No abstract

Summary Urban cities worldwide are filled with low‐rise to high‐rise buildings which may be vulnerable to both earthquake and wind excitations depending on their locations. Here, the performance of optimally designed nonlinear tuned mass dampers (TMDs) is evaluated for the vibration control of multi‐story structures under the multi‐hazard scenario. The functionality of the linear dashpot deteriorates with age; therefore, in this paper, nonlinearity is introduced in the damping element of the passive TMD. Two nonlinear TMDs are investigated, one with Bingham‐type damping element and another comprising viscous power law damping. The optimally designed TMDs are attached to five multi‐story structures with the number of stories ranging from 5 stories to 25 stories. Subsequently, the performances of the various TMD designs are evaluated when the structures are subjected to an ensemble of nonconcurrent earthquake and wind‐borne loads. Also, the efficacy of the equivalent pulse‐type ground acceleration in the prediction of structural response under near fault earthquake‐induced loads is studied. The degradation in the performance of the TMDs is discussed when the structures are subjected to earthquake‐induced loads, but the TMDs are designed to be effective against wind‐imparted loads, and vice versa. It is observed that the nonlinear TMDs could achieve reductions in the structural response comparable to that achieved by an optimally designed linear TMD, at the same time negating the shortcomings of the linear viscous damper.

The tuned mass damper (TMD) is a well-established vibration control device that has been implemented in several structures worldwide. The performance of passive TMD is greatly dependent on its design parameters. A key issue for the design of the optimal TMD is the identification of the parameters of the structure to which the TMD is to be attached. Here, it is important also to consider the perturbations that may arise in the structural frequency due to different practical issues. The present work focusses on this and aims to obtain the optimum TMD parameters in a Genetic Algorithm (GA) framework. The results of the proposed optimal strategy, in terms of optimal tuning ratio and optimal damping ratio, for a given value of the mass ratio, are compared with some of the existing optimal solutions for linear TMD under base excitation. The effectiveness of all these optimally designed TMDs in reducing the structural response is further demonstrated when the structure-TMD system is subjected to recorded earthquake ground motions. It is seen that in the tuned condition, the control performance obtained by the different designs of the TMD are similar to each other, although having some minor differences in the values of the optimum parameters. Also, the effectiveness of the different TMD designs in the detuned condition is investigated, in which the present design technique is found to be the most effective.

Lifeline structures such as hospital buildings need to be specifically designed such that they experience reduced vibrations when subjected to earthquake excitations because it will be difficult to vacate hospital buildings under the event of any earthquake. Therefore, to ensure operational condition under earthquake excitations in an existing hospital building, the present study utilizes flexible unbonded fiber-reinforced elastomeric isolators (UFREIs) for its seismic isolation. The UFREI-based isolation system is designed to restrict the structural acceleration within the tolerable limits for the building inhabitants even during earthquake hazards. However, the use of such flexible isolators results in excessively large bearing displacements, which either may not be practical and/or pose several serviceability issues. Therefore, tuned mass damper (TMD) is attached to the base floor of the UFREI-isolated hospital building to reduce the large isolator displacements. Properties of the hybrid vibration control system are designed according to the site-specific scenario in New Delhi, India. Further, nonlinear time-history analyses of the UFREI-isolated hospital building with the TMD are carried out, and responses are compared with its uncontrolled response. Results show that the peak bearing displacement response of the UFREI-isolated hospital building is reduced by 9% to 27%, due to the addition of the TMD. Importantly, the required design displacement of the UFREI-based isolation system is decreased by 27%, without compromising the effectiveness of base isolation. In fact, the performance of the hybrid vibration control system is superior to the base isolation system alone.