Load and resistance factor design for integral abutment bridges .

摘要

A prestressed concrete girder integral abutment bridge (IAB) requires a new load combination due to inherent uncertainties in loads and resistances and the significant inelastic and hysteretic behavior over bridge life. The present study presents development of simplified numerical modeling methodologies, development of nominal IAB response prediction models through an extensive parametric study, and establishment of IAB response statistics using Monte Carlo simulation. Finally, new load combinations in a load and resistance factor design (LRFD) format have been developed using reliability analyses.;For a robust, long-term simulation and numerical probabilistic study, a simplified numerical modeling methodology has been developed based on field monitoring results of four IABs. The numerical model includes temperature variation, temperature gradient, time-dependent loads, soil-structure interaction, and plastic behavior of the backwall/abutment construction joint. The four field tested IABs were modeled to validate the methodology. The proposed numerical model provides accurate, long-term prediction of IAB behavior and response.;IAB response prediction models have been developed using a parametric study. Current design specifications and guides do not provide clearly defined analysis methods, therefore, there is a need for easily implemented preliminary analysis methods. Based on the calibrated, nonlinear, 2D numerical modeling methodology, a parametric study of 243 cases was performed to obtain 75-year bridge response. The parametric study considered five parameters: (1) thermal expansion coefficient; (2) bridge length; (3) backfill height; (4) backfill stiffness; and (5) pile soil stiffness. The parametric study revealed that the thermal expansion coefficient, bridge length and pile soil stiffness significantly influence IAB response as measured by: (1) bridge axial force; (2) bridge bending moment at mid-span of the exterior span; (3) bridge bending moment at the abutment; (4) pile lateral force at pile head; (5) pile moment at pile head; (6) pile head/abutment displacement; and (7) abutment displacement at the centroid of a superstructure. The influence of backfill height and backfill stiffness are not significant relatively. The study results provide practical, preliminary estimates of bridge response and ranges for preliminary IAB design and analysis.;In order to establish IAB response statistics, Monte Carlo simulation has been performed based on the 2D numerical modeling methodology. Based on the established thermal load and resistance variable statistics, this study developed probabilistic numerical models and established IAB response statistics. Considered input variables to deal with uncertainties are resistance and load variables. IAB response statistics were established: (1) bridge axial force; (2) bridge bending moment; (3) pile lateral force; (4) pile moment; (5) pile head/abutment displacement; (6) compressive stress at the top fiber at the mid-span of the exterior span; and (7) tensile stress at the bottom fiber at the mid-span of the exterior span. IAB response statistics provide the basis for a reliability-based design. Reliability analyses were performed to develop new load combinations for IABs based on the developed IAB response prediction models and established statistics.