Seismic retrofit of deficient 3D RC beam–column joints using FRP and steel PT rods

The purpose of this paper is to evaluate the behavior of vulnerable joints of substandard RC frames, improved by two different methods, 1- Shear and flexural retrofit of beam–column joints using FRP sheets 2- Enlargement of beam–column joints using angles and pre-tensioned rods. In this study the behavior of joints with slab and transverse beam effect has been extracted by experimental study. For this purpose, 4 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 two control specimens, with and without special seismic details, and the other two retrofitted specimens include a joint without seismic detail, which has been improved once with FRP sheets and again with pre-tensioned rods and angles. 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.