The potential of improving the structural performance of concrete cantilever beams by extending the attachment of CFRP sheets to concrete columns through chamfers and fillets, constructed at beam-column connection, was investigated; while considering the impact of end anchorage using U-wraps of CFRP sheets or steel plates. Fourteen beam-column connections with 750-mm-long cantilever beams (150 x 150 mm) were load-tested after the attachment of CFRP sheets along the negative moment zone of the cantilever beams only or extending attachment of CFRP sheets' to the columns surface through creating chamfers and fillets at the beam-column joints. CFRP sheets' bond length and width, and number of layers, as well as the use of concrete chamfers and fillets had a significant impact upon mechanical performance of tested cantilever beams. End anchorage using U-wrap CFRP sheets was beneficial in delaying CFRP sheets debonding hence improving mechanical response; especially for cantilever beams, repaired by extending CFRP sheets to columns surface using large concrete chamfers.
Fiber reinforced polymer (FRP)
Worldwide, considerable numbers of degraded reinforced concrete (RC) structures are in need for repair to regain their serviceability and prevent their failure under service load. Externally bonded fiber reinforced polymer (EB FRP) sheets or strips have been increasingly used in repair works because of their many advantages over conventional repair methods which involve using steel plates and reinforced concrete jacketing. This is referred to EB FRP higher ultimate strength, lower mass/inertia ratio, and shorter installation time as compared to those of conventional repair methods; especially when applied to complicated shape structural elements, [1-4]. Present states of knowledge indicated great advantages of using EB FRP sheets or strips in enhancing flexure and shears performances of damaged beams and control their cracking status under field loads, [5-11].
The tendency of EB FRP composites to detach from concrete represents a limitation in their use on a large scale for repairing concrete flexural elements. End detachment starts at the edge of the FRP plate or sheet and develops inwards due to flexural or shear-flexural induced cracks, initiated at end interfaces between EB FRP and concrete, [12,13]. If such detachment is prevented, flexural and shear capacity of concrete elements would be substantially enhanced with ductile failure achieved through yielding of longitudinal or transverse reinforcement following sudden rapture of FRP composites [14,15]. Literature works stipulated that FRP sheets' detachment is affected by several factors; the most important of which are their width and thickness, [14,15]. Strengthening simply supported beams has become a relatively common practice as necessary development length can be easily provided. This is may not be the case of beams in frame systems, where FRP extension beyond the high negative moment zone is restricted by the presence of supporting columns.
Several anchorage systems had been proposed to solve the development length problem in frame structures. Using of longitudinal cold bend steel angles along beam-column corners with extensions along the FRP bond length was suggested in , whereas the use of U-wrapping...