International Concrete Abstracts Portal

The lattice model provides equivalent continuum formulations for a variety of constitutive equations. In this study, the Compression Field Theory (1) developed by Vecchio and Collins is re-formulated in the form of an equivalent lattice model and developed further for cyclic loading, beyond the scope of the original model. The RC column experiments of UCSD (2) are then analyzed by the method, for which the equivalent lattice model shows acceptable agreement with the experiments. It is noted that shear failure during cyclic loading after yielding of the flexural reinforcement is captured by the method, which is a characteristic feature of this numerical simulation.

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.

Finite element analyses were conducted of as-built and seismically retrofitted RC bridge columns tested at UCSD. The as-built columns were provided with the same rectangular cross section and shear reinforcement, resulting in approximately the same shear capacity, but were designed to fail at different levels of ductility in either a brittle or flexural shear failure. This was accomplished by adjusting the shear force demand by varying the column height (or aspect ratio) and the grade of longitudinal reinforcement. In the analysis the challenge was to capture the overall force-deformation hysteretic behavior and failure mechanism, as well as the individual deformation components of flexure and shear. The analysis focuses on the shear behavior of concrete under large tensile strains and calibrates the shear stress capacity to the concrete component of the UCSD shear model, which reduces as a function of curvature ductility at the critical section. Also, the shear modulus is reduced in proportion to the ratio of cracked to gross flexural stiffness. The results show that a relatively simple design oriented shear capacity model can be used to calibrate the required shear parameters of the 3-D plasticity concrete model. In the paper, detailed finite element analyses are conducted to assess the shear force capacity and post-peak deformation response of shear dominated RC bridge columns.

The paper presents the UCSD reinforced concrete shear columns, and measured test results, which participants have been invited to model as part of a benchmark analysis. Both as-built and seismically retrofitted column results are presented. The columns were l/3-scale, rectangular bridge columns that were loaded in double bending which produces twice the shear force demand of an equivalent cantilever column. While the shear force capacity of the as-built columns was essentially the same, the shear force demand was different for each of the columns due to the use of Grade 40 and Grade 60 vertical steel and due to the different column heights. This resulted in one column failing in a brittle shear manner prior to reaching nominal moment and ductility 1, another failing at displacement ductility 1.5 and the third failing at displacement ductility 3. The challenges to the participants of the benchmark analysis are to capture the peak shear force at failure and post-peak force-deformation behavior for the three as-built columns. In the paper a discussion is presented regarding difficulties with modeling and testing reinforced concrete structures.

This paper deals with the analysis of reinforced concrete structures subjected to seismic loading. The expressions of two constitutive relations based on damage mechanics are exposed. Physical behavior such as crack closure and frictional sliding are introduced at the local level and their influences towards structural computations (global damping) are exemplified by comparisons with experimental data.