Comparison of modal behaviour of integral abutment bridge with and without soil–structure interaction

Integral abutment bridges (IABs) have gained popularity over past few years. The main advantage of IAB over conventional bridges is the absence of any bearing at the deck–abutment junction which leads to reduced possibility of unseating of bridge deck during strong earthquake shaking. The seismic response of bridges with integral abutments depends significantly on the abutment–soil interaction in the longitudinal direction and soil–pile interaction in the transverse direction. In the present study, the modal behaviour of IAB is investigated with and without the presence of soil–structure interaction (SSI). The soil flexibility for soil–pile and abutment–backfill interactions is represented by springs. This leads to significant increase in the overall flexibility of the bridge system as compared to the model with all the degrees of freedom (DOFs) restrained at the bottom of pier. Due to higher longitudinal stiffness contributed by both the deck and the abutments, the SSI bridge model shows complete longitudinal mode of vibration in higher mode. By removing the abutments and end spans of the deck, the first longitudinal mode of vibration occurs in one of the lower modes. Hence, the numbers of spans in the bridge play an important role in the modal behaviour of the bridge. The importance of SSI in modal analysis highlights its need for inclusion in the seismic design of IABs.