Effect of Macro Synthetic and Steel Structural Fibers on the Shear Behaviour of GFRP Reinforced Concrete Beams

Dev, Amal and Prakash, Suriya S (2019) Effect of Macro Synthetic and Steel Structural Fibers on the Shear Behaviour of GFRP Reinforced Concrete Beams. Masters thesis, Indian institute of technology Hyderabad.

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Abstract

Fiber reinforced polymer (FRP) bars are increasingly used as a full or partial replacement for conventional steel reinforcements in reinforced concrete structures. The lesser axial stiffness of the FRP bars allows the tension crack to penetrate more depth resulting in reduction of shear capacity. Moreover, FRP being linear elastic till failure makes both the failure modes (concrete crushing and FRP rupture) brittle. Addition of structural fibers improves the shear behavior and ductility of the beams. The effect of structural fibers on the shear behavior and ductility of reinforced concrete (RC) beams with glass fiber reinforced polymer (GFRP) rebar as longitudinal reinforcement is investigated in this study. The objective is to understand the efficiency of macro-synthetic polyolefin (PO) and a hybrid combination of steel and PO fibers in improving the shear behavior of GFRP reinforced beams. Non-destructive testing methods such as digital image correlation (DIC) and acoustic emission (AE) technique is also used to analyze the behavior of the beams. In total, thirteen full-scale RC beams are cast with GFRP rebars as internal reinforcement and varying PO and hybrid fiber dosages. Three different fiber dosages by volume of concrete (vf ), namely 0.35%, 0.70%, and 1.0% are considered. The beams are tested under threepoint bending configuration with a shear span (a) to effective depth (d) ratio of 2.2 to simulate shear dominant behavior. Experimental results revealed that the addition of fibers increased the post-cracking stiffness, peak load, and ductility when compared to control beams with no fibers. Soon after cracking, an excessive load drop in the control specimen is observed due to the low elastic modulus of GFRP rebars. The addition of PO and hybrid fibers reduced the load drop significantly and enhanced the post-cracking performance by improving the aggregate interlock and through reduction of residual tensile stresses at the crack tip. The angle of crack increased with increase in fiber dosages indicating the change of the failure mode from brittle shear tension to ductile flexure at higher fiber dosages (0.7% and 1.0%). The shear strength predictions obtained from ACI and RILEM recommendations are found to be very conservative when compared to the test results. The crack width and crack slip at various loading points are found using DIC. The analysis shows that the crack width and slip for a particular load is decreasing with increase in fiber dosage. The shear load components viz., dowel action contribution, aggregate interlock and uncracked concrete contribution is found from the crack width and slip using the existing models. Various AE parameters such as AE events, AE hits and average RA value is analyzed to found the effect of fiber addition in the beams. An increase in AE activity is found with the increase in fiber dosage which is more for hybrid fiber addition compared to Abstract vii synthetic fiber addition. Parameter based AE analysis is done to classify the cracks into shear and tensile. An increase in shear events with fiber addition is observed due to the shear events generated by the fiber slipping and pullout events. The three dimensional crack mapping is done to find the fracture process zone which is found to be matching with the visual observations

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