TSCF 2016 Shipbuilders Meeting IACS Common Structural Rules for Bulk Carriers and Oil Tankers Complying with IMO GBS Gang Wang, IACS HP member Busan,Korea, 26 27 October 2016 1
Content 1 Introduction 2 CSR Harmonization and Amendments due to IMO GBS 3 CSR BC&OT Influence on the Scantling of Oil Tankers 4 Summary 2
1 Introduction Status Outcome of MSC 96 (May 2016) MSC.1/Circ.1518, Promulgation of rules confirmed to be in conformity with the goals and functional requirements of IMO GBS CSR Status CSR BC&OT based on harmonization of CSR BC and CSR OT entry into force from 1st July 2015, and being updated based on IACS Action Plan for Ncs and OBs from IMO GBS auditing 3
IMO GBS Requirements Tier I Goals High level objectives to be met 1 Introduction IMO GBS Tier II Functional requirements Criteria to be satisfied in order to conform to the goals. Tier III Verification of conformity Procedures for verifying that the rules and regulations for ship design and construction conform to the goals and functional requirements. Tier IV Rules and regulations for ship design and requirements. Tier V Industry practices and standards 4
1 Introduction CSR Status Current CSR BC&OT 2015 CSR BC&OT Entered into force 1 July 2015 plus Corrigenda 1 No Rule Change Notices applied in 2015 and 2016 due to year of stability 5
1 Introduction CSR Status 2016 Rule Change Proposal (RCP) development Changes to the Rules are continually needed to cover general maintenance, clarification of requirements, etc. A 2016 RCP was developed and did receive a full Industry review earlier this year Due to comments received from the Industry during the first review period, and wishing to focus our efforts on the achieving of full GBS compliance at coming MSC meetings, the 2016 CSR yearly maintenance is, as with that of 2015, being held in abeyance. The Rule Changes that were being proposed for this year s RCP will be further reviewed in light of comments received, amended where considered necessary, and will be added to a future RCP 6
1 Introduction CSR Status 2016 Urgent Rule Change Proposal(URCP) development For IMO GBS non conformities(nc) applicable to CSR BC &OT NC/01 Non uniform heading requirement Loading NC/03 Proportion of time in heavy ballast in NA Fatigue NC/04 Proportion of time in corrosive environment Fatigue Schedule for URCP Four weeks Industry and TC review in September 2016 Submission to IMO for audit mid December 2016 Scheduled to be published 1 January 2017 Entry into force on 1 July 2017 7
1 Introduction CSR Status 2016 Urgent Rule Change Proposal(URCP) development Technical details of URCP content NC/01 Increase in wave load for HSM & FSM load cases by 5% Impact on hull girder global strength / ultimate strength NC/03 Time in Heavy Ballast in NA increased from 15% to 25% for BC B and BC C ships with L<200m Impact on fatigue requirement in ballast hold NC/04 Time in corrosive environment for ballast / oil cargo tanks increased from 5 to 10 years. For cargo holds, void spaces and other areas increased from 2 to 5 years Impact on fatigue requirements Technical Background documents also available 8
2016 Technical Background development Technical Backgrounds developed in response to IMO GBS non conformity NC/02 applicable to CSR BC&OT (no associated Rule changes) Reports on imbedded Safety Margins, covering: Service Experience Loads Material Properties Net scantlings Direct Strength Analysis Acceptance criteria 1 Introduction CSR Status 9
2017 Rule Version Entry into force on 1 July 2017 Will incorporate the following: 2015 CSR BC&OT 2015 Corrigenda 1 Introduction CSR Status 2016 URCN (published 1.1.2017) Publishers should finalise circa March 2017 Publication on IACS web site 10
1 Introduction CSR Status IACS CSR Knowledge Centre Closed to non IACS Member view New procedure developed to respond to CSR queries from Industry The CSR KC database to be used internally for IACS internal control 11
