Field monitoring and numerical analysis of temperature effects on a super-tall structure

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Field monitoring and numerical analysis of temperature effects on a super-tall structure

 

Author: Zhang, Peng
Title: Field monitoring and numerical analysis of temperature effects on a super-tall structure
Degree: Ph.D.
Year: 2016
Subject: Tall buildings -- Thermal properties
Radio and television towers -- China -- Guangzhou -- Design and construction.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Civil and Environmental Engineering
Pages: xxii, 153 pages : color illustrations
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2890608
URI: http://theses.lib.polyu.edu.hk/handle/200/8475
Abstract: For super-tall buildings, temperature is one of the most significant factors to affect the structural response. Therefore, understanding the temperature distribution of these structures is of practical importance. Extensive studies of the temperature effects on structures have been conducted on bridges, whereas very few on super-tall buildings due to their large size and complicated configuration. A long-term structural health monitoring (SHM) system consisting of over 800 sensors of 16 types has been implemented on Canton Tower, a tube-in-tube super-tall structure with the height of 600 m for real-time monitoring at both construction and service stages. As part of this sophisticated SHM system, 184 temperature sensors and 412 strain sensors have been deployed at 12 cross-sections of the inner and outer tubes. The real-time temperature and strain data at these measurement points provide an excellent opportunity to investigate the temperature distribution and temperature-induced responses of the super-tall structures. In this PhD study, firstly the finite element (FE) models of the inner tube and members of the outer tube are established to investigate the temperature distribution through the heat transfer analysis. The simulated results are compared with the field monitoring data. The two sets of results show a good agreement with the measurements, indicating the effectiveness of the thermal analysis model. The temperature distribution obtained from the numerical analysis is then used as an input into the global FE model of the Canton Tower to calculate the temperature-induced deformation. The calculated results are compared with the global position system (GPS)-measured results. The two results are very close, indicating that the proposed method is effective. It could be also noticed that a small temperature difference (approximated 3 to 4°C) between different facades of the outer tube induces the significant horizontal displacement (larger than 10 cm) for this slender super-tall structures.
The other contribution of this study is to propose a new method for calculating structural deformation using real-time distributed strain data, which can be easily measured at different sections. Assuming the building flexure is of bending beam type, the horizontal displacement of the structure is associated with the longitudinal strain. The virtual work theory is then used to calculate the horizontal displacement and tilt angle of the structure on the basis of the strain data at different heights of the structure. The calculated deformation shows a good agreement with the measurements by using GPS and inclinometers. The error analysis demonstrates that the calculated displacements have higher accuracy than the GPS-measured counterparts, and that the calculated tilts have a similar accuracy as those measured by the inclinometer. The results verify that the proposed method is efficient and can be applied to other civil structures. The temperature effects on variations in modal properties of Canton Tower are finally investigated. The results show that an increase in temperature leads to a decrease in structural frequencies, whereas no clear correlation has been found between temperature and damping ration. Quantitative analysis shows that variations in frequencies are caused mainly by the change in the modulus of a material under different temperatures. That is, modal frequencies of the concrete structures decrease by approximately 0.15% when temperature increases by one degree Celsius. Frequencies of concrete structures are more sensitive to temperature change than steel structures.

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