Experimental Study of Square CFST Stub Columns With a Low Steel Ratio Under Axial Loading

Deren Lu,Yongzhi Gong,Chen Luo,Chao Deng,Tao Yuan,Liping Wang,Enhui Ren,Faxing Ding

doi:10.3389/fmats.2021.629819

Abstract

This paper presents an experimental and numerical study on large dimension concrete-filled square low steel ratio steel tubular (CFST) stub columns under axial loading. Four specimens were designed to investigate the effects of steel ratio on the confinement effect of square CFST stub columns with a low steel ratio. ABAQUS was used to establish 3D finite element (FE) models for simulation of square CFST stub columns with a low steel ratio under axial loading. Furthermore, based on the experimental verification, the definition of the confinement index (ϕ = fsAs/(fcAc)) was discussed and the effect of the grade of concrete and steel tube was also investigated. With the same cross-sectional dimensions, the confinement effect of the square CFST stub columns with a low steel ratio (less than 0.05) was better than the others. The stub columns with the yield strength of steel tube fs = 235 MPa (345, 420 MPa) and compressive cubic strength of concrete fcu = 40 MPa (60, 80 MPa) can give fully demonstrate the material performance and reflect the better confinement effect. Based on the experimental results and FE modeling, a practical calculation formula for the ultimate load-carrying capacity of square CFST stub columns with a low steel ratio was proposed. The formula calculation results presented in this paper show good agreement with the experimental results. Compared with the existing formulas, the proposed formula has better precision.

Highlights

Square concrete-filled steel tubular (CFST) columns are widely used in high-rise buildings because of its advantages such as convenient construction of joints, large section moment of inertia, and easy to take fire prevention measures
The results show that the average value of the transverse stress and the yield strength ratio of the circular steel tube at the ultimate load-carrying capacity is 0.55, which did not all play the role of confinement effect; The finite element analysis of the square CFST stub columns subjected to full-section compression was carried out by Ding (Ding et al, 2019)
The results show that the average value of the transverse stress and the yield strength ratio of the square steel tube at the ultimate load-carrying capacity is 0.33, which played a less restrictive role

Summary

INTRODUCTION

Square concrete-filled steel tubular (CFST) columns are widely used in high-rise buildings because of its advantages such as convenient construction of joints, large section moment of inertia, and easy to take fire prevention measures. Considering the improvement effect of bearing capacity and ductility, it can play better material properties that the steel tube with the yield strength of 235 MPa is paired with compressive cubic concrete strength of 60 MPa. Discussion on the Constraint Coefficient of Steel Tube and Concrete The definition of the confinement index (φ fsAs/(fcAc)) was derived from the axial compression test of circular CFST stub columns where only concrete subjected to compression. The results show that the average value of the transverse stress and the yield strength ratio of the circular steel tube at the ultimate load-carrying capacity is 0.55, which did not all play the role of confinement effect; The finite element analysis of the square CFST stub columns subjected to full-section compression was carried out by Ding (Ding et al, 2019). It is more appropriate to define the ratio of the axial pressures of concrete and steel tubes

Discussion on the Ordinary Calculation Formula

Findings

CONCLUSION

DATA AVAILABILITY STATEMENT