Zhuojin Pipe Fitting Co., LtdBond Performance Between Straight-Seam Welded Steel Pipes and Concrete Interface A Study of Push-Out Test Results
Literature Overview
This paper, published in Industrial Construction (2021, Vol. 51, No. 3, pp. 77-84) by Luo Peiyun, Lei Yongwang, Zhu Binrong, and Zhao Weiping, investigates the interfacial bond performance between longitudinally straight-seam welded steel pipes (LSWP) and concrete through push-out tests. The research was funded by the National Natural Science Foundation of China (Project No. 51474218) and the Central University Basic Research Business Fee (2021YQLJ06). The study is particularly relevant to large-span transmission tower engineering, where concrete-filled steel tube (CFST) structural design imposes stringent requirements on the steel-concrete interface bond.
Core Technical Content
The authors designed nine CFST push-out specimens using an orthogonal experimental method to systematically study the bond mechanism and bond stress distribution at the LSWP-concrete interface. The key findings are summarized as follows:
Bond Stress-Slip Curve Characteristics
The bond stress-slip relationship exhibits three distinct stages:
| Stage | Description | Behavior |
|---|---|---|
| Adhesion stage | Elastic bonding between steel and concrete | Similar rising trend |
| Non-linear initial slip stage | Progressive micro-cracking at interface | Similar rising trend |
| Slip stage | Significant relative displacement | Three development trends: Type I-1, I-2, and II |
In the slip stage, Type I-1 curves descend and then remain horizontal; Type I-2 curves descend and then exhibit a secondary rise; Type II curves form an inflection point followed by a gradual increase. These three development trends are attributed primarily to the "macroscopic deviation" in the manufacturing of straight-seam welded steel pipes.
Factor Influence Analysis
The influence factors on both adhesive strength and ultimate bond strength follow the same hierarchy:
| Factor | Influence on Adhesive Strength | Influence on Ultimate Bond Strength |
|---|---|---|
| Pipe diameter-to-thickness ratio (D/t) | Most significant (negative) | Most significant (negative) |
| Concrete compressive strength | Second most significant (positive) | Second most significant (positive) |
| Bond interface length | Least significant | Least significant |
The adhesive strength and ultimate bond strength decrease significantly as the D/t ratio increases and increase as the concrete strength improves. The authors also observed that bond stress at both ends of the specimens decreases with increasing load, revealing a peel failure mechanism that propagates from the ends toward the middle of the bond interface.
Engineering Practice Insights
From a steel pipe manufacturing perspective, this research highlights a critical but often overlooked issue: the macroscopic geometric deviations in LSWP production directly affect structural performance. In practice, longitudinal straight-seam welded pipes produced by ERW, HFW, or LSAW processes may exhibit variations in ovality, wall thickness uniformity, and weld bead geometry that are within standard tolerances but can significantly influence the bond stress distribution at the steel-concrete interface.
The finding that higher D/t ratios reduce bond strength is consistent with the understanding that thinner-walled tubes relative to diameter have lower confinement effectiveness. For engineers specifying pipe grades for CFST applications, this suggests that excessively large D/t ratios should be avoided, particularly when high bond performance is required for seismic or large-span applications.
The peel failure mechanism identified—initiating at the specimen ends and propagating inward—has important implications for the design of CFST columns and beams. In structural applications, this means that the effective bond length may be shorter than the theoretical value, and designers should consider potential premature interface debonding at member ends where stress concentrations are highest.
Key Reflections and Implications
The proposed empirical formula for bond strength, validated against other researchers' measured data, provides a practical tool for structural design. However, engineers should be cautious in applying this formula to production pipes that may have different manufacturing tolerances than those used in the test specimens. The "macroscopic deviation" concept deserves further attention in pipe manufacturing quality control—specifically, tighter tolerances on straightness, ovality, and weld bead profile may be warranted for CFST applications in critical infrastructure.