Zhuojin Pipe Fitting Co., LtdBonding Performance of High-Strength Steel Pipe Connection Nodes in Prefabricated Composite Structure Columns
Literature Overview
Zhu Zhangfeng et al., published in Industrial Construction in 2023 (Volume 53, Issue 4, pp. 120-124), present experimental research on the interface bonding performance of high-strength steel pipe connection nodes used in prefabricated composite structure columns. This work is particularly relevant to the growing trend of prefabricated construction in China, where high-strength steel pipes (Q420 grade) serve as critical structural elements requiring reliable mechanical connections. The study examines three pipe specifications—φ114×25, φ152×16, and φ194×10—and investigates the influence of bonding length, bonding material, and external spiral reinforcement on connection performance.
Experimental Configuration and Test Parameters
The push-out tests were conducted under systematically varied conditions:
| Test Variable | Conditions | Standard Reference |
|---|---|---|
| Bonding length | 600 mm, 800 mm | GB 50011-2010 |
| Bonding material | C35 concrete, M50 grout | GB/T 50448 |
| External reinforcement | None, φ6@50 spiral wire | GB 50010-2010 |
| Pipe grade | Q420 | GB/T 1591 |
| Pipe specifications | φ114×25, φ152×16, φ194×10 | GB/T 8162 |
The Q420 grade steel pipes used in this study represent the new generation of high-strength structural steel, offering a yield strength of 420 MPa compared to the traditional Q345 grade (345 MPa). This represents approximately a 22% increase in yield strength, which directly impacts the design of connection details and the required bonding lengths.
Key Experimental Findings
The load-displacement/slip curves and bonding strength results reveal several important technical conclusions:
- Bonding length effect: A bonding length of 600 mm is sufficient to achieve the bonding strength required by relevant codes. Increasing the bonding length to 800 mm delays slip initiation but results in a lower average bonding strength, indicating that the stress distribution along the interface is non-uniform.
- Bonding material effect: M50 grout significantly increases the peak load compared to C35 concrete, but the overall curve shape remains similar. This suggests that the failure mode is governed by the steel pipe interface condition rather than the grout strength alone.
- Slenderness ratio and diameter-to-thickness ratio: These geometric parameters showed no clear influence pattern on bonding performance, which is an important finding for design standardization.
- Section size effect: The φ114×25 section achieved the highest bonding strength under identical conditions, likely due to its higher wall thickness and resulting greater interfacial contact pressure.
- Spiral reinforcement effect: The addition of φ6@50 spiral wire on the pipe outer surface effectively improved bonding strength and delayed interface slip, while being simple to install during construction.
Welding and Fabrication Quality Considerations
From a steel pipe manufacturing and welding quality perspective, the performance of these connection nodes is critically dependent on the pipe surface condition and geometric accuracy:
| Quality Parameter | Acceptance Criteria | Inspection Method |
|---|---|---|
| Surface roughness | Ra ≤ 12.5 μm | Roughness tester |
| Ovality | ≤ 0.5% of nominal diameter | Caliper measurement |
| Wall thickness uniformity | ±10% of nominal | Ultrasonic thickness |
| Surface cleanliness | Free of scale, rust, oil | Visual + PT |
| End flatness | ≤ 1 mm deviation | Straightedge and gauge |
The Q420 grade steel pipe material, typically produced by ERW or seamless processes, must meet the requirements of GB/T 1591-2018 for structural steel. The chemical composition requirements, particularly carbon equivalent (CE ≤ 0.45%) and the ratio of nitrogen and oxygen content, directly affect the weldability and cold cracking susceptibility of any field connections.
Engineering Recommendations and Construction Control
The study's recommendation to adopt external spiral reinforcement (φ6@50) has significant practical implications for prefabricated construction workflows:
- Spiral reinforcement should be installed prior to grouting operations to ensure complete encapsulation
- The spacing of 50 mm provides adequate confinement without excessive material consumption
- Construction tolerance for spiral reinforcement placement should be controlled to ±3 mm
- Grout placement must be continuous to avoid voids that would compromise the bond interface
The finding that 600 mm bonding length is sufficient for code-compliant performance allows for optimization of prefabricated component dimensions and transportation logistics. However, the reduction in average bonding strength with increased length suggests that design should consider the non-uniform stress distribution rather than assuming uniform bond stress.
Study Insights and Implications for Standard Development
This research provides valuable experimental data for the development of design guidelines for prefabricated composite structures using high-strength steel pipes. The systematic investigation of bonding parameters, combined with the practical recommendation of spiral reinforcement, offers a clear path for standardization. The use of Q420 grade steel pipes in prefabricated connections represents a significant advancement in structural efficiency, and the findings on bonding behavior under various conditions will directly inform future revisions of GB 51246 (Technical Standard for Prefabricated Concrete Building) and related prefabrication standards. The emphasis on construction simplicity (spiral reinforcement) alongside performance optimization reflects the practical engineering philosophy that solutions must balance technical merit with constructability.