Experiences with offshore and other structures show that catastrophic accidents often are initiated by
human errors that cause accidental actions or abnormal resistance which escalate progressively into
undesirable consequences. It is therefore argued that damage tolerance or robustness is a desirable feature
of structures to complement other safety measures to achieve an acceptable risk level. Robustness
may be achieved by specific Accidental Collapse Limit State (ALS) criteria. A quantitative, semi-probabilistic
ALS procedure has been introduced for offshore structures in Norway in terms of a survival check of
damaged structural systems. The initial damage is considered to be due to accidental actions corresponding
to an annual exceedance probability of 104 or abnormal resistance, e.g. due to fabrication defects.
Survival of the damaged structure under relevant actions with environmental actions at an annual exceedance
probability of 102 should be demonstrated. The basis for an implementation of this approach is
outlined, with a focus on risk acceptance criteria. The risk analysis methodology on which this procedure
rests, is described with an emphasis on determining the characteristic accidental actions with due
account of possible risk reduction actions. Since the ALS procedure is based on an alternate path
approach, methods for predicting the initial accidental damage and the survival of the damaged structure
need to account for nonlinear structural behaviour. It is described how the recent development of computational
tools facilitates a realistic ALS approach for steel structures.