Advanced three-dimensional analysis of concrete structures using nonlinear truss models

Abstract

A three-dimensional truss-based simulation of reinforced concrete is presented in this study. The truss model has been implemented to simulate the response of columns under compression, shallow beams under bending, and deep beams under shear. The concrete truss elements are modeled based on advanced constitutive equations that account for confinement dependent hardening followed by softening. The reinforcing steel is modeled as an elastoplastic material, while the steel-concrete interface is modeled as one of perfect bonding. A computer program with an elaborate graphical interface was developed to implement this model. The program includes a three-dimensional mesh generation, a pre- and post-processing interface, and a computational component that implements a non-linear iterative finite element solution. The computational advantages, as well as the challenges of this approach are discussed. The model has been calibrated based on an extensive set of published experiments, which range in geometry, material parameters, loading, and levels of reinforcement. The validation of the truss model based on multiple experiments is followed by detailed observation on the progressive failure patterns that allow for improved insight of the mechanisms that eventually lead to the failure of columns, shallow beams and deep beams. This analysis verifies some well-established trends of ductility, strength, and failure pattern development. It also sheds new light on the limits of the contributions of transverse reinforcement to the strength and ductility of reinforced concrete elements. In conclusion, the model presented in this study is a useful research and design tool which enables the detailed analysis of reinforced concrete elements, where issues of strength, ductility, and progressive failure patterns can be examined.