Abstract
This paper evaluates the impact of newly recommended LRFD seismic design guidelines (NCHRP Project 12-49) on the seismic design of bridges on soft soils in New Jersey. Current LRFD provisions are mostly based on the Division I-A Seismic Design of the AASHTO Standard Specifications (1996). NCHRP Project 12-49 was initiated to address the inadequate performance of highway bridges in recent earthquakes and the deficiencies in the current seismic code and to develop comprehensive specifications for seismic design of bridges considering all aspects of the design process. The intent of the new specifications is to be nationally applicable with provisions for all seismic zones. Because of the several significant changes in the design criteria and approach provided in the new provisions, there are questions on how these new provisions will affect the design and performance of bridge in states in the eastern United States as well as the retrofit of existing bridges. There are also questions about the impact of new provisions on the design of abutments and retaining walls. Hence, there was a need to evaluate the impact of the new seismic design provisions proposed in NCHRP 12-49 on the seismic design and detailing of bridges in New Jersey and the eastern United States. Two examples were designed based on NCHRP 12-49 recommended guidelines and the current LRFD specifications showed that the soil site factors had a major effect on the design. Also the transverse reinforcement requirements in plastic hinge zones were higher in the new NCHRP 12-49 provisions for larger diameter columns with heavy reinforcement than those in the current AASHTO LRFD.
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