VERIFICATION AND CALIBRATION STUDIES FOR THE NEW CAN CSA-S472 FOUNDATIONS OF OFFSHORE STRUCTURES/

In June 1992, the Canadian Standards Association (CSA) published a cod e for the design, construction, and installation of fixed offshore str uctures. This code is relatively advanced in its application of limit states design to offshore structures. The part dealing with foundation s is written as a performance standard. It does not specify resistance factors (or safety factors) to achieve the target reliability of the structure. Although limit states design is common practice among geote chnical engineers, the application of resistance factors is a problem. This paper describes some of the studies and conclusions reached by t he Technical Committee in the development of the CSA foundations stand ard. As a first step, resistance factors were developed by calibration to conventional total factors of safety for the failure mechanisms co nsidered. This approach has severe limitations. In particular, the app licability of safety factors developed for onshore practice or other o ffshore areas to the ice-dominated environment of Canadian offshore re gions is questionable. In addition, many offshore structure designs in clude consideration of dynamic loading and scour or erosion problems t hat cannot be satisfactorily dealt with using factors of safety. An ex ample of the problem of applying separate load and resistance factors for a bearing-capacity problem is given to show that load and resistan ce are not independent of each other. Because of the problems with dev elopment of resistance factors, the CSA foundations standard dictates that offshore structure designs include a risk analysis of the foundat ion system. A simple form of such an analysis for a caisson-retained s and structure is included in the paper.