Seismic risk assessment of ageing existing reinforced concrete bridges accounting for uncertainty in bearing properties

A growing challenge in the seismic risk assessment of ageing existing bridge structures is the lack of knowledge of the key features of the structural components. In fact, the mechanical properties could change over time and the recommendations in the literature could be considerably different thus adopted modelling parameters can significantly alter the seismic response and risk estimates, e.g., expected annual losses (EAL) or mean annual frequency of collapse (MAFC). It is therefore crucial to understand the role of critical properties of structural components on seismic risk metrics before allocating further resources to estimate them more accurately. With the above in mind, this study focuses on analysing the importance of the frequently unknown properties of bridge bearings featuring un-reinforced thin elastomeric pads, typically used in bridges built in the ‘60 s and ‘70 s in Italy. For this purpose, a real case study bridge is selected and Latin Hypercube Sampling is performed to generate a large set of bearing parameters, namely the shear modulus and friction coefficient between rubber and concrete surfaces. Component-level seismic loss estimation of the bridge is performed for each bearing properties realisation, considering both the presence and absence of non-sacrificial shear keys at the cap beams. The EAL and MAFC results are scrutinised to analyse the impact of the variation in the bearing properties on such risk metrics. The main observations indicate that the influence of the shear modulus of rubber on these quantities is low, whereas the friction coefficient between concrete and rubber can lead to more impactful changes.