Deformation Behaviour of Beams Reinforced with Fibre Reinforced Polymer Bars under Bending and Shear

Several predictive equations and design guidelines are currently available to estimate the total deformation of FRP reinforced concrete members. Although existing approaches can adequately estimate deflections up to service load, however, can also largely underestimate deflections at load levels beyond service. The larger-than expected deflections can be partly attributed to the stiffness degradation caused by the shear-flexure interaction and the change in the stiffness of the load carrying mechanisms. Although studies dealing with the shear behaviour of FRP reinforced concrete beams are currently available in the literature, these tend to focus primarily on the development of models to estimate ultimate shear strength rather than examine the effect of the FRP reinforcement on overall deformation behaviour.
An experimental programme was designed to investigate the behaviour of FRP RC beams subjected to shear dominated actions, with a particular focus on their deformation behaviour. Six tests were carried out in two phases on three beams reinforced with FRP flexural and shear reinforcement. All specimens were tested in four point bending and two different shear span-to-depth ratios were examined, namely 3.5 and 2.8. Two different shear reinforcement ratios, 0.5% and 0.27%, were used to reinforce the two shear spans of each of the tested beams to examine the contribution of transverse reinforcement to the deformation behaviour.
An analytical framework, based on a non-linear cross section analysis, was developed to perform load deformation analyses of RC beams. The framework was then extended to enable the use of different material models and to account for the effects of shear induced phenomena on overall deflections.
On the basis of the results obtained from the experimental programme and the analytical framework, a new approach is proposed to model the development of a shear resisting truss mechanism and estimate the inclination of the compression struts. This concept is used to estimate shear induced deformation and improve existing models. Comparisons are carried out between the results provided by the analytical model and the experimental data, along with the load deflection responses estimated according to existing design guidelines and other models from current literature. This new model allows the inclusion of shear-induced deflection throughout the load history of the element and yields more accurate results.