Reliability-Based Procedure for Developing Load and Resistance Factor Seismic Bridge Design Specifications

Load and resistance factor design (LRFD) codes are calibrated to produce designs with consistent and uniform levels of risk for the whole range of design applications. Ongoing research concerned with the development of LRFD seismic design specifications for bridges has concentrated on the application of seismic hazard analysis procedures to propose uniform hazard design spectra without directly addressing the contributions of the uncertainties in bridge response estimation and material properties to the overall risk of bridge failure. A proposed procedure includes the uncertainties associated with estimating the response of concrete bridge columns as represented by their response modification factors during the risk analysis of typical bridge columns. The effects of the random nature of the material properties and those of the modeling uncertainties on the risk and reliability of bridge columns are evaluated. This information, along with results from probabilistic seismic hazard analyses, is used in a comprehensive reliability analysis to calibrate a balanced set of response modification factors for the force-based design of bridge columns at a representative high-seismicity site in San Francisco, California. The implementation of such a reliability-based calibration of the response modification factors into future versions of the AASHTO bridge seismic specifications will ensure that the code will provide uniform and consistent levels of reliability for bridges of different configurations situated in various regions of the United States.