Finite element modelling of externally shear-strengthened beams using fibre reinforced polymers
The need for structural rehabilitation of concrete structures all over the world is well known. A great amount of research is going on in this field. The use of fibre reinforced polymer (FRP) plate bonding has been shown to be a competitive solution regarding both the structural performance and the economical aspects. Shear strengthening of reinforced concrete beams is required when the beam is deficient in shear, or when its shear capacity falls below its flexural capacity after flexural strengthening. An accepted technique for the shear strengthening of reinforced concrete beams is to provide an additional FRP web reinforcement in the form of externally bonded FRP sheets. Over the last few years, a considerable amount of research has been conducted on shear strengthening with FRP composites and that has led to a better understanding of the behaviour. Hence, many design equations have been proposed to design shear-strengthened beams. Most of the parameters that control the behaviour of shear-strengthened beams have been addressed. However, the design equations describing the behaviour of shear-strengthened beams are not sufficient to properly evaluate the shear contribution of the FRP composites. This might be attributed to the absence of an accurate numerical model, which is more economical than the experimental tests, to capture the complexities of shear-strengthened beams and to lead to a better understanding of the failure mechanisms. Limited finite element analyses have been carried out on FRP shear-strengthened beams. As a contribution to fill this need, a versatile numerical model is developed in this study to predict the response of reinforced concrete beams strengthened in shear with bonded FRP composites, with a particular emphasis on the interfacial behaviour and debonding phenomena. This research consists of three phases. They are: (1) the development of a reliable numerical model that can capture the real behaviour of FRP shear-strengthened beams; (2) the use of the proposed numerical model to verify various cases having different strengthening configurations: beams with vertical and inclined side-bonded FRP sheets, the U-wrap scheme, as well as anchored FRP sheets and; (3) a parametric study conducted to identify design variables that have the greatest influence on the behaviour of shear-strengthened beams such as the steel stirrup reinforcement ratio, concrete compressive strength, FRP elastic modulus, FRP thickness, and ratio between FRP width to beam width. The proposed numerical model is validated against published experimental results. The predicted results are shown to compare very well with test results. It is shown that the formulation of the FRP/concrete interfacial behaviour is essential to analyses utilizing finite element models. The implementation of interface elements produces accurate predictions of the response of shear-strengthened beams. Furthermore, the numerical analysis provides useful information on the slips and propagation of debonding along the FRP/concrete interfaces. Predicted strain profiles along the FRP sheet depth are also presented. Regression equations based on the statistical approach of the response surface methodology (RSM) are developed. New design equations to describe the FRP axial effective strain at the state of debonding are proposed for both side-bonded and U-wrap strengthening schemes. The proposed design equations can be used to provide simple design guidelines to predict the FRP shear contribution. Some of the results of this thesis research can be found in Godat et al. [2007a,b].
- Génie – Thèses