Study of torsional behaviour of rectangular reinforced concrete beams wrapped with GFRP

Abstract

Fiber Reinforced Polymer (FRP) as an external reinforcement is used extensively to deal with the strength requirements related to flexure and shear in structural systems. But the strengthening of members subjected to torsion is explored only recently. Torsion failure is an undesirable brittle form of failure which should be avoided specially in the earthquake prone areas. In the present work, the behaviour and performance of rectangular reinforced concrete beams strengthened with externally bonded Glass Fibre Reinforced Polymer (GFRP) fabrics subjected to combined flexure and torsion is studied experimentally.
Rectangular RC beams externally bonded with GFRP fabrics were tested to failure using an arrangement which transfer torque to the central part of the beam through two opposite cantilevers called moment arms. Each arm is subjected to equal static loading during the experiment. Total nine RC beams were cast and tested for the study. All the beams were designed to fail in torsion. One of the beam was used as a control beam and eight beams were strengthened using different configurations and different types of GFRP fabrics. The study is restricted to continuously wrapped GFRP fabrics.
Experimental data on ultimate & first cracking loads, angle of twist and failure modes of each of the beams were obtained. The effect of different types and configuration of GFRP on first crack load, ultimate load carrying capacity and failure mode of the beams were investigated.
The experimental results have been validated with finite element analysis by using ANSYS software and found to be in good agreement with analytical values. The experimental results show that externally bonded GFRP can increase the torsional capacity of the beam significantly. The results also indicate that the most effective configuration is the full-wrap of GFRP fabrics. In addition GFRP applied in 450 with axis of the beam gives more strength than GFRP applied in 900 with the axis of the beam.