Wind Tunnel and Full-Scale Study of Wind Effects on China's Tallest Building

Engineering Structures 28 (2006) 1745–1758 www.elsevier.com/locate/engstruct

Wind tunnel and full-scale study of wind effects on China’s tallest building

Q.S. Lia,∗,J.Y.Fua,b,Y.Q.Xiaoa,Z.N.Lic,Z.H.Nid,Z.N.Xied,M.Gue

a Department of Building and Construction, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong b Department of Civil Engineering, Jinan University, Guangzhou 510632, China c College of Civil Engineering, Hunan University, Changsha, Hunan 410082, China d Department of Civil Engineering, Shantou University, Shantou 515063, China e Department of Bridge Engineering, Tongji University, Shanghai 200092, China

Received 16 May 2005; received in revised form 18 February 2006; accepted 28 February 2006 Available online 24 April 2006

Abstract

The Jin Mao Building with a height of 420.5 m and 88-storeys, located in Shanghai, is the highest tall building in Mainland China. This paper presents selected results from a combined wind tunnel and full-scale study of wind effects on the super tall building. In the wind tunnel test, mean and fluctuating force components on the building model for the cases of an isolated Jin Mao Building and the building with existing surrounding condition were measured by a high-frequency force balance technique under suburban and urban boundary layer wind flow configurations, respectively. Force coefficients, power spectral densities, displacement and acceleration responses were then presented and discussed. A detailed comparative study was conducted to investigate the influences of incident wind direction, upstream terrain conditions and interferences from the surroundings on the wind effects on the building. Serviceability of the super tall building under strong wind action was analyzed on the basis of the experimental results. On the other hand, full-scale measurements of wind effects on the Jin Mao Building were conducted under typhoon conditions. The field data, such as wind speed, wind direction and acceleration responses were simultaneously and continuously recorded during the passage of Typhoon Rananim in August, 2004. Analysis of the field data was carried out to investigate typhoon effects on the super tall building. Finally, the wind tunnel test results were found to be in good agreement with the full-scale measurements, illustrating that the wind tunnel tests can provide satisfactory predictions of wind-induced vibrations of the super tall building under typhoon conditions. c 2006 Elsevier Ltd. All rights reserved.

Keywords: Wind tunnel test; Wind effects; Tall building; Full-scale measurement; Typhoon

1. Introduction in Mainland China. The main structure of this building has 88 storeys and is about 365 m high from the ground. It is a steel Modern tall buildings are usually constructed with and concrete composite structure with a building plan form very innovative structural systems and high strength materials; close to a square shape. The longitudinal and transverse lengths tending to be more ﬂexible and lightly damped than those in the of the building are both 55.5 m. Therefore, the aspect ratio past. As a consequence, the sensitivity of these tall buildings between the height and transverse width is about 7, which has to dynamic excitations, such as strong wind, has increased. exceeded the criteria in the current design codes and standards This has resulted in a greater emphasis on understanding the of China. This illustrates that the Jin Mao Building is a ﬂexible structural behavior of modern tall buildings under strong wind and slender structure. On the other hand, Shanghai is close to actions. the edge of an active typhoon-generating area. Hence, this super The Jin Mao Building located in Pudong New Area, tall building may be susceptible to severe wind forces induced Shanghai, has a height of 420.5 m and is the highest building by strong typhoons. All these facts make a comprehensive study of wind effects on this super tall building of particular

∗ importance. Corresponding address: City University of Hong Kong, Department of It has been recognized that the most reliable evaluations Building and Construction, 83 Tat Chee Avenue, Kowloon, Hong Kong. Tel.: +852 2784 4677; fax: +852 2788 7612. of dynamic characteristics and wind effects are obtained E-mail address: [email protected] (Q.S. Li). from experimental measurements of a prototype building.

