Seismic vulnerability of bridges of some italian motorway networks

In recent years, Italian technical-scientific community has increased its interest on the evaluation of the seismic vulnerability of existing structures. Among this wide range of structures, motorway viaducts stand out for their strategic relevance and technical complexity. Most of these structures were built between ’60 and ’70 years, according to design procedures which ignored nowadays knowledge in seismic engineering. Thus, the necessity to evaluate the real strength capacity of these structures with modern analysis techniques has become essential, leading to the determination of their safety level in case of an earthquake. For the assessment of several bridges of a motorway network, a multi-modal pushover analysis approach has been considered. This analysis technique allows considering the nonlinear behaviour and the complex dynamic response of such a structures without exceeding in high computational costs. Some basic rules were defined (constitutive laws of materials, finite element type, plastic hinge models, etc.) for the modelling of viaducts in a commercial FEM software, in order to guarantee homogeneous comparable results among the large number of bridges of a network. Furthermore, a specific software routine was implemented. This routine starts from the pushover results of a FEM commercial software and executes the modal combinations and the safety verifications, reducing the time cost and the possibility of errors, following in the evaluation of the seismic vulnerability indexes. These risk indexes are then reported in seismic vulnerability forms collected by the Italian Hazard Management Agency (Italian Civil Protection) for risk management purposes.