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.