VERIFICATION OF THE MATERIAL RESISTANCE FACTORS IN THE CSA-S474 CODE FOR OFFSHORE CONCRETE STRUCTURES

The Canadian Standards Association has developed a national code for t he design, construction and installation of fixed offshore structures. This code was developed on the basis of probabilistic principles. It consists of five parts (CAN/CSA-S471 to S475), dealing with general lo ading and design requirements, foundations, steel structures, concrete structures, and sea operations. The material resistance factors cited in the part on concrete structures (S474-M1989) were verified using d ata typical of offshore structures for a set of representative design cases. The test cases were based on reinforced concrete ice resisting walls with configurations typical of those contemplated for offshore s tructures in Canada. They covered rare and frequent ice loading for sa fety classes I and II under flexure, combined flexure and axial force, and shear. The test cases were designed according to the CSA and DnV code provisions, and the reliabilities associated with the resulting m embers were calculated and assessed. The results indicate that the rel iabilities achieved by designing to the CSA standard for safety class I sections are greater than those obtained by designing to DnV rules f or all cases considered. Designs carried out according to CSA-S474 mee t the target reliabilities implied by CSA-S471 for values of the coeff icient of variation of the in situ concrete strength of up to 12% and are, in many cases, very conservative. Sensitivity analysis of safety class I members suggests that the material resistance factors can be i ncreased. Issues that need to be addressed in order to justify an incr ease in the factors include the acquisition of more data on in situ co ncrete strength and a more comprehensive consideration of the design c onditions covered by the code. The overall consistency of the reliabil ity levels associated with the CSA code can be improved by simultaneou s verification of the material factors in CSA-S474 and the load criter ia and factors in CSA-S471.