Nonlinear seismic response of underground structures using domain reduction method and considering soil structure interaction

Soil-structure interaction (SSI) represents the fundamental coupling between a structure and the soil supporting it. This complex phenomenon significantly impacts a structure's behavior, particularly under dynamic loads like earthquakes. Direct and sub-structuring methods are the two main used approaches in the analysis of soil structure systems. The main two difficulties of using the direct method are to apply absorbing boundaries that prevent wave reflections, and to define compatible seismic input motion at the soil boundaries. In this research, the direct method was applied for 2D box culvert - soil system by overcoming the previous difficulties using (i) verified finite element absorbing boundaries embedded in Abaqus, (ii) applying seismic input at the boundaries of soil using coded domain reduction method (DRM) in MATLAB. Three verifications were conducted for the utilized FE absorbing boundaries elements, seismic input forces, and for the model that include the RC structure, absorbing boundaries, and DRM seismic forces. These verifications showed a good agreement. The parametric study include studying the effect of changing structure thickness, and reinforcement bar diameter on the underground box culverts structures. The results were compared with the calculated forces and moments according to NCHRP 611 to indicate over and under estimation predictions in all studied structures.