Bond Performance Of Reinforcement In Concrete Subjected To Complex Lateral Pressure

The satisfactory use of reinforced concrete as a composite material in structures depends mainly on the fine bond action between reinforcing bars and concrete. The bond of reinforcing bars in concrete is a key factor affecting both the bearing capacity and the usability of reinforcing concrete structures, and is a requisite parameter for theoretical and numerical analysis of reinforced concrete structures. In real concrete structures, the bond action of reinforcing bars is usually influenced by the lateral confinement from surrounding concrete, and this confinement will exert significant influences on the bond performance. The main objective of this thesis is to study the bond performance of plain round and deformed reinforcing bars on pull-out specimens subjected to uniaxial and biaxial lateral pressures. The different failure modes of the bond specimens are examined and the bond parameters are analyzed with respected to the complex lateral pressure. Then, the bond constitutive relationships for plain round and deformed reinforcing bars are proposed. The main research contents and findings are summarized as follows:(1) The experimental study on plain round bars subjected to complex lateral pressure indicates that its bond mechanism is different before and after the lateral pressure is applied, and the corresponding bond stress-slip curves are also differs. The experimental results show that both the ultimate and the residual bond strength are increased by the increase in lateral pressure, but the residual to ultimate bond strength ratio basically remains constant. The slip at the ultimate bond strength firstly drops with the appearance of lateral pressure and then increases with the increase in lateral pressure. A regression analysis is conducted for the bond parameters with respected to the mean lateral pressure in this thesis. Then, a bond constitutive relation is proposed for plain round bars based on the characteristics of tested bond stress-slip curves, and the results show an agreement between the proposed and the experimental bond stress-slip curves.(2) The stress state at the interface between plain round bars and concrete subjected to complex stress state is analyzed theoretically. By equating the equilibrium of the stresses on a bar element, the analytic solutions for pull-out capacity and the bond strength of plain round bars are derived. The analytical predictions are then compared with the test results, and a parameter analysis is done. (3) The experimental study on deformed bars subjected to complex lateral pressure indicates that the failure mode of bond specimens depends on both the direction and the magnitude of complex lateral pressure. With the increase in complex lateral pressure, the failure mode changes from splitting failure, to splitting-pullout failure and to pullout failure. The variation of bond strength is related to the failure modes and generally increases with the increase in lateral pressure. Through analyzing the test data and combining the failure mode, the ultimate bond strength and the corresponding slip, and the residual strength and the corresponding slip are fitted with respected to the complex lateral pressures.(4) On the basis of the fictitious crack model considering the cohesive stress, a theoretical analysis is conducted for the splitting failure of bond specimens with deformed bars. In this analysis, the crack profile is assumed linear along the fictitious crack and the cracked zone of inner concrete follows an equivalent elastic circumferential deformation. The analytical predictions show a good agreement with the experimental results of both hydraulic pressure tests and bond tests. Subsequently, the whole process of splitting failure of bond specimens is numerically simulated based on the crack propagation criteria and then, the crack extension resistance curve is studied.(5) A suitable mathematical model is adopted for the bond constitutive relationship of deformed bars. With the regression of bond parameters, the present model reproduces the reasonable complete bond stress-slip curves under complex lateral pressure. The bond stress-slip curves are experimentally verified to be path-independent of the lateral complex pressure. As a result, the bond constitutive relations under variable complex lateral pressure can be considered as a superposition of numerous bond constitutive curves under constant complex lateral pressure.