Shear strength of URM walls retrofitted using FRP

This paper compares different models currently used to calculate the shear strength of unreinforced masonry (URM) walls retrofitted using fiber reinforced polymers (URM-FRP). The shear strengths of six recently tested URM-FRP walls were compared to shear strengths predicted by the models herein. Four of these specimens were tested under constant gravity load and incrementally increasing in-plane loading cycles. The other two specimens were tested on a uniaxial earthquake simulator. The specimens were subjected to synthetic earthquake motions with increasing intensity. Each specimen was retrofitted on the entire surface of a single side using FRP with different axial rigidities. One of the shear strength models compared in this study has been recently developed by the authors: The model was explicitly developed to predict the shear strength of unreinforced masonry walls retrofitted using FRP. The model idealized masonry, epoxy, and FRP in a URM-FRP as. different layers of isotropic homogeneous elastic materials. Then, using principles of the theory of elasticity, the governing differential equation of the system is formulated and linearly solved. Then, the material nonlinearity was implemented via a step-by-step degradation in the layer stiffness; after each step the equations were resolved linearly. In most cases, failure occurred in either the masonry or the epoxy and in no case did FRP reach its ultimate load. Comparisons between the different shear models showed that the authors' model is more conservative than the other existing models. In addition, for a small FRP axial rigidity, the difference between the models was insignificant. However, with increasing FRP axial rigidity the differences between the models became more significant. This paper highlighted the advantages and disadvantages of each model. It was found that the authors' model offered several advantages over the other available models. However, the authors' model also has its own disadvantages and limitations. One of these limitations is that it does not explicitly take into consideration the out-of-plane normal stresses. Finally, additional experimental verification of the authors' model is recommended. (c) 2006 Elsevier Ltd. All rights reserved.