In this study, to improve the efficiency of TLD, a Variably Baffled TUNED Liquid DAMPER (VBTLD) was used. The baffles are so that they divide the tank into three equal parts when they are fully closed. Furthermore, when they are open or partially closed, they can serve as some obstacles and improve the energy dissipation parameters. When this DAMPER meets an excitation with a specific frequency, the baffles can be TUNED to make the frequency of sloshing equal to that frequency. VBTLD used in this paper could be set for frequency range from 1. 73 to 3 times of a specific frequency. Compared to a simple TLD, VBTLD can be TUNED to a range of frequencies and improve the performance of structure against external excitation. At first, the benchmark building was modeled in OpenSees, then the performance of the device was verified by previous test results. To examine performance of VBTLD, TUNED MASS DAMPER (TMD) with optimal parameters was used in this study. Results show that when the baffles are at the best angle, VBTLD with water depths of 42 mm has maximum response reduction for the numerical model subjected to the Kobe earthquake at intensities of 2, 4, 6 and 8% of the Initial maximum acceleration of the earthquake (PGA=0. 87g). The improvement of structural behavior compared to the optimal MASS DAMPER at maximum acceleration are respectively 23. 1, 22, 14. 6 and 10. 5% while for DAMPER with water depths of 63 mm, they are respectively 8. 2, 9. 5, 6. 7 and 6. 8%.

One of the most up-to-date seismic control devices are friction TUNED MASS DAMPER (FTMD). This type of DAMPER is a combination of a TUNED MASS DAMPER (TMD) and a nonlinear frictional DAMPER. In this paper, the governing equations for a single-degree-of-freedom (SDOF) structure equipped with a FTMD and effective parameters on these systems performance are expressed first. Then, SDOF structures with linear behavior equipped with a FTMD are modeled and validated in OpenSEES software. Finally, the sensitivity analysis of these models to their effective parameters is performed. The structures MASS is assumed to be 10 tons, their period is 0. 5 second and their damping ratio is assumed to be 2%. Nonlinear time history analyses are done for these structures using 40 strong ground motions from the SAC project. These ground motions consist of 20 records (La01-La20) at design basis earthquake (DBE) level and 20 records (La21-La40) at maximum considered earthquake (MCE) level for the Los Angeles area. Effective parameters on the performance of FTMD assumed in this study are the friction coefficient of the DAMPER, the MASS ratio of the DAMPER to the structure and the frequency ratio of the DAMPER to the structure. Average of the structures' maximum displacement is determined for two ground motion records sets and effects of the mentioned parameters on the structural performance are discussed. Results show that the responses are more sensitive to frequency ratio rather than friction coefficient and MASS ratio. The best value for the friction coefficient varies between 0. 1 and 0. 3 at DBE level, and varies between 0. 2 and 0. 4 for MCE level. Based on the results obtained for SDOF structures, application of FTMD on multi-degree-of-freedom (MDOF) is discussed in the next step. This is done for short period structures because this type of DAMPER is more effective on these structures. Three MDOF structures with linear behavior and period of 0. 3, 0. 5 and 1 second are selected and the seismic performance of these structures equipped with FTMD is investigated and compared with the same structures equipped with TUNED MASS DAMPER (TMD). The MASS of stories is uniformly distributed among structure and the MASS of each story is 10 ton. In addition, the damping ratio for the main structure in all models is assumed to be 2% and the stiffness of the stories is decreased linearly with the triangular pattern. Same ground motion records are used for the nonlinear time history analysis of MDOF structures and the results for the mean maximum relative displacement of the stories under DBE and MCE levels are compared for structures with FTMD and TMD. Results show that the structures equipped with FTMD have better performance than the structures equipped with TMD, but with increasing structures period, performance of two systems approach each other. In addition, 3 and 5 story structures equipped with FTMD have better performance at DBE level while a 10-story structure equipped with this DAMPER has better performance at DBE level

In practical applications, it is difficult to link dashpot absolutely rigidly between the structure and the MASS blocks of the multiple TUNED MASS DAMPERs (MTMD). In order to cope with this practical issue, Maxwell DAMPER based multiple TUNED MASS DAMPERs (referred to as the MD-MTMD) have been presented for attenuating the response of structures excited by the ground acceleration. By resorting to the formulated transfer functions of the MD-MTMD structure system, the dynamic magnification factors (DMF) are then defined of the MDMTMD structure system. The criterion for the optimum searching can thus be selected as the minimization of the minimum values of the maximum DMF (min. min. max. DMF).Employing this criterion, the effects of the normalized relaxation time constant (NRTC) are investigated on the optimum parameters and effectiveness of the MD-MTMD. Likewise, the effects of the RTC on the stroke of the MD-MTMD are estimated in terms of maximizing the dynamic magnification factors (DMF) of each MD-TMD in the MD-MTMD. The numerical results have indicated that the MD-MTMD is a feasible solution for the practical issue mentioned above of the traditional MTMD.

