Accidental Limit-State Design

Abstract

Introduction As discussed in Chapters 3 and 5, limit states are classified into four categories: serviceability limit states (SLS), ultimate limit states (ULS), fatigue limit states (FLS), and accidental limit states (ALS). This chapter presents ALS design principles and criteria together with some related practices applicable for ship-shaped offshore units. ALS potentially leads to a threat of serious injury or loss of life, pollution, damage, and loss of property or significant financial expenditure. The intention of ALS design is to ensure that the structure is able to tolerate specified accidental events and, when accidents occur, subsequently maintains structural integrity for a sufficient period under specified (usually reduced) environmental conditions to enable the following risk mitigation and recovery measures to take place, as relevant: Evacuation of personnel from the structure Control of undesirable movement or motion of the structure Temporary repairs Safe refuge and firefighting in the case of fire and explosion Minimizing outflow of cargo or other hazardous material Different types of accidental events may require different methodologies or different levels of refinement of the same methodology to analyze structural resistance or capacity during and following such events (demands). The ALS design is then necessarily an important part of design and operation in terms of risk assessment and management that consists of hazard identification, structural evaluation, and mitigation measure development for specific types of accidents, as we describe in Chapter 13.