INTRODUCTION AND LITERATURE REVIEW
1.2 LITERATURE REVIEW
1.2.2 Rehabilitation / strengthening of damaged RC beam-column joints and connections
1.2.2.4 Fiber reinforced polymer (FRP)
specimens, they concluded that epoxy resin injection technique was appropriate for rehabilitations of damaged joints, since no damages were observed at the joint area of the specimen after testing of the repaired joint. Further, a combination of epoxy injection with C-FRP sheets led to significant improvement of the load carrying capacity, energy absorption capacity and ductility. Finally it led to improvement on the type of damaged compared with the damage modes of the original specimens.
gave eight recommendations for future research. Out of these, one was to see the effect by changing the specimen size and varying the beam and column cross sections.
Four beam-column joints without transverse reinforcement in the joints and in accordance with the strong-beam weak-column concept were tested by Ghobarah and said [2002].
The specimens were rehabilitated and strengthened using four different rehabilitation schemes, some specimens with and without mechanical anchorage, including steel plates and threaded rods core-drilled through the joints. The applied composites was extended above and below the joint and wrapped around the column. The flexural strength of the column increased as a result. The beams with no anchorage ruptured by joint shear failure whereas those with anchorage failed by flexural hinging of the beam. This result clearly indicated the importance of anchoring for the FRP joints strengthening technique.
Mukherjee and Joshi [2005] conducted tests on two sets of scaled down RC beam-column joints to study the performance of FRP used for up gradation. One set of joints were cast with ductile adequate steel reinforcement following ductile joint reinforcement, while the other set were cast non-ductile joint reinforcement. Both sets of specimens were strengthened with different strategies. Some specimens were retrofitted with GFRP/CFRP sheets, some with GFRP/CFRP wraps, while some with CFRP plates and wraps. CFRP plates were used to improve bending stiffness. The control specimens were rehabilitated after testing, and their performance were also checked. A constant axial load was maintained during the application of displacement-controlled cyclic loading. There was considerable increase in initial stiffness, yield load, deflection at yield, ultimate deflection and energy dissipation for all the strengthened cases. The authors concluded that both GFRP and CFRP could be used for seismic retrofitting and rehabilitation of damaged specimens.
Al-Salloum and Almusallam [2007] examined the performance of interior beam-column joints retrofitted and rehabilitated using two different schemes. The scheme comprised of using externally bonded CFRP with and without mechanical anchorage. Three numbers of cycles in each displacement amplitude were gradually applied to the specimens till failure. The test results showed that using any of the two schemes, shear failure of the joints was delayed substantially. The specimens with no anchorage experienced a joint shear failure proceed by debonding of FRP. By contrast, the specimens with anchorage failed by flexural hinging of the beam.
Karayannis et al. [2008b] experimentally investigated the behaviour of 12 critical external beam-column joints repaired or/and strengthened with a combination of epoxy resin injections and carbon-fibre reinforced polymers sheets. It was observed that combination of the two techniques leads to a significant improvement of the loading carrying capacity, energy absorption capacity and ductility. Finally it leads to improved type of damages compared with the damage modes of the specimens during the initial loading.
More recently, Saleh et al. [2010] employed two different schemes to upgrade and rehabilitate the exterior beam-column joints. The scheme comprised of using externally bonded CFRP with and without mechanical anchorage. The authors observed that the shear failure of the joints was delayed substantially. Further, the specimens with mechanical anchorage failed with flexural hinging of the beam. While specimens with no anchorage experienced a joint shear failure, proceed by debonding of FRP.
Thus, from the detailed review of literature on various rehabilitation / strengthening techniques, the following observation may be made:
• Epoxy repair techniques have been used extensively for the repair of damaged
effectiveness of this technique. Systematic studies to evaluate the performance of rehabilitated RC beam-column connection having different deficiencies under cyclic loading at different stages of damage level are still limited and are not well established.
• A combination of epoxy injection with FRP jacketing could overcome the limitation encountered by other techniques in rehabilitating damaged structures. FRP jacket further acts as a confining layer on the damaged area. This led to the change in failure mode and improved the ductile behaviour of the potential plastic hinge area.
However, anchoring of FRP were observed to be a difficult for ensuring the effectiveness of this technique. Using FRP as confining materials will be more difficult with common constructional limitation (spandrel beams, existence of slabs and transverse beam) which needs reliable mechanical anchorage.
• Partial or total removal and replacement of concrete was done prior to injection and FRP wrapping of heavily damaged joints region with crushed concrete, buckled longitudinal bars. Generally, high strength, low-or non shrink concrete is used for the replacement. Transverse reinforcement of a repaired specimens might be relaxed with the used of high strength concrete.
• Concrete jacketing is labour-intensive involving drilling through the beams, floor slabs and even in-place bending of the added joint transverse reinforcement.
• Steel jacketing is vulnerable to corrosion, difficult to handle due to heavy weight and has objectionable aesthetics.
• The investigation related to the evaluation of seismic behavior of repaired and strengthened specimens were limited to testing of scale models which may not truly represent the actual behavior of a prototype structure.