to the following formula, nodes representing the hopper webs at the hopper top. see also Fig. B.11. B.3.ll 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 B.3.8 axis of these elements should be defined in the plane of the Adjacent longitudinal double bottom elements arc assumed hopper side. to be separated halfway between the girder webs. The sloping hopper side plate and the bottom plating outside of B.3.12 the hopper side girder should be disregarded when the hopper side girder element cros~ - sectional properties arc The rotational spring stiffness representing the transverse determined. bulkhead, KRB• in accordance with B.2.6, may for each longitudinal girder be determined from the transverse bulkhead calculation.

DET NORSKE VERITAS 48 Classification Notes No. 31.1

June 1999

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 he determined from the transvcn;e bulkhead calculation.

I I I TraTlS\r'a"Se seclioo

Roar rrodels - .

Q) -0 0 E -l x .... Cl> ~ -0 a....

t

Figure B.10 Double bottom grillage element mesh

DET NORSKE VERITAS Classification Notes- No. 31.1 49

June 1999

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 LC6 and LC7 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 he I... // ~1..- // •I 1~ // ... ,... // ~ 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 Figure B.J 1 Lower stool torsional moment of inertia bulkheads for effective support of deck cargo loads etc.

B.4 Top wing tank I Deck structure. B.4.5 B.4.l Three-dimensional models of the top wing tank and deck The top wing tank web frame structure is in some cases structure should normally extend over minimum two half analysed as a two-

A0 == cross-sectional area of deck part. AL = cross-sectional area of lower stool and bottom part.

DETNORSKE VERITAS so Classification Notes No. 31.1

June 1999

H = distance between neutral axis of deck part and B.5.5 lower stool and bottom part. The normal stress in the upper deck, oo , due to the bulkhead bending may be determined according to the following Cc mean thickness of bulkhead corrugation. = formula: b. = breadth of corrugation. cr - ---MsHo be = breadth of corrugation measured along the 0 - KH Ao - - -,--- ..!-- ___ r;.1 _ "'v11 u t;a.uuu p• v•' 1c, 8 .5.6 B.5.3 Similarly the normal stress in the lower stool, crts , due to the For the stool and bottom part, see Fig. B.12, the cross­ bulkhead bending may be determined according to the sectional properties, 15 and A5, should be determined as normal. Based on the above, a correction factor, K, may be following formula: determined by the formula:

I = K le

A=KAs

A NEU TAAL AXIS DECK r 0 I . A l

I + + I H

I tc I ~s • 1s, As, AL - AL -- NEUTRAL AXIS ~ r II LOWER STOOL AND BOTIOM PART

-1~~~0_.2_B_(max~) ~~~~

Figure B.12 Bulkhead double bottom grillage element definition

DET NORSKE VERITAS Classification Notes- No. 31.l 51

June 1999

B.6 Stress Analysis, general. B.8.2 The shear area of the pipe tunnel transverse members may B.6.1 normally be expressed as follows: The analysis procedures described in the following refer to beam calculations carried out in accordance with B.1-B.4. Inner bottom transverse member:

B.6.2 The described stress analyses generally refer to allowable stress limits given in the Rules. In addition compressive Bottom transverse member: normal stresses and shear stresses shall be considered with respect to buckling in accordance with Pt.3 Ch. l Sec.14 of the Rules, also for cases where no special reference to buckling control has been included in the text following. F = mean calculated shear force (N) in floor in way B.6.3 of pipe tunnel. ln the following calculated forces and moments are assumed given in N and Nmm, and material scantlings referred in = (F1 +pi)s formulae are assumed to be net scanUings, i.e. corrosion 2sr additions as stated in the Rules Pt.3 Ch.I Sec.2 0400 deducted. = 0 for pipe tunnels in the ships' centreline.

B.7 Double bottom bending strength. k B.7.1 s spacing in m of transverse stiffening members Allowable normal ginlcr stresses as given in the Rules Pt.3 = of in pipe tunnel. Ch. I Sec.13 B400 and buckling requirements given in Pl.3 Ch. l Sec.14 B200 and B400 are generally to be complied sr = mean spacing in m of double bottom floors in with. For the sum of longitudinal normal stress due to hull way of the considered transverse tunnel girder bending and longitudinal double bottom stress in members. nonhompgeneous loading conditions (Rule allowable stress = 2 190f1 N/mm ), the still water hull girder stress may generally = span of transverse pipe tunnel members in m. be based on the mean stiU water bending moment value, Msivh which for the middle of hold position is given by: IF.J 11 denote moment of inertia of stiffeners including plate . 4 flangem cm. M - Ms1+Ms2 SM - z 2 Ai:. A1 denote shear area of stiffeners in cm • Msi. denote still water hull girder hending moments Msz Other symbols are illustrated in Fig. B.13 calculated for the aft and forward transverse bulkhead positions of the cargo hold for the loading condition being Note the allowable .shear stress is to be taken according to the considered. 2 Rules Pt3 Ch. l Sec.13 D400 (= 90 f 1 N/mm ).

