Behaviour of continuous concrete T-beams reinforced with hybrid FRP/Steel bars

Abstract

This work aims to investigate the flexural behaviour of continuous hybrid reinforced concrete T-beams (HRCT). The investigations consist of three parts; the computational part, the experimental part and the finite element analysis. The computational part included two parts, the first one is developing an analytical programme using MATLAB software to investigate the moment-curvature behaviour of HRCT-beams and to design the experimental specimens. This was followed by the experimental part, where six full-scale reinforced concrete continuous T beams were prepared and tested. One beam was reinforced with glass fibre reinforced polymer (GFRP) bars while the other five beams were reinforced with a different combination of GFRP and steel bars. The ratio of GFRP to steel reinforcement at both mid-span and middle-support sections was the main parameter investigated. The results showed that adding steel reinforcement to GFRP reinforced concrete T-beams improves the axial stiffness, ductility and serviceability in terms of crack width and deflection control. However, the moment redistribution at failure was limited because of the early yielding of steel reinforcement at the beam section that did not reach its moment capacity and could still carry more loads due to the presence of FRP reinforcement.

The second part of the computational part included the comparison between the experimental results with the ultimate moment prediction of ACI 440.2R-17, and with the existing theoretical equations for moment capacity, load capacity, and deflection prediction. It was found that the ACI 440.2R-17 design code equations reasonably estimated the moment capacity of both mid-span and middle-support sections and consequently predicted the load capacity of the HRCT-beams based on fully ductile behaviour. However, Qu's and Safan's equations underestimated the predicted moment and load-capacity of HRCT-beams. Also, Bischoff's and Yoon's models underestimated the deflection at all stages of the load for both GFRP and HRCT- beams. For the numerical part, a three-dimensional finite element model has been developed using ABAQUS software to examine the behaviour of HRCT-beams. The experimental results were used to validate the accuracy of the FEM, where an acceptable agreement between the simulated and experimental results was observed. Accordingly, the model was used to predict the structural behaviour of continuous HRCT-beams by testing different parameters.