Bridge construction in Japan mostly includes steel superstructures supported by bearings which themselves are supported by concrete substructures. Multiple bearing fractures were observed in this type of bridges after the Great kobe earthquake. In this earthquake, following the substructure damages, the bearings were the second most vulnerable structural elements. However, in some cases, although the bearings were damaged, the substructures remained untouched.
Design of bearings and substructures is highly dependent on the amount of the vertical load. Load estimation for usual earthquakes, i.e. far-field earthquakes, is carried out using EN 1998-1 standard, while the issue remains ambiguous for near-field earthquakes. Therefore, the present study aimed to compare the vertical component of earthquake acceleration in near-field conditions with that proposed by the EN 1998-1 standard by designing and modeling an isolated two-span concrete-deck bridge based on the regulations of Eurocode standards in the OpenSEES software package.
Analyses and investigations revealed that the EN 1998-1 standard yields an underestimation of the vertical component of acceleration in near-field earthquakes. Nevertheless, we managed to obtain an interval for the variations in this component. Then, the vertical component of acceleration was compared in two cases, in one of which the soil-structure interactions were taken into account, and in the other a fixed pier was considered. The results showed that the vertical component of acceleration is decreased in the former case.