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Engineering Structures 26 (2004) 233–244
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Field measurements of typhoon effects on a super tall building
Q.S. Li a,, Y.Q. Xiao a,b, C.K. Wong a, A.P. Jeary a,c
a
Department of Building and Construction, City University of Hong Kong, 83, Tat Chee Avenue, Kowloon, Hong Kong
b
Institute of Engineering Mechanics, China Seismological Bureau, Harbin, China
c
School of Building and Construction Science, University of Western Sydney, Australia
Received 21 May 2003; received in revised form 2 September 2003; accepted 30 September 2003
Abstract
Di Wang Tower located in Shenzhen has a height of approximately 325 m and was the tallest building in Mainland China
when it was built several years ago. The aspect ratio between the building’s height and transverse width is about 9, which has largely exceeded the criteria in the current design codes and standards in China. This super tall building may be susceptible to severe
vibration induced by strong winds. This paper describes some results obtained from the full-scale measurements of wind effects on
Di Wang Tower under typhoon condition. The field data, such as wind speed, wind direction and acceleration responses were
simultaneously and continuously measured from this building during the passage of Typhoon Sally in 1996. Detailed analysis of
the field data was conducted to investigate the typhoon effects on the super tall building. The characteristics of the typhoon-generated wind and the structural responses of the building are presented and discussed in detail. Dynamic characteristics of the
building are reported, and comparisons with those from the analysis of the three-dimensional finite element model of Di Wang
Tower are made. The serviceability of this super tall building under typhoon conditions is assessed based on the field measurements. The damping ratios of the building during the typhoon are evaluated, and the amplitude-dependent characteristics of
damping that were obtained using the random decrement technique are presented on the basis of the field measurements. Furthermore, the full-scale measurements are compared with the wind tunnel test results to verify the reliability of wind tunnel experimental techniques.
# 2003 Elsevier Ltd. All rights reserved.
Keywords: Wind effect; Tall building; Vibration; Damping; Full-scale measurements; Wind tunnel test; Typhoon
1. Introduction
Modern tall buildings are usually constructed with
innovative structural systems and high strength materials; tend to be more flexible and lightly damped than
those in the past. As a consequence, the sensitivity of
these tall buildings to dynamic excitations, such as
strong wind, has increased. This has resulted in a greater emphasis on understanding the structural behavior
of modern tall buildings under wind action. Although
there have been many advances in wind tunnel testing
and numerical simulation techniques, there are still
many critical phenomena which can only be investigated by full-scale experiments. Field measurement is
Corresponding author. Tel.: +852-2784-4677; fax: +852-27887612.
E-mail address: [email protected] (Q.S. Li).
0141-0296/$ - see front matter # 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.engstruct.2003.09.013
considered to be the most reliable method for evaluating wind effects on and dynamic properties of buildings
and structures. The monitoring of wind effects on tall
buildings can provide important validation of design
procedures and assurance of acceptable behavior. The
measurements from prototype tall buildings are very
useful to further the understanding of wind-resistant
design of tall buildings. Meanwhile, the experimental
results can be used to verify the reliability of wind tunnel test techniques and to refine the numerical models
for structural analysis.
Di Wang Tower, as shown in Fig. 1, is located in the
central district of Shenzhen City, Guangdong province,
PR China, including a 68-storey main office tower, plus
11-storey facility and refuge floors, as well as top tower
structures. Totally, the main structure of Di Wang
Tower has 79 storeys and is about 325 m high from
ground level. There are two 59 m masts erected on top
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Fig. 1.
Overview of Di Wang Tower.
