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Xie J.,Zhejiang University | Garber J.,RWDI Inc.
Wind and Structures, An International Journal | Year: 2014

The high-frequency force-balance (HFFB) technique and its subsequent improvements are reviewed in this paper, including a discussion about nonlinear mode shape corrections, multi-force balance measurements, and using HFFB model to identify aeroelastic parameters. To apply the HFFB technique in engineering practice, various validation studies have been conducted. This paper presents the results from an analytical validation study for a simple building with nonlinear mode shapes, three experimental validation studies for more complicated buildings, and a field measurement comparison for a super-tall building in Hong Kong. The results of these validations confirm that the improved HFFB technique is generally adequate for engineering applications. Some technical limitations of HFFB are also discussed in this paper, especially for higher-order mode response that could be considerable for super tall buildings. © 2014 Techno-Press, Ltd.

Love J.S.,RWDI Inc. | Tait M.J.,McMaster University
Journal of Sound and Vibration | Year: 2015

Dynamic vibration absorbers (DVAs) with nonlinear damping are often modelled using a power-law equivalent viscous damping relationship. There is currently not a method available to predict the peak response of this type of nonlinear DVA without resorting to computationally expensive nonlinear simulations. Since the peak response of the DVA is required during the design process, it is advantageous to have a simplified method to estimate the peak response. In this study, statistical linearization is employed to represent the nonlinear damping as amplitude-dependent viscous damping and predict the rms response of the structure-DVA system. Subsequently, statistical nonlinearization is used to describe the probability density function of the DVA response amplitude. A probability density function is developed, which enables the peak response expected during an interval of time (e.g. 1-h) to be estimated from the rms response of the structure-DVA system. Higher power-law damping exponents are shown to result in smaller peak factors. Results of nonlinear simulations reveal that the model can estimate the peak structural and DVA responses with acceptable accuracy. A plot is developed to show the peak factors for nonlinear DVAs as a function of the number of system cycles for several power-law damping exponents. This plot can be used to estimate the peak response of a nonlinear DVA as a function of its rms response. © 2015 Elsevier Ltd All rights reserved.

Love J.S.,RWDI Inc. | Tait M.J.,McMaster University
JVC/Journal of Vibration and Control | Year: 2015

Tuned liquid dampers (TLDs) employ sloshing fluid to reduce the resonant response of structures. Existing structure-TLD models are limited to rectangular or circular tanks, shapes that may not always be feasible in practice due to geometric restrictions of the building floor plan. This paper utilizes an equivalent linearized mechanical model and a nonlinear multimodal model to predict the response of the structure-TLD systems where the TLD tank geometry is irregular.Experimental structure-TLD system tests are conducted that consider two irregular tank shapes. Response history plots and frequency response plots of the structural displacement and TLD wave heights are created to evaluate the models using the experimental results. The parent distributions and 10-minute peak distributions of the structural displacements and TLD wave heights are created for the simulated and experimental results. These distributions indicate that both the linearized and nonlinear models can accurately predict the structural response; however, the linearized model substantially underestimates the peak wave heights. Since wave heights are required to establish the required tank free board, or roof impact pressures, it is concluded that nonlinear analysis of the structure-TLD system model is required before a TLD design is finalized. © The Author(s) 2013.

Love J.S.,RWDI Inc. | Tait M.J.,McMaster University
Computers and Fluids | Year: 2013

Tuned liquid dampers (TLDs) utilize sloshing fluid to absorb and dissipate structural vibrational energy. A prerequisite to TLD design is establishing a suitable model to describe the fluid response. Numerous fluid models have been presented in literature; each utilizes simplifying assumptions which make the model valid under certain flow conditions. TLDs are often designed with fluid depth to tank length ratios less than 25%. At these depths, response characteristics change relatively rapidly with decreasing fluid depth, making it unlikely that one model is suitable over the entire range. The goal of this study is to determine when certain fluid models can be used.Three fluid models are considered: shallow water wave theory, a small depth multimodal model, and an intermediate depth multimodal model. The models are briefly presented and their basic assumptions are identified. A parametric shake table testing program is conducted which varies the fluid depth of a rectangular tank equipped with damping screens. Experimental time history and frequency response plots are created for comparison with each fluid model at several fluid depth ratios and excitation amplitudes. The range of validity for each model is described in terms of the fluid depth ratio, and the Ursell parameter. The results of this study will help TLD designers determine a suitable fluid model for dynamic analysis of a structure-TLD system. © 2013 Elsevier Ltd.

Love J.S.,RWDI Inc. | Tait M.J.,McMaster University
Structural Control and Health Monitoring | Year: 2014

Tuned liquid dampers (TLDs) control the wind-induced vibrations of tall buildings using sloshing fluid. TLD tanks of complex geometry may be required in practice due to space limitations; however, their behaviour has not been considered in the literature. This study develops and experimentally validates a model to describe the structure-TLD interaction of a 2D system when the TLD tank geometry is complex. The equations of motion of the structure-TLD system are developed using Lagrange's equation. In general, the 2D structure-TLD interaction must be represented as a coupled four degree of freedom system. The model is validated using new structure-TLD system tests where the structure is subjected to 1D and 2D harmonic and random excitation. Two TLD tanks of complex geometry are considered; the first tank is anti-symmetric about both axes, whereas the second tank is symmetric about both axes. For the anti-symmetric tank, energy transfer between orthogonal structural sway modes and sloshing modes is significant; however, for the symmetric tank, this energy transfer is negligible. Experimental results indicate that the model adequately predicts the structural response; however, the nonlinear behaviour of the fluid response cannot be captured by the linearized model. © 2013 John Wiley & Sons, Ltd.

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