Nonlinear Finite Element Analysis Of Reinforced Concrete Members With Bond-Slip Effect

Nonlinear finite element analysis of RC(Reinforced Concrete) structures with bond-slip effect is one of the significant research topics all the time. Although in recent years, with improvements in testing technology and finite element analytic methodology, both the experimentation and analytic modeling of bond-slip have got significant development, it is still very difficult to unveil the bond-slip mechanism by more careful measurements in experiemnts on finer-scale level. As a result, there is still a long way to go to simulate the response of the structures considering bond-slip effect both on global and local level, due to the complexity of the problem itself.This paper focuses on 2D nonlinear finite element analysis of RC structure with bond-slip effect under monotonic loading, on the basis of open software platform, FEAPpv(Finite Element Analysis Program Personal Version). Two-node truss element, four-node RC rectangular element and two-node link element are added in by making use of user defined elements. In the meantime, constitutive models of concrete,steel and bond-slip are also implemented. By inserting the link element between the common nodes of concrete element and steel element, effect of bond-slip on the interface of concrete and steel can be taken into account. Isolated finite element model is used to form the global stiffness matrix and restoring force vector.Analytical simulations on both pull-out specimens and simply supported RC beams have shown that satisfactory agreement with that of experiments has been achieved both on the global and local levels, which also lays foundation for future research.The major achievements are summerized as follows:①Nonlinear finite element analytical model of RC element considering bond-slip effect is established in chapter two, on the basis of available experimental data and analytical methodology by reference review.②User defined four-node rectangular RC element, two-node truss element and bond-slip link element are added in the software platform FEAPpv, using Fortran language to form the subroutine module.③Concrete, steel and bond-slip constitutive models are added in the platform FEAPpv by adopting user defined materials module.④The link element is inserted on the interface of reinforced steel and concrete.On the basis of the relative displacement between the pairing nodes, the element tangential stiffness ( K t) and restoring force are formed by calling the bond-slip constitutive model. The radial stiffness is assigned a large value of 100×K_t to suppress the radial displacement of the steel element.⑤In the program, the pairing concrete and steel nodes have a relative displacement when effect of bond-slip is taken into consideration. At this time, the isolated finite element analytical model is adopted. When bond is assumed perfect, the pairing concrete and steel nodes have the same displacements, at this time, composite finite element analytical model is chosen.⑥The pull-out test specimens under monotonic loading,carried out by Xu Youlin,are simulated.⑦Simply supported RC beams under monotonic loading are simluated.The major conclusions in this paper are as follows:①By adopting the models in this paper, pull out specimens by Xu Youlin are successfully simulated.The analytical global load-slip response agrees well with that from the experiments. In the meantime, the local response of the elemental stress and strain, together with the slip along anchorage length of the rebar are described, from which the gradual transfer of elemental stress and slip from the loading point to the free end can be clearly observed.②Simply supported beams both assuming perfect bond and considering bond slip are analysized respectively. From the load-displacement curve obtained by the analysis, before concrete cracks, the stiffness hardly degrades and the influence of bond-slip cannot be significantly observed at the initial stages of loading. At the later stages of loading, degradation of the stiffness is becoming obvious because of the gradual infiltration of the bond breakage. From the load-displacement curve, it is observed that as far as the bond-slip is considered, the load capacity declines compared with that when bond is perfect, which means that the bond-slip has a greater influence on the later stages in load-displacement curve. The analytical results agrees with the testing results.