Seismic Performance of Prefabricated Double-Skin Steel Tube Concrete Joints

Literature Overview

This paper, published in Journal of Harbin Institute of Technology (2023, Vol. 55, No. 10, pp. 49-62) by Fan Junchao, Zhao Junhai, and You Haoqiang from Chang'an University, presents quasi-static test results on a novel prefabricated double-skin steel tube concrete (DSTC) joint designed for post-disaster repairability. The research was funded by the National Natural Science Foundation (51878056).

Core Technical Content

Six scaled specimens (scale ratio 1:2) were tested under cyclic quasi-static loading to investigate the influence of end-plate thickness, column axial compression ratio, bolt diameter, concrete fill ratio, and inner steel tube section shape on the seismic performance of the proposed prefabricated joint.

Failure Modes

Failure Mode	Description
End-plate bending	Flexural deformation of the connecting end-plate
Steel beam flange buckling	Local instability of beam flange
End-plate to flange weld fracture	Cracking at the weld between end-plate and beam flange
Bolt bending and fracture	Bending deformation followed by rupture of connecting bolts

Seismic Performance Parameters

Performance Indicator	Test Results	Assessment
Hysteresis loop fullness	All six specimens show full loops	Strong energy dissipation
Displacement ductility coefficient	All > 4.89	Excellent plastic deformation capacity
Strength degradation coefficient	0.9-1.0	Good load-bearing stability

Influence of Design Parameters

Parameter	Effect on Load-Bearing Capacity	Effect on Energy Dissipation
End-plate thickness increase	Significant improvement	Significant improvement
Column axial compression ratio increase	Capacity increase	Negligible effect
Concrete fill ratio increase	Capacity increase	Significant reduction
Square inner tube replacing circular	Capacity increase	Significant reduction
Bolt diameter increase	Negligible effect	Negligible effect

Engineering Practice Insights

The concept of a prefabricated DSTC joint with post-disaster repairability represents a paradigm shift in seismic-resistant structural design. Traditional welded or bolted connections are difficult to inspect and repair after an earthquake, often requiring complete replacement. This prefabricated design, utilizing end-plates and high-strength bolts, enables rapid disassembly and replacement of damaged components.

From a steel pipe manufacturing standpoint, the double-skin steel tube concept requires precise dimensional control of both the outer and inner tubes to ensure proper concentricity and gap uniformity. The inner tube section shape (circular versus square) significantly affects energy dissipation capacity—square inner tubes reduce energy dissipation despite increasing load-bearing capacity. This trade-off must be carefully considered during design.

The finding that bolt diameter has almost no influence on either load-bearing capacity or energy dissipation is practically significant. It suggests that bolt size selection can be optimized for ease of assembly and disassembly rather than being driven by strength requirements, provided the minimum bolt size specified by design codes is met.

The nonlinear finite element model developed in this study, which reproduces the test results well in terms of failure modes and load-bearing capacity, provides a reliable tool for parametric studies and design optimization of similar joints.

Key Reflections and Implications

This research addresses a critical gap in earthquake-resistant design: the repairability of structural connections after seismic events. The proposed prefabricated joint achieves ductility coefficients exceeding 4.89 while maintaining strength degradation coefficients between 0.9 and 1.0, indicating that it can sustain multiple loading cycles with minimal strength loss. For engineers involved in designing critical infrastructure in seismic zones—such as hospitals, emergency response centers, and nuclear facilities—this joint design offers a compelling solution that combines high seismic performance with practical repairability.