Experimental Study And Numerical Simulation Of Bond Behavior Of High-strength Prestressed Reinforcement

Prestressed concrete structures with the high-strength, good-ductility and high-quality prestressed reinforcement as reinforcing bars become an inevitable trend of development of modem buildings with long-span, heavy-load and fine-structure performance. In recent years, round steel bar, deformed steel bar and helical rib steel wire for prestressed concrete are new kinds of high strength prestressed reinforcement. With the improvement of prestressed reinforcements strength and variation of surface configuration of rebar, and necessarily considering bond decay in earthquake-resistant design, problems of bond anchorage between reinforcement and concrete are getting increasingly stringent. In this paper, the bond anchorage behaviours of round steel bar, deformed steel bar and helical rib steel wire are investigated by experimental research, theoretical analysis and numerical simulation. The major contributions are summarized as follows:1. The pullout specimens of 6 different surface configurations of reinforcements are tested under monotonic loading. The whole processes of bond failure with various reinforcements are studied. The differences of bond behaviour between various surface configurations of reinforcements and concrete are analyzed. The main influences on bond anchorage performance are discussed as well. Based on the experimental results, the equation to analyze bond strength for new types of helical high-strength prestressed reinforcement is derived. The analytical results agree well with the test results.2. The pullout tests on 4 kinds of high-strength prestressed reinforcements are studied under a long anchorage length condition. The bond behaviours between various surface configurations of reinforcements and concrete are compared. The different influences on bond anchorage performance are analyzed. Based on the experimental studies, the suggested anchorage lengths of helical rib steel wire and deformed steel bar are given by reliability analysis, which can provide references for engineering design and so that the anchorage lengths could be reduced from 5d to 20d than those of Code for design of concrete structures.3. Due to defonned steel bar and helical rib steel wire with the unique helical surface configuration, the obvious rotational phenomena appear during the pullout processes. The bond mechanisms between the helical prestressed reinforcements and concrete can be explained by analyzing the rotational phenomena.4. The pullout specimens of round steel bar, deformed steel bar and helical rib steel wire are tested under repeated loadings. The differences of bond failure between 3 various surface configurations of prestressed reinforcements and concrete are compared. The relationships between characteristic loads and maximum values of stress levels are obtained under constant amplitude repeated loading.5. According to the space axisymmetric method, the whole process of bond failure between reinforcement and concrete is simulated. The basic mechanical properties of reinforcement and concrete are determined by the tests. The simulation uses the FEM mixed method for elastic contact problems, and introduces the no-thickness contact computation model. The numerical calculation results agree well with the experimental results. Meanwhile, the distribution situations of bond stresses along the interface between reinforcement and concrete are obtained by using the mathematic model.