Experimental and Numerical Investigation of Rectangular R/C Beams Retrofitted Against Shear Utilising Frp Strips

Abstract eng:
Reinforced concrete structures, designed and constructed according to old earthquake resistant design provisions are in need of retrofitting. This paper presents results from an investigation aiming to examine the behaviour of rectangular R/C beams in need of being retrofitted against shear. Towards this objective, ten (10) R/C beam specimens of prototype dimensions were constructed and tested under four point flexure. The retrofitted scheme which was investigated was based on fiber polymer sheets, either made of carbon (CFRP) or steel (SFRP); strips of such FRP sheets were attached externally on the R/C beam specimens as transverse reinforcement in order to upgrade their bearing capacity in shear. One potentially weak point of such a retrofitting scheme was investigated in depth; that is the debonding mode of failure of the FRP strips from the concrete surface, when these strips develop considerable stresses that cannot be transferred to the main volume of the structural element solely by the bonding surface. This mode of failure limits the potential of the high tensile strength capability of these FRP strips and inhibits the aimed increase of the shear capacity of the R/C beams. In order to confront with this limitation the effectiveness of an innovative type of anchoring device that can be incorporated together with such FRP strips was specially examined. The obtained experimental results are discussed in order to demonstrate the capability of such a retrofitting scheme, when proper anchoring of the FRP strips is utilized, to efficiently upgrade the shear capacity of such R/C beams. The experimental results were validated through a numerical simulation of the experimental set-up employing the ABAQUS finite element software. This numerical simulation took into consideration the non-linear behaviour of the concrete and steel as well as the cohesive surface zone between concrete and FRP strips in their contact area. Moreover, the presence or not of an anchoring device was also simulated numerically. From the comparison between the observed behavior, in terms of either load-displacement response or mode of failure, with the results of the numerical simulation the reliability of such a numerical simulation is demonstrated. This research was conducted in the framework of an initiative introduced by the Hellenic Earthquake Planning and Protection Organization aiming to support relevant provisions of the Greek Code for the repair and strengthening of R/C structures.

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