Zhuojin Pipe Fitting Co., LtdMechanical Properties of Novel Square Steel Tube Column Internal Sleeve Assembly Connection
Literature Overview
The paper by Liu Xiuli, Sun Fengbin, Lu Yang, and Cao Yuanzheng (2021), published in Science Technology and Engineering (Vol. 21, No. 3, pp. 1123-1130), presents a novel prefabricated connection design for square steel tube columns using an internal sleeve mechanism. Funded by the National Natural Science Foundation Youth Science Fund (Grant No. 51508290), this research addresses practical challenges in prefabricated steel construction, specifically the difficulty of installing high-strength bolts at beam-column joints when column splices coincide with joint locations. The proposed solution repositions the column splice above the beam-column joint core zone, creating installation space while maintaining structural continuity.
Connection Design Concept
The novel internal sleeve assembly connection relocates the column splice position from within the beam-column joint to above the joint core region. This design modification achieves two objectives: it provides adequate access for high-strength bolt installation at the beam-column connection, and it preserves the structural continuity of the joint zone by using an internal sleeve to transfer forces between column segments.
| Design Parameter | Effect on Performance |
|---|---|
| Sleeve thickness | Increases ultimate capacity and energy dissipation; significant improvement when sleeve thickness exceeds column wall thickness by 2 mm |
| Sleeve length | Longer sleeves reduce stiffness, ductility, and energy dissipation; shorter sleeves preferred within constructability limits |
| Through-bolt spacing | Moderate increase in spacing improves joint behavior; excessive spacing reduces effectiveness |
| End plate thickness | Moderate increase improves performance and ductility; excessive thickness is uneconomical |
The finite element analysis was conducted using ANSYS with nonlinear material and contact modeling to capture the complex interaction between the sleeve, column segments, and through-bolts under cyclic loading.
Seismic Performance Characteristics
The hysteresis performance of the novel connection demonstrates good seismic behavior:
- The connection exhibits stable hysteresis loops with full energy dissipation characteristics, indicating reliable inelastic deformation capacity.
- The displacement ductility factor meets or exceeds typical requirements for ductile steel connections under seismic loading.
- The energy dissipation capacity is primarily derived from plastic deformation of the sleeve material and bolt elongation, providing predictable and controllable failure modes.
- The connection maintains load-carrying capacity throughout the deformation range, without sudden strength degradation.
The parametric study reveals important design sensitivities:
- Sleeve thickness is the most influential parameter, with capacity and energy dissipation increasing substantially when the sleeve is made thicker than the column wall by more than 2 mm.
- Sleeve length has an inverse relationship with performance metrics: longer sleeves introduce additional flexibility that reduces overall joint stiffness and ductility.
- Through-bolt spacing requires optimization: closer spacing provides better constraint but increases installation complexity, while wider spacing allows easier construction but may reduce load transfer efficiency.
- End plate thickness should be sufficient to prevent local yielding but should not be excessively thick to maintain economic efficiency.
Engineering Application and Prefabrication Benefits
The proposed connection design offers significant advantages for prefabricated steel construction:
- Field assembly is simplified because the column splice is separated from the beam-column joint, allowing independent installation sequences.
- High-strength bolt installation at the beam-column joint is no longer obstructed by column splice geometry.
| Application Aspect | Benefit |
|---|---|
| Construction speed | Reduced field welding; bolted connections only |
| Quality control | Factory-controlled sleeve fabrication; field bolt tightening verification |
| Design flexibility | Parameters can be optimized for specific seismic demands |
| Cost efficiency | Reduced field labor; standardized sleeve components |
| Seismic performance | Predictable ductile behavior; energy dissipation through controlled yielding |
The connection design is particularly suitable for mid-to-high-rise steel buildings where prefabrication is economically advantageous and seismic performance is critical. The internal sleeve mechanism provides a concealed force transfer path that does not interfere with architectural finishes or MEP routing.
Design Guidelines and Recommendations
Based on the parametric study results, the following design guidelines are recommended:
- Sleeve thickness should be at least 2 mm greater than the column wall thickness to achieve significant performance improvement.
- Sleeve length should be minimized to satisfy constructability requirements while maintaining adequate overlap for load transfer, typically 1.5 to 2 times the column width.
- Through-bolt spacing should be optimized within the range of 150-250 mm to balance structural performance with installation practicality.
- End plate thickness should be selected to prevent local yielding under design forces, with a practical upper limit to maintain economic efficiency.
- All bolt connections should be designed for slip-critical behavior to ensure full moment transfer capacity.
Study Insights and Future Directions
This research contributes a practical and innovative solution to the longstanding challenge of integrating column splices with beam-column joints in prefabricated steel construction. The separation of splice and joint functions through the internal sleeve mechanism represents a conceptually elegant approach that simplifies field construction while maintaining structural integrity. Engineers should note that the finite element results, while comprehensive, should be validated through physical testing of full-scale specimens before widespread adoption in critical applications. Future research should investigate the connection behavior under combined gravity and lateral loading, long-term fatigue performance, and fire resistance characteristics to complete the technical basis for code-based design provisions.