Degree

Doctor of Engineering (DEng)

Department

Civil and Environmental Engineering

Document Type

Dissertation

Abstract

High-rise buildings and wind turbines under dynamic environmental loads experience excessive vibrations. Excessive vibration in tall buildings can exceed both strength and serviceability limit states, leading to structural damage and occupant discomfort. In contrast, unwanted vibration in wind turbines can have adverse effects on energy generation, fatigue life, and initial cost. The current research investigates two high-rise buildings and a 5 MW wind turbine from the National Renewable Energy Laboratory (NREL) numerically and experimentally to single out the optimal vibration mitigation techniques under diverse environmental loads. A performance-based design of viscous dampers with magnifying mechanism was employed to mitigate the vibration in 76 story benchmarks building under seismic and wind loads. Displacement, acceleration, inter-story drift ratio, shear force, and base bending moment are considered along with other concise sets of system-level performance criteria that are easily understood by decision-makers and/or stakeholders of diverse technical backgrounds. The results suggest viscous dampers as a viable solution for vibration attenuation in high-rise buildings. Viscous dampers can reduce structural and nonstructural damage by counteracting multi-hazard forces in real-time. We proposed a robust pendulum-pounding tuned mass damper (PTMD) to attenuate vibration in wind turbines. The NREL wind turbine equipped with the pendulum PTMD was modeled following the Lagrangian method to facilitate the numerical study. The results reveal that the optimum frequency ratio of the pendulum PTMD can be far different from the corresponding tuned mass damper (TMD) frequency ratio. The pendulum PTMD exhibits higher performance over the corresponding TMD, in terms of robustness and capabilities to reduce maximum accelerations and displacements under earthquakes. We verified the numerical results using a shake table experiment under several earthquake excitations. We carried out dynamic analysis investigations of a 42-story timber-hybrid building, along with a comparative control performance study of three mass dampers: (1) pendulum pounding tuned mass damper (PTMD), (2) tuned mass damper inerter (TMDI), and (3) tuned mass damper (TMD) under the earthquake excitations. Coupling the inerter with TMD to form TMDI can impact the optimal frequency ratio and damping ratio of TMD, resulting in reduced performance. Compared to TMD/TMDI, the pendulum PTMD was more robust, with a higher potential to reduce building responses under seismic loads. We performed aerodynamic investigations of a large-scale high-rise building model at a high Reynolds number (~1 million) to evaluate wind pressure distribution and wind loads. To demonstrate, aerodynamic testing of a 1:50 scale test model was executed with two aspect ratios (B/D = 0.67 and 1.5), and the test results were compared to the results from a wind tunnel experiment at a smaller scale (1:200). The wind-induced responses were evaluated by applying wind loads on an equivalent lumped mass model. The pendulum PTMD was suggested to reduce excessive vibration. On the one hand, finding from this study will ensure the occupant comfort under wind loads and reduce structural/nonstructural damage under seismic loads in tall buildings. On the other hand, it will enhance the performance of wind turbines leading to higher efficiency, lower maintenance, and higher operational life.

Date

11-1-2021

Committee Chair

Aly, Aly Mousaad

Available for download on Friday, October 27, 2028

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