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In order to further demonstrate the effectiveness of engineered cementitious composites (ECC) in repairing and strengthening the post-earthquake damaged structure, at the overall structural level, experimental and numerical comparative analysis of structural seismic performance before and after "retrofitted with ECC" is conducted in this paper. A 1:2-scale reinforced concrete frame is tested under cyclic reversed loading and a new ECC material's constitutive model is proposed in this paper for improving the accuracy and feasibility of numerical modelling. The modelling method and newly proposed constitutive model of ECC has been demonstrated to be workable and accurate. Based on numerical and experimental data, the increase of the average yielding displacement after the installation of ECC is relatively significant (80.4% to 156.4%), and the repairing method using ECC in post-earthquake damaged RC frame can restore and even exceed the original frame's load bearing capacity. Comparing the ultimate inter-story drift ratio, the ratio with ECC is about 31.0% higher, indicating that ECC has good deformation capacity and the usage of ECC is indeed an effective method to improve deformation capacity in repairing and strengthening post-earthquake damaged structures. The results confirm the effectiveness and superiority of retrofitting ECC in post-earthquake damaged structures for the reason that the repaired structure can reach the same level of seismic performance as the original structure. The "repairable" characteristic can be used in the design of earthquake resilient structures. [ABSTRACT FROM AUTHOR]

The seismic performance of a five-story, four-bay, self-centering precast reinforced concrete frame (SC-RCF), which was redesigned using the direct displacement-based design method, was analytically investigated. The analytical model of the overall structure was developed in OpenSees. The multi-spring contact element was adopted to simulate gap open-close behavior at connection interfaces. The limit states of external mild steel dampers and unbonded post-tensioning strands were considered. Static pushover analyses were performed up to the roof drift of 10%. The nonlinear dynamic responses under four groups of ground motions (with different fault distances and site conditions) at six hazard levels (from the service to the very rare earthquake (VRE)) were compared. Incremental dynamic analyses were implemented to quantify the structural collapse risk. The results showed that the structural responses of SC-RCF were satisfactory under all levels of earthquakes. The collapse safety of the structure under earthquakes up to VRE1 was adequate, while the structure would collapse to a large extent under VRE2 and VRE3. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study on the seismic performance of a bidirectional self-centering reinforced concrete (RC) frame structure. In the structure, the column-base joints, which were installed with external mild steel (MS) dampers, could uplift freely and the beam-column joints could open effectively under earthquake excitations. Angle steels and MS dampers were installed at the beam-column joints in the structural X and Y directions, respectively. During the gap opening of the joints, unbonded posttensioned (PT) steel wires, which passed through the plastic ducts inserted in the RC beams and columns, provided the structure with the ability to return to pre-earthquake positions, and the yielding MS dampers and angle steels dissipated the seismic energy. A 1/2-scale two-story model structure was designed and constructed. Shaking table tests were performed on the structure under four different types of earthquake excitations with increasing seismic hazard levels. The test results indicated that the self-centering RC frames installed in both the directions showed satisfactory seismic performance, with only slight damage to the main structure after extreme earthquakes. The natural frequencies of the self-centering frames installed in both the directions degraded progressively, mainly because of the prestress loss of the PT steel wires and the yielding of the MS dampers. The structure showed desirable self-centering ability with very small residual deformation under ground motions of all hazard levels. The structural deformation was mainly concentrated at the column-base and beam-column joints, and hence, damage to the concrete beams and columns was considerably alleviated. In addition, the residual gap opening of the joints was minimal. [ABSTRACT FROM AUTHOR]

To improve the brittle fracture mode of coupling beams with small span-depth ratio in RC frame-shear wall structure, a shape memory alloy (SMA) damper is installed into coupling beams in this study. The seismic performance of the structure is studied by numerical analysis. A planner 18-story frame-shear wall structure is utilized. SMA dampers are installed into coupling beams at each story. Static monotonic and cyclic loading are applied on the structure. Influence of two parameters of the coupling beam with SMA damper, the yield force ratio and the yield displacement ratio, on the nonlinear behavior of the whole structure is addressed. The analysis results indicate that the failure mode is remarkably affected by the yield force ratio. For the structures with the same yield displacement ratio, when their yield force ratio decrease, the dampers yield more early and deformation of the coupling beams is more easily to be concentrated in the dampers. At the same time, the structure has good re-centering ability. With the same yield force ratio, the increasing of yield displacement ratio results in the delay of SMA damper yielding and the concrete members damage early. [ABSTRACT FROM AUTHOR]