A Measure Method Research Of Peeling Stress In Concrete Cover Of Mid-span Of FRP Strengthening RC Beams

While using fiber-reinforced polymer (FRP) to strengthen reinforced concrete (RC) beams for increasing flexural capacity, peeling failure may happen in the concrete cover of beam ends and mid-span. The peeling failure makes the load carrying capacity and ductility of the strengthened beams to decrease significantly. As a result, peeling-failure-study has become a hot spot in the structural repair field of the world. Peeling failure of beam ends has only been researched because of the complexity of the problem. This thesis then tried to develop a test method, which may not only simplify the experimental procedure but also approach the practical loading conditions for testing peeling stress in concrete cover of mid-span of FRP strengthening (RC) beams.Base on gluing the experiment research methods of the bond between reinforcing bar and concrete, as well as the bond between FRP and concrete, the calculation method for predicting the bond stress between FRP and concrete, this thesis tries to develop a new thought to simulate the working state of FRP and concrete interface in mid-span of FRP strengthening RC beam. A beam segment between two cracks in mid-span of a FRP strengthening RC beam was taken as the research object. A shallow to deep research strategy was planned to close to the practical loading conditions of the beam segment gradually. A three stage (with five groups of specimens) experimental research, namely FRP and concrete interface, FRP and RC interface (reinforcing bar wasn't been loaded), FRP and RC (FRP and reinforcing bar were loaded step by step) was performed. A special fit was designed and made for realizing the step by step load-procedure. After a detailed exploring and experimental research, it was indicated that this kind of experimental method not only approaches the practical loading conditions but also greatly simplifies the experimental procedure, and is suitable for an experimental research with a large number of specimens.At last some suggestions and outlook for experimental research in the future are put forward base on the problems encountered in this research.