International Concrete Abstracts Portal

The load-deformation response of R/C membrane elements (panels) subjected to reversed cyclic shear showed that the orientation of the steel bars with respect to the principal coordinate of the applied stresses has a strong effect on the pinching effect in the post-yield hysteretic loops. When the steel bars were oriented in the directions of the applied principal stresses, there was no pinching effect. When the steel bars were oriented at an angle of 45’ to the applied principal stresses, there was severe pinching effect. It was obvious that the pinching effect is caused by the orientation of the steel bars, rather than the bond slips between the steel bars and the concrete as surmised by many researchers. A non-linear analytical model capable of describing this pinching behavior is presented in this paper. The model is actually an extension of the fixed-angle softened truss model (FA-STM) proposed by Hsu and his colleagues for monotonic loading. The extension of FA-STM for application to reversed cyclic loading requires new constitutive models for concrete and steel in the unloading and reloading ranges. This rational theory satisfies Navier’s three principles of the mechanics of materials: equilibrium, compatibility and constitutive relationships of materials. The validity of this theory is illustrated by comparing the behavior of three panels with three different steel bar angles. The predicted cyclic behavior compared well with the experimental behavior, except in the descending branch.

A stress hybrid element that incorporates an internal displacement dis-continuity is presented for the modeling of concrete fracture. This stress hybrid formulation is superior to similar stiffness-based embedded crack formulations in that it explicitly accounts for boundary tractions so that the equilibrium of the traction fields at the element boundary and the internal crack interface can be enforced in a consistent manner. As a consequence, it also allows for the modeling of crack initiation in an accurate and consistent manner. Numerical examples are provided to compare the performance of the new element to that of a smeared crack model and to demonstrate its superiority in capturing the sliding shear behavior of fractured concrete. The element achieves the realism of the discrete crack approach without the need for remeshing or knowing the location and orientation of a crack a priori.

As a structural material, reinforced concrete requires bond between plain concrete and reinforcing steel. Accurate numerical modeling of structures that exhibit severe bond-stress demand requires explicit representation of bond-zone response. A bond element is presented for use in high-resolution finite element modeling of reinforced concrete structures subjected to general loading. The model is defined by a bond stress versus slip relationship and a relationship between maximum bond strength and the concrete and steel stress-strain state. A finite element implementation of the model is proposed that enables a one-or two-dimensional representation of bond-zone action. Non-local modeling is used to incorporate the dependence of bond strength on the concrete and steel material state. Comparisons of simulated and observed response for systems with uniform and variable bond-zone conditions are presented.

The buckling of reinforcing bars is investigated analytically and several indices which characterize the buckling behavior are introduced based on the analytical results. In this paper, buckling analysis of the reinforcing bars is performed by the finite element method using large deflection theory of layered beam elements. The buckling behavior is considered under monotonic and cyclic loading. Based on the analytical results, several indices such as the buckling stress, the residual stress and the buckling mode are used to characterize the buckling behavior. Considering these results, a stress-average strain relationship of the reinforcing bars is developed accounting for inelastic buckling. The model features a post-buckling softening branch, since the buckling behavior is considered in the form of a material property, which is an easy method to introduce the effect of buckling in the finite element method.

In this paper, numerical simulations were carried out to examine the performance of constitutive models for describing the cracking behavior and the load-displacement characteristics of shear failure of concrete structures. The problem of shear failure of RC beams was employed as a practical application of numerical modeling. Concrete deep beams without web reinforcement, in different shear-span ratios (0.5 to 1.5), were analyzed. In addition, in order to expand the comprehension on the effect of constitutive model parameters in the deep beams to slender beams, the beams in the shear-span ratio of 4.0 were numerically simulated. The structural analysis was carried out by means of the nonlinear finite element method. A smeared crack approach using a rotating crack model without shear strain on the crack plane was employed. Based on this analytical work, the effect of the compressive strength reduction after cracking and the post-peak ductility in the compressive constitutive law on shear fracture behavior for different shear-span ratios was discussed. Furthermore, the sensitivity of numerical results to the tensile constitutive laws was investigated.