Many older bridges in Washington State contain split reinforced concrete columns as common members between adjacent bridge sections. The split detail was incorporated in columns to allow for movements in the bridge due to temperature and shrinkage effects. It is expected that these split columns will perform poorly in the event of a significant earthquake. This study investigated retrofitting measures for improving the seismic performance of existing split columns.
Experimental tests were conducted on one-third scale split column specimens which were representative of the split column present in the Spokane Street Overcrossing near Seattle. Various retrofit measures were evaluated. Specimen performance was evaluated on the basis of load capacity, displacement ductility, and hysteretic behavior.
Tests on specimens representing as-built conditions revealed vulnerabilities that have previously been observed in the field or are expected to occur during a major earthquake. Poor performance evident in the as-built specimens included crack propagation from the base of the split, lap splice degradation, and shear failure in the split sections. Retrofit design focused on enhancing the column seismic performance while at the same time preserving as much of the gap between the split sections as possible. Procedures were developed for the design of steel jacketing as a retrofit measure for the split columns. Circular jacketing was used for the section below the split and for retrofitting a deficient lap splice. "D" shaped jackets were used for the split sections to provide confinement in flexural hinging regions and to increase shear strength. Tests on specimens retrofitted with the steel jacketing showed significant improvements in performance when compared to that for the as-built specimens.
Three companies who manufacture composite retrofit systems were invited to participate in this project. Each company was provided with unretrofitted specimens for which they designed and installed their company's retrofit system. While some differences in performance were obtained with the various retrofit systems, all retrofitted specimens showed significant improvements in performance when compared to that for the as-built specimen.