Seismic Retrofit of Deficient RC Structures with Internal Steel Frames

This paper describes an experimental study on internal steel frames (ISFs) to retrofit seismically deficient reinforced concrete (RC) frames. One reference and six strengthened frame specimens were tested under constant gravity load and cyclic lateral displacement excursions. Installation of the ISF with and without anchors to the RC frame was examined. Test results showed that the snug tight ISF installed inside an RC frame may suffice to realize the benefit of implementing ISFs. If the horizontal shear strength of the RC beam-column joint is smaller than the target lateral strength enhancement, anchors should be used between the RC and ISF members to provide an additional load path for the lateral load and limit the force demand on the RC beam-column joint. A case study building was analyzed to demonstrate the performance of an ISF retrofitted deficient RC frame by using a numerical model calibrated with cyclic test results.