Circumferential Prestress Three-Tube Buckling-Restrained Brace Force Performance

Literature Overview

This paper by Gao Qingshui et al., published in 2019 in Progress in Steel Structure, presents a novel three-tube buckling-restrained brace (TTBRB) incorporating circumferential prestress technology. The research was funded by the Guangdong Power Grid Science and Technology Project (GDKJQQ20153008) and involves collaboration between the Electric Power Research Institute of Guangdong Power Grid Co., Ltd., Guangdong Electric Power Research Institute Energy Technology Co., Ltd., and China Zhongtong Steel Structure Co., Ltd. The work addresses a critical gap in seismic energy dissipation systems by proposing a design that eliminates concrete infill while maintaining superior buckling resistance through a three-layer concentric tube configuration with polymer friction-reduction layers.

Core Technical Concept and Structural Configuration

The TTBRB consists of three concentric tubes: a core tube providing axial stiffness and energy dissipation, an outer sleeve restraining global buckling, and an inner sleeve restraining local buckling. Polyethylene friction-reduction layers are placed between the core tube and both the inner and outer sleeves to minimize friction during axial deformation. This design fundamentally differs from conventional buckling-restrained braces that use solid-section cores with concrete infill.

The key innovation lies in the use of a hollow circular tube as the core material, which provides a larger radius of gyration compared to solid sections. By eliminating concrete infill, the system achieves significant weight reduction and avoids the energy dissipation degradation caused by concrete cracking and damage. The inner and outer sleeves apply circumferential prestress to the core tube through assembly interference fit, thereby modifying the tensile and compressive yield strength of the core tube.

Finite Element Analysis and Key Findings

A verified finite element model was used to investigate the effects of the gap between the inner/outer sleeves and the core tube, as well as the magnitude of circumferential prestress, on the hysteresis performance of the TTBRB. The analysis revealed several critical findings regarding the interaction between gap geometry and prestress level.

When the gap between the sleeves and the core tube is small, the circumferential deformation of the core tube under axial force is constrained by the sleeves, generating circumferential stress. Further application of circumferential prestress significantly alters the axial tensile and compressive strength of the TTBRB. This demonstrates that the prestress mechanism effectively shifts the yield surface of the core tube in the biaxial stress state.

A particularly important finding is that when a gap exists only between the outer sleeve and the core tube (with no gap on the inner side), the TTBRB yields prematurely in tension while its compressive yield strength remains unaffected. The authors recommend this configuration as the preferred scheme for TTBRB implementation, as it provides asymmetric yield behavior that can be strategically exploited in seismic design.

Engineering Practice Implications

From a steel pipe manufacturing and assembly perspective, this research has several practical implications. First, the interference fit assembly method requires precise dimensional control of the three concentric tubes to achieve the desired circumferential prestress level. The tolerance specifications for the inner diameter of the sleeves and the outer diameter of the core tube must be carefully defined to ensure consistent prestress application across production batches.

The polymer friction-reduction layers introduce a new quality control dimension. The thickness, coefficient of friction, and durability of the polyethylene layer directly affect the hysteresis loop shape and energy dissipation capacity. During assembly, surface cleanliness and uniform coating of the friction material must be verified through inspection procedures.

The recommended asymmetric gap configuration (gap only on the outer sleeve side) simplifies the assembly process while providing predictable mechanical behavior. This configuration also reduces the number of critical dimensional interfaces that require tight tolerance control, potentially improving manufacturing yield rates. For seismic isolation applications in power transmission infrastructure, this brace type offers a lightweight, high-performance alternative to conventional concrete-filled buckling-restrained braces.

Study Insights and Conclusions

The TTBRB concept represents a meaningful advancement in seismic energy dissipation technology by leveraging hollow tube geometry and circumferential prestress to achieve enhanced mechanical performance without the weight and durability penalties of concrete infill. The research demonstrates that the interaction between geometric clearance and prestress level creates a tunable mechanical response that can be optimized for specific seismic design requirements. The recommended asymmetric gap configuration provides a practical implementation pathway that balances performance, manufacturability, and cost considerations for engineering applications in critical infrastructure protection.