Experimental And Numerical Investigations on Axial-Flexural Behavior of Steel-Concrete Composite Column

Abstract

However, very limited Experimental studies were carried out for CFST columns with square and rectangular cross=section. Through, A few numerical studies using Finite Element Analysis (FEA) have been conducted for CFST columns with rectangular crosssections considering capital investment, time, and effort required for experimental investigations. A Concrete Filled Steel Tube (CFST) composite column in which a Hollow Steel Tube (HST) is filled with concrete that can support heavy loads. Experimental Studies coroneted have shown that the CFST column outperforms the HST column in terms of strength, deformation, and stiffness. This benefit results from the confinement of the outer steel tube due to the yielding of infilled concrete that delays buckling. These days, CFST columns are frequently used in the construction of tall buildings, bridges, large industrial structures, and deep foundations. Extensive experimental and numerical investigations have been carried out on CFST columns under purely axial compression loading while axial-flexural behaviour studies are relatively lower. Various design codes such as EC-4, ACI-381-05, AISC-360-2010, and AIJ-2001 provide detailed guidelines for designing CFST columns under axial compression and axial-flexural loading. Euro code guidelines, EC-4 provides strength estimation of CFST column utilizing a plastic method with simplified four-point based P-M intersection curve. Note that, EC-4 considers the confinement effect for a circular cross-section of the CFST column only and not for a rectangular cross-section. Additionally, it also enforces strength criteria of confinement effect consideration, i.e. eccentricity to the diameter of outer tube ratio (e/D) should be less than or equal to 1 for CFST column with circular cross-section. Therefore, there is a need to study the axial-flexural behavior of CFST columns with different cross-sections under axial-flexural loading. The major objective of the present study is to study the axial-flexural behavior of CFST column experimentally for Circular and square cross-sections. It has been found from the literature review that most experimental investigations on CFST columns were conducted on circular cross-sections and mostly compression loading with uniaxial moments. The present study considers CFST columns of circular and square cross-sections with compression loading applied bi-axially, i.e. axial compression loading with with bi-axial moment. HST columns under purely axial compression loading have been tested for comparison. A total of 14 nos. of column test specimens comprising CFST column test specimens (04 nos.), CFST beam-column test specimens (08 nos.), and HST column test specimens (02 nos.) have been fabricated and tested through a loading frame. Each specimen was instrumented with strain gauges, displacement sensors, and load sensors to measure physical parameters; strain, displacement, and load. The Finite Element (FE) model of the CFST column of circular and square cross-section and HST column has been developed using commercial FE-based software ABAQUS (CAE 2020). Mechanical properties of concrete and steel obtained through the experimental program were used as input to evaluate the strength of the CFST column, CFST beam-column, and HST column test specimen. Comparison of parameters, ultimate load, axial displacement, lateral displacement, strain, and confinement factor was carried out for experimental and numerical results of all test specimens. It was observed that the CFST column with circular and square cross-sections yields 1.392 % and 1.597 % higher peak axial load vis-a-vis the HST column. The peak axial load of the circular CFST column is 1.386 % higher on compared to square CFST columns. While the square CFST column test specimen failed by local buckling, the circular CFST column test specimen failed by global buckling. Square CFST column and beam-column test specimen exhibit the presence of confinement of the order of 2.61 %.