Effect of Tie Bars on Axial Compressive Behavior of Round-Ended Rectangular CFST Stub Columns.

Zhigang Ren,Chuang Liu,Qi Li

doi:10.3390/ma15031137

Abstract

Round-ended rectangular concrete-filled steel tube (RRCFST) columns are prone to local buckling that are close to straight steel plates when used as piers of a bridge and affect its long-term use. In order to solve this problem, tie bars were used in this research to stiffen RRCFST columns. Eleven specimens with tie bars and three specimens without tie bars were tested to analyze influences of cross-sectional aspect ratio, longitudinal spacing, limb numbers and diameter of the tie bar on failure model, confined effect, bearing capacity and ductility of RRCFST stub columns. Finite element models (FEM) with different concrete constitutive models for rectangular and circle parts were established and validated to reveal the mechanism of the constrained effect of tie bars. Experimental and FEM results show that the local buckling scope was decreased and gradually moved to middle height with decreased longitudinal spacings tie bars. The addition of tie bars in RRCFST columns with large aspect ratios slightly enhanced the ultimate bearing capacity, the diameter of tie bars changing from 8 mm to 12 mm greatly enhanced displacement and energy ductility by 58.4% and 85.1%, respectively. However, more tie bars (e.g., two or three limbs) utilization could not further improve the bearing capacity and failure mode. While, the tie bars had very limited contribution to bearing capacity and ductility for RRCFST columns with small aspect ratios, because the outer steel tubes already individually provided for enough confinement on inner concrete. By considering different concrete confined models for rectangular and round-ended parts, an analytical model was proposed and validated to predict the ultimate bearing load for RRCFST stub columns with tie bars.

Highlights

Published: 1 February 2022As a relatively new type of structural member, concrete-filled steel tubes (CFSTs) have lots of advantages, such as good bearing capacity, high seismic property, lightweight, and fast construction speed [1]
Local buckling could still occur at the outside of the rectangular concrete-filled steel tube (RRCFST) column due to the ineffective confined of the steel tube and the shear failure of infilled concrete [13], significantly reducing the bearing capacity and ductility [14]
Fourteen RRCFST columns based on three designed aspect ratios (B/D = 1.5, 2, 3, of which B and D are the length and width of the cross-section, respectively, and the steel tubes produce errors in dimension after fabrication, and D and B in this paper from the actual measured value), height (L) of the cross-section, the thickness of the steel tube (t), the limb number (n), the diameter (d), the longitudinal and the horizontal span of tie bras were experimentally studied by axial compressive test

Summary

Introduction

Published: 1 February 2022As a relatively new type of structural member, concrete-filled steel tubes (CFSTs) have lots of advantages, such as good bearing capacity, high seismic property, lightweight, and fast construction speed [1]. Round-ended rectangular CFST (RRCFST) column could be suggested for architectural [9] and aesthetical purposes [10]. RRCFST columns own a comparable axial bearing capacity to the circular one [11] and excellent bending strength on the major axis like the rectangular one. RRCFST column has reduced water flow resistance and enhanced impact resistance by the round-ended part in the bridge pier [12]. Local buckling could still occur at the outside of the RRCFST column due to the ineffective confined of the steel tube and the shear failure of infilled concrete [13], significantly reducing the bearing capacity and ductility [14]

Methods

Results

Conclusion