Seismic Repair of Reinforced Concrete Bridges Substructure

Modern seismic design practices for bridge structures involve the use of capacity design principles that locate plastic hinges in columns, while protecting against other modes of failure or locations of damage. For large earthquakes, the formation of plastic hinges in columns can lead to buckling and rupture of longitudinal steel. Traditionally, once buckling occurs, bridge columns are demolished and rebuilt because the cost to replace portions of columns can be prohibitive. Replacement is deemed necessary since the inelastic strain capacity of reinforcing bars is severely diminished once buckling occurs, rendering the structure vulnerable to collapse in future earthquakes. Bridge column repair has been studied for some time with several established techniques for repair for shear and confinement critical columns. To the knowledge of the principal investigators (PIs), there is little data available on repair of columns that are otherwise designed to modern standards. Similarly, there is little data available on developing an understanding of when repair is truly needed, and when repair is truly no longer feasible. A recent pilot study conducted at North Carolina State University (NCSU) demonstrated the feasibility of a repair technique which employed the relocation of the plastic hinge to a previously undamaged location within the column. This was successfully employed for columns that sustained buckled reinforcing bars, and showed promise for columns with fractured bars. In this proposal, the pilot study is expanded by developing a suite of repair techniques aimed at achieving plastic hinge relocation in damaged columns. Techniques may include the use of fiber reinforced polymers, high strength steel, reinforced concrete and structural steel. The focus will be on the concept of ‘hinge relocation for repair’ and will consider variables such as the need for rapid deployment following an event, environmental conditions at the time of repair, and expertise of potential repair workers in Alaska. The research will utilize columns that will be built and damaged as part of another Alaska Department of Transportation (AKDOT) research project, thus maximizing resources. Recommendations will consist of analysis and design guidelines, as a function of damage level (i.e. strain limits), for repair design of reinforced concrete (RC) bridge column to footing connections. The recommendations will also be applicable to some RC column to cap connections, although specific tests on that configuration are not part of this phase of work.. In addition, analytical studies will be conducted on other bridge column connection types (e.g., reinforced concrete filled steel pipes to pile cap beams) such that the direction for future experimental work on those connections may proceed.