Field Measurements of Wind Effects on the Tallest Building in Hong Kong†

______________________________________________________________________http://www.paper.edu.cn THE STRUCTURAL DESIGN OF TALL AND SPECIAL BUILDINGS Struct. Design Tall Spec. Build. 12, 67–82 (2003) Published online in Wiley InterScience (www.interscience.wiley.com). DOI:10.1002/tal.213 FIELD MEASUREMENTS OF WIND EFFECTS ON THE TALLEST BUILDING IN HONG KONG† Q. S. LI1*, Y. Q. XIAO1,2, C. K. WONG1 AND A. P. JEARY3 1Department of Building and Construction, City University of Hong Kong, Kowloon, Hong Kong 2School of Civil Engineering, Harbin Institute of Technology, Harbin, China 3School of Building and Construction Science, University of Western Sydney, NSW, Australia SUMMARY Central Plaza has a height of approximately 374 m and is 78-storeys tall. It is the tallest structure in Hong Kong and was the highest reinforced-concrete building in the world when it was built several years ago. This paper describes some results obtained from the full-scale measurements of wind effects on Central Plaza. The field data such as wind speed, wind direction and acceleration responses have been measured during the close passage of several typhoons in recent years. Detailed analysis of the field data is conducted to investigate wind effects on the tall building. The full-scale measurements are compared with the wind tunnel results. The amplitude-dependent characteristics of damping that were obtained by using the random decrement technique are investigated on the basis of the field measurements. Copyright 2003 John Wiley & Sons, Ltd. 1. INTRODUCTION Hong Kong is close to the most active typhoon-generating area in the world, with tropical cyclones formed in the western Pacific Ocean or in the South China Sea several times each year. This makes an accurate determination of design wind loading for high-rise structures of vital importance for Hong Kong. Recently, many super-tall buildings (building height greater than 350 m) have been or are being built in Hong Kong and mainland China in response to expanding economies. As most codes for structural design are made for usual tall buildings, the current codes are not guaranteed to cover the design of super-tall buildings. It is thus necessary to investigate wind effects on such tall buildings. Although there have been many advances in wind tunnel testing and numerical simulation techniques, many critical phenomena can still only be investigated by full-scale experiments. The most reliable evaluations of dynamic characteristics and wind effects are obtained from experimental measurements of a prototype building. Field measurements of wind effects on buildings and structures date back about 100 years. However, practical difficulties associated with operation and maintenance and problems with instrumentation reliability led to many of the early field measurements to be unreliable. Furthermore, very-low-frequency activity often introduces bias and nonstationarity into data records. More modern techniques to avoid such problems are available and are being used in isolated cases. During the past two decades a revolution in data handling and collection has made enormous strides possible in full-scale measurements of wind effects on tall buildings. However, reliable full-scale measurement of wind effects on super-tall buildings is still very limited, in particular under typhoon conditions. Hence, there is a need for building up such a database. Central Plaza, which has a height of approximately 374 m and 78 storeys, is the tallest structure in * Correspondence to: Q. S. Li, Department of Building and Construction, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong. E-mail: [email protected] † This article was originally published online as an EarlyView article under the journal’s previous title of The Structural Design of Tall Buildings, ISSN 1062-8002. The DOI of the online article is unchanged but the article should now be cited under the journal’s new title, The Structural Design of Tall and Special Buildings. ISSN 1541-7794. Copyright 2003 John Wiley & Sons, Ltd. Received February 2002 Accepted March 2002 中国科技论文在线 http://www.paper.edu.cn 68 Q. S. LI ET AL. Figure 1. The building site Hong Kong and was the tallest reinforced-concrete building in the world when it was built several years ago. The basic planform of the building is essentially triangular. This tall building is located in Wanchai North commercial district in the heart of Hong Kong’s expanding business centre. Figure 1 shows a diagram of the Hong Kong area, and the point represents the location of the building. The siting of the building is very close to the seashore and on the lee slope of extremely hilly terrain in a typhoon area; therefore, this tall building may be subjected to extreme horizontal wind forces under typhoon conditions. This fact makes a study of the wind effects on this tall building of particular importance. Therefore, full-scale measurements of wind effects on this building under Typhoon conditions were conducted