of the tower. The height from the ground to the top of
the masts is about 384 m. Meanwhile, there is a 33storey apartment building of 116-m height and 4-storey
shopping mall of 21 m height. The main office tower
and apartment building are linked by the shopping
mall at its east and west direction. Di Wang Tower was
the tallest structure in Mainland China when it was
built several years ago, and now it is the second tallest
building in China. The structural system utilizes both
steel and reinforced concrete (SRC), including core
wall systems and perimeter steel frame coupled by outrigger trusses at four levels (2nd, 22nd, 41st and 66th
floors). Besides this, two rows of vertical bracing are
arranged along the building height. The box-type steel
columns at the outer frame are filled with C45 concrete
to increase the column stiffness. The basic plan form of
the tower is essentially rectangular with two semi-circles of 12.5 m radius on two sides. The lengths of the
main building in direction 1 (longitudinal) and direction 2 (transverse) are 68.55 m and 35.5 m, respect-
ively, as shown in Fig. 1. Therefore, the aspect ratio
between height and transverse width is about 9, which
has largely exceeded the criteria in the current design
codes and standards in China such as ‘‘The Standard
of Construction Design against Earthquake’’ (GBJ1189) and ‘‘The Reinforcement Concrete Tall Building
Design and Construction Sequences’’ (JGJ3-91). This
illustrates that Di Wang Tower is a flexible and slender
structure. Shenzhen is located at the edge of the most
active typhoon generating area in the world. Hence,
this super tall building may be susceptible to severe
vibration induced by typhoons. All these facts make a
field study of wind effects on this super tall building
under typhoon conditions of particular importance.
Therefore, full-scale measurements of the wind effects
and wind-induced vibration of 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.
The results presented in this paper were measured
from Di Wang Tower during the passage of typhoon
Sally on 8–9 September in 1996. Simultaneous and
continuous data of wind speeds, wind directions and
acceleration responses were recorded at the top part of
the tall building. Detailed analysis of the field data was
conducted to investigate the wind effects on the super
tall building under typhoon conditions. The characteristics of the typhoon-generated wind and the structural
responses of the building are presented and discussed
in detail.
The dynamic response of a structural system is considered to be greatly affected by the amount of damping
exhibited by each mode of vibration. The damping
parameter is thus dominant in determining the response
of structures. Therefore, accurate determination of
structural damping is very important for structural
design. Previous studies [2,3,5–7,8–10,11,12,13] show
that damping is a non-linear parameter depending on
structural amplitude. However, reliable full-scale
measurement of amplitude-dependent damping for
super tall buildings (building height >300 m) is still very
limited. New measurements will certainly serve to
advance the state-of-the-art. The amplitude-dependent
damping ratios of the high-rise structure were evaluated
by the random decrement technique based on the measurements of wind-induced responses in this paper.
In general, it is difficult to reproduce the exact field
conditions such as incident turbulence and terrain
characteristics in wind tunnel tests. A direct comparison of model test results to full-scale measurements is
always desirable, not only to evaluate the accuracy of
the model test results and the adequacy of the techniques used in wind tunnel tests, but also to provide better understanding of the physics. So, it is very useful to
compare model test results with actual performance to
Q.S. Li et al. / Engineering Structures 26 (2004) 233–244
235
improve the modeling techniques in wind tunnel tests.
The full-scale measurements from Di Wang Tower are
compared with the wind tunnel test results obtained in
the Boundary Layer Wind Tunnel Laboratory at the
University of Western Ontario to evaluate the accuracy
of the model test results and the adequacy of the techniques used in the wind tunnel tests. In fact, such comparison has rarely been made for super tall buildings
under typhoon conditions.
Most existing structural design codes are developed
for normal tall buildings and may not be particularly
applicable for flexible super tall buildings, such as the
Di Wang Tower. Although extensive studies on wind
effects on tall buildings have been conducted in wind
tunnel tests, reliable measurements from prototype
buildings are still insufficient, in particular those measured from super tall buildings under typhoon conditions. The main objective of this study is to further
the understanding of wind effects on super tall buildings and the behavior of high-rise structures under
typhoon conditions in order to apply such knowledge
to design.
2. Measurement instrumentation
Two accelerometers were installed at the floor corresponding to a height of 298.34 m of the building to
provide measurement of the accelerations, and the
accelerometers were placed orthogonally as shown in
Fig. 1. Acceleration responses are continuously
acquired and digitized at 20 Hz and were amplified and
low pass filtered at 10 Hz before digitization. In order
to provide detailed information on the local wind
regime, two Gill-type propeller anemometers were
installed on each of the masts located at the top of the
building at a height of 347.5 m from the ground. The
two propeller anemometers produced analog voltage
output proportional to wind speeds and wind directions which were synchronized with the response of the
accelerometers sampled at 20 Hz. The data outputs
include acceleration responses (two channels), wind
speeds (two channels) and wind directions (two channels), all of which were measured simultaneously from
Di Wang Tower. Fig. 2 shows the typical samples of
the simultaneous measurements.
3. Introduction to Typhoon Sally
The measurements of wind action and wind-induced
vibration of Di Wang Tower during the passage of
Typhoon Sally were made on 8–9 September in 1996.
