Numerical Simulation of Compressive Failure Behaviors of Concrete-Filled Steel Tube Using Coupled Discrete Model and Shell Finite Element

Abstract

After the Great Hanshin earthquake in 1995, a large number of existing concrete structures were retrofitted by steel jacketing method in order to adjust in the increased design loads. In addition, the assessment of safety against excessive load and restorability performance is becoming increasingly important in Japan. In order to assess the above performance reasonably, an accurate evaluation method for strength, deformation capacity, and localized damage distributions of retrofitted concrete structures is required. This study presents the development of a tool that allows the prediction of strength and deformation, including softening and localized failure behaviors of concrete structures retrofitted by steel jacket. In the proposed method, concrete is modeled using three-dimensional Rigid-Body-Spring Model (RBSM) which represents concrete as an assemblage of rigid particles interconnected by normal and shear springs. The random geometry of concrete particles is discretized using Voronoi diagram. Constitutive models introduced by authors in their past studies were utilized which were proven effective in simulating cracking and localized failure behaviors of concrete material and reinforced concrete members. The steel tube, on the other hand, is modeled using finite shell element based on degenerated shell concept that allows large displacement-large rotation effects. Interaction between RBSM and shell is provided by zero-length interface elements which consist of normal and shear springs. The normal spring is limited to compression while a Mohr-Coulomb model is utilized for shear interface which represents frictional behavior. The accuracy of the proposed model was validated against published experimental results of concrete-filled steel tube under uni-axial compression. Results of the validations confirmed the capability of proposed model to provide a qualitative measure of damage as well as a reasonable prediction of strength.