The effectiveness of TUNED MASS friction DAMPER (TMFD) in suppressing the dynamic response of the structure is investigated. The TMFD is a DAMPER which consists of a TUNED MASS DAMPER (TMD) with linear stiffness and pure friction DAMPER and exhibits non-linear behavior. The response of the single-degree-of-freedom (SDOF) structure with TMFD is investigated under harmonic and seismic ground excitations. The governing equations of motion of the system are derived. The response of the system is obtained by solving the equations of motion, numerically using the state-space method. A parametric study is also conducted to investigate the effects of important parameters such as MASS ratio, tuning frequency ratio and slip force on the performance of TMFD. The response of system with TMFD is compared with the response of the system without TMFD. It was found that at a given level of excitation, an optimum value of MASS ratio, tuning frequency ratio and DAMPER slip force exist at which the peak displacement of primary structure attains its minimum value. It is also observed that, if the slip force of the DAMPER is appropriately selected, the TMFD can be a more effective and potential device to control undesirable response of the system.

Since there is no closed-form formula for designing TMD (TUNED MASS DAMPER) for nonlinear structures, some researchers have proposed numerical optimization procedures such as a genetic algorithm to obtain the optimal values of TMD parameters for nonlinear structures. These methods are based on determining the optimal values of TMD parameters to minimize the maximum response (e.g. inter story drift) of the controlled structure subjected to a specific earthquake record. Therefore, the performance of TMD that has been designed using a specific record strongly depends on the characteristics of the earthquake record. By changing the characteristics of the input earthquake record, the efficiency of TMD is changed and in some cases, it is possible that the response of the controlled structure is increased. To overcome the shortcomings of the previous researches, in this paper, an efficient method for designing optimal TMD on nonlinear structures is proposed, in which the effect of different ground motion records is considered in the design procedure. In the proposed method, the optimal value of the TMD parameters are determined so that the average maximum response (e.g. inter story drift) resulting from different records in the controlled structure is minimized. To illustrate the procedure of the propose method, the method is used to design optimal TMD for a sample structure. The results of numerical simulations show that the average maximum response of controlled structure resulting from different records is reduced significantly. Hence, it can be concluded that the proposed method for designing optimal TMD under different earthquakes is effective.

One of the most promising and effective passive vibration control DAMPERs is the TUNED MASS DAMPER (TMD). Many conventional optimization criteria are based on the implicit assumption that all parameters involved are deterministically known. Removing this assumption means to convert a conventional optimization into a robust one. In this paper, a model for the robust optimum design of TMD is provided so that the optimal design of DAMPER by considering the uncertainties possible in the earthquake load and also the structure properties can be achieved. The structural vibration control of the main system with a single linear TMD under a stochastic dynamic load is investigated. The dynamic input is represented by a random base acceleration, modeled by a stationary filtered white noise process. It is assumed that not only mechanical parameters of the main structure but also the input spectral contents are affected by uncertainty. The standard deviation of displacement of the protected main structure (dimensionless by dividing to the unprotected one) is calculated as the deterministic objective function (OF), and to achieve a robust design the mean and standard deviation of OF are considered as a multi-objective function which shall be minimum. The damping ratio and the frequency of TMD have been selected as design parameters. The results provide the different choices for designers to select an optimal TMD based on the priority of minimum mean of the maximum displacement of the structure or the minimum dispersion in a random space.

In this paper, designing variable stiffness semi-active TUNED MASS DAMPER (SATMD) for mitigating the responses of nonlinear structures under earthquake excitation has been studied. Two semi-active control algorithms based on instantaneous optimal control and clipping control concept as well as modified balance control have been developed to determine the optimal stiffness of SATMD for nonlinear structures in each time step. For determining optimal parameters of semi-active control system including the weighting matrices in performance index of control algorithm as well as the maximum and minimum values of SATMD stiffness, an optimization problem for minimization of structure maximum response has been defined where genetic algorithm (GA) has been used for optimization. For numerical simulations, an eight-story nonlinear shear building with bilinear hysteresis behavior has been subjected to a white noise excitation and optimal SATMDs have been designed. The results showed that optimal variable stiffness SATMD using both control algorithms has been effective in suppressing the seismic responses of nonlinear structure. Also, variable stiffness SATMD shows better performance than TMD and variable damping SATMD in structural response controlling. Comparing the performance of the variable stiffness SATMD under testing earthquakes which were different from design record, showed that the efficiency of SATMD depends on the characteristics of excitation, hence design record needs to be chosen properly.

This study is investigated the optimum parameters for a TUNED MASS DAMPER (TMD) under the seismic excitation. Shuffled complex evolution (SCE) is a meta-heuristic optimization method which is used to find the optimum damping and tuning frequency ratio for a TMD. The efficiency of the TMD is evaluated by decreasing the structural displacement dynamic magnification factor (DDMF) and acceleration dynamic magnification factor (ADMF) for a specific vibration mode of the structure. The optimum TMD parameters and the corresponding optimized DDMF and ADMF are achieved for two control levels (displacement control and acceleration control), different structural damping ratio and MASS ratio of the TMD system. The optimum TMD parameters are checked for a 10-storey building under earthquake excitations. The maximum storey displacement and acceleration obtained by SCE method are compared with the results of other existing approaches. The results show that the peak building response decreased with decreases of about 20% for displacement and 30% for acceleration of the top floor. To show the efficiency of the adopted algorithm (SCE), a comparison is also made between SCE and other meta-heuristic optimization methods such as genetic algorithm (GA), particle swarm optimization (PSO) method and harmony search (HS) algorithm in terms of success rate and computational processing time. The results show that the proposed algorithm outperforms other meta-heuristic optimization methods.