Seismic Performance Improvement of Chevron Braced Frames Employing a Two-Level Energy Dissipation System with Knee Braces and Ring Dampers

Astract

In recent decades, seismic engineering has shifted from conventional strength-based design to Performance-Based Design (PBD) to address the limitations of traditional methodologies. While strength-based approaches successfully prevent catastrophic structural collapse, they often result in extensive structural and non-structural damage and severe economic losses. PBD addresses these shortcomings by prioritizing precise control over a structure’s dynamic response during seismic events, with a primary focus on managing and dissipating kinetic energy to ensure post-earthquake functionality.

A critical strategy for achieving these objectives is the integration of Passive Energy Dissipation (PED) systems. These systems function as sacrificial elements designed to intercept and absorb a significant portion of seismic energy before it can impact the primary load-bearing components. By effectively diverting this destructive energy away from the main structural frame, PED systems substantially reduce stress and deformation demands. This proactive energy management enhances the overall resilience of the built environment, ensuring that structures remain operational even after major seismic events. Consequently, the implementation of PED technology represents a vital advancement in the pursuit of safer, more sustainable, and economically efficient infrastructure in regions susceptible to high seismic hazards.

This research investigates the seismic performance of a novel chevron bracing system equipped with hybrid knee and ring steel dampers exhibiting a two-stage yielding mechanism. In this system, the knee damper acts as an initial fuse at low load levels, while the ring dampers engage at higher levels, completing the energy dissipation process and enhancing structural response stability. This sequential yielding, in addition to increasing ductility, contributes to a more balanced distribution of energy demand within the system. To control excessive deformations in the knee element, a high-stiffness displacement-limiting mechanism based on slotted holes is proposed. This mechanism remains within the elastic range, preventing premature detachment of the element from the load cycle. Furthermore, a design framework and governing relationships are developed to determine the strength and stiffness of the system components and to achieve the desired sequence of fuse activation. The performance of the proposed system was evaluated through nonlinear finite element modeling in ABAQUS, validation of the numerical model against experimental results, and parametric analyses on several models with varying geometric parameters. The validation results showed that the difference in cumulative dissipated energy between the numerical and experimental results was less than 4%, while the difference in the slopes of the hysteretic responses was less than 3%, indicating good agreement between the numerical model and experimental observations. Results indicate that increasing the thickness of the ring dampers significantly enhances the ultimate strength and post-yield stiffness, while having a negligible impact on the initial stiffness. Furthermore, an investigation into the effect of the web thickness of the knee members revealed that a 25% increase in their thickness leads to approximately a 24% increase in the initial yield strength, whereas a 25% reduction results in approximately a 23% decrease in this parameter. In addition, variations in the length of the knee element have a noticeable effect on the initial stiffness of the system, while their effects on the yield strength and ultimate strength are relatively limited; a 20% change in the knee element length results in approximately a 10% change in the yield strength. A comparison of the hysteretic curves of the proposed MRD+DKBF braced frame with single-stage braced frames (MRBF and DKBF) demonstrates a more stable behavior and higher ductility in the proposed system. The energy dissipation in the MRD+DKBF frame increased by approximately 1.50 and 2.33 times compared to the MRBF and DKBF specimens, respectively. The concentration of plastic deformations within the dampers further supports the effective performance of the capacity design in this system. Based on the findings, the utilization of hybrid dampers with a two-stage yielding mechanism can be considered an effective approach for enhancing seismic performance, increasing ductility, and improving the energy dissipation capacity of structures.