Nonlinear load-deformation characteristics of bridge abutments and footings under cyclic loading

This dissertation documents research on load-deformation characteristics of bridge abutments and footings under cyclic loading. The overall objective of this research was to improve current methods to characterize the lateral load capacity and nonlinear stiffness of abutments in the longitudinal direction and the moment-rotation relationships of footings about the transverse axis.; A large-strain finite difference computer program called FLAC was employed in this research. To better represent the nonlinear constitutive behavior of soils, a multiple yield surface plasticity model was implemented into FLAC. The program FLAC, equipped with this model, was validated through simulations of triaxial laboratory tests and prediction of shallow footing bearing capacity.; To study load-deformation characteristics of abutments, analyses were first performed to simulate cyclically loaded field abutment tests conducted at the University of California, Davis, and centrifuge abutment tests conducted at Rensselaer Polytechnic Institute. The test results were successfully simulated by the computer model. A parametric study was then performed to understand the various factors influencing the passive resistance of an abutment-soil system. Load-deformation curves of abutments were developed for typical soil types, using stress-strain and strength parameters obtained from triaxial tests. Several case studies with different soil type combinations for the abutment backfill and embankment were performed. The numerical results indicate that the soil type and strength, wall friction and height have major effects on the passive resistance and load-deformation characteristics of abutments. The load-deformation curves developed from this research provide a useful design tool for modeling abutment stiffness in bridge response analyses.; To study moment-rotation relationships of bridge footings, analyses were performed to simulate model footing tests conducted at the University of Auckland. These tests were conducted to evaluate the nonlinear moment-rotation behavior of footings including the effects of uplift. The test results were successfully simulated by the analyses and the results show that the soil type and strength, and initial factor of safety under vertical loading play a major role in the moment-rotation relationships. Yielding of the foundation soil and uplift of the footing contribute to highly nonlinear moment-rotation behavior.