It is common in the practice of bridge design to analyze the superstructure, substructure, and foundation components separately. Applying this kind of modeling, soil-structure interaction effects can only be approximated with moderate accuracy. The foundation stiffness can greatly influence the internal forces, stresses, and displacements of superstructure. This is especially true for portal frame and integral bridges. Better modeling of soil-structure interaction can use three-dimensional geotechnical FEM programs, where the true soil-stucture environment can be analyzed. It is possible to use nonlinear constitutive models; capable of modeling soil behavior accurately, however it is difficult, time consuming, and costly in day-to-day practice.