Study On The Behavior Of Concrete Structure Strengthened With Glass Fiber Reinforced Plastic (GFRP)

Strengthening Concrete structure with Fiber Reinforced Plastic (FRP) is a new Structural repair method in recent year. This method has been found to be economical and efficient to apply, because of its resistance to electrochemical erosion, low manpower demand for application and minimal changes in geometrical dimensions of the member.Based on the predecessors' work, this paper investigates strengthening effect, failure mechanism and theory analysis by large quantities experiments of reinforced concrete beams, columns and beam-column joints strengthened with the Glass Fiber Reinforced Plastic (GFRP) sheet. The financial support is provided by the Fujian Science Committee (Grant No. 98-Z-35) and the Fujian Construction Committee (Grant No. JK-99-10). The following are summarizes of experimental study and theoretical analysis:1. Six reinforced concrete beams externally bonded by the GFRP sheet are tested for flexural strengthening. An analytical model is presented to predict the stresses and deformations in concrete beam section, and the results agree well with the experimental results. A parametric study is conducted to investigate the effects of design variables such as thickness, stiffness and strength of the GFRP sheet, concrete compressive strength, and steel reinforcement ratio. The moment versus curvature diagrams for various combinations of these variables are plotted and compared. The results indicate that bonding GFRP sheet to a concrete beam can increase the stiffness and flexural strength of the beam. The method is particularly effective for beams with a relatively low steel reinforcement ratio.2. Experiments have indicated local failure of the concrete layer between the GFRP sheet and longitudinal reinforcement in retrofitted beams. This mode of failure is caused by local stress concentration at the sheet end. Based on the linear elastic theory, a method has been developed to calculate the bonding shear stress and the peeling normal stress of a reinforcement beam with a strengthening sheet and loaded with an arbitrary linear distributed load. The results agree well with the finite element method and the experimental results. The parametric study shows that the bonding shear stress and the peeling normal stress are influenced not only by the thickness, the elastic modulus and the length of the GFRP sheet, but also by the thickness and the elastic modulus of the adhesive. This method can be used to check the maximum bonding shear stress and the maximum peeling normal stress at the end of the GFRP sheet, and to prevent the local bonding failure.3. Fifteen reinforced concrete beams externally bonded by the GFRP sheet are tested for shear strengthening. Test variables include GFRP strengthening method and shear span-depth ratio. The experiment results show that the contribution of GFRP sheet to shear capacity is same as steel stirrups, and the shear capacity isdepend on the effective GFRP sheet strain. The effective GFRP sheet strain decreases with increasing GFRP sheet axial rigidity. Based on the experimental results, an analytical model for the effective GFRP sheet strain is developed, and a calculated method for the design with the framework of modern code formats is presented.4. Twenty concrete square columns externally wrapped by GFRP sheet are tested for axial compression strengthening. Test variables include thickness and spacing of GFRP strap, GFRP strengthening ratio and concrete compressive strength. The experiment results indicate that GFRP sheet can enhance the strength and ductility of concrete, and the confining action of GFRP sheet decreases with increasing the thickness of GFRP sheet. A method to determine the areas of effectively confined concrete and ineffectively confined concrete on the rectangular column section is presented. The compressive stress-strain relationship of concrete confined by GFRP sheet is proposed. A comparison between the experimental results and those of analytical results indicates that the proposed model provides satisfactory predictions of ul...