Investigating the effect of span-length and earthquake directivity on the response of multi-span continuous girder bridges isolated by friction bearings

Abstract

 Bridges are of particular importance among the structures built by human beings. Therefore, the desired seismic behaviour of this type of structures during the earthquake is of utmost importance. The friction pendulum system is considered as a type of sliding isolator in which sliding motion and recursive force are combined by isolator’s geometry. The effects of the earthquake directivity and the span-length of two multi-span continuous steel girder bridges were investigated in this study. The base shear created in the bridges depends on the bridge span, so that more base shear is applied on the bridge with longer spans. In both bridges, the base shear under records of a side with directivity feature was more than the other side. Deck displacement in the bridges in the side with directivity feature was significantly larger than the other side. This increase in structural displacement can lead to the pounding of the bridge deck on abutments. For this reason, it seems necessary to embed the appropriate expansion joints considering the effect of directivity of the earthquakes.