Progressive collapse fragility of European reinforced concrete buildings

Abstract

Structural safety is generally assessed without consideration of abnormal load conditions that may give rise to global system collapse after local failure in one or a few components. Particularly in the case of high-risk structures, Eurocode 1 recommends a systematic risk assessment of the structure, considering either identified threats or unspecified damaging events. Nonetheless, a comprehensive probabilistic assessment of European structures is strongly needed. In such a context, this paper presents the outcomes of fragility analyses performed on reinforced concrete framed buildings, proposing a set of fragility models that can be used for probabilistic assessment and management of the risk of progressive collapse. Gravity-load designed and earthquake-resistant building structures were considered and respectively designed in accordance with Eurocodes 2 and 8. Fiber-based finite element models were developed and analyzed under sudden removal of one or more columns, allowing structural performance and damage propagation to be evaluated. Based upon statistics and probability distribution functions for material properties, geometry, and design loads of the building class under study, a Monte Carlo simulation was performed to generate both 2D and 3D models. Structural performance was assessed by incremental-mass nonlinear dynamic analysis, capturing the attainment of limit states either at sectional or global levels. Probability distribution functions were then fitted to fragility points in order to provide fragility functions at multiple damage states for their use in progressive collapse risk assessment. The analysis results show the significant impact of seismic design rules and secondary beams on progressive collapse fragility.