Two new unified requirements relating to the strength of double side skin (DSS) bulk carriers are now being developed by working groups in IACS. This work is being carried out in response to the agreement with MSC76 which states that there is a need to develop uniform international standards for double side skin construction, preferably in collaboration with IACS.
The philosophy of the requirements will be based on North Atlantic wave conditions, ultimate limit state check (yield and buckling), fatigue check (ship’s life), and corrosion (net scantlings and corrosion additions).
The loading conditions will cover standard loading conditions defined in URS25 and flooded conditions defined in UR S17, S18, and S20 as applicable. The design loads will be related to hull girder strength, local structures (plating and stiffeners), global strength (3D Finite Element Analysis) and fatigue analysis.
DSS local scantlings URSXX (Local scantlings of Double Side Skin Structure of Bulk Carriers)
The Working Party of Strength, WP/S, is working on this task and in short their work related to double side skin bulk carriers can be summarised as follows:
1. UR for local scantlings of the double side skin. This is under development and a draft proposal, URSXX, is now under testing among the IACS members and is scheduled to be completed by WP/S within November 2003. This proposal will also contain fatigue requirements relating to the side longitudinals.
2. Amendment of UR S18, S20 and S17 to comply for DSS BCs. These tasks have been the subject of initial discussion within WP/S. The scope of the amendments is presently under some discussion in the IACS General Policy Group (GPG), and subject to their decision the amendments will be completed by WP/S.
3. Revision of UR S11 to incorporate an Ultimate Limit State, ULS, requirement for hull girder. Also the general buckling requirements of UR S11 are to be amended. These are urgent tasks for WP/S to process in parallel with items 1 above. Note the amendment of UR S11 will have direct implications for UR S17.
4. URs for remaining local cargo hold structures of DSS BCs. These are on the WP/S task list (completion dates to be decided).
DSS Global strength Analysis (UR SYY)
This task is being carried out by the Ad Hoc Group for Direct Strength Analysis, AHD/DSA.
The objective is to develop unified requirements containing detailed criteria for the direct strength analysis of DSS bulk carriers’ cargo hold structures, based on Finite Element calculations. This includes a load model that is suitable for structural analyses based on cargo hold models and the associated checking criteria. Among the items covered are:
Finite element modelling and analysis (Cargo hold analysis)
• Scope of the analysis
• Standardised structural analysis procedures
• Criteria for modelling
• Net thickness philosophy and corrosion additions
Loads & loading conditions to be applied in the FEM analysis
• Design sea state
• Standardised design waves
• Local and global dynamic loads
• Consistent load combinations
• Application of UR S25
• Still water bending moments
Strength checks
• Yielding criteria
• Buckling criteria
• Ultimate strength criteria
The requirements will be applicable to the cargo holds and ballast tanks in the cargo area. The proposals regarding URSYY are now being tested by the IACS members using a selection of DSS bulk carriers.