Fig. 2.
Samples acquired from the measurements.
As reported by the Hong Kong Observatory [4],
Typhoon Sally developed as a tropical depression about
1300 km east of Manila on 5 September 1996. Moving
west-northwest, it intensified over water and attained
typhoon strength on 7 September. Typhoon Sally
entered the South China Sea the next morning and
moved rapidly towards the coast of western Guangdong
province, PR China. After crossing Leizhou peninsula
and Guangxi province on 9 September, Sally moved
into northern Vietnam and dissipated over land the next
day. Fig. 3 shows the route of Typhoon Sally [4].
From 2:00 pm on 8 September to 3:00 pm on 9 September, 25 h of data recorded during the passage of the
typhoon were analyzed and some selected results are
presented and discussed in this paper. The maximum
instantaneous wind speed measured from the two Gillpropeller-type anemometers during the passage of
Typhoon Sally was 33.5 m/s, suggesting that the
strength of Typhoon Sally was moderate, since it did
not hit Shenzhen directly, as shown in Fig. 3.
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Fig. 3. Moving track of Typhoon Sally.
3.1. Wind speed and wind direction
As Typhoon Sally moved towards Shenzhen, the
wind speed in Shenzhen increased. The characteristics
of mean wind speed in each 10 min period are shown in
Fig. 4. The maximum mean wind speed was 22.5 m/s
during the typhoon. The variation of wind speed with
time can also be clearly seen from this figure. The
duration of this building subjected to high wind
speed action (>20 m/s) was about 4 h during the
passage of Typhoon Sally.
The variations of mean wind direction in each 10min period with time are shown in Fig. 5. A significant
v
v
transition of wind direction (varying from 30 to 103 )
was observed during the passage of the typhoon. From
3:00 pm to 10:00 pm on 8 September, the mean wind
v
direction varied around 50 . After 12:00 pm on 8 September, the mean wind direction just varied in the
v
v
range of 95 –105 . Therefore, the mean wind directions
Fig. 5. Ten minutes mean wind direction during Typhoon Sally
measured on top of Di Wang Tower.
can be approximately regarded as constants during
these periods.
3.2. Turbulence integral scale and spectrum of wind
velocity
The turbulence integral scale (Lx) that is one of the
important parameters for describing the turbulent characteristics of wind flows can be estimated by fixing the
power spectra of velocity fluctuations. The Von-Karman velocity spectrum is one that is usually used to fit
the measured spectra for estimation of the integral
scale using Lx as the fitting parameter. This method
has the advantage of fitting the whole spectrum rather
than only the position of the peak. The Von Karman
spectrum has the form of
fSv ðf Þ
4Lx f =V
¼
2
Þ2 5=6
rv
½1 þ 70:7ðLx f =V
Fig. 4. Ten minutes mean wind speed during Typhoon Sally measured on top of Di Wang Tower.
ð1Þ
Sv ðf Þ is the power spectrum of wind velocity; f is the
frequency (Hz); rv is the standard deviation of fluctuating velocity, V is mean wind speed.
The Von Karman-type spectrum has been used to fit
the measured spectra for the purpose of estimating the
turbulence integral scale of the wind velocity measured
on top of Di Wang Tower. The variation of turbulence
integral scale with recording time is shown in Fig. 6.
Data presented in the figure were calculated based on 1
h wind speed record. It was found that the turbulence
integral scale varies from 100 to 515 m during the passage of Typhoon Sally. The figure also shows the turbulence integral scale against mean wind speed. It is
found that there is a tendency for the turbulence integral scale to increase with mean wind speed.
Q.S. Li et al. / Engineering Structures 26 (2004) 233–244
by the following equations were also determined.
rv
Iu ¼
V
Vmax
Gu ¼
V
Fig. 6. Turbulence integral scale measured during Typhoon Sally.
Fig. 7 shows the normalized spectrum of wind speed
calculated on the basis of the measured data with a
long sample (25 h) in Typhoon Sally. The spectrum
estimated using the Von Karman spectrum is also presented in Fig. 7 for comparison purposes. It can be
seen that the shape of the power spectral density of
wind speed that was measured well above the central
district in Shenzhen agrees fairly well with the Von
Karman spectrum. The value of the turbulence integral
scale determined based on the data measured during
the 25 h record period is 255 m.
