Mechanism based assessment of damage-dependent fragility curves for RC building classes

Seismic fragility curves play a critical role in risk assessment because they represent the probability of attaining different damage states given the ground motion intensity. However, in case of repeated earthquakes, the seismic vulnerability of buildings varies due to damage and this shall be properly considered for the realistic estimate of evolving seismic risk during a seismic sequence. This paper presents a methodology for the assessment of damage-dependent fragility curves for existing reinforced concrete (RC) building classes. The derivation of fragility curves is based on a hybrid method that combines observational based “empirical” curves and mechanical based assessment of buildings’ residual capacity (REC), that is a measure of seismic capacity, which may be reduced due to seismic damage. A mechanism based procedure to assess building REC, and its variation for increasing ductility demand, is presented. Then, in order to be able to apply such procedure to RC building classes, a simulated design procedure is implemented that allows the automatic design of elements dimensions and reinforcement, as well as the characterization of the building nonlinear model needed for mechanism based analysis. Applying a Monte Carlo simulation procedure the geometric, structural and mechanical parameters, from which the design depends on, are varied according to representative distributions and populations of building models are generated and analyzed with mechanism based approach. The procedure is implemented for buildings that are prone to first storey mechanism and is applied for existing RC building classes in L’Aquila.