Strength and Load-Carrying Capacity of T-Shaped Steel Tube Concrete Compression-Bending Members

Literature Overview

This paper by Lei Min, Shen Zuyan, Li Yuanqi, and Luo Jinhui, published in the Journal of Tongji University (Natural Science) in 2016, investigates the strength and load-carrying performance of T-shaped steel tube concrete (T-SRC) compression-bending members under both uniaxial and biaxial eccentric compression. Funded by the National Natural Science Foundation (51208375) and the Central University Fund Science and Technology Innovation Project (268015C_X081), the research originates from Southwest Jiaotong University and Tongji University. The work is significant because T-shaped SRC columns are widely used in industrial and commercial structures where architectural and functional requirements demand non-circular cross-sections.

Core Technical Content

The authors adopt an equivalent uniaxial constitutive relationship for the core concrete in T-shaped SRC columns, which is essential for fiber model analysis. A fiber-based numerical program is developed to analyze the influence of multiple parameters on the cross-sectional strength of T-SRC columns under uniaxial and biaxial eccentric compression. The parameters studied include steel yield strength, concrete compressive strength, tube wall width-to-thickness ratio, section limb width-to-thickness ratio, loading angle, and axial compression ratio.

Key findings from the parametric study reveal that the concrete work coefficient and the loading angle have a significant influence on the shape of the normalized axial force-moment interaction curve. The section limb width-to-thickness ratio and the axial compression ratio significantly affect the shape of the normalized biaxial moment interaction curve. These findings are important because they identify which design parameters most critically influence the structural performance.

Based on the assumption of full plasticity of the cross-section and regression analysis of extensive numerical results, simplified calculation methods are proposed for the pure bending, uniaxial eccentric compression, and biaxial eccentric compression cross-sectional strength capacities of T-SRC columns. The simplified methods show good agreement with the fiber model analysis results.

Fabrication and Welding Considerations

The T-shaped SRC column presents unique fabrication challenges. The typical construction involves welding two rectangular or square steel tubes together in a T-configuration, or welding a rectangular tube to a square tube. The critical weld joint is the fillet or groove weld connecting the two tube sections. According to ASME B31.3 and GB/T 19847, this joint must achieve full fusion with no porosity, cracks, or incomplete penetration.

The limb width-to-thickness ratio identified as a critical parameter in this study has direct implications for welding quality control. A high width-to-thickness ratio indicates a relatively thin wall, which is more susceptible to warping during welding and more difficult to achieve full penetration. In practice, for T-SRC columns with limb width-to-thickness ratios exceeding 40, multi-pass welding with appropriate preheating and interpass temperature control is recommended to minimize residual stress and distortion. Post-weld heat treatment (PWHT) in accordance with SY/T 0459 or ASME B31.3 may be necessary to relieve welding residual stresses, particularly when the steel grade exceeds Q345 or the wall thickness exceeds 20 mm.

Engineering Practice Integration

In practical engineering design, the simplified methods proposed in this paper can be directly applied for preliminary design and verification of T-SRC columns. The fiber model approach, while more accurate, is computationally intensive and is better suited for detailed analysis of critical structural elements. Engineers should note that the simplified methods are based on the full plasticity assumption, which is appropriate for ductile design but may overestimate capacity in the elastic range.

For quality assurance, the manufacturing process should be documented according to ISO 3834 or AWS D1.1, with specific attention to the weld joint at the T-connection. Non-destructive testing (NDT) should include at least 20% radiographic testing (RT) or phased array ultrasonic testing (PAUT) on the critical T-joint welds. Mechanical property verification of the weld metal should confirm that the tensile strength meets or exceeds the base metal requirement, and the impact toughness at the HAZ should satisfy the minimum Charpy V-notch energy specified in the applicable code.

Key Reflections and Conclusions

The identification of concrete work coefficient and loading angle as dominant parameters for uniaxial eccentric compression, and limb width-to-thickness ratio and axial compression ratio as dominant for biaxial moment interaction, provides clear guidance for engineers on which design parameters require the most careful attention. The simplified calculation methods offer a practical alternative to full fiber analysis for routine design work. However, engineers should be aware that the simplified methods are calibrated against numerical results rather than extensive experimental data, and the applicability to very high strength materials or unusual geometric proportions should be verified by additional analysis or testing. The fabrication quality of the T-joint weld is paramount, as any deficiency in the weld integrity directly compromises the composite action between the steel tubes and the concrete core, potentially reducing the actual capacity below the predicted values.