Comparative Assessment of Variable Loads and Seismic Actions on Bridges: A Case Study in Italy Using a Multimodal Approach

The structural safety of the infrastructure stock is an important issue in modern seismic performance assessments. Following recent seismic events, reports have highlighted the increased vulnerability of physical infrastructural assets, particularly for many bridges across the Italian road and motorway network. Italy possesses one of the most complex and intricate road systems in Europe which was constructed across irregular territories in terms of plan and elevation and of varying dimensions. As such, a comparative case study is presented herein. This case study aims to characterise the seismic vulnerability of the Vizzana-Zampogna viaduct which is part of the A15 Parma-La Spezia motorway, near the locality of Selva Bocchetto. The viaduct is considered representative of the 1970s construction period. It is approximately 342 m in length and is characterized by a flat curvilinear prestressed concrete deck consisting of 15 spans simply supported on reinforced concrete piers. To better understand the seismic structural response of the individual piers of the viaduct, a "multi-modal" nonlinear static analysis was developed, which allows the effects of sectional stresses relative to the variable load profiles of the single modes to be combined through the quadratic modal combination, and to be compared with the relevant limit state. The research aims to qualitatively identify the piers most vulnerable to seismic action and to study the effects that are induced by introducing variable loads and intensity scenarios of different earthquakes.