in order to provide important validation of design procedures and an assurance of acceptable behavior of this high-rise structure as well as to evaluate the accuracy of wind tunnel test technologies. Some selected results are presented in this paper. Long-term field measurements of wind effects on several tall buildings in the vicinity of Central Plaza are also being made. 2. MEASUREMENT INSTRUMENTATION Two accelerometers were installed at the elevation of the 73th floor of the building to provide measurement of the accelerations. The accelerometers were placed orthogonally, as shown in Figure 2. Acceleration responses are continuously acquired and digitized at 20 Hz and were amplified and low- pass filtered at 10 Hz before digitization. Two rotating cup-type anemometers were installed on the 75th floor of Central Plaza by the Hong Kong Observatory Department. However, these mechanical cup-type anemometers are too slow to offer the frequency resolution of 20 Hz that we need for the study of turbulence characteristics. For this reason, two Gill-propeller-type anemometers were installed on the masts erected on top of a tall building nearby (approximately at an elevation of 350 m from the ground). These Gill-propeller-type anemometers produce analog output voltages proportional to the wind speed and wind direction at the height equivalent to the top-floor level of Central Plaza. The data outputs of the present field measurements include acceleration responses (two channels), wind speeds (two channels) and wind directions (two channels), all of which were measured simultaneously. Figure 3 shows samples of the measurements. Meanwhile, the wind velocity data Copyright 2003 John Wiley & Sons, Ltd. Struct. Design Tall Spec. Build. 12, 67–82 (2003) 中国科技论文在线 http://www.paper.edu.cn WIND EFFECTS ON CENTRAL PLAZA 69 Figure 2. The top view and orientation of the building &, locations of accelerometers. Note; there are two accelerometers, on the level of the 73rd floor, pointing as indicated by the arrows recorded by the Hong Kong Observatory Department on the 75th floor were also analysed for the purposes of wind velocity calibration. 3. SPECTRAL ANALYSIS OF WIND SPEED AND ACCELERATION RESPONSE The measurements of wind action and wind-induced vibration of this tall building during the passage of Typhoon Sally were made in September 1996. As reported by the Hong Kong Observatory (1996), Typhoon Sally developed as a tropical depression about 1300 km east of Manila on 5 September 1996. Moving west-northwestwards, it intensified over water and attained typhoon strength on the 7 September. Typhoon Sally entered the South China Sea the next morning and moved rapidly towards the coast of western Guangdong province, People’s Republic of China. After traversing Leizhou peninsula and Guangxi province on 9 September, Typhoon Sally moved into northern Vietnam and dissipated over land the next day. Figure 4 shows the route of Typhoon Sally (Hong Kong Observatory, 1996). Some 27 hours of data recorded during the passage of the typhoon were analysed and some results are presented in this paper. The maximum instantaneous wind speed measured from the two Gill-propeller-type anemometers during the passage of Typhoon Sally is 30 m sÀ1, suggesting that the strength of Typhoon Sally was moderate, since it did not hit Hong Kong directly, as shown in Figure 4. The first 15-hour wind velocity record was used for spectral analysis and the obtained spectrum is presented in Figures 5; a sampling number of 1080000 corresponding to a continuous record of 15 hours was adopted for the spectral analysis presented in this figure. In the first 4-hour period Typhoon Sally blew approximately parallel to one accelerometer axis (direction 2 in Figure 2); that is, the measurement axes of acceleration responses were along-wind and cross-wind during this period. Figures 6(a) and 7(a) present the corresponding acceleration response spectra measured in direction 1 (cross-wind direction) and direction 2 (along-wind direction), respectively. In order to examine the participation of the various modes of vibration, the logarithmic plots of the acceleration spectra in the two directions are presented in Figures 6(b) and 7(b). These spectra of wind action and Copyright 2003 John Wiley & Sons, Ltd. Struct. Design Tall Spec. Build. 12, 67–82 (2003) 中国科技论文在线 http://www.paper.edu.cn 70 Q. S. LI ET AL. Figure 3. Samples acquired from the measurements Acc., acceleration; Ch., channel acceleration were all obtained from a direct analysis of the anemometer and accelerometer output data that were measured simultaneously. Figure 5 shows the normalized spectrum of wind speed calculated on the basis of the measured data with a long sample (15-hours) in Typhoon Sally. The spectrum estimated using the Von Karman spectrum is also presented in Figure 5 for comparison purposes. The Von Karman type spectrum was calculated on the basis of the turbulence integral scale determined from the full-scale measurements.

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