Shear capacity of FRP-strengthened reinforced concrete T-beams

All over the world, many existing reinforced concrete structures are deemed no longer capable of sustaining current capacity demands. Structural strengthening with externally bonded fibre- reinforced polymer (FRP) sheets has been an effective technique for improving the performance of structurally deficient reinforced concrete beam structures in shear for over 20 years now. Despite the increasing amount of research devoted to the use of these extraordinary materials in civil engineering, a little is known about the true mechanical behaviour of such strengthened structures, especially on a large scale.
This paper addresses the urgent need for greater understanding of the mechanical behaviour of concrete structures shear-strengthened externally with fabric bonded FRP. The comprehensive experimental and analytical study is driven by the lack of research considering the FRP fabric stretched at an oblique angle to its principal fibre direction, which is invariably the case in shear-strengthening practice. Therefore, a targeted approach to assess the limits of effectiveness of FRP shear strengthening and to define failure mechanisms has been developed. A series of experiments was conducted on uncracked steel reinforced T-beams representing nominally understrength historic concrete slab-on-beam structures. Studied parameters included the amount of FRP applied to the beam as well as the effects of a novel bar-in-slot anchorage system on the overall structural performance. Reinforced concrete structures are known for exhibiting a strong size effect and therefore, two different sizes of test specimens were considered in order to observe this phenomenon experimentally. In order to investigate the effectiveness of various shear-strengthening solutions, specimens strengthened with comparable amounts of FRP applied internally (deep embedded bars) as additional shear reinforcement were included in this study for comparison.
True representation of the key factors influencing the effectiveness of FRP shear-strengthening systems determined from extensive experimental research leads to accurate analytical formulation of the problem. This in particular has immediate and urgent implications in terms of development of revised mechanics-based design recommendations for industry and governmental bodies for FRP shear-strengthened reinforced concrete structures.