The present paper describes an extension to a recent study which was undertaken to determine the appropriateness of the recommended value of the load combination factor relating to the combined effects of wave and iceberg loads on offshore structures, as described in the Canadian Standards Association (1992) code for the design and construction of fixed offshore structures. The present extension has been carried out in order to examine the sensitivity of the load combination factor to various iceberg and wave parameters. The method is based on a numerical analysis in which loads due to waves alone, an iceberg alone, and an iceberg and waves in combination, have been calculated for a range of iceberg and wave parameters, with the results applied to a first-order reliability analysis in order to study force levels corresponding to specified annual exceedence probabilities. The results indicate that the recommended value of the load combination factor is insensitive to iceberg arrival rate but is relatively sensitive to wave climate, so that it may be taken to be site dependent.
The selection of suitable environmental events and loads is of critical importance in the design of offshore structures. The CSA Offshore Structures Code CAN/CSA-S471-92 (Canadian Standards Association, 1992) describes the use of such loads in offshore design, including those due to wind, waves, earthquakes, ice and iceberg collisions, and indicates the use of probabilistic methods on which the selection of load events and design loads should be based. The Code has been subjected to a comprehensive verification process, and this has identified several issues which warrant further study. At present, this combination is treated by the use of a load combination factor which is used to determine a design value for the load due to a companion frequent environmental process (waves) acting in combination with a rare environmental event (iceberg collision).
