Seismic Assessment and Retrofit of Existing Multi-Column Bent Bridges

The main objective of this research was to assess the seismic vulnerability of typical pre-1975 WSDOT prestressed concrete multi-column bent bridges. Additional objectives included determining the influence of soil-structure-interaction on the bridge assessment and evaluating the effects of non-traditional retrofit schemes on the global response of the bridges. Overall this research highlighted the vulnerability of non-monolithic bridge decks and shear-dominated bridge columns in pre-1975 WSDOT prestressed concrete multi-column bent bridges as well as the importance of including soil-structure-interaction, calibrating the force/displacement characterization of the columns to experimental test data and detailed modeling of the bridges such as expansion joint/girder interaction. In the end, the seismic assessment of bridges is a cost/efficiency issue. Each bridge is different, therefore, investing in improved analyses up front will enable an efficient use of the limited funds for bridge improvement, resulting in a significant savings overall. None None 63 iii DISCLAIMER The contents of this report reflect the view of the author, who is responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the The Washington State Department of Transportation (WSDOT) has implemented retrofit schemes to improve the seismic performance of single column bent bridges throughout western Washington State. However, numerous multi-column bent bridges are also in need of seismic upgrade. Multi-column bent bridges targeted for retrofit include 2 to 5 column bents with simple precast prestressed concrete spans as well as continuous reinforced and prestressed concrete spans. The majority of these bridges were constructed in the 1950's and 1960's. The main objective of this research was to assess the seismic vulnerability of typical pre-1975 WSDOT prestressed concrete multi-column bent bridges. Additional objectives included determining the influence of soil-structure-interaction on the bridge assessment and evaluating the effects of non-traditional retrofit schemes on the global response of the bridges. WSDOT bridges 5/518, 5/826, and 5/227 were chosen in collaboration with WSDOT Bridge engineers for these studies. The bridges varied in span length, column aspect ratio, bridge deck design, and abutment and column foundation configurations.