Alongwind Responses Of Tall Buildings Research Articles

LQG Control of Along-Wind Responses of Tall Building Using Composite Tuned Mass Dampers

A composite tuned mass damper(CTMD) is a vibration control device consisting of an active-passive tuned mass dampers supported on the primary vibrating structure. The performance of CTMD in mitigating wind-induced vibration of tall building is investigated. Optimum parameters of a passive tuned mass damper(PTMD)for minimizing the variance response of the damped primary structure under random loads, with different mass ratio of an active tuned mass damper(ATMD) to a PTMD have been used for the optimum parameters of CTMD. The active control force generated by ATMD actuator was estimated by using linear quadratic Gaussian(LQG) controller, and the fluctuating along-wind load, treated as a stationary random process ,was simulated numerically using the along-wind load spectrum proposed by Solari .Comparing the along-wind rms response of tall building without a CTMD, the CTMD is effective in reducing the response to 40%~45% of the response without the CTMD. Therefore, the CTMD system was effective in reducing wind-induced vibration of tall building.

Passive control of along-wind response of tall building

Most of modern tall buildings using lighter construction materials with high strength and less stiffness are more flexible, which occurs excessive wind-induced vibration, resulting in occupant discomfort and structural unsafety. It is necessary to predict wind-induced vibration response and find out a method to mitigate such an excessive wind-induced vibration at the preliminary design stage. Recently, many studies have been conducted in using actuator control force based on the linear quadratic optimum control algorithm. It was accepted as a common knowledge that the performance of passive tuned mass damper (TMD) could increase by incorporating a feedback active control force in the design of TMD, which is called active tuned mass damper (ATMD). However, the fact that ATMD is superior to TMD to reduce wind-induced vibration of a tall building is still a question. The effectiveness of TMD for mitigating the along-wind vibration of a tall building was investigated. Optimum parameters of tuning frequency and damping ratio for TMD under a random load which has a white noise spectra were used. Fluctuating along-wind load acting on a tall building treated as a stationary Gaussian random process was simulated numerically using the along-wind load spectra. And using this simulated along-wind load, along-wind responses of a tall building with and without TMD were calculated and the effectiveness of TMD in mitigating the along-wind response of a tall building was found out.

Parametric study on the along-wind response of the CAARC building to downbursts in the time domain

A primary investigation on the along-wind responses of tall buildings to thunderstorm downbursts is presented in this paper. Related characteristics of downbursts are first reviewed. By assuming that downbursts are fully correlated over the building height, a simple model is applied for downburst wind speeds. As a representative, the CAARC building is modelled as a linear 2-D cantilever beam and a base-pivoted single degree of freedom rigid body as well, and subjected to non-stationary conceptual, actual, and wind tunnel-simulated downburst velocity time histories. For comparison, a typical stationary wind speed record is also applied to the building. The maximum dynamic magnification factor (MDMF) is introduced as a non-dimensional variable to measure and compare the effect of non-stationary downbursts on the building. The definition of MDMF is the ratio of the maximum dynamic response to the corresponding maximum static response. Relationships between MDMF of the first normal coordinate and MDMFs of responses are derived. For the parametric study, MDMFs of the first normal coordinate for all the time histories are obtained as functions of the building first circular frequency and the first modal damping ratio. Effects of gust profiles and building characteristics on MDMFs and structural along-wind responses are observed theoretically and by the parametric study. The characterizing period for downbursts could be 36 s . Differences between MDMFs from the downbursts and those from the typical wind are noted. In practice, the procedure and the results presented here may be used to estimate the maximum dynamic response of a tall building subjected to severe downburst winds.

Codification of Wind-Induced Dynamic Responses of Tall Buildings

This paper discusses the codification of wind- induced dynamic responses on tall buildings based on the dynamic gust factor method and the Implication on the design wind loads according to the background data of the current Hong Kong Wind Code. The principles of the dynamic gust factor approach to the estimation of along-wind responses of tall buildings are reviewed first. Dynamic gust factors of generic tall buildings exposed to Hong Kong conditions are then calculated. It found that the introduction of the dynamic gust factor will always result in design wind loads higher than the present code prediction based on the quasi-steady method. The damping ratio of the building and the turbulence intensity profile of the wind are shown to play an influencing role on the value of the dynamic gust factor.

Alongwind static equivalent wind loads and responses of tall buildings. Part II: Effects of mode shapes

Abstract The reconsideration of the alongwind responses of tall buildings in part I is continued in the present paper. According to the literature to date, the effects of mode shape on the alongwind responses of tall buildings are taken to be negligible. In this paper, it is pointed out that only the effect of the first-mode displacement response has been included in the previous literature. Closed form expressions for the mode-shape correction are provided. The factor for the first-mode displacement response is in good agreement with that in the literature, and it can be neglected; but the factors for some other wind-induced responses, such as the base shear force, cannot be neglected. Finally a new correction procedure, which provides directly the static equivalent wind load, is developed.