Reliability analysis of ice loads on arctic offshore structures

In Arctic regions, the calculation of ice loads is a key issue in the design of offshore structures. International Standards Organization (ISO) 19906 provides a deterministic approach to calculate ice forces on Arctic offshore structures. The approach combines environmental forces of an ice floe with structural parameters to estimate the imposed ice load. However, owing to large uncertainties in the underlying parameters, a statistical formulation is needed. The parameters include annual number of floes, floe size, ice thickness, and ridge geometry, among others. This paper focuses on the development of a procedure for determining design ice loads on Arctic offshore structures using a reliability approach. Level ice and ice ridges are considered as major load sources interacting with the offshore structure in the ice regime. Referring to ISO 19906 and available literatures, a deterministic methodology to calculate ice loads has been developed based on two limit mechanisms, including limit strength and limit force. In this study, ice loads on offshore structures mainly result from the first-year ridges interacting with the structure. The geometric parameters of ice floes are assumed as random variables in the probabilistic approach. A reliability-based approach using the First-Order Reliability Method (FORM) has been developed to incorporate the uncertainties in the underlying ice floe and environmental parameters. Specific site data is then used with the FORM approach to demonstrate the results which are compared to Monte Carlo simulations. The reliability-based method and the Monte Carlo simulation method are both implemented to determine design ice loads on Arctic offshore structures.