Page - 1051 - in Book of Full Papers - Symposium Hydro Engineering

specimen SS-110, its extreme bearing capacity of interface is highest, which can also be attributed to above reason. (3) Strain distribution of FRP plates surface Ali-Ahmad [10] and his fellows pointed out that when the test of bonding performance of FRP-concrete was conducted, the FRP plate remains in the elastic range and the strain distribution of FRP plate surface can reflect the strain distribution of FRP-concrete bonding surface quite well. Analyze the data collected by DIC and select the strain distribution of FRP plate alongside the plate length direction of specimen SS-100 and SS-150 at different load time (which means different load stages)-20%, 40%, 80% and 100% of extreme load. （a）SS-100 specimen （b）SS-150 specimen Fig. 5 The strain of FRP plate in different loading moments We can see from Fig. 5 as follows: (1) During the stage of 20% to 40% of extreme load, the strain increases obviously except for the region within 40mm from the load end. There is not much increment in strain at other positions on the FRP plate. So we can conclude that the effective bonding length of FRP-concrete is about 100mm or slightly lower than 100mm; (2) With the external load continues to increase, the overall strain of FRP plate increases and the free end begins to transmit shearing strain stress towards the concrete surface. However, the strain value is relatively smaller compared to other parts. (3) With the load increases, the strain keeps increasing while the position of peak value of strain moves forward little by little, which indicates that the FRP at original positions of peak value of strain starts de-bonding away from the concrete surface gradually until the external load reaches the maximum shearing stress which the FRP plate and concrete can withstand. When there is no subsequent FRP plate sharing this external load at the free end, the de-bonding failure happens to the specimen. Collect the strain distribution of each specimen at extreme load as shown in Fig. 6. 1051