Modeling of Concrete for Nonlinear Analysis using Finite Element Code ABAQUS

Abstract

ABSTRACT Concrete is the main constituent material in many structures. The behavior of concrete is nonlinear and complex. Increasing use of computer based methods for designing and simulation have also increased the urge for the exact solution of the problems. This leads to difficulties in simulation and modeling of concrete structures. A good approach is to use the general purpose finite element software ABAQUS. In this paper a 3D model of a concrete cube is prepared using smeared crack model and concrete damage plasticity approach. The validation of the model to the desired behavior under monotonic loading is then discussed. Keywords Finite element, ABAQUS, smeared cracking, concrete damage plasticity, tension stiffening. 1. ultimate INTRODUCTION Since 1970, analyses of reinforced concrete structures using finite element method, have witnessed a remarkable advancement. Many researchers have made valuable contributions in understanding the behavior of concrete and have developed sophisticated methods of analysis. These achievements are well documented and available in various reports and technical papers but still there are many areas in which much remains to be understood and researched. The past decade with the advancement in computing techniques and the computational capabilities of the high end computers has led to a better study of the behavior of concrete. However the complex behavior of concrete sets some limitations in implementing FEM. The complexity is mainly due to non-linear stress-strain relation of the concrete under multi-axial stress conditions, strain softening and anisotropic stiffness reduction, progressive cracking caused by tensile stresses and strains, bond between concrete and reinforcement, aggregation interlocks and dowel action of reinforcement, time dependant behavior as creep and shrinkage [1]. Several researchers have documented about nonlinear analysis of reinforced concrete and prestressed concrete structures. For nonlinear analysis many commercial software are available, such as ANSYS, ABAQUS, NASTARAN, and ADINA. All these softwares are not tailor made applications which can work automatically on just feeding few data and the requirements. An acceptable analysis of any structure as a whole or a part there in, using Finite element software, and the correctness of it totally depends on the input values, especially the material properties used. However when one is working with concrete a sound technical background is required to use them in a proper manner and get the desired results. Concrete used in common engineering structures, basically is a composite material, produced using cement, aggregate and water. Sometimes, as per need some chemicals and mineral admixtures are also added. Experimental tests show that concrete behaves in a highly nonlinear manner in uniaxial compression. Figure.1 shows a typical stress-strain relationship subjected to uniaxial compression. This stress-strain curve is linearly elastic up to 30% of the maximum compressive strength. Above this point tie curve increases gradually up to about 70-90% of the maximum compressive strength. Eventually it reaches the pick value which is the maximum compressive strength