Theoretical And Experimental Study On Bond Stress-Slip Relationship Between Ribbed Bar And Concrete

The bond performance of reinforcing bars in concrete is a key factor affecting the bearing capacity, ductility and the servicebility of reinforced concrete structures. The bond stress-slip constitutive relationship is also regarded as a requisite parameter for theoretical and numerical analysis of reinforced concrete structures. In this thesis, firstly the local bond stress-slip relationship between concrete and reinforcing steel bar is derived based on the energy conservation law. Then the pull-out tests are carried out to investigate the magnitude of pressure created by wedging action between concrete and the ribbed bar for the case of splitting bond failure. The principal contents and findings of the work are summarized as follows:(1) The process of splitting model of the bond failure is divided into the elastic stage before cracking and the cracked stage. The thick-walled cylinder model is used for the initially elastic stage, while the cracked thick-walled cylinder model with softening behavior of concrete is applied to the latter cracked stage. The energy equations of the two models are constructed respectively and the characteristic of energy varying during the process of concrete splitting is discussed. Based on the energy conservation law, the differential equation accounting for the bond stress-slip relationship is derived, which is used to obtain the local bond stress-slip relationship by numerical integration. The model shows a good agreement with the available experimental results and accounts for the parameters of concrete and steel, which influence the local bond stress-slip response as observed in the experiment. Finally, the theoretical and the experimental results are compared and analyzed.(2) Experimental study is carried out to investigate the magnitude of pressure created by wedging action on steel in reinforced concrete that would cause surface cracking of the concrete cover. The pull-out tests were specially designed and performed with a total of six specimens. In the specimen, along the anchorage length of steel bar two inner-embedded load transducers are arranged at different positions to measure the cracking resistance of cover. The test results indicate that the bond stress is proportional to the cracking resistance of cover and the distribution of bond stress along the anchorage length is influenced by the thickness of concrete cover. Based on the test results, realistic ranges of the effective rib face angle are proposed. The maximum pressure products on steel, which is obtained by using the cracked thick-wall cylinder model with consideration of the softening behavior of concrete is found to be in good agreement with the test results.