Seismic Performance of Composite Steel Tube Concrete Prefabricated Connection Nodes with Single-Sided Bolted T-Joints

Literature Overview

This paper, published in the Journal of Architecture and Civil Engineering in 2022, presents experimental research on the seismic behavior of composite steel tube concrete (CSTC) prefabricated connection nodes. The authors from Hebei University of Technology designed five single-sided bolted CSTC node specimens and one through-bolted comparison specimen, subjecting them to pseudo-static cyclic loading tests under constant axial compression. The study investigates the influence of T-piece rib reinforcement, T-piece flange thickness, and beam-column linear stiffness ratio on failure modes, load-displacement curves, ultimate bearing capacity, ductility, energy dissipation, and stiffness degradation. This work is particularly relevant to engineers working on prefabricated steel-concrete composite structures in seismic regions, as it addresses a critical gap in the seismic design of bolted connections for CSTC columns.

Core Technical Findings

The experimental results reveal several important engineering insights regarding the seismic performance of single-sided bolted T-piece connections in CSTC columns. The hysteresis curves of the CSTC single-sided bolted T-piece connection nodes are full and exhibit strong deformation energy dissipation capacity, which is a positive indicator for seismic resilience. The rib reinforcement on the T-piece significantly enhances the ultimate bearing capacity: single-rib reinforcement improves the ultimate bearing capacity by 39%, while double-rib reinforcement provides a 44% improvement compared to unreinforced T-pieces.

The flange thickness of the T-piece also plays a critical role in connection performance. Nodes with a 20 mm flange thickness demonstrate a 13% increase in ultimate bearing capacity compared to those with 14 mm flange thickness, and the ultimate displacement increases correspondingly. Furthermore, when the beam-column linear stiffness ratio increases, both the ultimate bearing capacity and energy dissipation capacity of the node specimens improve significantly.

Comparison with Through-Bolted Connections

A key contribution of this study is the systematic comparison between single-sided bolted and through-bolted connection nodes. The single-sided bolted node exhibits slightly lower initial stiffness but slightly higher ultimate bearing capacity compared to the through-bolted counterpart. The equivalent viscous damping coefficients of both connection types are essentially comparable, indicating similar energy dissipation efficiency per cycle. However, the single-sided bolted connection demonstrates significantly improved deformation capacity and ductility.

This finding is particularly significant for prefabricated construction practice. The single-sided bolted approach leverages the one-sided locking advantage of the inner steel tube in CSTC columns. While the inner steel tube experiences relatively large strain values, the node panel zone shows no obvious deformation, indicating reliable force transmission and good structural integrity. This suggests that the single-sided bolted prefabricated connection can effectively guarantee both the stability and seismic performance of the joint.

Engineering Practice Implications

From a practical engineering perspective, this research offers several actionable insights for structural designers and construction engineers. First, the prefabricated nature of the single-sided bolted connection is advantageous for on-site construction efficiency, as it eliminates the need for through-bolt assembly which requires access from both sides of the column. Second, the rib reinforcement strategy provides a straightforward yet highly effective means of enhancing node capacity without significantly increasing the complexity of prefabricated components.

The finding that the inner steel tube strain is relatively high while the node panel zone remains undeformed suggests that the CSTC composite action is effectively mobilized. This is consistent with the confinement mechanism inherent in CSTC columns, where the outer steel tube provides lateral restraint to the concrete core and the inner steel tube contributes additional flexural and shear resistance. Engineers should pay attention to the strain levels in the inner steel tube during seismic events, as excessive strain could lead to local buckling or fracture in severe scenarios.

The beam-column stiffness ratio finding has direct implications for structural system design. Engineers should carefully balance the relative stiffness of beams and columns to ensure that the connection nodes are not the weak link in the structural hierarchy. A higher beam-column stiffness ratio, which typically implies stiffer beams relative to columns, appears beneficial for the connection performance studied here, but this should be verified against overall structural behavior including story drift and base shear distribution.

Key Questions and Reflections

Several important questions remain open for further investigation. The experimental study was conducted on individual node specimens under pseudo-static loading, which does not fully capture the dynamic effects of real earthquake loading. The strain rates experienced during seismic events can significantly affect the material behavior of both steel and concrete, potentially leading to different failure modes and capacity levels compared to quasi-static conditions. Dynamic testing, including shake-table experiments, would provide more comprehensive validation of the design recommendations derived from this study.

Additionally, the long-term performance of the prefabricated connections under repeated seismic cycles and potential fatigue degradation warrants further study. The single-sided bolted connection relies on the friction and mechanical interlock between the T-piece and the CSTC column, and the degradation of this interface over multiple loading cycles could affect the residual capacity of the structure after a major earthquake. Engineers should consider incorporating provisions for post-earthquake inspection and potential repair of these connections in their design philosophy.

The study also does not extensively address the effect of concrete strength grade and steel tube material grade on the connection performance. In practice, a wide range of material combinations may be used, and the interaction between material properties and connection geometry could lead to different performance outcomes. Future research should systematically vary material parameters to establish more robust design guidelines.

Study Insights and Implications

This research represents a meaningful advancement in the understanding of prefabricated CSTC connection behavior under seismic loading. The demonstration that single-sided bolted connections can achieve comparable energy dissipation and superior ductility to through-bolted connections is particularly encouraging for the promotion of prefabricated construction in seismic regions. The quantification of rib reinforcement benefits provides engineers with clear, actionable design parameters for enhancing connection capacity.

The overall approach taken by the authors, combining systematic parametric variation with detailed mechanical analysis, exemplifies good experimental research methodology in structural engineering. The comparison with through-bolted connections adds credibility to the findings by providing a benchmark against which the novel single-sided approach can be evaluated. For engineers involved in the design of prefabricated steel-concrete composite structures, this paper provides valuable experimental data and design guidance that can inform the development of more resilient and efficient construction systems.