Zhuojin Pipe Fitting Co., LtdExternal Tension Self-Centering Square Steel Tube Concrete Column Base: Seismic Performance and Design Method
Literature Overview
The paper by Wang Xiantie, Lin Linhui, Chen Fengmei, Zhang Li, Luo Yao, and Zheng Jiang, published in the Journal of Xi'an University of Architecture and Technology (Natural Science) in 2017, proposes and investigates an external tension self-centering square steel tube concrete (SSRC) column base. Funded by the National Natural Science Foundation (51678474) and Shaanxi Provincial Natural Science Foundation (2015JM5170), the research originates from Xi'an University of Architecture and Technology and Zhongshan Chunxing Construction Technology Co., Ltd. Self-centering structural systems are of great interest in modern earthquake-resistant design because they can return to their original position after seismic loading, minimizing residual drifts and enabling rapid post-earthquake recovery.
Core Technical Concept
The proposed self-centering column base is based on a spatial hinged mechanism. The square steel tube concrete column is connected to the foundation through a base plate that can lift off from the foundation under seismic moment loading. External post-tensioned tendons (prestressed bars or strands) are anchored outside the column to provide the restoring force that pulls the base plate back to its original position after uplift. The design incorporates replaceable energy-dissipating components, typically friction dampers or metallic yielding devices, which concentrate the inelastic deformation and energy dissipation in easily replaceable elements.
The key mechanical behavior is characterized by two phases: (1) the elastic phase, where the base plate remains in contact with the foundation and the restoring moment is provided by the initial prestress in the tendons; and (2) the uplift phase, where the base plate lifts off and the restoring moment is provided by the combined action of the initial prestress, the incremental tendon tension, the column axial force, and the tensile force generated by the anti-buckling steel plate.
| Design Parameter | Influence on Performance | Design Consideration |
|---|---|---|
| Column cross-section size | Affects uplift moment capacity | Larger sections provide greater axial force contribution |
| Column axial force | Contributes to restoring moment during uplift | Higher gravity loads enhance self-centering |
| Initial prestress level | Determines uplift initiation moment | Must be calibrated against expected seismic demand |
| Anti-buckling steel plate | Provides additional restoring force and prevents base plate buckling | Must be designed for adequate tensile capacity |
| Replaceable energy dissipation component | Controls energy dissipation and ductility | Must be designed for sufficient deformation capacity |
Welding and Fabrication Requirements
The fabrication of the self-centering column base involves several critical weld joints that must meet high quality standards. The base plate-to-column weld is typically a full-penetration groove weld that must achieve full fusion throughout the entire joint. According to GB/T 19847, ASME B31.3, and AWS D1.1, this weld requires 100% radiographic testing (RT) or phased array ultrasonic testing (PAUT) to verify the absence of cracks, lack of fusion, porosity, and incomplete penetration.
The anti-buckling steel plate welds and the anchor bolt welds are also critical joints. The anchor bolts, which house the post-tensioned tendons, must be welded to the base plate with full penetration and inspected for any defects that could compromise the tendon anchorage. Any weld defect in the tendon anchorage zone could lead to catastrophic failure during a seismic event, as the tendon would lose its ability to provide the restoring force.
Post-weld heat treatment (PWHT) should be considered for the base plate assembly if the steel grade exceeds Q345 or the combined thickness of the base plate and column exceeds 40 mm, in accordance with SY/T 0459 or ASME B31.3. The PWHT reduces welding residual stresses that could otherwise contribute to stress corrosion cracking or fatigue failure under cyclic seismic loading.
Design Method and Verification
The authors propose a systematic design method based on the equilibrium of forces and moments at the column base. The uplift moment is determined by the column axial force, the initial prestress, and the geometric configuration of the base plate. The maximum tendon tension is calculated from the maximum expected base rotation, which is determined by the interstory drift ratio specified in the seismic design code. The replaceable energy dissipation components are designed to yield at a predetermined force level, providing controlled energy dissipation while maintaining the self-centering capacity.
Finite element analysis is performed to verify the proposed design method. The FE model captures the nonlinear behavior of the base plate uplift, tendon elongation, concrete bearing, and energy dissipation component yielding. The results confirm that the proposed column base achieves the desired hinged mechanism, satisfies the spatial deformation requirements of the structure, and exhibits good self-centering capability with replaceable energy dissipation.
Study Insights and Conclusions
The external tension self-centering column base represents a significant advancement in seismic-resistant design for steel tube concrete structures. The key advantage is the concentration of energy dissipation in replaceable components, which enables rapid post-earthquake repair and structural recovery. For fabrication and welding professionals, the critical challenge lies in ensuring the quality of the base plate welds and tendon anchorage welds, as these joints directly affect the seismic performance of the entire system. The design method provides a rational framework for determining the tendon prestress, base plate dimensions, and energy dissipation component capacity. Engineers should ensure that all weld joints in the column base assembly meet the highest quality standards, with full NDT coverage and documented material traceability, to guarantee the reliable performance of the self-centering mechanism under seismic loading.