Title:
Performance of Retrofitted Reinforced Concrete Bridge Columns in Cascadia Subduction Zone Earthquakes
Author(s):
Christopher Motter
Publication:
Web Session
Volume:
ws_F23_ChristopherMotter.pdf
Issue:
Appears on pages(s):
Keywords:
DOI:
Date:
10/29/2023
Abstract:
Many bridges in the western United States, including those built for the Interstate Highway System in the 1950s and 1960s, have seismically vulnerable reinforced concrete (RC) columns. Retrofit of reinforced concrete bridge columns with steel jackets or fiber reinforced polymer (FRP) jackets is a commonly implemented strategy to increase column ductility in earthquakes. Previous research has not specifically studied behavior under long-duration Cascadia Subduction Zone (CSZ) demands. Six reinforced concrete bridge columns retrofitted with steel jackets and another set of six with FRP jackets were designed, constructed, and tested under simulated CSZ demands. The inventory of retrofitted columns in western Washington was characterized and used to inform the parameters of the test columns. Strength degradation in the test columns was caused by fatigue fracture of longitudinal reinforcement. In addition to the column tests, cyclic testing of modern and historic reinforcement was conducted to better characterize fatigue properties of reinforcement characteristic of 1950s and 1960s bridges. Using experimental results, a model was developed in OpenSees to estimate the load-deformation response and fatigue fracture of longitudinal reinforcement in steel and FRP jacket retrofitted reinforced concrete columns. The model was validated with existing test data, and single degree of freedom nonlinear time history analyses were conducted using the model. Site-specific Magnitude-9.0 Cascadia Subduction Zone simulated ground motions for western Washington State were used. Fragility relationships that provided the probability of lateral failure were developed for a practical range of bridge column parameters and bridge periods, strengths, and locations.