3.3. Turbulence intensity and gust factor
Through the analysis of the measured data, the turbulence intensity (Iu) and the gust factor (Gu) defined
Fig. 7. Power spectral density of wind speed (during a 25 h record
period).
237
ð2Þ
ð3Þ
where V is mean wind speed measured at the top of the
building, Vmax and rv are the maximum 3 s averaged
wind speed and the standard deviation of wind speed
within 10 min, respectively.
Fig. 8 shows the characteristics of turbulence intensities. The values of turbulence intensity are widely
scattered (from 5–25%) in the range of wind speed
measured. During the passage of Typhoon Sally, the
averaged turbulence intensity on top of the tall building is 11.5% and the corresponding mean wind speed is
12.2 m/s.
Fig. 9 shows the variation of gust factor with recording time. From the figure, it is found that the mean
value of the gust factor is 1.26 during the typhoon.
Fig. 10 presents the variation of turbulence intensity
with mean wind speed on top of the building. There is
no obvious tendency for turbulence intensity to
increase or decrease with mean wind speed.
Fig. 11 shows the relationship between the gust factor and the turbulence intensity. The gust factor and
turbulence intensity are all calculated based on 10 min
records. It can be seen that all the points in the figure
lie approximately on a straight line. Thus, the relationship of the gust factor, Gu, and turbulence intensity, Iu,
can be expressed by the following linear equation
Gu ¼ 2:2138Iu þ 1:0087
Fig. 8.
ð4Þ
Turbulence intensity measured during Typhoon Sally.
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Fig. 9. Gust factor measured during Typhoon Sally.
Fig. 12. FEM computational model and three mode shapes of Di
Wang Tower.
Fig. 10. Mean wind speed vs. turbulence intensity.
Fig. 11. The gust factor vs. the turbulence intensity.
4. Structural dynamic characteristics and windinduced vibrations
In general, experimental measurements can provide
reliable but limited information (i.e. modal parameters
of several modes). The numerical study gives much
more but perhaps unreliable results. Therefore, the
experimental and numerical studies are complementary,
and their combined usage can further the understanding of dynamic behavior of tall buildings. In parallel
with the full-scale measurements, a three-dimensional
finite element (FE) model shown in Fig. 12 was built to
model the structural system of Di Wang Tower based
on the structural design drawings. Free vibration
analysis of the building was conducted to identify the
vibration mechanisms of each vibration mode, and the
calculated natural frequencies and mode shapes of several modes are presented in Table 1 and Fig. 12,
respectively.
A typical example of locus of the acceleration
responses measured during Typhoon Sally is shown in
Fig. 13. It can be seen from the figure that the windinduced response of this building in direction 1 (along
Y axis) is less than the magnitude of the response in
direction 2 (along X axis). This is due to the fact that
structural stiffness along Y axis is larger and the projected area normal to Y axis is much smaller.
Figs. 14a and 15a present the acceleration response
spectra measured in direction 1 and direction 2,
respectively. In order to examine the participation of
the various modes of vibration, logarithmic plots of the
acceleration spectra in the two directions are also
shown in Figs. 14b and 15b. These spectra were
obtained from a direct analysis of the accelerometer
output data that were measured simultaneously. The
spectra of acceleration responses illustrate that the
Table 1
Natural frequencies of Di Wang Tower
The order
of mode
Results of FEM
(Hz)
Results of field
measurement
(Hz)
Mode shape
1st
2nd
3rd
4th
5th
6th
0.160
0.208
0.254
0.509
0.690
0.720
0.173
0.208
0.293
0.540
0.688
0.886
along X axis
along Y axis
torsion
along X axis
along Y axis
torsion
Q.S. Li et al. / Engineering Structures 26 (2004) 233–244
Fig. 13. Locus of the building accelerations.
wind-induced responses of the building in the two
directions are primarily in the two fundamental translational modes of vibration, but high translational
modes and torsional modes are also clearly present.
The natural frequencies of the first six modes of this
building determined from Figs. 14b and 15b are presented in Table 1 for comparison purposes. It was
found from Table 1 that there are some differences
between the FEM results and field measurements,
especially for the torsional vibration modes. Except the
vibration modes along Y axis, the measured natural
frequencies are larger than those calculated. This may
be attributable to several reasons, including that the
effective mass of the building is less than that assumed
at the design stage or the effective stiffness of the building is higher than that determined at the design stage
due to the contribution of non-structural components.
