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Information Journal Paper

Title

REPARABILITY ASSESSMENT OF STRUCTURES STRENGTHENED BY CFRP COMPOSITES

Pages

 Start Page 71 | End Page 79

Abstract

 The scope of this study is the investigation of the REHABILITATION of structures retrofitted by use of carbon-fb01brereinforced plastics (CFRPs) to achieve a safe, economic and practicable level of seismic damage. This paper investigates analytically the efficiency of the strengthening technique for improving the seismic behavior of damaged structures. 4 BEAM-COLUMN CONNECTIONs are tested under reversed cyclic load. The connections have none-seismic detailing of rebars, i.e., no transverse rebar and seismic stirrups are used in the joint core and beam and column critical end zones. The joints are damaged in different levels and then retrofitted by CFRP sheets. The strengthened joints are tested again to reach the ultimate drift capacity. Then, the tested joints, such as reference joint and retrofitted joints, are analyzed by Opensees nonlinear software. The results of joint analysis are compared with experimental behavior of specimens. The hysteresis curves of the modeled joints had a high level of accuracy in terms of stiness degradation, moment carrying capacity, capacity degradation and energy dissipation. In the following, a multi-story/multibay moment-resisting frame is selected for assessment of seismic response of damaged frames. So, a step-by step pushover analysis is done in order to find the plastic hinge positions and the level of plasticity on the moment resisting frame. The plastic hinges are developed on the beam ends and middle length of the frame beams. As the analysis progresses, the damaged frames are categorized in 7 levels according to PERFORMANCE LEVELs defined by FEMA 356. The damaged Frames are retrofitted by CFRP sheets, considering the level of damage similar to the tested joints mentioned above. At the end, the retrofitted frames are subjected to El-Centro base acceleration. The root mean square parameter of roof displacement is also calculated for nonlinear time history response of frames. The retrofitting of the plastic hinges improved the RMS of the responses and compensated the lost capacity and stiffness. The results show that reparability level of frames retrofitted by CFRP sheets is equal to the level that the hinges on all of the beams are formed in collapse-preventing PERFORMANCE LEVEL. This level for specific frame investigated in this study is equal to 1.03% storey drift. Also, the results show that structures could be retro fitted by external bonding of FRP SHEETS to a limited level. If the damage level of structures is higher than this reparability level, other REHABILITATION methods may be useful.

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