SHEAR STRESS REDUCTION TREATMENT AROUND THE END OF PRESTRESSED FIBER REINFORCED POLYMER SHEETS

摘要

Prestressing the FRP materials before bonding them to the structural surfaces has been proved to enhance the serviceability of the structures to be strengthened as well as the maximum load carrying capacity. But due to the highly concentrated stresses at the ends of FRP sheets after releasing the prestressing and due to the limited shear strength of concrete to transfer these stresses, debonding failure may occur unless special precautions are taken into consideration. In the current study, an innovative method using a soft layer around the FRP cutoff points is introduced. In this method the concrete cover around the FRP cutoff points is cut and replaced with epoxy putty having low stiffness accompanied with creation of a narrow notch in the concrete cover. A parametric study based on numerical simulation is carried out to optimize the thickness and the stiffness of the soft layer as well as the thickness of the adhesive layer. Based on this study, it is concluded that (1) Increasing the thickness of the adhesive layer is beneficial in relieving shear stresses in the interfacial layer; (2) using soft layer method is highly effective in relieving stress concentrations near FRP termination points; (3) using low-stiffness ep-oxy putty improves the efficiency of the soft layer method; (4) applying a soft layer outside the area of high stress concentration has a marginal enhancement effect on shear stresses.