B.7.2 B.8.3 The transverse axial force of the double bollom structure due The total normal stress of pipe tunnel transverse memhers to external sea pressure on the sides need not be considered may normally be determined according to the following when the bottom panel is evaluated wilh respect to biaxial formula: buckling in accordance with Pt.3 Ch. I Sec. l 4B of the Rules, provided the inner bottom structure is able to effectively Inner bottom transverse member: support the external sea pressure load.

B.8 Pipe tunnel strength. CJ= B.8.1 The modelling technique applied normally reflects the Bottom transverse member: 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.

DET NORSKE VERIT AS 52 Classification Notes No. 31.l

June 1999

F,l,s = as given in B.8.2 B.9 Strength of double bottom below transverse bulkhead stool. = transverse stress (N/mm2) "in inner bottom in way of pipe tunnel according to double bottom B.9. 1 calculation. When vertically corrugated transverse bulkheads arc subjected to lateral load, large support forces, Pp, occurs by O"h = transverse stress (N/mm2) in bollom in way of the bulkhead bending at the lower stool side or the pipe tunnel according to double bottom corrugation fiange (if no iower stooi is fitted) attachment to calculation. the double bottom as illustrated in Fig. B.14. = height in m of transverse inner bottom pipe The force, PF. may he determined from the calculaled tunnel memher. bending moment of the transverse bulkhead at the inner height in m of transverse hottom pipe tunnel bollom, Ms (Nmm), as follows: member. Pp= MB (N). = height of double bottom at pipe tunnel in m. bs p; = internal pressure from cargo ai; given in the b, = breadth (mm) of stool at inner hntlom. Rules Pt.3 Ch.I Sec.4 C400 for the load case considered. For wide stools the force Pp will be balanced by the shear forces, Fs and Fs2, in the adjoining longitudinal bottom external lateral sea pressure according to the 1 Pe girder. For narrow stools the vertical stool side force may load case considered. become very large giving rise to high shear stress in the wch = section modulus of pipe tunnel members area below the stool. The nominal shear stress in the web 3 (cm ) . may normally be determined as the larger of:

p Other symbols arc defined under B.8.2 and in Pig. B.13. = JOO As Note the allowable normal stress is Lo be taken according to 2 _ _P _b...... __ (N/nun2) . the Rules Pt. 3 Ch. I Sec. 13 B400 (= l 60 f1 N/nun in = general). 100 hdb Ah

P (2 Pr - (I Psi I + I Fs1 I) )'2 (N)

As the (vertical) shear area of Lhe longitudinal 2 girder below stool in cm •

STRUCTURAL = I 0 t(hdu · h1). DESIGN the (horizontal) shear area of the longitudinal 2 girder hclow the stool in cm •

= 10 t(b. - b,).

Pi hdb = as given in B.8.3.

h, = height in m of lightening hole arranged in DISTR. PRESSURES F, double bottom girder below stool. t +F 2 FORCES h, = breadth in m of lightening hole arranged in double bottom girder below stool. Pe = thickness of longitudinal double bottom girder below stool in mm.

Figure B.13 Analysis of pipe tunnel transverse members F.~1 and Fs2 de note shear forces (N) of the longitudinal girder at the bulkhead stool, taken from the douhlc bottom grillage calculation.

DETNORSKE VERITAS Classification Notes- No. 31.l 53

June 1999

The allowable nominal shear stress is to be taken in accordance wilh the Rules Pt.3 Ch. l Sec. I 3 B400 (= 100 f1 2 N/mm ).

B.9.2 Where the floors below the stool side arc discontinous, e.g. at pipe tunnels, large stress concentrations may occur when the hdb normal force, P, is transmitted from the stool lo the double or, bottom. With reference to Fig. B.15, the nominal normal ~ stress of the stool side, cs, at inner bottom may be calculated to: ~ b., ~ ip, P = force (N) transmitted between stool side and jp, double bottom in way of the longitudinal girder considered. F,. 1 rF,, b breadth of stool side in mm corresponding to longitudinal girder.

h1+h2 = 2 Figure B.14 Stress analysis Of longitudinal web below transverse bulkhead (stool) = 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.

