Pseudo-Dynamic Testing of Hollow Layered Steel Tubular Concrete Column with Single-Side Bolt Connection

Literature Overview

This paper by Wang Jingfeng and colleagues from Hefei University of Technology, published in the China Civil Engineering Journal (Volume 52, Issue 9, 2019, pages 1-11), investigates the seismic performance of a square-in-square hollow layered steel tubular concrete (HLSTC) column connected to beams via single-side bolt end-plate connections. The study employs pseudo-dynamic testing methodology to evaluate the dynamic characteristics and failure modes of the connection under simulated earthquake loading. The research was supported by the National Natural Science Foundation of China (Grants 51478158 and 51178156).

Structural System Description

The hollow layered steel tubular concrete column system employs a square-in-square configuration, where an outer steel tube encloses an inner steel tube, with concrete filling the space between them. This layered configuration provides several advantages over conventional solid-section STC columns:

• Reduced self-weight due to the hollow inner tube
• Improved confinement of the core concrete through the double-tube system
• Enhanced ductility through the interaction between the two tube layers
• Potential for modular construction and prefabrication

The single-side bolt end-plate connection is a bolted connection where the beam end plate is connected to the column flange using bolts on only one side, as opposed to conventional double-side bolted connections. This arrangement simplifies field assembly and facilitates disassembly for building maintenance or relocation.

Pseudo-Dynamic Testing Methodology

Pseudo-dynamic testing is a hybrid experimental-numerical method that combines real-time numerical integration of the equation of motion with quasi-static experimental loading. The test setup involves:

• A typical interior column connection as the test model
• Real-time control system connecting the hydraulic loading apparatus to a numerical model
• Incremental displacement loading based on the computed dynamic response at each time step
• Measurement of displacement, acceleration, and load time histories

The study investigated three primary variables:

Key Performance Indicators

The following seismic performance indicators were evaluated:

1. Damping ratio - The energy dissipation capacity of the connection, derived from the hysteresis loops
2. Stiffness degradation - The progressive reduction in connection stiffness under cyclic loading
3. Cumulative hysteresis energy - The total energy dissipated through the loading cycles
4. Maximum displacement time history - The peak displacement response under each seismic scenario
5. Maximum acceleration time history - The peak acceleration response, critical for non-structural components

Results and Technical Analysis

The test results demonstrated that the square-in-square HLSTC column with single-side bolt end-plate connections exhibits superior seismic performance and good ductility. The key findings include:

• The connection maintained stable load-carrying capacity through multiple loading cycles
• The hollow ratio significantly influenced the connection stiffness; a higher hollow ratio generally reduced initial stiffness but improved ductility
• The end-plate configuration affected the failure mode; thicker end plates promoted beam yielding before connection failure
• The use of detachable composite floor slabs had minimal adverse effect on the seismic performance of the connection
• The connection demonstrated stable hysteresis loops with minimal pinching, indicating good energy dissipation

From a fabrication and welding perspective, the square-in-square column configuration requires careful attention to the welding of the inner and outer tubes. The inner tube must be precisely positioned within the outer tube, and the connection between the two tubes (if welded) must maintain adequate spacing for concrete placement. The bolted end-plate connection reduces the need for field welding, which is advantageous for construction quality control, but the factory welding of the end plates to the beam sections must be of high quality.

Engineering Practice Considerations

The single-side bolt connection offers distinct advantages for prefabricated steel structure applications:

• Field assembly requires no welding, reducing construction quality variability
• Disassembly capability supports building reuse and retrofitting
• The connection is suitable for high-seismicity regions where ductile connection behavior is essential
• The hollow layered column system reduces material consumption while maintaining structural performance

However, engineers should note that the single-side bolt arrangement creates an asymmetric load path, which may lead to torsional effects in the connection. The bolt group must be designed to resist both shear and moment, and the end plate must be thick enough to prevent local yielding. The hollow ratio selection involves a trade-off between weight reduction and stiffness retention, and should be optimized for each specific application.

Study Insights

This research contributes valuable experimental data for the seismic design of hollow layered STC columns, a relatively new structural system. The pseudo-dynamic testing methodology provides more realistic dynamic response data than quasi-static cyclic tests, making the findings particularly relevant for performance-based seismic design. The combination of the hollow layered column with the single-side bolt connection represents a promising approach for prefabricated steel structures in high-seismicity regions. The study validates that proper design of the connection detail can achieve the desired "strong connection, weak member" seismic design concept, ensuring that plastic deformation is concentrated in the beams rather than at the connections.