SP-205 Nonlinear finite element analysis (NLFEA) of reinforced concrete is close to being a practical tool for everyday use by design engineers. The first in this collection of 18 papers takes a critical look at the accuracy of this analysis procedure, then identifies and discusses reasons for caution in applying nonlinear analysis methods. Subsequent papers cover topics that include: * Seismic behavior predictions of structures; * Three-dimensional cyclic analysis of compressive diagonal shear failure; * Finite element analysis of shear columns; and * Simulation strategies to predict seismic response of reinforced concrete structures. Designers and researchers who use NLFEA models and procedures for reinforced concrete must be experienced and cautious. The papers in this volume will enable the users to better understand modeling, analysis, and interpretation of results.

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.

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.

A computationally efftcient procedure is presented for analyzing the performance of reinforced concrete structures under cyclic loading. A rigid-body-spring network is used as a basis of a material representation. Concrete is modeled as an assemblage of discrete particles interconnected along their boundaries through flexible interfaces. Random geometry is introduced using Voronoi diagrams in order to reduce mesh bias on crack propagation. Rather than averaging the effects of reinforcing over a regional material volume, rein-forcing bars are explicitly modeled using line elements with nonlinear linkage springs. The spring network has the advantage to model material discontinuities and provides realistic predictions of concrete cracking. The network performance is demonstrated through analyses of reinforced concrete columns under cyclic loading. Numerical results reasonably agree with experimental observations in terms of load carrying capacity and crack propagation. Deterioration of load carrying capacity due to shear failure after or before yielding of main reinforcing steel is discussed through the numerical predictions.

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.