PF = as given in B.9.1 b = b1 +b2 STRUCTURAL 2 DESIGN The allowable normal stress may be taken in accordance with 2 the Rules Pt.3 Ch.1 Sec.13 B400 (= 160f1 N/mm ).

The nominal shear stress, i:, at the intersection between floor and longitudinal girder may be calculated to: EFFECTIVE BREADTH AT INNER BOTTOM

Asi. As2 denotes shear areas as indicated in Fig. B.15. ----S2 ·- The allowable nominaJ shear stress may be taken in accord­ EFFECTIVE SHEAR 2 ! ance with the Rules Pt.3 Ch.I Sec.13 B400 (= 90 f1 N/mm ). []r=: AREA

Figure B.15 Stress analysis of floors below stool sides in way of double bottom tunnel

DET NORSKE VERITAS 54 Classification Notes No. 31.l

June 1999

B.10 Shear strength of webs with cutouts. B.11 Strength of transverse bulkhead.

B.10.1 B.11.1 The nominal shear stress, 't , in webs in way of scallops and The shear connection of the transverse bulkhead structure to holes may in general calculated as: the side shell, and compressive I tensile stresses in the transverse deck structure are matters of importance when the 2 overall strength of the transverse bulkhead is evaluated. Both -c =_ft_ (N/mm ) . 100 As are of particular interest when the bulkhead is of the vertically corrugated type, and when special load conditions Fs = calculated shear force in N at section considered. 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. The allowable nominal shear stress for

s Ps (N/mmz). maximum calculated shear force in the = IOOhdbAs1 = transverse bulkhead at the section considered according to the double bottom (or quivalent) = nominal shear stress between stiffeners at calculation, see Bl-B.4. bottom (or at inner bottom). K = as given in B.5. = h~ = height of lower stool (m). effective thickness of bulkhead plating. The allowable nominal shear stress is to be taken as given in = B.10.l. = thickness of corrugation in way of corrugated part of bulkhead.

t (h, - h,) for diaphragm plate fitted in top = h1 wing tank in line with bulkhead corrugation.

= plate thickness of diaphragm plate in the top 0 1-u--1 wing tank. l____ {\_, __ _ = height of top wing tank in way of considered section. --1~ _ s - ...i As2 CRITICAL HORIZONTAL h, = height of lightening holes in diaphragm plate in STRUCTURAL DESIGN SECTIONS OF SHEAR way of considered section.

The allowable nominal shear stress is to be taken in

accordance with the Rules Pt.3 Ch.I Sec.13 B 400 (= 90f1 2 Figure B.16 Shear stress analysis of girder webs with N/mm ). Within the top wing tank (above the top wing tank cutouts 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.

DET NORSKE VERITAS Classification Notes- No. 31.1 SS

June 1999

B.11.3 Generally the Ostool should not exceed l .2cr, where a denotes The strength of the bulkhead corrugation in way of its the allowable stress given in the Rules Pt.3 Ch. I Sec.9 C attachment to the lower stool shall generally be considered in 302. accordance with the Rules Pt.3 Ch.I Sec.9 C 305. For stools with sloping stool top plate note in addition that the bending B.12 Strength of main frames. moment applicable for the control of stresses in way of the attachment of the corrugation to the stool need generally only B.12.1 be related to the bending moment at the level of the top of Generally the main frames of bulkcarricrs arc to comply with the sloped stool top plate. section modulus requirements as given in the Rules Pt.5 Ch.2 Sec. I0 B. For ships with long cargo holds, the main frames B.11.4 will normally be subjected to considerable prescribed The stress of the stool side plate at the attachment to the deformation caused hy the rotational deformation of the bulkhead corrugation may generally be determined based on hopper and top wing tanks. Such prescribed deformation the following formula: occurs in particular for the empty holds and the ore holds in bulkcarriers in the alternate loading condition and for the

- crcorr tcorr condition with ballast cargo hold filled. 11stool - fl tstool COSp B.12.2 Ocorr = nominal bending stress in bulkhead corrugation Main frames subjected to prescribed deformations shall at attachment to stool. comply with the allowable stress given in Pt.3 Ch. I Sec. 13 B400. The occurring stresses may be determined by lcorr = thickness of bulkhead corrugation, corrosion including the main frames in the double bottom- or wing margin tk deducted. tank models described in B.l-B.4, or by separate direct calculation. lstool = thickness of stool side plate, corrosion addition t" deducted. = angle of stool side plate with the vertical.

DET NORSKE VERITAS