This paper presents an experimental work on repair of partially damaged reinforced concrete beam- column joints using carbon fiber-reinforced plastics (CFRP) plates. The investigation carried out is mainly dedicated to study the behavior of repaired RC beam-column joints under cyclic loading with a variety of retrofitting schemes. Eight specimens were prepared and tested to investigate the repairing efficiency for improving strength-capacity, stiffness and behavior of partially damaged RC joints. The control specimen was tested up-to-failure under cyclic loading. Seven specimens were loaded up-to a certain load level which was about 80% of expected failure load (known as preload). Then, they were retested after repairing using various schemes of CFRP-plates. The results were examined through load versus drift-ratio; initial-stiffness of curve, ductility index and maximum load. Besides, strains in CFRP-plates were measured and the failure modes of the test specimens; due to crack-pattern and CFRP-debonding, were monitored. The results showed the important issue of repairing and enhancing the joint-performance and hence delaying premature debonding of the various CFRP-configurations. All repaired joints show improved strength, which reached almost the existing shear-strength of the beam-column joint. Hence, the resulted repaired joints enhanced a much larger strength-capacity than the reference joints.
RC beam-column joints
Fibre reinforced polymer (FRP)
In reinforced concrete (RC) buildings, the connections between beam and column called beam-column joints are crucial parts of a building. Several parameters affect the behavior of RC beam, column joints such as relative stiffness between beam and column, strength of concrete and reinforcement details. In fact, only vertical load is taken into consideration. This joint is the most critical portion of a building under earthquake due to diagonal-crack failure, which leads to the collapse. Therefore, such joints need special attention to increase the capacity of existing damaged joints through retrofitting.
Nowadays, the fiber-reinforced polymer (FRP) becomes preferable for strengthening and retrofitting of RC structural elements due to its high strength-to-weight and high-stiffness-to- weight ratios [1-5]. Different modes of failure can happen in a beam, wall, column or joint, strengthened with CFRP loaded in-plane or out-of-plane. Some of these modes involve debonding. Examples of the latter are concrete crushing with or without yielding of steel reinforcement, CFRP-laminates tension failure with steel yielding and shear failure which occur, if the shear capacity is reached before any kind of flexural failure occurs. Debonding initiation will generally take place in regions of stress-concentration in concrete-CFRP laminate at interface. This includes the ends of the adhesive and concrete or concrete-cover peel off including the complete concrete cover or parts of it. It is thus of great importance to build-up understanding and knowledge of how the strengthening or repairing should be carried out in order to benefit from its full potential without debonding failure [6-8]. There has been several research studies conducted on strengthened RC beam-column joints [6-13]. An experimental study by Choudhury et al.  was carried out to investigate the size-effect of retrofitted RC beam-column joints subjected to displacement-control cyclic loading. They found...