Seismic Performance Evaluation of Reinforced Concrete Buildings Retrofitted with a New Concrete Filled Tube Composite Strengthening System

This study proposes a concrete-filled tube composite strengthening system (CCSS), which is a new concept that can improve and supplement the vulnerability of existing CFT seismic strengthening methods. The CCSS seismic reinforcement method is easy to construct and integrates with the existing frame and reinforcement. It is one of the seismic strengthening methods that allows the simple calculation of the required amount of seismic reinforcement and can efficiently increase the strength when applied to existing reinforced concrete (R/C) buildings with non-seismic details dominated by shear failure. To examine the seismic safety of the proposed CCSS, two framework specimens were prepared based on an existing R/C building with non-seismic details. A pseudo-dynamic test was conducted on the unreinforced framework specimen and the framework specimen reinforced with CCSS to verify the seismic strengthening effect of applying CCSS to the existing R/C framework, i.e., in terms of the load–displacement characteristics and seismic response control capability. Based on the pseudo-dynamic test results, restoration of the force characteristics was proposed for the nonlinear dynamic analysis of the building reinforced with CCSS. Nonlinear dynamic analysis was conducted based on the proposed restoration of the force characteristics, and the results were compared with the pseudo-dynamic test results. Finally, for the commercialization of CCSS, nonlinear dynamic analysis was conducted on the existing whole R/C building with non-seismic details that was reinforced with CCSS. The seismic strengthening effect was then verified by examining the seismic response load, displacement characteristics, and the degree of seismic damage to the members based on the ductility ratio before and after seismic strengthening. The study results show that under a design basis earthquake with a magnitude of 200 cm/s2, the unreinforced R/C building exhibits shear failure, and light seismic damage is expected on the CCSS-reinforced building.