Cost Impact Study for a Typical Highway Bridge Using Different Return Period Seismic Design Maps

摘要

This paper compares the costs of a typical three-span P/S I-girder bridge designed for seismic categories A, B, C, and D based on the current 1996 AASHTO Standard Specifications for Highway Bridges for a 500-year return period earthquake (i.e. 10% probability of exceedance in 50 years) as well as for different spectral response accelerations specified in the current USGS map (1997 NEHRP Provisions) for a 2500-year return period earthquake (i.e. 2% PE in 50 years) which is being considered for future AASHTO Seismic Design Guidelines for Highway Bridges. For both 500-year and 2500-year design earthquakes, the mitigation of potential ground spreading due to abutment slope instability associated with liquefaction potential of soil using stone columns and deep mixed (cement-soil mix) columns are included in the cost estimation. The foundation flexibility is also taken into account in the bridge analysis and design. The cost comparison of this study can provide a general guideline on the bridge preliminary cost estimation, which can be very helpful for the preparation of the budget for highway projects. It also provides the cost impact on the significance of designing a bridge in the New Madrid seismic zone from a 500-year return period design earthquake to a 2500-year design earthquake. It indicates that the cost impact of changing from 10% PE design earthquake map to 2% PE design earthquake map is not significant for bridges at locations being classified as the current seismic categories B and C, if some conservative design provisions in the current AASHTO seismic design specifications are not adopted. However the cost may increase 19%, if a bridge located in the current seismic category D is designed using 2% PE design earthquake map instead of 10% PE design earthquake map. It also indicates that the improvement of abutment slope stability may increase bridge cost significantly if 2% PE earthquake is used.