Modeled Behavior Of Steel Jacket Retrofitted Reinforced Concrete Bridge Columns

The aftermath of the San Fernando, Whittier, and Loma Prieta slip-strike earthquakes in 1971, 1987, and 1989, respectively, showed the inadequacy of pre-1971 reinforced concrete bridge columns and led to extensive research in the United States on seismic retrofitting of these columns. Providing steel jackets around the columns was determined to be effective in increasing lateral deformation capacity under seismic demand. The jacket can confine the concrete, such that failure occurs due to fatigue fracture of longitudinal reinforcement. Previous research did not focus specifically on behavior under long-duration subduction zone earthquakes, which can increase the likelihood of fatigue fracture relative to strike-slip earthquakes. This study focuses on behavior under demands from both strike slip and long-duration earthquakes. In this research, an analytical model of a steel jacket retrofitted reinforced concrete bridge column was developed in OpenSEES. The model consisted of a linear elastic element for the jacketed portion of the column, a fiber section to capture plasticity at the gap between the bottom of the steel jacket and top of the footing, and zero-length bond slip elements at the column-footing interface and the bottom of the jacket. The OpenSEES model was used in combination with a fatigue model to predict the fatigue failure of the longitudinal reinforcement. The column model was validated using ten test columns. This included four columns with loading protocols more reflective of strike-slip earthquakes and six columns with loading protocols reflective of long duration demands.