1 COMPARATIVE ANALYSIS OF INTENSITY MEASURES FOR REINFORCED CONCRETE BRIDGES Claudia ZELASCHI 1 , Ricardo MONTEIRO 2 , Mário MARQUES 3 and Rui PINHO 4 ABSTRACT When carrying out seismic loss assessment of an infrastructure network within a certain region, the characterization of the fragility of bridges, which represent nodes of the network, is one of the most important aspects. The fragility assessment largely depends on the characterization of the seismic demand that such structures face and, for this reason, a proper intensity measure (IM) is necessary. Many different IMs have been proposed over the years and recent studies have proposed new approaches based on different parameters or on the coupling of previously tested IMs on an individual fashion (vector-based IMs). These studies have however been focused only on building structures whereas the available literature on analysis of IMs for bridges has considered a limited number of structural configurations. Indeed, both the seismic response of bridges and the corresponding fragility are strongly dictated by the structural configuration, material properties and seismic excitation intensity, which in turn will significantly influence the performance of the IM under analysis. In order to take into account such variability and to overcome the aforementioned limitations of the current state-of-the-art, the study presented herein considered optimized numerical simulation techniques, through the Latin Hypercube sampling method, for the generation of a population of reinforced concrete bridges. Such case study was used to assess the correlation between a considerable amount of traditional and innovative IMs and the nonlinear structural response of bridges, estimated through nonlinear dynamic analysis using a selected set of suitable ground motion records as input excitation. The capability of predicting the seismic response of the structure using distinct IMs has been extensively scrutinized and compared for the population of generated bridges, in terms of practicality, efficiency and proficiency. An optimal IM has been sought calculating the Pearson Moment Correlation Coefficient (PMCC). The comparative study outlined the Fajfar Index, peak ground velocity and root mean square velocity as the most promising intensity measures. Typically employed IMs (peak ground and spectral accelerations) performed reasonably well. On the other hand, using vector-based intensity measures did not significantly improve the results in terms of efficiency, practicality and proficiency. INTRODUCTION As far as bridges are concerned, during the last decades, the earthquake engineering community has mostly paid attention to the improvement of the procedures for the assessment of single structures however when an extreme event, such as an earthquake, occurs structures of a vast area can be damaged, with important consequences on the economy of the interested region. Indeed, in the recent 1 PhD Student, ROSE Programme, UME School, Pavia, Italy, claudia.zelaschi@umeschool.it 2 Assistant Professor, IUSS Pavia, Pavia, Italy, ricardo.monteiro@iusspavia.it 3 Post-Doctoral Researcher, University of Porto, Porto, Portugal, mariom@fe.up.pt 4 Assistant Professor, University of Pavia, Pavia, Italy, rui.pinho@unipv.it