USE AND DESIGN OF ACTIVE BRACING SYSTEMS IN THE PROTECTION OF STRUCTURES UNDER SEISMIC EXCITATION

Abstract

Earthquakes can cause significant deformation, loss of performance and various types of cracks in the view of structures. Higher buildings are especially vulnerable to these effects due to their greater flexibility and increased peak displacements. This situation poses serious risks to both life safety and the durability of structures. As a result, vibration control has become an increasingly critical research area in earthquake engineering. Earthquake engineers have developed control mechanisms in this field, categorized as passive and active systems. While passive control systems can be effective under certain conditions, their limited adaptability, inability to be reused after earthquakes and dependence on the specific characteristics of seismic events mean they are not always sufficient. Therefore, active control systems offering higher performance have been developed. Among active control systems, the Active Bracing System (ABS) stands out. ABS uses diagonally placed steel rods and cables, along with actuators, to generate

counteracting control forces. These forces help dissipate a significant portion of the energy generated during an earthquake, reducing vibrations in the structure. In this study, two different control approaches—LQR (Linear Quadratic Regulator) and Lyapunov-based control—were used together to enhance the effectiveness of ABS. The LQR method determines the optimal force to reduce system responses with minimal control energy, while the Lyapunov approach ensures system stability and keeps the control forces within physical limits. Combining these two methods enables both effective and safe control performance. In short, LQR optimizes the control force, while Lyapunov ensures the system operates within safe boundaries, making the system more reliable and realistic. In the scope of this study, two reinforced concrete building models—one with 6 stories and the other with 10 stories—designed. ABS elements were implemented on the 1st and 4th floors of the 6-story building, and on the 1st, 5th and 9th floors of the 10-story building. The mathematical model of the structures was developed using mass, stiffness, and damping matrices, and analyses were carried out using Mathematica software. El Centro earthquake values were used as ground acceleration. Time-domain analyses were performed and for both controlled and uncontrolled systems, displacement, velocity, and acceleration responses, actuator forces, modal analysis findings, and peak values at each floor were obtained. The results showed that all dynamic responses were significantly reduced in systems equipped with ABS using LQR and Lyapunov-based control. In particular, the reduction of displacement and acceleration at upper floors demonstrated that the applied control system noticeably improved the structural performance. Additionally, by integrating LQR and Lyapunov-based control with In the ABS system, control forces are kept within physical limits to ensure system stability. In conclusion, the LQR and Lyapunov-supported Active Bracing System (ABS) has proven to be a highly effective method for enhancing the earthquake performance for multi-story buildings with reinforced concrete. The findings indicate that active control technologies like ABS can be successfully applied to improve safety and durability in tall buildings, bridges and critical public structure