1 Introduction CSR Status GBS Audit Observations(OB) In addition to the NC items there are several OB items that IACS needs to address A large proportion of OB items relate to the CSR BC&OT IACS has action plans for all items Some items will be quick to resolve, others will take longer Status reports will be provided to IMO Secretariat at end 2016 OB related CSR BC&OT Rule changes will feed into the normal Rule change cycle First OB related Rule change complete and will be added to the next RCP 12
Wave Loads Principle North Atlantic, IACS Rec.34 Envelope of hull girder loads EDW Hull girder&acceleration Pressure Selection&validation 25 years design life, Speed consideration Rule Loads Extreme loads Fatigue loads 2 CSR Harmonization and Amendments due to IMO GBS 13
Wave Loads Extreme Loads 10 8 probability level 7 selected EDWs, 5knots Load case accelerations 2 CSR Harmonization and Amendments due to IMO GBS Load case external pressures Envelop values of acceleration and external pressure TB supplementation for IMO GBS verification 14
Wave Loads Fatigue Loads 2 CSR Harmonization and Amendments due to IMO GBS 10 2 probability level,shape factor=1.0 5 selected EDWs, 3/4V design Speed effect considered External pressure Load case stress range TB supplementation for IMO GBS verification 15
Prescriptive Requirements Hull Girder HG strength Bending Moments&Shear Forces HG ultimate strength 2 CSR Harmonization and Amendments due to IMO GBS HG ultimate residual strength Scope cargo holds region and engine room region Direct calculation of shear flow and Incremental iterative method (Smith) 16
2 CSR Harmonization and Amendments due to IMO GBS Prescriptive Requirements Local requirements Minimum thickness requirements Design loads sets for local requirements Ship type specific requirements 17
Finite Element Analysis (FEA) Scope and Objeives Modelling Model extent,mesh,plates,eccentric beam, Openings,Face plate of PSM,Sniped stiffener Boundary conditions Evaluation areas 2 CSR Harmonization and Amendments due to IMO GBS 18
2 CSR Harmonization and Amendments due to IMO GBS Finite Element Analysis (FEA) Equilibrium method for BM&SF Load combinations Yielding Stress criteria Fine mesh analysis and Screening 19
Buckling strength Basis Various failure modes Various type of structural elements Most critical buckling failure mode Net scantling approach 2 CSR Harmonization and Amendments due to IMO GBS Slenderness requirements Plates, longitudinal and transverse stiffeners, primary supporting members and brackets Prescriptive buckling requirements Plates, longitudinal and transverse stiffeners, primary supporting members (PSM) and other structures 20
2 CSR Harmonization and Amendments due to IMO GBS Buckling strength FE buckling requirements Plates, stiffened panels and other structures Buckling capability by CFM and criteria Overall stiffened panel capacity Plate capacity Ultimate stiffener capacity Structural redundancy (IMO GBS) 21
Fatigue strength Basis 2 CSR Harmonization and Amendments due to IMO GBS 25 years Design life, North Atlantic, ¾ V design 10 2 probability level, shape factor=1.0 Long term weibull distributed stress range PM linear accumulative damage model S N curve in air and corrosive environment Stress corrections at welded joints Loading conditions and Fraction of time for fatigue life 22
Fatigue strength Simplified stress analysis Longitudinal stiffeners 2 CSR Harmonization and Amendments due to IMO GBS Hull girder bending, Relative deflections in way of transv. bhd, Local stiffener bending Stress concentration factors Very fine mesh FE analysis Mandatory for specific details If fatigue screening fails and detail design standard not followed Screening fatigue assessment 23
Corrosion and welding Net scantling approach Design In service Corrosion addition Corrosion model Corrosion data Welding 2 CSR Harmonization and Amendments due to IMO GBS Updating fillet welds scantlings Welding in high stress areas 24
Others Subject to the IMO GBS functional requirements and auditing requirements, CSR BC&OT carrying out supplementation, and providing verification information and documents to rules and technical supporting documents on: Human element consideration Design transparency Structural accessibility Survey during construction Survey & maintenance etc. 2 CSR Harmonization and Amendments due to IMO GBS 25
