HYSTERETIC EVALUATION OF SEISMIC BEHAVIOR OF RC SHEAR WALLS STRENGTHENED WITH FRP SHEETS

摘要

The development of nonlinear finite element methods with increasing computational capacity, has improved the reliability of seismic analysis of complex structure. The effectiveness of Fiber Reinforced Polymer (FRP) externally bonded reinforcement has been widely recognized with respect to increasing shear strength of RC members, particularly of those not satisfying the requirements of modern seismic codes, and also providing confinement to critical regions of such members. Application of externally bonded Fiber Reinforced Polymer sheets is an effective seismic strengthening procedure in order to improve the behavior of reinforced concrete shear walls. In the retrofit method using FRP sheets, the flexural and shear strength would be increased by applying the FRP sheets with the fibers oriented in the vertical or horizontal direction. The carbon fiber sheets are used to increase the pre-cracked stiffness, the cracking load and the ultimate flexural capacity of RC walls.Finally, wrapped FRP sheet around plastic hinge area of RC wall in parallel with boundary elements, provides not only enough shear strength which results in a ductile flexure failure mode but also confinement of concrete in the plastic hinge leads to increase the ductility of the RC wall.The main purpose of this research project is to present results from numerical analysis that was obtained during the analyzing of RC wall structural models strengthened using FRP reinforcement. The strengthening of these walls aimed at the increase of both the flexural and shear strength, whereas in seismic interventions with FRPs only the latter is usually attempted.Issues that are critical with respect to the seismic performance, i.e. horizontal displacement, ductility, and energy dissipation capacity are presented and discussed. Also envelopes of cyclic load vs. displacement curves were compared. The total displacement of an RC member is made up of three components, each contributed by a different deformation mechanism, namely flexure, shear, and sliding shear; the relative contribution of each mechanism varies with the level of inelasticity. Also the hysteretic responses of structural models are presented in order to achieve the capacity of energy dissipation of the RC walls and effectiveness of using FRP sheets on them. Hysteretic loops are somehow fat that shows the excellent capacity of energy dissipation during earthquake event. Also by comparing the results between models it can be declared that by using an extra layer of FRP on the plastic hinge area of the shear wall, its behavior during the seismic loading would be improved.This result is very similar to the result that had been obtained when applying the monotonic loading on shear walls.