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Home > Publications > International Concrete Abstracts Portal
The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.
Showing 1-10 of 19 Abstracts search results
January 1, 2002
Dilatational Response of Concrete
Materials: Facts and Fiction
Confinement is the key to the performance of reinforced concrete structures when ductility demands are of primary interest. Hence dilatancy and restraining effects are critical for the behavior of reinforced concrete under seismic environments. In fact, restrained dilatancy is the determinant factor ensuring strength and ductility of reinforced concrete members in compression. In this paper, the issue of the dilatancy of concrete at different levels of active confinement is revisited. Experimental observations on 150x300 mm concrete cylinders, which were recently tested in a large capacity triaxial chamber, are presented. For the analysis of the dilatancy data, the elastoplastic concrete model known as the Extended Leon Model is applied. The study is focused on the volumetric behavior of concrete, which in plasticity terminlogy refers to inelastic dilatancy and the concomitant issue of normality. In particular, the test data is examined within the framework of the non-associated flow theory of plasticity. In this context, the origin of discontinuous failure mechanisms in the high confinement regime is questioned, where inelastic dilatancy together with the loss of axisymmetry are the primary reasons for localized failure in the form of discontinuous faulting.
When designing concrete structures, fatigue related problems are not among the first that come to mind. However, structures subjected to strong cyclic loads such as those associated with destructive earthquakes experience strength and stiffness degradation that are most aptly described as a low-cycle fatigue phenomenon and are related to the damage accumulated under such loading. This paper briefly discusses the various elements of a rational, i.e. mechanics-based design methodology. Results of an experimental test program are summarized, in which 4-inch cubes with or without fiber reinforcement are subjected to uni- and biaxial cyclic compression until failure. The review concludes with a brief review of the various aspects of material behavior that need to be modeled, if the response of reinforced concrete members is to be simulated numerically.
B. Spencer and P. B. Shing
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.
M. Y. Mansour, T. T. C. Hsu, and J. Y. lee
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.
H. Nakamura and T. Higai
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.
L. N. Lowes
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.
T. Tanabe and A. ltoh
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.
Y. Kaneko and H. Mihashi
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.
T.-S. Han, S. 1. Billington, and A. R. lngraffea
Seismic analyses of reinforced concrete structures are performed using the finite element method. A shake table test of a lightly reinforced concrete three story frame building and a shake table test of a seismically designed shear wall are simulated. The effects of modeling boundary conditions and of considering the initial micro-cracking of concrete on natural frequency change are investigated. These parameters are used to calibrate finite element models to experimental models. The simulations predict the overall seismic behavior of reinforced concrete structures. However, the analyses of both structures showed that accuracy of material degradation is lacking and the computational efficiency of such models needs improvement for large-scale seismic analyses.
N. Shirai, K. Moriizumi, and K. Terasawa
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.
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