Zhuojin Pipe Fitting Co., LtdAxial Compression Performance of Square High-Strength Steel Tube-Concrete Composite Columns in Cold Regions
Literature Overview
This 2022 study by Yan Jiabao and colleagues from Tianjin University investigates the low-temperature axial compression behavior of square high-strength steel tube-concrete composite columns. The research is motivated by the growing demand for composite structures in cold-region civil engineering, where materials are subjected to sustained low temperatures that can significantly alter their mechanical properties. Ten specimens using Q690 and Q960 square high-strength steel tubes were tested under low-temperature conditions to reveal failure modes, load-displacement curves, ultimate bearing capacity, and ductility characteristics.
Experimental Design and Test Parameters
The experimental program encompasses a systematic variation of key parameters including low-temperature level, steel tube wall thickness, and steel material strength. The Q690 and Q960 grades represent the upper end of structural steel strength, making this study particularly relevant for high-rise and heavy-load applications in cold climates. The square cross-section is chosen for its common use in composite column systems, and the low-temperature environment simulates the conditions encountered in northern China and other cold regions.
| Test Parameter | Values Investigated | Effect on Performance |
|---|---|---|
| Steel grade | Q690, Q960 | Higher strength improves bearing capacity and stiffness |
| Tube wall thickness | Multiple thicknesses | Thicker walls improve cold-temperature performance |
| Low-temperature level | Ambient to sub-zero | Improves strength and stiffness but reduces ductility |
| Cross-section | Square hollow section | Corner welds are critical failure locations |
Failure Modes and Mechanical Behavior
The study identifies three primary failure modes under low-temperature axial compression: local buckling of the steel tube, crushing of the core concrete, and cracking of the corner welds. The failure sequence is consistent with the load-displacement curve stages, where concrete crushing occurs at peak load and steel tube local buckling and corner weld cracking occur during the descending branch. The corner welds are particularly vulnerable because the stress concentration at the re-entrant corner of the square section is exacerbated by the reduced ductility of high-strength steel at low temperatures.
The load-displacement curves under low temperature retain the same general shape as ambient-temperature curves, comprising linear, nonlinear, and descending stages. However, the peak load is higher and the post-peak deformation capacity is reduced, indicating improved strength but compromised ductility. This strength-ductility trade-off is a critical design consideration for cold-region applications where seismic resilience may also be required.
Standards Comparison and Design Recommendations
The study compares the predicted ultimate axial compression capacity using the Chinese code GB 50936-2014 and the American code AISC 360-10. The Chinese code is found to be conservative for high-strength steel tube concrete columns, while the American code provides more accurate predictions. This discrepancy arises because the Chinese code's empirical formulas were calibrated primarily for lower-strength materials, and the confinement effect of high-strength steel on the core concrete is not fully captured.
For engineering practice, the study recommends that designers in cold regions consider the reduced ductility of high-strength steel tube concrete columns when seismic detailing is required. The corner weld quality becomes even more critical under low-temperature conditions, and weld inspection standards should be tightened for these applications. The finite element model developed in the study, which incorporates temperature-dependent material properties, provides a valuable tool for parametric analysis and design verification.
Study Insights and Manufacturing Implications
From a steel pipe manufacturing perspective, this research underscores the importance of material quality control for high-strength steel tubes intended for cold-region composite columns. The Q690 and Q960 grades require strict adherence to chemical composition and heat treatment specifications to ensure consistent low-temperature toughness. The corner welds of square hollow sections are a critical quality control point, and non-destructive testing methods such as ultrasonic testing should be applied with particular rigor. The study also suggests that future research should explore the combined effects of low temperature and cyclic loading to better understand the seismic performance of these columns in cold regions.