Seismic Performance of Prefabricated Composite Steel Tube Concrete Connection Nodes with Single-Side Bolt T-Joints

Literature Overview

The paper by Zhang Yufen, Bu Hongfan, Cao Shengxi, and Jia Hongxin, published in 2022 in the Journal of Architecture and Civil Engineering (Volume 39, Issue 1, pages 44–54), investigates the seismic behavior of prefabricated composite steel tube concrete (CSTC) connection nodes employing single-side bolt T-type joints. Funded by the National Natural Science Foundation of China (Grants 51478004 and 52078179), the study originates from Hebei University of Technology's School of Civil and Transportation Engineering and the Tianjin Key Laboratory of Prefabricated Construction and Intelligent Building, in collaboration with North China Engineering Design and Research Institute Co., Ltd. The research is directly relevant to engineers working in prefabricated structural steel and composite construction, where connection design governs overall seismic resilience.

Core Technical Approach and Test Configuration

The authors designed six specimens in total: five composite steel tube concrete single-side bolt node specimens and one through-bolt comparative node specimen. The specimens were subjected to column-end fixed axial compression combined with horizontal reciprocating loading, simulating realistic seismic demand conditions. The primary variables investigated were the presence and configuration of T-piece ribs, the flange thickness of the T-piece, and the beam-to-column linear stiffness ratio. The composite steel tube concrete column consists of an outer steel tube, an inner steel tube, and concrete infill, creating a dual-layer confinement effect that enhances ductility and energy dissipation.

The following table summarizes the key experimental variables and their levels:

Key Findings and Technical Analysis

The test results demonstrate that the single-side bolt T-piece connection nodes exhibit full and stable hysteresis loops, indicating strong deformation and energy dissipation capacity. The addition of a single rib to the T-piece increased the ultimate load capacity by 39% compared to the unribbed specimen, while a double-rib configuration yielded a 44% improvement. This rib reinforcement mechanism effectively redistributes stress concentration at the bolt hole region and prevents local buckling of the T-piece web under cyclic loading.

The flange thickness of the T-piece proved significant: nodes with 20 mm flange thickness achieved a 13% higher ultimate load capacity compared to those with 14 mm flange thickness, with a corresponding increase in ultimate displacement. This finding aligns with classical plastic hinge theory, where increased flange thickness provides greater plastic moment resistance and delays flange yielding.

When the beam-to-column linear stiffness ratio was increased, both the ultimate load capacity and energy dissipation capacity of the node specimens improved markedly. This observation is consistent with the principle that a stiffer beam relative to the column promotes a more favorable force distribution, reducing the demand on the connection zone while maintaining overall structural integrity.

Comparison with Through-Bolt Connections

The comparative analysis between single-side bolt and through-bolt nodes reveals nuanced performance differences. The single-side bolt node exhibited slightly lower initial stiffness but marginally higher ultimate load capacity compared to the through-bolt node. The equivalent viscous damping coefficients of both connection types were essentially equivalent, indicating comparable energy dissipation efficiency per cycle. However, the single-side bolt node demonstrated significantly improved deformation capacity and ductility, which is the most critical parameter for seismic design.

From an engineering practice perspective, the single-side bolt connection leverages the single-side locking advantage of the inner steel tube in the composite CSTC column. Although the inner tube strain values are relatively high, the node zone shows no obvious deformation, confirming reliable force transmission and good structural integrity. This is particularly advantageous for prefabricated construction where field assembly efficiency and accessibility are paramount.

Engineering Practice Implications

For engineers designing prefabricated composite steel tube concrete structures in seismic regions, several practical recommendations emerge from this study. First, T-piece ribs should be incorporated as a standard design feature; the 39–44% capacity improvement justifies the additional fabrication cost. Second, flange thickness of at least 20 mm is recommended for medium-to-large scale connections to ensure adequate ductility. Third, the single-side bolt solution offers a practical prefabricated connection that does not compromise seismic performance relative to through-bolt alternatives, while providing superior field assembly convenience.

The study also highlights the importance of the beam-to-column stiffness ratio in seismic design. Engineers should carefully calibrate member sizes to achieve an optimal stiffness ratio that maximizes connection performance without over-designing the beam elements.

Critical Reflection and Study Insights

This research contributes meaningfully to the understanding of prefabricated composite steel tube concrete connections, a rapidly growing construction methodology in China's infrastructure sector. The experimental approach is rigorous, with controlled variables and a clear comparative framework. However, the study is limited to quasi-static cyclic loading; future work incorporating pseudo-dynamic or real-time substructuring tests would provide additional confidence in the dynamic performance of these connections. Additionally, the study does not address long-term durability concerns such as corrosion protection of the bolted connections in harsh environments, which is a critical consideration for long-span bridge and offshore applications. The findings nonetheless provide a solid empirical basis for incorporating single-side bolt T-piece connections into seismic design codes for prefabricated composite structures.