The main purpose of this study is to identify a suitable control method for semi-active tuned vibration absorbers (TVAs) in structural vibration applications. Four control policies are considered. The semi-active control schemes include the following: velocity-based, on-off groundhook control (on-off VBG); velocity-based, continuous groundhook control (continuous VBG); displacement-based, on-off groundhook control (on-off DBG); and displacement-based, continuous groundhook control (continuous DBG). A force-excited model that can be representative of many structural systems is adapted as the baseline model for our analysis. Each of the control policies is applied to the baseline model coupled with a TVA. In order to equally evaluate the control policies, the TVA parameters are optimized according to each policy using numerical optimization techniques. The optimal design parameters are obtained based on minimization of peak transmissibility. The performances of each of the optimized cases are then compared along with the equivalent passive model using the peak transmissibility criteria. The results indicate that all of the semi-active peak transmissibilities are lower than those of the passive, implying that the semi-active TVAs are more effective in reducing vibration levels. The results further indicate that on-off DBG performs the best among the considered control polices.
Annoying levels of vibration on long-cantilevered structures owing to crowd movements during musical concerts, sporting events, aerobics exercises and so on, have become more common in recent years. There are still a number of issues related to excessive floor vibrations owing to human activities that need to be addressed such as: guidelines for more accurate analytical representation of structural parameters to predict floor dynamic response, better definition of forcing functions to simulate human activities in a computer model and finally more consistent methods of evaluation and assessment of vibrations. This paper focuses on the requirements and guidelines for the evaluation and assessment of vibrations as related to acceptability for human exposure. It briefly reviews the provision of several current standards and design guides for the evaluation and assessment of building vibrations owing to human rhythmic activities. Using the measured vibrations generated by crowd activities on a large cantilevered structure during several rock concerts, collected by way of a remote vibration monitoring system, this paper compares these provisions with each other and draws conclusions on their applicability. New relationships between the current vibration evaluation parameters along with guidance for the assessment of human exposure to vibration owing to rhythmic activities are proposed. Notation a p absolute peak acceleration a rms root-mean-square (rms) of acceleration a w (t ) frequency-weighted acceleration a w (t o ) running rms of weighted acceleration a w, p absolute peak frequency-weighted acceleration a w,rms rms of frequency-weighted acceleration a w,rms1 rms of frequency-weighted acceleration when the structure started to fill a w,rms2 rms of frequency-weighted acceleration at the end of the event C F crest factor MTVV maximum transient vibration dose MTVV 1 MTVV using one-second integration time MTVV 10 MTVV using ten-second integration time p 1 , p 2 , p 3 curve-fit equation coefficients T vibration exposure time, time period that the structure was mostly occupied T 1 record time when the structure started to fill T 2 record time at the end of the event t time variable t9 integration time t o instantaneous time VDV vibration dose value VDV 1 VDV when the structure started to fill VDV 2 VDV at the end of event W b frequency-weighting function for vertical vibrations based on BS 6472-1: 2008 or BS 6841: 1987 W d frequency-weighting function for horizontal vibrations based on BS 6472-1: 2008 or BS 6841: 1987 or ISO 2631-1: 1989 or ISO 2631-1: 1997 or ISO 10137: 2007 W g frequency-weighting function for vertical vibrations based on ISO10137: 2007 or ISO 2631-2: 1989 W k frequency-weighting function for vertical vibrations based on ISO 2631-1: 1997 W m frequency weighting function for vibrations based on ISO 2631-2: 2003
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