Introduction

This chapter describes models for loads that have a fundamental variability and their load effects on structures. These load effects are applied in the design and reassessment of structures during operation to ensure adequate structural performance; i.e., serviceability and safety in, say, a period of 20–50 years (ISO 2394, 1998). Serviceability requirements refer to motions, deformations, vibrations, etc., that can hamper the operation, but do not represent a threat to the safety. Safety means the absence of failures and damages, and is ensured by fulfilling requirements to overall stability and ultimate strength, and fatigue life under repetitive loading to avoid ultimate consequences such as fatalities, environmental damage, or property damage. The corresponding so-called limit state criteria are defined by limit states for ultimate failure (ultimate limit state (ULS)) and fatigue failure (fatigue limit state (FLS)), respectively.

ULS criteria for overall stability of bottom-supported structures are based on overturning forces due to wave, current, wind, and stabilizing forces due to permanent and variable payloads. Stability of floating structures is considered in terms of overturning moment by wind only, and uprighting moment due to hydrostatics of the inclined body.

ULS and FLS criteria for relevant components were developed for the relevant failure modes dependent on geometry and load conditions. Permanent and variable payloads, fluid pressure loads, and environmental loads are considered. Environmental loads due to waves, current, wind, and possibly ice and earthquakes are considered.