Study on the fragility assessment of existing reinforced concrete buildings considering ageing processes

Abstract

A common method for estimating building damage is the use of fragility functions. When developing fragility curves, it is essential to consider the specific characteristics, i.e. the age and changes over the lifetime, to ensure a reliable damage assessment. Existing buildings are more vulnerable to the effects of ageing due to their lower material strengths and concrete covers. This paper analyses the impact of corrosion and pre-damage on the fragility curves for existing buildings with a developed multiscale approach. Considering the consequences of corrosion, three effects are taken into account: reduction of reinforcement cross-section, reduction of steel ductility, and deterioration of concrete. For the pre-damage, a sequence of loading and unloading is simulated. The analysis focuses on a reinforced concrete building constructed in 1943, initially in its original state, with particular attention to its original material and reinforcement properties, and under the impact of corrosion attack after 80 years as well as pre-damage. A moderate corrosion attack can result in a 64% reduction in the overall shear base and an increase in fragility of up to 33% compared to a new building from 2023. The analysis of pre-damage has been demonstrated to result in a maximum increase of 18% in the probability of exceedance, contingent on the extent of pre-damage. The utilisation of fragility curves, developed for new buildings, results in a substantial underestimation of vulnerability when applied to existing structures.