Seismic Performance Design Criteria of Existing Bridge Bent Plastic Hinge Region and Rapid Repair Measures of Earthquake Damaged Bridges Considering Future Resilience

Abstract

The main objective of this research was to evaluate the seismic performance of existing sub-standard reinforced concrete (RC) bridge column-spread footing subassemblies and to quantify the material strain limits through a full-scale experimental program. A total of six column-footing test specimens with pre-1990 construction details were subjected to reverse cyclic lateral loading, utilizing a conventional three-cycle symmetric loading protocol and a protocol representing the demands expected from a CSZ earthquake. Additionally, the tests were designed so that variable axial loading could be applied to simulate the secondary load effects experienced during an earthquake in a column that is part of a multi-column bent. Despite having sub-standard seismic detailing, all the test specimens with moderate lap splice length or continuous rebar demonstrated a ductile response, reaching a minimum displacement ductility of μ = 5.4. The surprisingly ductile response can be attributed to the moderate splice length that ensured flexural plastic hinging and the low longitudinal steel ratio that resulted in significant rocking at the column-footing interface. Furthermore, flexural cracking of the accompanying spread footing and splice failure of the column dowel bars were also observed for specimens having different reinforcing and splice details. The performance of these test specimens was evaluated in terms of global and local deformation quantities, i.e., hysteretic load-deformation response, measured strains, flexural curvature profiles, etc. Finally, the experimentally obtained strain values at different damage states were used to define probabilistic operational and life safety performance criteria for seismic evaluation of the representative bridge bents. The spread of plasticity was also examined with respect to the existing plastic hinge model to be used for limit state evaluation. A rapid repair method incorporating semi-permanent installation was also developed, anticipating the need for quick measures following the Cascadia Subduction Zone (CSZ) earthquake, which is expected to damage the existing bridges in the Pacific Northwest and spread geographically throughout the region. While the conventional repair methods are effective in restoring the strength in the damaged zones, often lead to higher stiffness and strength that would likely result in shifting the failure to other parts of the structure under future earthquake or aftershock demands. The proposed repair methodology uses capacity design principles to protect the remainder of the bridge from future earthquakes and eradicates the need for establishing rebar continuity, resulting in a less labor-intensive repair method. The adopted concept is to utilize U-shaped metallic plates as externally attached ductile fuses to