The convergent bracing system has served as a lateral load-bearing mechanism in buildings for many decades. Despite its widespread application, it exhibits two significant weaknesses: low energy dissipation capacity and susceptibility to buckling under high compressive loads. To address these issues, yielding dampers have been introduced in recent decades. These dampers enhance the energy dissipation capacity of bracing elements in convergent bracing frames and help prevent buckling. Numerous types of yielding dampers have been proposed; however, most suffer from one or more of the following drawbacks: they exhibit different behaviors in tension and compression, they are complex and difficult to manufacture, and they lack a straightforward design methodology.
This paper introduces a novel yield-based energy damper known as the double square tube steel damper. This system is designed for installation in bracing elements and demonstrates consistent behavior under both compression and tension, making it simple to manufacture and design. The proposed damper dissipates energy through two square tubular sections, which are integrated with the bracing element, in such a way that when subjected to axial force, one section experiences tension while the other experiences compression.
The paper initially presents the hysteretic load-displacement behavior of the damper through laboratory testing and finite element analysis. The laboratory samples and finite element models provide insights into the damper’s performance, confirming its capacity for stable and efficient energy dissipation. Based on the results of the finite element analysis for the double square steel damper, which considers various sizes and thicknesses of the square parts, two simple formulas are derived. These formulas relate the initial stiffness and yield strength of the damper to the mechanical and geometric characteristics of the yielding components, providing a straightforward method for design.
To further demonstrate the effectiveness of the proposed damper in reducing the seismic response of buildings, its performance is evaluated in a five-story building equipped with chevron bracing. This evaluation is conducted through a series of nonlinear time history analyses that simulate the building's response to seismic events. The results of these analyses reveal that the implementation of the proposed dampers, with appropriate stiffness and strength, can significantly mitigate seismic impacts. Specifically, the maximum roof acceleration and the maximum base shear of the building can be reduced by approximately 30% and 20%, respectively, compared to a building utilizing conventional bracing systems.
The force-displacement hysteresis diagram of the double square tube steel damper exhibits symmetrical geometry and an optimal width, which indicate its stability and high energy absorption capacity. This symmetrical behavior in both tension and compression presents a significant advantage over the buckling-prone behavior of conventional braces. The consistent performance under different loading conditions ensures that the damper can reliably dissipate energy, enhancing the overall resilience of the structure during seismic events.
Another significant advantage of the proposed damper is its replaceable nature within the bracing system. This feature not only facilitates maintenance and replacement but also offers substantial economic benefits. By allowing easy replacement of the damper after a seismic event, the overall cost of structural maintenance and repair are reduced.
Moreover, the improved performance characteristics of the damper elevate the structure's performance level from Life Safety (LS) to Immediate Occupancy (IO), offering improved protection for both the building and its occupants.
In conclusion, the double square tube steel damper addresses the critical weaknesses of conventional convergent bracing systems by offering improved energy dissipation and resistance to buckling. Its simple design, ease of manufacturing, and reliable performance under both tension and compression make it a practical and effective solution for enhancing the seismic resilience of buildings. The positive results from both experimental testing and finite element analysis, coupled with its successful application in a five-story building, underscore the potential of this innovative damper to enhance safety and economic efficiency of seismic design.