Page - 1047 - in Book of Full Papers - Symposium Hydro Engineering

the value of strain gauges, used to calculate the local average bond shearing stress and local slippage. However, many test outcomes have shown that the constitutive relation of bond slippage derived from above tests cannot demonstrate satisfying law because the material components of concrete and the cracks caused during tests were randomly distributed. Furthermore, when the strain gauges were adopted for measurement, there would be certain difference between the strain values read from the strain gauges at the measurement points and the actual strain values because of the limit on measurement gauge length [5,6]. Therefore, we should find a brand-new measurement method which can accurately measure the overall deformation of FRP plate. DIC (digital image correlation) was put forward by one Japanese scholar- Yamaguchi [7] and two American scholars-Prof. Peters and Prof. Ranson [8] independently in the 1980s. The research thought of Yamaguchi [7] was to adopt laser beam to irradiate to object surface to form speckles and to measure the peak value of relevant function of light strength before and after the object was deformed. In the meanwhile, he derived the object displacement based on relevant theories, thus achieving the real-time measurement of small deformation in small regions. Prof. Peters and Prof. Ranson [8] used computers and image scanning devices to acquire the speckle diagram before and after the object was deformed. In addition, they found out the extreme value of correlation coefficient through iterative algorithm on the grey field before and after the object was deformed, thus obtaining the displacement field and stress strain field inside the closed regions and then acquiring the deformation field through boundary integral equation. This experiment measures the surface deformation of FRP plate with the assistance of relevant advanced digital image technologies and can overcome some limitations of above tests quite well, thus eliminating some disadvantages of strain gauges. Besides, this experiment analyzes the stress transmission in different de-bonding stages through careful observations of FRP-concrete de- bonding process, thus establishing the de-bonding law of FRP-concrete interface and providing technical instructions for the disposal of FRP-concrete bonding interface in real hazard elimination and reinforcement projects. 2. DIRECT SHEAR BETWEEN FRP - CONCRETE BONDING INTERFACE BASED ON DIC 2.1. EXPERIMENTAL APPARATUS All tests are conducted on equipment which is autonomously designed and manufactured. This equipment consists of following parts: upper baseboard with four holes, lower baseboard with eight holes, four pieces of steel bars with screw- thread, two pieces of baffles welded with small steel bars (as clamping chuck for lower pull head connection testing machine), upper pull head and fixture. 2.2. SPECIMENS (1) concrete sample 1047