Fig. 14. Power spectral density of acceleration in direction 1.
239
Fig. 15. Power spectral density of acceleration in direction 2.
The relationships between the measured acceleration
response averaged over a 10-min period and the mean
wind speed measured from the Gill-propeller-type
anemometers are shown in Figs. 16 and 17 for direction 1 and direction 2, respectively. It appears that
both components of acceleration responses increase
monotonically as the wind speed increases.
For the data presented in Figs. 16 and 17, the
regression curves of acceleration response for each
direction are expressed by
3:72
rA1 ¼ 0:00000483V
3:31
rA2 ¼ 0:0000285V
ðMILLI-GÞ ðdirection 1Þ
ðMILLI-GÞ ðdirection 2Þ
ð5Þ
ð6Þ
Fig. 16. Relation between wind speed and acceleration response in
direction 1.
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Q.S. Li et al. / Engineering Structures 26 (2004) 233–244
The resultant acceleration responses, which are plotted as a function of mean wind speed and mean azi-
muth angle, are shown in Fig. 18. It is evident that the
resultant acceleration responses of this building depend
on both the wind speed and angle of attack. It is
shown through this figure that the effect of magnitude
of wind speed on the resultant responses of this building is more significant.
For modern flexible tall buildings, such as Di Wang
Tower, wind-related serviceability issues due to excessive wind-induced motion during strong windstorms,
which may influence occupant comfort, are often the
limiting design criterion. It has been widely accepted
that building acceleration is the most appropriate
response component for establishing checking procedure for structural serviceability requirements under
wind action. It was observed that the maximum RMS
value of the resultant acceleration measured on top of
the building during the passage of Typhoon Sally was
less than 2.0 mg, which was below the serviceability criterion for occupancy comfort (e.g. 5 mg RMS criteria
for a 6-year return period event according to the ISO
6897 Standard). Thus, from the field measurements, Di
Wang Tower would appear to satisfactorily meet the
occupancy comfort criteria during Typhoon Sally.
Figs. 19 and 20 show the relationship of wind speed
fluctuation and the acceleration responses in direction
1 and 2, respectively. It can be seen from Fig. 19 that
the increase in dynamic response along direction 1 is
associated with the increase in wind speed fluctuation.
Fig. 20 also shows the same tendency and it is evident
that the acceleration response in direction 2 is more
sensitive to the variation of wind speed fluctuation.
Fig. 18. Relationship of RMS acceleration response with mean
wind speed and mean wind direction.
Fig. 19. Standard deviation of acceleration response in direction 1
vs. wind speed fluctuation.
Fig. 17. Relation between wind speed and acceleration response in
direction 2.
The measured data during Typhoon Sally show that
the standard deviation of acceleration response in
direction 1 is proportional to the wind speed at the top
of the building raised to a power of 3.72, and to 3.31
power in direction 2.
One way to combine the accelerations from two
orthogonal motions is to take the square root of the
sum of the squares, i.e.
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
rT ¼ r2A1 þ r2A2
ð7Þ
Q.S. Li et al. / Engineering Structures 26 (2004) 233–244
Fig. 20. Standard deviation of acceleration response in direction 2
vs. wind speed fluctuation.
241
In the remaining time, wind direction mainly varied in
v
the range of 95–105 with the mean wind direction of
v
101 . This implies that the wind directions during these
v
two periods can be regarded as constant (52 and
v
101 ). Fig. 21 shows the comparison between the fullscale measurements and the model test results at different wind speeds for these two azimuth sectors.
In Fig. 21, the wind tunnel data were extracted from
Crooks et al. [1] and the field data were measured during the passage of Typhoon Sally, except those corresponding to the wind speed of more than 25 m/s which
were estimated from eqs. (5) and (6). The smooth
curves presented in Fig. 21 were obtained by curve fitting to the present field measurements and the wind
tunnel test results [1]. It can be seen from Fig. 21 that
the measured field acceleration data are consistent with
those obtained in the model tests. In fact, the agreement between the two sets of data is quite satisfactory,
5. Comparison with the wind tunnel measurements
It is always useful to compare model test results with
actual performance, in particular, for a super tall building, such as Di Wang Tower. Such comparison has
rarely been made for a super tall building under
typhoon conditions.