3 CSR BC&OT Influence on the Scantling of Oil Tankers Consequence Assessment (2014CA Reports) Ship type 10 typical existing oil tankers, including VLCC, Suezmax,Aframax, Panamax and Handymax in compliance with CSR OT Scope and Principle Local scantling requirements (yielding, buckling, and simplified fatigue assessment) HGUS and HGURS Direct strengths assessment (yielding, buckling assessment, and fatigue assessment) Not altering structure Application of CSR BC&OT (2014) 26
3 CSR BC&OT Influence on the Scantling of Oil Tankers Local Scantling Requirements Cargo Tanks Area For most of oil tankers, Keel plating and sheer strake increases due to increased minimum thickness Plating and stiffeners on the inner bottom, inner hull and main deck increase of various degree due to local pressure and buckling Fatigue life less than 25 years for longitudinal stiffeners on the bottom shell and side shell at mid part. 27
3 CSR BC&OT Influence on the Scantling of Oil Tankers Local Scantling Requirements Fore/Aft Part and Machinery Space Requirements for plating and stiffeners generally more conservative than CSR OT Transverse Bhd and Transverse Web Frame The plating thickness and stiffener section modulus of transverse bulkhead increases at the upper part and lower of the bulkhead The requirements for plating and stiffeners of transverse web frame are more conservative than CSR OT 28
HGUS and HGURS 3 CSR BC&OT Influence on the Scantling of Oil Tankers Hull Girder Ultimate Strength(HGUS) Hull Girder Ultimate Residual Strength(HGURS) 29
3 CSR BC&OT Influence on the Scantling of Oil Tankers Direct Strengths Assessment Cargo Tanks Area FE yielding assessment has limited impact for the oil tankers. FE buckling assessment leads to scantling impact. Generally the some areas located in hopper structure, inner hull upper part, longitudinal bulkhead upper part, horizontal stringers in the double hull and double bottom floors do not satisfy CSR BC&OT buckling requirements 30
3 CSR BC&OT Influence on the Scantling of Oil Tankers Direct Strengths Assessment Transverse Bhd and Transverse Web Frame FE buckling assessment leading to the scantling increase,but FE yielding not. FE buckling and/or FE yielding, which increase leading to the scanling increase for typical web frame. 31
3 CSR BC&OT Influence on the Scantling of Oil Tankers Direct Strengths Assessment Local Fine Mesh, Screening, and Very fine Mesh For most oil tankers, Local fine mesh requirement of FE yielding assessment not normally leading to any scantling increase. Screening hardly impacting on the scantling of local strength. For most oil tankers, Very fine mesh requirement of FE fatigue strength has impact on lower hopper knuckle connection, Normally fatigue life of some hot spots of lower hopper knuckle connection less than 25 years. 32
4 Summary Released CSR BC&OT is in compliance with the 15 functional requirements of IMO GBS and its verification requirements. Having overall harmonized on general principles of rules (net scantling approach, corrosion addition, welding, etc.), loads, prescriptive requirements (hull girder strength, minimum thickness requirements, local strength, etc.), direct calculation requirements, buckling strength, fatigue strength, etc.; Having supplemented or improved new rule requirements and related technical supporting materials for structural redundancy, human element consideration, design transparency, structural accessibility, survey during construction, survey & maintenance, etc. 33
4 Summary CSR BC&OT complying with IMO GBS requirements entry into force. IACS being constantly improving and maintaining the current CSR BC&OT according to IACS Action Plan submitted to IMO GBS. The existing oil tankers to be strengthened and upgraded by increase of scantlings of local structural members or change of local structural connection, etc. Structural optimization analysis to be also carried out. The other influences to be considered including increment of work loads of designers and Societies, implementation of design transparency requirement, and etc.. 34
4 Summary Thank You 35
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