Bending Performance of T-Shaped Steel Tube Concrete Composite Members

Literature Overview

This paper by Xu Lihua and colleagues from Wuhan University investigates the bending performance of a novel T-shaped steel tube concrete (CFST) composite member formed by welding two rectangular steel tubes directly together. Published in the Journal of Huazhong University of Science and Technology (Natural Science Edition) in 2009, the research was funded by the Hubei Provincial Construction Department (Project K200513). The study combines experimental testing with finite element analysis to evaluate the bending behavior of this innovative structural member.

Experimental Program and Key Parameters

The researchers conducted 16 bending tests on 8 groups of T-shaped CFST composite members. The parametric study considered the following variables:

The ABAQUS finite element analysis provided full-process analysis of moment-deflection curves, with numerical results agreeing well with experimental results (bearing capacity difference within 5%). A formula for the ultimate bending capacity was proposed, with calculation results showing a maximum error of 14% compared to test results.

Comparison with Conventional T-Shaped CFST Members

The novel T-shaped CFST composite member, formed by direct welding of two rectangular steel tubes, was compared with traditional T-shaped CFST composite members. The comparison reveals advantages in:

• Fabrication simplicity: direct welding of standard rectangular steel tubes avoids complex formwork and concrete pouring
• Connection efficiency: the welded T-joint provides inherent composite action
• Material utilization: the steel tubes provide both structural strength and formwork for concrete

The welding process for forming the T-joint requires careful attention to weld quality, as the joint represents a geometric discontinuity that may initiate failure under bending loads. The weld HAZ must be controlled to avoid strength and toughness degradation, particularly for high-strength steel tubes.

Finite Element Modeling Insights

The ABAQUS finite element model employed in this study provides valuable insights into the stress distribution and failure mechanisms of T-shaped CFST composite members under bending:

• The concrete in the compression zone of the T-shape provides significant contribution to bending capacity
• The steel tubes in the tension zone yield first, followed by progressive concrete crushing in the compression zone
• The weld joint region experiences complex multiaxial stress states that require careful modeling
• Mesh refinement near the weld joint and concrete-steel interface is critical for accurate stress predictions

The proposed ultimate bending capacity formula provides a practical design tool for engineers, though the 14% maximum error suggests that the formula should be used with appropriate safety factors in design applications.

Engineering Practice Recommendations

For engineers considering T-shaped CFST composite members in structural applications, the following recommendations are provided:

• Welding procedures must be qualified according to applicable standards (e.g., GB/T 985, AWS D1.1)
• Pre-qualification testing of weld procedures for specific steel grades and tube dimensions is essential
• Non-destructive testing (RT or UT) of weld joints is recommended for critical applications
• The proposed capacity formula should be used as a preliminary design tool with verification through detailed FEA
• Construction tolerances for tube alignment and welding fit-up must be tightly controlled

Study Insights and Outlook

This research introduces an innovative structural member concept that combines the advantages of CFST and welded steel tube construction. The direct welding approach simplifies fabrication while maintaining composite action between steel and concrete. The finite element methodology validated in this study provides a reliable tool for parametric design optimization.

Future research should investigate the seismic performance of T-shaped CFST composite members under cyclic loading, as well as the long-term durability of the welded joints under environmental exposure. Additionally, the effect of different welding processes (SMAW, GMAW, SAW) on joint performance should be systematically studied to provide fabrication guidelines. The concept of welded composite members has potential applications in bridge girders, building frames, and industrial structures where fabrication efficiency and structural performance are both important design objectives.