Zhuojin Pipe Fitting Co., LtdPerformance of Double Yield Point Multi-Tube Buckling-Restrained Energy Dissipating Braces
Literature Overview
This paper presents a novel double yield point multi-tube buckling-restrained energy dissipating brace (DYM-DBR) and investigates its seismic performance through analytical modeling and experimental testing. The DYM-DBR brace is designed to provide enhanced energy dissipation capacity and ductility for steel structures subjected to seismic loading. The brace features multiple concentric steel tubes with different yield points, allowing for a staged yielding mechanism that provides a more stable and predictable force-displacement response compared to conventional buckling-restrained braces (BRBs).
Core Technical Viewpoints
The DYM-DBR brace consists of an inner steel tube that yields first at a lower yield point, followed by an outer steel tube that yields at a higher yield point. The multi-tube configuration provides a larger yielding area and more stable energy dissipation compared to single-tube BRBs. The study demonstrates that the DYM-DBR brace exhibits a stable hysteresis loop with a high energy dissipation capacity and good post-yield strength retention. The double yield point mechanism ensures that the brace can sustain large displacements without significant strength degradation, making it suitable for use in high-seismicity regions.
Interpretation of Key Technical Points
The seismic performance of the DYM-DBR brace is evaluated through cyclic loading tests and numerical simulation. The following table summarizes the key performance parameters of the DYM-DBR brace compared to conventional BRBs:
| Performance Parameter | DYM-DBR Brace | Conventional BRB | Improvement |
|---|---|---|---|
| Yield Load (kN) | 1200 | 950 | 26 percent |
| Ultimate Load (kN) | 1550 | 1100 | 41 percent |
| Energy Dissipation (kN-m) | 485 | 280 | 73 percent |
| Ductility Ratio | 8.5 | 6.0 | 42 percent |
| Post-Yield Stiffness | 15 kN/mm | 8 kN/mm | 88 percent |
| Strength Retention at 6 percent Strain | 95 percent | 75 percent | 20 percent |
The study reveals that the double yield point mechanism provides a more stable force-displacement response compared to single yield point BRBs. The first yield point occurs when the inner tube reaches its yield stress, and the second yield point occurs when the outer tube yields. The staged yielding mechanism ensures that the brace maintains a stable load-carrying capacity throughout the loading cycle, even at large displacements. The multi-tube configuration also provides a larger yielding area, which increases the energy dissipation capacity and improves the overall seismic performance of the structure.
Engineering Practice Integration
The fabrication of the DYM-DBR brace requires precise control of the steel tube dimensions and welding quality to ensure proper yielding behavior. The inner and outer steel tubes should be fabricated from low-yield-point steel grades such as Q235 or Q345, while the outer restraining tube should be made from high-strength steel such as Q460 or Q550 to provide adequate confinement. The welding between the tubes and the end plates should be performed using full-penetration butt welds with post-weld heat treatment to relieve residual stresses and prevent brittle fracture. The welding procedure should be qualified in accordance with AWS D1.1 or ISO 3834, and the welds should be inspected using ultrasonic testing (UT) and magnetic particle testing (MT) to ensure full fusion and absence of defects.
The concrete infill in the DYM-DBR brace should be designed with low-strength concrete (C20 to C30) to provide adequate confinement without interfering with the yielding of the steel tubes. The concrete placement should be performed using self-compacting concrete to ensure proper filling of the space between the tubes and the restraining tube. The concrete should be placed in thin layers to control the lateral pressure on the tubes during the setting period. The end plates of the DYM-DBR brace should be designed with sufficient thickness and reinforcement to prevent premature failure at the connections.
Key Questions and Reflections
The study raises important questions about the long-term performance of the DYM-DBR brace under repeated seismic loading. The multi-tube configuration introduces additional interfaces between the tubes, which could be potential sources of fatigue damage under cyclic loading. The study does not fully address the effect of strain rate on the yielding behavior of the steel tubes, which is an important consideration for seismic loading. Additionally, the study does not consider the effect of temperature on the performance of the DYM-DBR brace, which is an important consideration for structures located in extreme temperature environments. The connection details between the DYM-DBR brace and the structural frame also require careful design to ensure proper load transfer and prevent premature failure at the connections.
Study Insights and Implications
The DYM-DBR brace represents an innovative approach to seismic energy dissipation that combines the advantages of multiple yield points and multi-tube configuration to provide enhanced energy dissipation capacity and ductility. The study provides valuable insights into the design and fabrication of DYM-DBR braces, highlighting the importance of controlling the steel tube dimensions, welding quality, and concrete placement to ensure proper yielding behavior. For practicing engineers, the key takeaway is that DYM-DBR braces offer a viable alternative to conventional BRBs for seismic energy dissipation, provided that the unique design and fabrication challenges associated with multi-tube configuration are properly addressed. The study should be extended to include fatigue performance evaluation and temperature effect analysis to provide a comprehensive basis for the widespread adoption of DYM-DBR braces in seismic design.