International Concrete Abstracts Portal

A critical look is taken at the state-of-the-art in nonlinear finite element analysis of reinforced concrete structures. In examining the results of recent prediction competitions, the accuracy of such analysis procedures is gauged. Reasons for caution when applying nonlinear analysis methods are then identified and discussed. Finally, the results of a test program involving shear critical beams are presented in support of the contention that the behaviour of reinforced concrete is still not well understood. The tests represent a good challenge for validating current procedures.

This paper addresses a three-dimensional finite element analysis of compressive shear failure. Results are presented for the specific case of concrete column tested at the University of California, San Diego. The numerical analysis is carried out with the special purpose finite element code MASA (A FE code based on the microplane material model and smeared crack concept). The model of the reinforced concrete column is first loaded by a normal compressive force and is subsequently loaded by shear loads with monotonic and cyclic load histories. It is demonstrated that a three-dimensional, local continuum, finite element analysis based on the smeared crack concept is able to capture relatively complex diagonal shear failure mechanisms. Moreover, a parametric study is carried out which investigates the influence of the concrete fracture energy on the column response. Fracture energy was observed to significantly influence ductility, ultimate load capacity and resistance to the cyclic loading. Reasonably good agreement between the numerical and experimental results is shown.

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.

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.

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.