Experimental investigation of damaged RC joints retrofitted by stiffened angles and bars

Experimental studies reveal that weakness in joint core leads to the formation of a shear hinge in this area, loss of load carrying capacity in the both regions of cyclic curve and decrease of ductility. Generally, the recent mentioned results are related to the previous studies, in which the effect of slabs and lateral beams (2D joints) have been neglected. However, these effects can lead to different responses in real joints compared to ideal 2D joints, in the term of changes in capacity and demand. Consequently, in this study the effect of slab and lateral beam has been considered (3D joints). Four 3D external joints with a scale of 1/2 are made in the laboratory. Specimens include two control joints and two damaged joints retrofitted by stiffened angles and post-tensioned bars. The results show that the use of retrofit method for damaged joints results in the formation of a flexural plastic hinge in the beam and shift of the shear hinge out of the joint core. Furthermore, the effect of slab and lateral beam in the bare non-seismic joint may lead to the increase of the ductility, compared to the similar 2D joints in previous studies.