Seismic behaviour of isolated RC bridges subjected to asynchronous seismic input

The seismic actions used to design long structures, as bridges, should be attentively evaluated, since, due to seismic wave propagation through soil, at distant foundation points signals are different. Signal frequency content varies from point to point for at least two reasons: soil-wave interaction; wave traveling time from one point to the other. Asynchronous seismic waves produce distortions at the bridge foundations which are usually not considered in design practice. In this paper, the responses of two RC bridges, one with deck supported by traditional bearing and one by Lead Rubber Bearings (isolators), subjected to asynchronous or synchronous signals were studied. These signals were generated at the surface starting from the EW components of the main shock recorded at two recording stations (AQA, AQV) near L'Aquila city (Italy) on 4-06-2009. The soil distortions which produce maximum stresses on deck or on piers were evaluated for the two bridges (non-isolated and isolated) in case of synchronous and non-synchronous excitations. The first results are discussed to understand the effects of asynchronous excitation on the responses of the two bridges.