Wind tunnel tests for the tall building were conducted in the Boundary Layer Wind Tunnel Laboratory at
University of Western Ontario (UWO) in 1993 before
the building was constructed [1]. The wind engineering
study carried out at UWO included the determination
of overall wind loads and dynamic responses of the Di
Wang Tower. The wind-induced vibration of the tall
building was determined through the force balance
model tests conducted in the Boundary Layer Wind
Tunnel Laboratory at UWO.
As introduced by Crooks et al. [1], the force balance
wind tunnel tests were carried out at a geometric scale
of 1:400. Measurements were made of the mean and
dynamic components of the model forces at the foundation level of the building. The model of the wind
tunnel tests reproduced the topography and all major
buildings around the project site. Based on the model
test results and the statistical analysis of the local wind
climate, predictions were made of peak accelerations
and standard deviation of accelerations etc., at a fullscale height of 307.5 m above ground. Crooks et al. [1]
gave a detailed introduction about the wind tunnel
tests.
By examining the measured wind velocity data, it
was found that during the passage of Typhoon Sally,
the wind direction in the first 6 h duration mainly varv
v
ied around 45–55 with a mean wind direction of 52 .
Fig. 21. Comparison between the field measurements and the wind
v
v
tunnel test data. (a) Azimuth angle ¼ 52 (b) Azimuth angle ¼ 101 .
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Q.S. Li et al. / Engineering Structures 26 (2004) 233–244
thus verifying the accuracy of the model test results
and illustrating that wind tunnel tests can provide
accurate predictions of wind-induced vibrations of
super tall buildings under typhoon conditions.
6. Amplitude-dependent damping characteristics of
the tall building
The determination of damping ratios is very important in exactly estimating responses of high-rise structures at the design stage. Over the last three decades
significant measurements for structural damping have
been made throughout the world. However, our literature review reveals that the amplitude-dependent
damping contained in the literature mostly concerns
mid-rise buildings in the vicinity of 20 storeys or less.
Thus, there is a serious scarcity of damping data for
high-rise buildings taller than 20 storeys, especially for
super tall buildings, such as Di Wang Tower.
The measured acceleration data are used to obtain
the dynamic characteristics of the building (damping,
natural frequencies, etc.). The modified random decrement technique that was developed by the authors
was employed to evaluate the amplitude-dependent
damping in this building. As pointed out by Jeary [7]
and Li et al. [9], the random decrement technique
represents a quick and practical method for establishing the non-linear damping characteristics. As discussed previously, the wind-induced response of the
building is primarily in the two fundamental translational modes of vibration, but higher modes are also
present. In order to obtain the damping ratio of each
mode, the measured signals of acceleration responses
were band-pass filtered before processing the random
decrement to remove the components not concerned
with the mode under consideration. The damping
curves of the first two translational modes in each
direction evaluated from the measured acceleration
data are shown in Fig. 22, which comprise both structural damping and aerodynamic damping.
Information on amplitude-dependent damping
obtained from Di Wang Town should be very useful
since similar measurements are still very limited for
such a super tall building, in particular, the characteristics of amplitude-dependent damping of higher modes
have rarely been reported in the past. The damping
curves shown in Fig. 22 clearly demonstrate non-linear
energy dissipation characteristics of the building. It is
clear that the damping increases with increase in amplitude during the passage of Typhoon Sally. Meanwhile,
lower values of amplitude-dependent damping in the
second translational modes are observed in comparison
with the first modes in both directions.
As yet there is no widely accepted method available
for evaluating damping ratios of buildings prior to
Fig. 22. Variation of damping ratios with amplitudes of the building.
construction. In the wind tunnel tests at the design
stage, Crooks et al. [1] predicted the loads and
response of this building for the cases of structural
damping assumed to be 1, 1.5, 2 and 2.5%. The measured acceleration responses are also used to evaluate
the damping values without taking account of
vibration
amplitudes.
The
first
longitudinal
(in direction 1) and lateral (in direction 2) modal
damping ratios are determined as 0.57 and 0.58%,
respectively, based on the field data measured during
Typhoon Sally, using the random decrement technique.
