ABSTRACT
One of the biggest problems troubling the international technical world is the need for strengthening RC beams. There are a lot of reasons that could force an engineer to increase the loading capacity of structure, such as increase of load requirements or damage induced to the structural members due to seismic or other action, or even cases of design and construction faults. There are two different solutions to overcome such a structural deficiency, resulting to a partial repair or complete replacement of the damaged part of the structure. Various techniques have been developed in the last years for strengthening RC beams concluding that the use of FRP materials for structural repair presents several advantages [Baaza & Missihoum (1996), Chajes & Thomson (1994), Crasto & Kim (1996), Nakamura & Sakai, Meier (1997)] as is the high strength to weight ratio of FRP, the corrosion resistance of composite materials,
the ease application and the little equipment needed and finally the increase of durability that make FRPs a very reliable solution. The flexural behavior of members strengthened with FRPs has been investigated [Hutchinson & Rahimi (1993),Triantafillou & Plevris. (1990), Wei & Saadatmanesh (1991)]. The results of all these studies lead to conclusion that the lack of an effective anchorage of the composite material didn’t allow the RC member to reach its maximum flexural design capacity. Thus, researches focus their efforts to develop an easy application of FRP anchorage, in order to increase the load carrying capacity and ductility of strengthened beams. Further studies [Spadea & Bencardino (1998)] have shown that carefully designed external anchorages of the FRP sheets applied to RC beams can increase the load capacity of the beam and at the same time regain beam’s ductility. Particularly, it has been shown that the absence of end sheet anchorages, at beams strengthen by FRP sheets can lead to a brittle and catastrophic brittle failure
in the form of plate or sheet peeling [Hutchinson & Rahimi (1993) Ritchie & Thomas, 1991, Ahmed & Van Gemert, (1999)]. The ratio of the length of bonded plate within the shear span of the beam to the length of shear span has been considered as a parameter affecting the plate anchorage of strengthened RC beams with CFRP plates [Fanning & Kelly, (2000)]. The use of mechanical anchorage provided at the strip ends prevents a catastrophic brittle failure of the strengthened beam by strip detachment [Spadea & Bencardino (1988)]. It is considered that sheet end anchorages have a greater effect in shorter beams, with a high ratio of shear force to bending moment, than in longer beams. Usually anchorage is provided either by anchor bolts or cover plates or by FRP U-shaped external stirrups. The use of multiple small fasteners without any bonding in opposite to large diameter bolts, distributes the load more evenly over the strip and reduces stress concentrations at the holes in the strip, which can lead to premature failure [Lamana & Bank (2001)]. In a recent paper [Demakos (2008)], It was investigated the use of U-strips from FRPs combined with glass fiber bolts, as a composite anchorage system, that can be applied easily at FRP ends to strengthen RC beams. In this paper, beneficial effects of this anchorage system were presented on the loading capacity as well as on the ductility of strengthened beams.
