طراحی بهینه مبتنی بر MOCS به وسیله TMD و FTMD برای ساختمانهای بلند
Abstract
1- Introduction
2- The governing equation of motion for the structure equipped with FTMD including SSI effects
3- A Multi-objective cuckoo search algorithm
4- Numerical studies
5- Results and discussion
6- Conclusions
References
Abstract
The use of TMDs is commonly discouraged for structures subjected to short-duration, pulse-like ground motions such as near-field earthquake excitations. Friction tuned mass damper (FTMD) is an innovative device compound of the traditional linear TMD with the idea of a friction damper which is still in the developmental stage for the seismic applications. The present paper investigates the performance of TMD and FTMD for seismic control of tall buildings under near-field earthquakes including soil-structure interaction (SSI) effects. A 40-story structure with a height-to-width ratio of four, a uniform mass distribution and a linear stiffness distribution in its height is considered in this study. Different conditions of the ground state are also considered for numerical studies. A design process based on a multi-objective cuckoo search (MOCS) algorithm is utilized for the optimum design of TMD and FTMD parameters. The simulation results indicate that ignoring the SSI effects may result in an inappropriate and unrealistic estimation of seismic responses and performance of TMD and FTMD in the high-rise structure. In terms of maximum displacement, acceleration, and drift of floors, it is found that the FTMD is capable of mitigating the structural responses better than the TMD. The efficiency of the FTMD is also compared with the TMD from the energy point of view for dissipation of the seismic input energy. The results show the superiority of the FTMD in the reduction of the maximum seismic input, kinetic and strain energies of the main structure, which confirm the capability of the FTMD being more than the TMD for mitigation of the seismic damages in the tall structure during near-field earthquakes. By increasing the soil softness, an increased trend is often achieved in the maximum seismic input and damage energies, thus ignoring the SSI effects may give an unrealistic result of the performance of TMD and FTMD in reducing the damage of seismic-excited tall buildings.
Introduction
TMD is one of the oldest passive control devices to enhance the safety of the tall structures and to improve the performance of the structures subjected to environmental dynamic loads. TMDs dissipate a portion of the seismic input energy and only a part of this energy is transferred to the main system. TMDs have been implemented in a number of high-rise buildings, towers, and bridges. Citigroup Center in New York City, Yokohama Landmark Tower in Yokohama, Burj Al Arab in Dubai, Trump World Tower in New York City, Taipei 101 in Taipei and The TV Tower in Berlin are some examples of the buildings equipped with TMD [1]. A TMD system consists of a mass, a spring, and a viscous damper. Optimal design of TMD parameters for a single degree of freedom (SDOF) system subjected to certain loads such as external harmonic force, harmonic base acceleration and etc. has been taken into account [2–7]. In these researches, it has been attempted to propose some formulations for optimum tuning of TMD for an SDOF system. However, these formulas are not advisable to use in the highrise structures equipped with TMD because of the consideration of a single vibration mode in the optimum design process of TMD parameters. Moreover, they may not be suitable and applicable for seismicexcited structures. In addition, the only main purpose of the design of TMD is the reduction of the maximum displacement of the main system and the reduction of the maximum acceleration has not been considered in these methods. Hence, the evaluation of the performance of TMDs for mitigation of the seismic responses of the multi-story structures is still an important topic of research [8–12]. In recent years, some meta-heuristic based methods have been employed with the aim of overcoming the above-mentioned design problems. The superiority of meta-heuristic algorithms to the other methods in the literature has been reported [8–11,13,14].