Numerical Analysis of Seismic Performance of Fully Bolted Prefabricated Connections for Square Steel Tube Concrete Columns

Literature Overview

This study investigates the seismic behavior of fully bolted prefabricated connection nodes in square steel tube concrete (SC) columns through numerical analysis. The research addresses a critical gap in prefabricated steel-concrete composite construction, where traditional welded connections are replaced entirely by bolted assemblies to enable rapid, site-efficient erection. The numerical framework typically employs finite element methods with explicit dynamic analysis to capture the nonlinear interaction between the steel tube, confined concrete, and bolted joint components under cyclic lateral loading. The work is highly relevant to engineers designing earthquake-resistant high-rise and industrial structures where construction speed and seismic resilience must coexist.

Core Technical Points

The study examines several key aspects of the bolted connection design, including the bolt layout configuration, the connection plate geometry, and the interaction between the steel tube wall and the external connection plates. The fully bolted approach eliminates field welding, which significantly reduces construction time and eliminates the risk of weld defects in seismic joints. However, the connection must still achieve sufficient ductility, energy dissipation capacity, and strength to meet seismic design codes such as GB 50011 and AISC 341.

The numerical model must accurately represent the material nonlinearity of both steel and concrete, including the confinement effect of the steel tube on the internal concrete. The bolted connection components introduce additional nonlinearities through bolt slippage, bearing deformation, and contact separation. The study likely employs a combination of beam elements for the column shaft and shell elements for the connection plates, with bolt connections modeled using spring elements or explicit bolt geometry.

Process and Standards Analysis

From a fabrication standpoint, the fully bolted connection requires precision-machined connection plates with tight tolerances on bolt hole positioning. The hole diameter tolerance typically follows GB/T 50017 Class B or C fit requirements, allowing for easy field assembly without forcing. The bolt pretension level must be controlled to ensure proper clamping force, typically 70% of the bolt's proof load as specified in GB/T 1228 through GB/T 1231.

The seismic performance evaluation follows the capacity design principle, where the connection is designed to yield in a controlled manner before the column itself fails. Key performance indicators include:

• Peak bearing capacity and ductility ratio
• Energy dissipation capacity measured by hysteretic loop area
• Stiffness degradation rate under cyclic loading
• Damage index based on displacement ductility

Standards such as GB 50011-2010 (Seismic Design Code for Building Structures) and GB 51248-2016 (Technical Code for Composite Structures) provide the design framework, while AISC 341-16 (Seismic Provisions for Structural Steel Buildings) offers complementary guidance for international projects. The numerical results must be validated against experimental data when available, with particular attention to the connection's failure mode and the column's overall collapse mechanism.

Integration with Engineering Practice

In practical engineering, the transition from welded to bolted connections introduces several challenges that this study helps address. First, the connection plates must be designed to avoid stress concentrations at bolt holes, which can initiate cracking under cyclic loading. Second, the bolted connection must maintain its integrity through multiple loading cycles without progressive loosening. Third, the prefabricated nature of the connection requires that all critical components be manufactured and inspected in the factory, shifting quality control from the field to the production line.

From a quality assurance perspective, the bolted connection offers advantages: the factory-controlled fabrication ensures consistent weld quality on the steel tube itself, and the bolted assembly can be inspected visually and by torque verification without destructive testing. However, the connection plates and bolts require careful material certification, including tensile testing, hardness verification, and ultrasonic inspection for internal defects. The PDCA cycle applies directly here: Plan the bolt layout and pretension, Do the fabrication and assembly, Check through inspection and testing, and Act by adjusting the design or process based on results.

Key Questions and Reflections

A fundamental question raised by this study is whether a fully bolted connection can match the ductility and energy dissipation of a welded connection under severe seismic demand. The numerical results suggest that with proper design, the bolted connection can achieve comparable performance, but the connection plate thickness and bolt arrangement become critical design parameters. The study also highlights the importance of the steel tube-concrete interface in the overall seismic response, as the confinement effect significantly enhances the column's post-yield behavior.

Another important consideration is the connection's behavior under combined axial and lateral loading, which is the actual condition in a building column during an earthquake. The numerical model must capture this combined loading accurately, and the results should inform practical design guidelines for bolt size, plate thickness, and connection geometry. The study contributes valuable data for code development and design standardization in the prefabricated composite construction field.

Study Insights and Implications

This research reinforces the growing trend toward prefabricated, bolted connections in seismic design, which aligns with broader industry goals of faster construction, reduced labor dependency, and improved quality control. The numerical approach enables parametric studies that would be prohibitively expensive in the laboratory, allowing engineers to optimize connection designs efficiently. For practicing engineers, the key takeaway is that fully bolted connections are a viable alternative to welded connections for seismic applications, provided that the connection geometry, bolt grade, and plate thickness are carefully selected through rigorous analysis and validated through testing. The study also underscores the need for further experimental validation and code provisions specific to fully bolted prefabricated connections in steel tube concrete columns.