Experimental Study on Axial Compressive Capacity of High-Strength Steel Pipe High-Strength Concrete Short Columns

Literature Overview

This paper by Zeng Zhiwei, Huang Yonghui, Chen Bijing, and Tan Dingrong from the Research Center of Wind Engineering and Engineering Vibration, Guangzhou University, published in Building Structures (2022, Vol. 52, No. 18, pp. 72-77), presents a systematic experimental investigation into the axial compressive behavior of short columns combining high-strength steel pipes with both high-strength concrete and ordinary concrete. The study was supported by the National Natural Science Foundation of China (Grants 51878188 and 51678169). A total of 9 groups comprising 27 specimens were tested under axial compression, with the primary objective of comparing the load-displacement behavior and failure modes across different material combinations. The confinement coefficient is identified as a key variable governing the ductility enhancement of the composite system.

Core Technical Findings

The experimental results reveal several critical observations that carry significant implications for structural engineering practice. First, a clear distinction exists between the load-displacement curves of high-strength steel pipe with ordinary concrete versus high-strength steel pipe with high-strength concrete specimens. Notably, the high-strength steel pipe with ordinary concrete specimens exhibit superior ductility compared to the high-strength steel pipe with high-strength concrete specimens. This finding is somewhat counterintuitive, as one might expect higher-strength materials to correlate with better overall mechanical performance, but the brittleness inherent in high-strength concrete partially offsets the confinement benefits provided by the steel pipe.

The confinement effect of the steel pipe is confirmed to significantly enhance the ultimate bearing capacity of the concrete core, with the improvement being particularly pronounced for high-strength concrete. The originally brittle high-strength concrete demonstrates a measurable degree of ductility when confined within a high-strength steel pipe, and this ductility increases progressively with the confinement coefficient. The confinement coefficient, defined as the ratio of the steel pipe's confining pressure to the concrete's compressive strength, emerges as the dominant parameter governing the post-peak behavior of the composite column.

Standards Compliance and Design Formula Validation

A particularly noteworthy finding is that all specimens' calculated values using the formula specified in GB 50936-2014 (Code for Design of Concrete-Filled Steel Tubular Structures) showed good agreement with the experimentally measured values. This validation extends the applicability of the existing design formula from high-strength steel pipe with ordinary concrete to high-strength steel pipe with high-strength concrete combinations. This is significant because the original standard was not specifically developed for this material combination, and the successful verification suggests that the underlying mechanics-based formulation captures the essential confinement interaction adequately.

Engineering Practice Implications

From a practical standpoint, this research addresses an important gap in the design of high-rise and heavy-load structures where both high compressive strength and compact cross-sections are required. The use of high-strength steel pipes (typically Q460 or Q550 grade and above) combined with high-strength concrete (C60 and above) represents an emerging trend in modern structural engineering, particularly in seismic regions where ductility demands are stringent. The finding that ductility can be restored to high-strength concrete through adequate steel pipe confinement provides designers with a viable pathway to utilize high-strength concrete in composite columns without compromising seismic performance.

However, engineers should note that the superior ductility of ordinary concrete specimens does not negate the advantages of high-strength concrete in terms of ultimate capacity. The selection between the two material combinations should be governed by the specific design demands: capacity-critical applications favor high-strength concrete, while ductility-critical applications may warrant ordinary concrete or require higher confinement coefficients to compensate for the inherent brittleness.

Key Reflections

The study reinforces the principle that composite action in steel-concrete systems is not merely additive but synergistic, with the confinement effect creating a fundamentally different stress state in the concrete core. The progressive increase in ductility with confinement coefficient suggests that design optimization should focus on maximizing the confinement ratio within practical fabrication constraints. The validation of GB 50936-2014 formulas for high-strength concrete combinations provides confidence for code-based design, though engineers should maintain awareness of the test specimen limitations, including the short column geometry which does not account for buckling effects relevant to slender columns in actual structures.