Seismic responses of a highway viaduct considering vehicles of design live load as dynamic system during moderate earthquakes

This study is intended to investigate the seismic response of a highway viaduct under vehicle loadings during moderate earthquakes of high probability occurrence. The highway bridge design code of the Japan Road Association (JRA code) does not consider the live load in the seismic design of highway bridges because of the low possibility that both heavy traffic and an earthquake occur at the same time. However, frequent traffic jams in urban areas involve a high possibility of encountering an earthquake during a traffic jam. To clarify the effect of traffic to seismic responses of highway viaducts, heavy vehicles are considered as dynamic system in a three-dimensional dynamic response analysis. The design live load of the JRA code is assumed to be a critical traffic condition for the highway bridges, even during earthquakes. Observations through numerical analyses demonstrate that considering heavy vehicles as a dynamic system reduces seismic responses of the highway viaduct compared with those responses disregarding vehicular loadings and considering vehicles as additional mass.