Analytical and Computational Modeling of Integral Abutment Bridges Foundation Movement due to Seasonal Temperature Variations

Classical mechanics theory is used to develop an analytical model for determining pile displacement due to temperature variations, in integral abutment bridges (IABs). The advantage of this model, as opposed to simple techniques proposed by AASHTO, is that it includes the forces that develop in the bridge due to soil pressure constraining the piles. A three-dimensional, nonlinear finite-element model (FEM) of the superstructure and substructure is developed to determine the displacement and cyclic behavior of piles. FEM is used to analyze the cyclic stress-strain behavior of piles and determine their inelastic deformation. Both the analytical model and FEM are used to calculate the displacements in piles for variety of bridge lengths under thermos-mechanical loading due to daily and seasonal temperature variations. Displacement calculations using the analytical model are then compared with the finite element and AASHTO results. The results show that although the new analytical model takes into account soil pressure on the piles, it does not include the soil pressure on the abutment. Therefore, the amount of deformation that FEM shows for expansion of the bridge is less than that determined by the analytical model. However, results of the analytical model are less than the AASHTO results. This shows that in conservative designs AASHTO can be used comfortably. If more accurate, less conservative design is desirable, the analytical model and FEM are proposed. FEM results show that maximum lateral displacement in (contraction) occurs during the winter. The displacement of piles in the summer and during high temperature times of the day shows a nonmonotonic trend with respect to depth providing buckling behavior in the piles. The piles’ displacement is completely monotonic during the winter and cold times of the night. For the bridge studied maximum stress occurs in the pile that is furthest from the center of the bridge. The cyclic stress-strain loop and inelastic deformation, both found from the FEM, are studied closely to identify the most likely location of a fatigue crack. Since plastic deformation occurs in piles, low cycle fatigue is expected. The most likely crack location is found in the flange of the pile right below the concrete abutment.