Improving the cyclic behavior of reinforced concrete non-standard seismic frames using FRP sheets

The purpose of this paper is to evaluate the behavior of vulnerable joints of substandard RC frames, improved by Shear and flexural retrofit of beam-column joints using FRP sheets. For this purpose, the behavior of the retrofitted joints is compared with the control joints with and without special seismic details. Considering the main focus of previous studies on two-dimensional joints and not considering the real conditions including the effect of slab and transverse beam in the joints, in order to apply geometric conditions and constructional limitations, in this study the behavior of joints with slab and transverse beam effect has been extracted by experimental study. For this purpose, 2 experimental specimens of concrete exterior beam-column joint with a scale of 1/2 are made and subjected to a cyclic load. The specimens include one control specimen, without special seismic details, and the other retrofitted specimen include a joint without seismic detail, which has been improved with FRP sheets. Finally, the studied joints were modeled using OpenSees software and compared with the experimental results of the research. The results of the retrofitted joint behavior show no strength drop, stable cyclic behavior, reduced pinching effects, improved cyclic behavior due to change of the failure mode from shear failure of the joints to the formation of flexural plastic hinges in the beam. This performance can be attributed to the effectiveness of the proposed retrofit methods in promoting the behavior of vulnerable joints with real geometric conditions