Shear Behavior of Rectangular Beams Strengthened with either Carbon or Steel Fiber Reinforced Polymers

Abstract

The aim of this study is to upgrade the shear capacity of reinforced concrete (R/C) beams strengthened with either Carbon (CFRP) or Steel (SRP) fiber Reinforced Polymers with strips having the form of either closed or open hoop external transverse reinforcement. This investigation also includes the use an anchoring device. Seven prototype specimens in need of shear strength upgrade were tested having a span of 3000mm. The strengthened R/C beams along with a non-strengthened control R/C beams were tested monotonically under four point bending loading conditions. The experimental results indicate that the shear failure of the closed hoop strengthened beams is accompanied with the tensile fracture of the CFRP/SRP strips together with an increase in the shear capacity. A considerable increase in the shear strength was observed when open hoop CFRP/SRP strips with no anchoring were used; however, the debonding of these strips posed a limitation to this upgrade. When these open hoop CFRP/SRP strips were provided with anchoring devices the shear strength of the R/C beams was further increased and the shear failure was accompanied this time by either the fracture of the CFRP/SRP strips or the failure of the anchoring system. In conclusion, a shear strengthening system for R/C beams utilizing open hoop CFRP/SRP strips with properly designed anchoring it is easily applicable, it increases significantly the shear capacity of such R/C beams and it exploits at the same time the high tensile strength of these fiber polymer materials in a cost effective way. An analytical procedure used to predict the shear strength for of such R/C beams yielded good comparison with the measured values.

Experimental Investigation and Numerical Simulation of Shear Behaviour of Rc T-Beam Specimens With or Without SFRP-Strips Under Cyclic Loading

“…The values adopted for the relevant material parameters, namely the angle of dilation h, the eccentricity, the ratio of equibiaxial to uni-axial compressive stress fb0/fc0, the ratio of the second stress invariant on the tensile meridian to that on the compressive meridian at initial yield Kc and the viscosity parameter were 40, 0.1, 1.16, 0.666 and 0 respectively and were all within the range encountered in literature [23]. In accordance with similar studies [18], the stress strain response of concrete in compression was derived according to Saenz [23], whilst the tension stiffening response was defined in terms of tensile stress and axial deformation according to Cornelissen et al [12], assuming a fracture energy equal to 0.06. The Young's modulus E and tensile strength f ct were determined according to ACI [1] as a function of the compressive cylindrical strength, whilst Poisson's ratio was assumed equal to 0.2.…”

“…Its effectiveness has been experimentally verified. [18,25,26] The aim of the present study is to replicate numerically the experimentally obtained results and to identify the key parameters controlling the structural response of reinforced concrete T-beams strengthened against shear by external FRP reinforcement, that will allow the optimization of the anchorage device and hence the more effective utilization of the FRP sheets, thus leading to more efficient design. Finally the R/C concrete T-beams are imposed to a cyclic loading sequence.…”

“…This ductile behavior is also desirable when one is faced with the task of designing a retrofitting scheme that aims at upgrading the seismic performance of R/C structures designed by older design codes [19]. This paper deals with the objective of upgrading the shear capacity of R/C T-beams, that are poorly reinforced against shear, as part of such a retrofitting scheme [5,17,18,20].…”

“…Moreover, the rapid evolution of seismic codes over the past two decades, which utilizes the knowledge gained following devastating earthquakes, necessitates the structural upgrading of most concrete structures that were built according to older design regulations, following a different design philosophy, in which the role of ductility was not central to the design process. On the contrary, all current seismic design codes pay particular attention to enforce ductile behavior on the various R/C structural elements, which is accomplished by prohibiting shear types of failure and favoring instead flexural types of failure with sufficient ductility [1][2][3][4][10][11][12][13][14][15][16][17][18]. This ductile behavior is also desirable when one is faced with the task of designing a retrofitting scheme that aims at upgrading the seismic performance of R/C structures designed by older design codes [19].…”

Investigation of the Force Transfer Mechanisms for Open Hoop FRP Strips Bonded on R/C Beams with or without Anchoring Devices

“…below 0.2 mm for one layer, can develop substantial tensile forces in the direction of their fiber. This property accompanied with their low weight and the very easy external application to structural elements, by attaching them on the external surfaces by proper organic or inorganic matrices, results in their being used as effective longitudinal or transverse reinforcement for such structural elements that are in need of strengthening [10][11][12][13]. However, the following limitations exist for this type of application.…”