Development of Reliability-Based Assessment Criteria Against Extreme Environments For Steel Fixed Offshore Structures With Significant Permanent Loading

Abstract

Many fixed steel offshore platforms in the Arabian Gulf are situated in shallow water and have a relatively high proportion of dead loading to environmental loading. As such their capacity is governed by the combined effect of extreme environmental loading and vertical dead loading. Reliability-based assessment methods normally consider the probability of the lateral capacity being exceeded by the extreme environmental loading. This assessment is typically performed by considering the pushover capacity of the platform compared with the regional environmental hazard curve. Allowance is made for uncertainty in the capacity and load model when evaluating the reliability. In the presence of significant dead loading, and for some ultimate failure modes, the sensitivity of pushover capacity to dead load plays an important role in the reliability analysis. This paper describes the methodology for reliability analysis against the extreme load hazard and which can be implemented into future assessment codes. Particular attention is focussed on the sensitivity of structures to high levels of dead load and how this may be incorporated into reliability analysis. The development of acceptance criteria for reserve strength ratios (RSRs) which depend on regional hazard curves and dead load is also described.