Long-Term Response Prediction of Integral Abutment Bridges

The importance of long-term behavior in integral abutment (IA) bridges has long been recognized. This paper presents an analytical, long-term, response prediction methodology using finite-element (FE) models and compares results to measured response. Three instrumented Pennsylvania IA bridges have been continuously monitored since November 2002, November 2003, and September 2004 to capture bridge response. An evaluation of measured responses indicates that bridge movement progresses year to year with long-term response being significant with respect to static predictions. Both two-dimensional and three-dimensional FE models were developed using ANSYS to determine an efficient and accurate analysis level. Seasonal cyclic ambient temperature and equivalent temperature derived from time-dependent strains using the age adjusted effective modulus method were employed as major loads in all FE models. The elastoplastic $p\text{-}y$ curve method, classical earth pressure theory, and moment-rotation relationships with parallel unloading paths were used to model hysteretic behavior of soil-pile interaction, soil-abutment interaction, and abutment-to-backwall connection. Predicted soil pressures obtained from all FE models are similar to the measured response. Predicted abutment displacements and corresponding design forces and moments at the end of the analytically simulated $100\text{-}\text{year}$ period indicate the significance of long-term behavior that should be considered in IA bridge design.