Transient reliability evaluation of a stochastic structural system in fire : application of a probability density evolution method supported by evacuation models

Structural fire resistance is a fundamental component of the overall fire safety strategy for buildings. Specifically, with respect to life safety, the structural fire resistance is intended to allow for the safe evacuation of the occupants and access for the fire & rescue service. With the proliferation of performance-based design (PBD) methodologies, the efficiency of fire safety measures is increasingly being challenged. For low-rise buildings, with limited travel distances to a place of ultimate safety, evacuation may be very efficient, and from the perspective of life safety only limited structural fire resistance needed. For high-rise buildings with long evacuation times the opposite may be true. However, such interactions between structural and human response in fire are currently not clearly quantified, nor by extension explicitly considered in guidance. In support of rational decision making and cost-optimisation for (fire) life safety investments, the current paper tentatively explores the relationship between evacuation times in model office buildings on the one hand, and the time-dependent failure probability of critical structural components on the other hand. As a case study, the timedependent failure probability of an insulated steel beam is evaluated, and the expected number of fatalities assessed for different model office building heights (i.e. affecting evacuation duration)