International Concrete Abstracts Portal

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.

The shear failure of a reinforced concrete beam and a column without stirrups is known to have substantial scale effect. In other words, softening characteristics of concrete play a dominant role in its pre- and post-peak behavior. The post-peak static behavior of reinforced concrete members are directly related to the dynamic post-peak behavior of reinforced concrete structures or the extent of energy absorbing capacity of a member and consequently to the safety margin to be allocated in a beam or a column in seismic design. It become more so when a structure fail in snap-back instability allowing more energy to come in a structure to be converted to dynamic energy passing the peak loading capacity. The numerical difficulty encountered to capture snap-back is itself a good challenging target. The snap-back instability is explained for the case of uniaxial tension, and the shear characteristics of reinforced concrete beams with snap-back are examined by changing the beam dimensions and the span over depth ratio.

The Modified Compression Field Theory (MCFT), developed over the last 20 years at the University of Toronto, is a general method for the analysis of reinforced concrete elements subjected to shear. Implementations of the MCFT range from simple hand techniques in the AASHTO code through computer based sectional analysis methods to nonlinear finite element analysis procedures. In this paper the MCFT is briefly explained and used to calculate the behavior of six University of California, San Diego Columns. The results indicate conservative modeling from the AASHTO code. The sectional model Response-2000 was able to model the behavior of the steel jacketed columns well, but was quite conservative for the columns without jackets. The finite element program TRIX97 did a good job of modeling the behavior of all the columns, though the displacement at failure was underestimated.

The objective of the present study is to examine the performance of the proposed approach in simulating monotonic and cyclic behaviors of shear-dominated RC columns. The macro-element model is formulated on the basis that the total deformation of the RC column can be decomposed into flexural and shear components. The flexural behavior is simulated by the layered element model, and the shear behavior is simulated by the so-called shear element model. The shear element model is a single plane stress RC element which is developed on the basis of the smeared reinforcement and smeared rotating crack concept. Then, the total model is formulated by coupling these two models in series. Three shear-dominated RC column specimens, tested at the University of California at San Diego, are analyzed under monotonic and cyclic loading. It is shown that the proposed model can reproduce the monotonic and cyclic response behavior reasonably well.