Seismic Performance Design Criteria For Bridge Bent Plastic Hinge Regions

The main objective of this research was to quantify the material strain limits for seismic assessment of existing sub-standard reinforced concrete bridge bents considering operational performance design criteria. Limited confidence exists in the current material strain limit state for operational performance criteria due to lack of experimental results considering the typical detailing of Oregon bridges and the cumulative damage effect resulting from an anticipated long-duration Cascadia Subduction Zone (CSZ) event. Component details for bridge bents such as geometry and reinforcing details were determined through a statistical analysis of available bridge drawings built prior to 1990 in the State of Oregon. Three full-scale bridge bent column-footing subassembly specimens were constructed and subjected to reverse cyclic lateral deformations utilizing a traditional loading protocol and a protocol representing the demands expected from a CSZ earthquake. The tests were designed so that variable axial loading could be applied in order to simulate the secondary effects experienced in a column that is part of a multi-column bent during an earthquake event. Material strains along with global and local deformation quantities were measured with a suite of external and internal sensors mounted to and embedded in the specimens. Despite having sub-standard seismic detailing, all three specimens exhibited ductile behavior under reverse cyclic lateral loading, achieving a minimum displacement ductility of 8.0. The obtained results also suggest that the material strain limits currently used for the seismic evaluation of existing bridges in Oregon considering operational performance criteria are conservative, but may still require further experimental validation. Finally, strain limits based on previous research at Portland State University (PSU) were compiled and combined with the results from this study to propose recommended strain limit values.