Seismic capacity evaluation of existing reinforced concrete buildings strengthened with a novel prestressing steel frame system for increasing lateral strength

In this study, a new concept of seismic retrofit, the Prestressing Steel Frame (PSF) system, is proposed to improve and compensate for the weaknesses of the existing strength-enhancing seismic retrofit method. The PSF system, a construction method that maximizes the advantages of the H-shaped steel frame, innovatively improves the constructability and integrity of existing reinforced concrete (R/C) frames and reinforcement joints. This method is a type of typical strength-increasing reinforcement method that facilitates calculation of the required seismic reinforcement amount, and easily enhances the horizontal strength of shear collapse-type R/C buildings with non-seismic detailing. To review the seismic performance of the proposed PSF method, pseudo-dynamic tests were conducted on a real two-story frame based on an existing R/C building without seismic detailing, and seismic performance was evaluated in terms of load and displacement characteristics, seismic damage level, strength enhancement effect, and displacement control. In addition, based on the results of pseudo-dynamic testing, a hysteresis model was proposed to perform non-linear dynamic analysis of the seismically reinforced structure (two-story frame) with the PSF method. Non-linear dynamic analysis was performed based on the proposed hysteresis model, and the results were compared against that of pseudo-dynamic testing. For the commercialization of the method, non-linear dynamic analysis was conducted on the entire R/C building reinforced with PSF, and the effectiveness of seismic reinforcement was verified by comparing the seismic response load and displacement response before and after reinforcement. In the event of an earthquake with a maximum ground acceleration of 200 cm/s2, which is 2/3 of major earthquakes with a 2400-year recurrence interval stipulated in Korea Design Standard (KDS) 41, shear failure is expected for R/C buildings with non-seismic detailing, while small-scale damage is predicted for buildings reinforced with the PSF method. This shows that the PSF strengthening method is effective in minimizing earthquake damage.