Experimental Investigation Of Seismic Behavior Of FRP-retrofitted Earthquake-damaged RC Frames And Damage Assessment

Reinforced concrete (RC) frame structures are widely used in earthquake regions. However RC frames have been reported damaged in both domestic and international earthquakes. In addition to a small part of serious damaged RC frames which should be demolished and reconstructed, a large number of minor and moderate earthquake-damaged RC frames need seismic retrofit. Fiber reinforced polymer (FRP) has been widely used in the retrofit of undamaged RC structures in recent years. However, there are few studies concerning FRP-retrofitted earthquake-damaged RC components and structures at present.In response to these problems, this dissertation inverstigated the mechanical behavior of FRP-confined concrete, and the seimic capacities of FRP-retrofitted RC columns and frames; the damage process during the reloading of FRP-retrofitted damaged concrete and components was also studied through AE monitoring and assessment method. The main contents of this dissertation are as follows:(1) The mechanical behaviors of FRP-retrofitted concrete with different damage levels were studied through experiments. The effect and mechanism of damage level on the stress-strain constitutive relationship were revealed and the damage patterns of FRP-retrofitted concrete were analyzed. The characteristics of AE signals emitted from concrete damage and crack were studied and the characteristics of the crack process of FRP-retrofitted damaged concrete were revealed.(2) Simulating the retrofitting process of earthquake-damaged structures under actual conditions, the seismic capacities of FRP-retrofitted RC columns were studied through reversed cyclic quasi-static tests. The effects of earthquake-damage level, residual displacement and axial load on the seismic capacities of FRP-retrofitted earthquake-damaged RC columns were analyzed. The characteristics of AE signals emitted from the damage process of the concrete in the plastic region of FRP-retrofitted RC columns were studied. Based on the AE signals, a failure mode diagnostic method of the concrete in the plastic region was proposed.(3) Based on the capacity relationship of the RC frame beam, column and joint, a failure mode judgment method and a FRP seismic retrofit design method for earthquake-damaged RC frame under horizontal seismic action were proposed. A two-story RC frame with severe earthquake damage in joints was retrofitted with FRP and retested through shake table tests. The seismic capacity and dynamic characteristic of the RC frame before and after FRP retrofitting were studied. A rapid damage assessment method for earthquake-damaged RC frames was proposed. (4) Based on the constitutive models of damaged concrete and FRP-retrofitted damaged concrete, the nonlinear cyclic behaviors of FRP-retrofitted RC columns were simulated using OpenSees (Open System for Earthquake Engineering Simulation). The effect of earthquake damage level and residual displacement on the seismic capacity curves of FRP-retrofitted RC column and multi-floor RC frame was studied through theoretical derivation and pushover analysis. Based on the capacity spectrum method, the analysis method for the residual seismic capacity of earthquake-damaged RC frame and the seismic capacity of FRP-retrofitted earthquake-damaged RC frame was proposed.