The corresponding damping values are found to be
0.88 and 1.06%, using the spectrally based half-power
bandwidth method. It is clear that the damping values
estimated by the random decrement technique are
smaller than those evaluated by the half-power bandwidth method, suggesting that damping estimates vary
with the identification methods. It was suggested by
Q.S. Li et al. / Engineering Structures 26 (2004) 233–244
Jeary [7] that the random decrement technique usually
provides more realistic damping estimates. Obviously,
the accuracy of the spectrally based method depends
on the spectral resolution. From the above results and
Fig. 22, it appears that the value of 1.0% of damping
ratio assumed in the design stage is reasonable at least
as far as an amplitude appropriate to the serviceability
criterion for this building is concerned, as the damping
curve presented in Fig. 22 was measured in moderate
wind condition. Further research is aimed at determining the characteristics of damping ratio at higher
amplitude.
7. Concluding remarks
The objective of this study is to investigate wind
effects on Di Wang Tower under typhoon condition.
Wind speeds, wind directions and acceleration responses presented in this paper were measured on top of the
tall building during the passage of Typhoon Sally.
Characteristics of the typhoon-generated wind, structural dynamic properties and wind-induced responses
of this super tall building were presented and discussed.
Furthermore, the full-scale measurements are compared with the wind tunnel test results. Some results
are summarized as follows.
1. During the passage of Typhoon Sally, the averaged
turbulence intensity on top of the tall building is
11.5% and the mean value of gust factor is 1.26. The
values of turbulence intensity are widely scattered
(from 5–25%) in the range of wind speed measured.
2. The Von Karman-type spectrum is found to be able
to describe the energy distribution fairly well for
wind speed above the central district in Shenzhen. It
was found that the turbulence integral scale varies
from 100 to 515 m during the passage of Typhoon
Sally. There is a tendency for turbulence integral
scale to increase with mean wind speed. The average
value of the turbulence integral scale is 255 m during
a 25 h record period for the Typhoon.
3. Based on the spectral analysis of data measured
from relatively long samples during Typhoon Sally
(25 h) and dynamic analysis from the 3-D finite
element model of Di Wang Tower, it was found that
the wind-induced response of the building is primarily in the two fundamental translational modes of
vibration, but higher translational modes and torsional modes are also present. There are some differences between the FEM results and the field
measurements, especially for the torsional vibration
modes. Except the vibration modes along Y axis, the
measured natural frequencies are larger than those
calculated. This may be attributable to several rea-
243
sons, such as that the effective mass of the building
is less than that assumed at the design stage, or the
effective stiffness of the building is higher than that
determined at the design stage due to the contribution of non-structural components.
4. Wind-induced acceleration responses were found to
be monotonically increasing with wind speed on top
of the building. The measured field data show that
the standard deviation of acceleration response in
direction 1 is proportional to 3.72 powers of wind
speed on top of the building, to 3.31 powers in
direction 2. It was found from the field measurements that Di Wang Tower satisfactorily met occupancy comfort criteria during Typhoon Sally.
5. Information on structural damping obtained from
the building is extremely useful since similar measurements are still very limited for super tall buildings. The first longitudinal (in direction 1) and
lateral (in direction 2) modal damping ratios are
determined as 0.57 and 0.58%, respectively, based on
the field data measured during Typhoon Sally using
the random decrement technique. The corresponding
damping values are found to be 0.88 and 1.06%
using the spectrally based half-power bandwidth
method. It is evident that the damping values estimated by the random decrement technique are smaller than those evaluated by the latter method. The
measured damping ratios demonstrate obvious
amplitude-dependent characteristics and increases
with increasing amplitude during Typhoon Sally.
Lower values of amplitude-dependent damping in
the second translational modes are observed in comparison with the first modes in both directions.
6. The field-measured acceleration responses have been
compared with the wind tunnel results obtained in
the Boundary Layer Wind Tunnel Laboratory at
Western Ontario University. The measured acceleration data are consistent with those obtained in the
force balance model study. In fact, the agreement
between the two sets of data is quite satisfactory,
thus verifying the accuracy of the model test results
and illustrating that wind tunnel tests can provide
accurate predictions of wind-induced vibrations of
super tall buildings under typhoon conditions.
Acknowledgements
The work described in this paper was fully supported
by two grants from the Research Grant Council of
Hong Kong Special Administrative Region, China
(Project No. CityU 1143/99E, CityU 1131/00E) and a
grant from City University of Hong Kong (Project No.
7001341). Thanks are due to Dr. Les Robertson for his
valuable contributions to this study.
244
Q.S. Li et al. / Engineering Structures 26 (2004) 233–244
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