Effect of offset between beam outside and neutral surfaces on dynamic soil-structure interactions

In finite element analyses of the dynamic soil-structure interaction (SSI), structures are often modelled as beam or shell elements in structural mechanics, while the soil requires discretization using solid elements in solid mechanics. The beam and shell elements are coupled with the solid elements on their outer surfaces, while the mechanical behaviour of the beam and shell elements are usually represented by variables defined at their neutral surfaces. The offset between the beam outer surface and the neutral surface in several dynamic SSI analyses is often ignored, which can cause large errors in the coupling analysis of solid and structural mechanics. This paper investigates the effect of the offset between the beam outer surface and neutral surface on the dynamic SSIs. First, the coupling conditions between the beam and the solid considering the offset between the beam outer surface and the neutral surface are deduced. In this process, the tangential interaction stress on the beam outer surface is transformed into an axial force and a moment acting on the beam neutral surface, and the tangential displacement on the beam outer surface is related to the axial displacement at the beam neutral surface as well as the cross-section rotation angle. Then, the coupling condition is implemented in the finite element analysis by modifying the mass and stiffness matrices of the beam element. The offset effects between beam outer surfaces and neutral surfaces on dynamic SSIs are finally discussed in detail through the seismic responses of a retaining wall, subway station and tunnel. •Effect of beam offset on soil-structure interactions are investigated.•A coupling condition of soil and structure considering the beam offset is deduced.•Effects of the beam offset on dynamic responses of structures are detailed discussed.