Comfort assessment of tower-like slender structures under typhoons and earthquakes

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Comfort assessment of tower-like slender structures under typhoons and earthquakes

 

Author: Liao, Weiyang
Title: Comfort assessment of tower-like slender structures under typhoons and earthquakes
Degree: Ph.D.
Year: 2012
Subject: Tall buildings -- Earthquake effects.
Tall buildings -- Vibration.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Civil and Environmental Engineering
Pages: xxviii, 289 leaves : ill. ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2551316
URI: http://theses.lib.polyu.edu.hk/handle/200/6825
Abstract: Recently there has been an increasing demand for high-rise buildings and skyscrapers in urban areas all around the world. Due to their large scale and impressive height, flexible high-rise structures experience discomfort for the inhabitants in terms of excessive perceived motion caused by strong winds and earthquakes. Design of tall buildings should meet the serviceability criteria such that the wind and earthquake induced motions of a tall building within an acceptable range for occupant comfort, which may govern the design. Practices in this topic are usually based on the design wind and earthquake parameters according to historical experiences. Field measurement data of real structures, especially those of several hundred meters high, are very rare. Field monitoring of dynamic responses of a high-rise structure during typhoons and earthquakes provides a unique approach to verifying the parameters and assumptions adopted in design of the structure and to validating the wind tunnel or shaking table testing results. Particularly, a sophisticated structural health monitoring (SHM) system consisting of over 800 sensors has been implemented on the Canton Tower of 600 m high for both in-construction and in-service real-time monitoring. In the past three years, the Canton Tower has experienced several typhoons and earthquakes, during which both static and dynamic responses have been successfully collected through the SHM system. Taking the Canton Tower as the test bed, the research presented in this thesis is devoted to the investigation of comfort assessment of high-rise structures under typhoons and earthquakes. This PhD study has developed a vibration comfort assessment framework by considering various factors such as section type, torsion effect, whole structure response, and uncertainties. First, methodologies in signal processing for vibration comfort assessment are discussed. The torsion effect has been taken into consideration because of the asymmetry of the structure. Second, assessment of the comfort of top floor of the main tower and the contour map of serviceability are developed accounting for the torsion effect. Third, a procedure for assessing average comfort of the whole structure has been proposed by considering the structural profile and dynamic characteristics of the structure. Finally, a probability based reliability evaluation method of vibration comfort with the use of field monitoring responses is developed.
The framework is then applied to the comfort assessment of the Canton Tower using the monitoring data acquired during four typhoons. The wind properties such as mean wind and speed, turbulence and integral scale, gust factor and wind spectra, are first obtained. The acceleration responses at different levels under typhoons have also been investigated. The vibration comfort assessment considering the wind properties and spatial distribution of sensors has been conducted. A regression model is obtained to account for the torsion effect and wind properties. The real probability distribution of acceleration peak values has been obtained and compared with that used in the design. In this study, the principle of equivalent normalization is introduced to evaluate the reliability index because both the monitoring-obtained distribution and the distribution assumed in design do not obey the normal distribution. In a similar manner, the vibration comfort assessment framework is employed to assess the comfort of the Canton Tower under earthquakes. The vibration acceleration responses at each monitoring level under earthquakes are first investigated and discussed, in terms of depth, magnitude, and distance of the earthquakes. The acceleration responses are then used to assess the comfort of the top floor and the structure as a whole. In this context, the comfort index for the whole structure is developed according to the earthquake parameters. The corresponding regression model is also derived. In consideration of the uncertainties in both structure responses and criteria used in this assessment framework, a probability based comfort assessment method for the top floor is proposed in which the distributions of peak values under earthquakes are addressed. In summary, the research addressed in this thesis mainly contributes to the development of a vibration serviceability assessment framework for high-rise structures under typhoons and earthquakes using the field monitoring data. This study also benefits the design assumption verification and the improvement of design parameters for future high-rise structures.

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