Behavior Of Composite Column Section Subjected To Axial And Torsional Loads

Abstract

This paper presents the behavior and performance of composite column subjected to axial load with torsion. Torsion failure is an undesirable brittle form of failure which should be avoided specially in the earthquake prone areas. Torsion in buildings during earthquake shaking may be caused from non-symmetrical distribution of mass and stiffness. So for un-symmetrical building it is necessary to design the beam and column for torsional moment. In order to achieve the goal of study, a parametric investigation procedure is undertaken, on a series of sample column with different section of steel tube as circular, rectangular, square and encased I-section steel with and without providing longitudinal reinforcement. The material quality used for all composite column are of the same grade. Each composite column is made to be subjected to 0.4, 0.5 and 0.6 of its ultimate axial capacity with a constant Torsion of about 60 KN-m. In this work, four specimens of composite column(rectangular ,square circular composite column) is taken for analysis with making bottom end restrained against all degrees of freedom and the top end is restrained in two direction and free in direction of load. In this study behavior of composite column conceived as dependant variable and type and magnitude of load as independent variable. The analysis is performed by finite element method using the software package Abaqus. A three dimensional model is defined using solid elements for both materials and paying special attention to the steel to concrete contact. Nonlinear behavior of steel and concrete is taken into account steel rigid plate is placed at the top and bottom of each composite column. Concentrated load and Torsion is applied on steel rigid plate placed at the top along y-direction. The FEM output was then examined to determine the effect of different levels of axial loads on behavior of columns under torsion loading. Assessing and identifying the high stress and strain zones as the axial load is applied with and without torsion and evaluating the effects of the level of axial load on deflection/compression, rotation and twisting of the column by keeping torsion constant while axial load applied is increasing. The finite element analysis results demonstrate that the encased composite columns reached the highest rotation/Twisting among column specimens due to the encased steel while concrete filled circular composite column shows lower rotation and twisting under torsion. Moreover, the elastic flexural stiffness as well as ductility decreases significantly with an increase in the axial loads level under constant torsion.