Monitoring of wind effects on super tall buildings such as Ho et al. [2] are not consistent with the current surrounding the Jin Mao Building can give important validation of design situations around the Jin Mao Building. Therefore, it is not procedures and assurance of acceptable behaviour. In fact, appropriate to compare the field measurements made in 2004 measurements of wind effects on prototype structures are very with the wind tunnel test results [1,2] directly for the above useful to further the understanding of wind-resistant structural reasons. In order to make a meaningful comparison, a new design. Therefore, full-scale measurements of wind effects on wind tunnel test with proper modeling of the real existing the Jin Mao Building were thus conducted during the passage of surrounding conditions such as those in 2004 and the turbulence Typhoon Rananim on 12–13 August, 2004. The field data, such intensity profiles should be conducted. Therefore, a wind tunnel as wind speed, wind direction and acceleration responses, were experiment is carried out in this study with consideration of all simultaneously and continuously measured during Typhoon the major existing buildings around the Jin Mao Building in Rananim. Analysis of the field data was conducted in this study 2004. Meanwhile, boundary layer wind flows with relatively to investigate the characteristics of typhoon-generated wind, larger turbulence intensities such as those found in the natural structural dynamic properties and wind-induced vibrations of wind around tall buildings in urban areas are simulated in the the super tall building under typhoon conditions. present model test. Force coefficients, power spectral densities, Wind tunnel testing is an effective method for investigating displacement and acceleration responses are obtained in the wind effects on buildings and structures. However, in general, wind tunnel test by a high-frequency force balance technique. it is difficult to reproduce the exact field conditions such as A detailed comparative study is conducted to investigate incident turbulence and terrain characteristics in wind tunnel the influences of incident wind direction, upstream terrain tests. A direct comparison of model test results to full-scale conditions and interferences from the surroundings on the measurements is always desirable, not only to evaluate the wind effects on the Jin Mao Building. Furthermore, the full- accuracy of the model test results and the adequacy of the scale measurements of wind effects on the Jin Mao Building techniques used in wind tunnel tests, but also to provide better are compared with the wind tunnel test results to verify the understanding of the physics. However, such comparison has accuracy of the model test results and the adequacy of the rarely been made for super tall buildings (building height > technique used in the wind tunnel test. 400 m) under typhoon conditions. The full-scale measurements This paper presents selected results from the combined obtained in this study can actually provide some useful results wind tunnel and full-scale study. The full-scale measurements of wind effects on the Jin Mao Building. Meanwhile, this also can provide reliable but limited information. The wind tunnel provided an excellent opportunity to compare the real structural test can generate detailed and additional results that are not performance of the super tall building with wind tunnel test available from the field measurements. Therefore, the full-scale results for the purpose of improving the modeling techniques measurements and the wind tunnel study are complementary so in wind tunnel tests. that the understanding of wind effects on the super tall building Most existing structural design codes were developed for can be improved. The main objective of this study is to further normal tall buildings and may not be particularly applicable the understanding of wind effects on super tall buildings and for the design of super tall buildings such as the Jin Mao the behavior of high-rise structures under typhoon conditions Building. Therefore, in designing a super tall building, it is by means of wind tunnel tests and full-scale measurements in usually necessary to conduct wind tunnel tests to determine order to apply such knowledge to design. its wind load and wind-induced responses. Gu et al. [1] andHoetal.[2] did wind tunnel experiments to determine 2. Wind tunnel experiments wind effects on the Jin Mao Building at the design stage and provided very useful information for the wind-resistant 2.1. Experimental arrangements design of the super tall building [1–3]. Nevertheless, in the wind tunnel experiment [1], the incident turbulence intensity A rigid model with a geometric length scale of 1:500 was levels created in the model tests were lower than the field made to represent the Jin Mao Building. The model was made measurements made at similar sites [4–6] and those specified of balsa and foam, and was mounted on a metal frame which in the Japanese standard [7]. It has been widely recognized that was rigidly connected to the force balance reaction bar. the turbulence intensity of incident wind flow has significant The wind tunnel experiment was carried out in the boundary effects on surface pressures on building models [8–13]. On the layer wind tunnel at Shantou University in China. The other hand, Ho et al. [2] conducted their wind tunnel tests for dimensions of the working section in the wind tunnel are the Jin Mao Building with consideration of the surrounding 3mwide× 2 m high and 20 m long. Two typical boundary site condition in 1994 and the future master plan development layer wind flows respectively representing the suburban flow termed the “developed Podong” condition, respectively. The environment (denoted as BL1 in this paper) and the urban flow surrounding site condition in 1994 essentially consisted of low- configuration (called BL2 in this paper), as specified in the rise buildings (3–5 storeys in height). The “developed Pudong” China National Load Code [14] as terrain B and terrain D, were condition included some 30–50 storey buildings and two ultra- simulated for the model test by means of placing a barrier at tall towers (96-storeys and 100-storeys) located within 600 m the entrance of the wind tunnel, triangular shaped spires and of the Jin Mao Building. Since the two ultra-tall towers have arrayed cubic roughness elements with different sizes on the not been built yet, the two site conditions considered by tunnel floor upstream of the building model. The mean wind Q.S. Li et al. / Engineering Structures 28 (2006) 1745–1758 1747

Fig. 1. Mean wind speed and turbulence intensity proﬁles for BL1.

Fig. 3. Immediate surroundings of the Jin Mao Building and illustration of the approaching wind direction.

Fig. 4. The models in the wind tunnel test.

Fig. 2. Mean wind speed and turbulence intensity profiles for BL2. Mao Building (see Fig. 3). For the isolated building case, no neighboring building around the Jin Mao Building was speed profiles of the two fully developed boundary layer flows considered in the wind tunnel test. Fig. 4 shows a photo of the were found to follow a power law with exponents of α = 0.16 models mounted in the wind tunnel representing the existing and α = 0.30 with the gradient heights of 350 m and 450 m for surrounding conditions. BL1 and BL2, respectively. The turbulence intensities at the top Measurements of wind forces acting on the building model of the building (excluding the mast erected atop the building) were made with a carefully calibrated six-component high- corresponding to 365 m in the full-scale situation (0.7296 m in frequency force balance (JR3 made in Japan). Since the largest the wind tunnel) were about 9% and 18% for BL1 and BL2, portion of dynamic energy was associated with frequency respectively. The measured mean wind speeds and turbulence components below 50 Hz, the output voltage signals from the intensities at various heights over the test section are illustrated balance were filtered with a cut-off frequency of 50 Hz to in Figs. 1 and 2 for BL1 and BL2, respectively. avoid aliasing in the spectral analysis. Among the six force The wind tunnel test was carried out for both cases of an component outputs, the orthogonal horizontal forces Fx and Fy, isolated Jin Mao Building and the building with the existing as defined in Fig. 5, or the drag and lift forces, are presented and surrounding conditions. The models at a geometric scale of discussed in this paper. 1:500 reproduced all major existing buildings in 2004 within In the wind tunnel test, wind direction was defined as an a full-scale radius of approximately 600 m from the Jin angle β from the north along an anti-clockwise direction varied 1748 Q.S. Li et al. / Engineering Structures 28 (2006) 1745–1758

The displacement response can be broken down into two components: a quasi-static component σB, and a resonant component σRe, which are deﬁned by [15] ⎧ σ ⎪ F ⎨⎪σB = K (6) ⎪ π 1 f SF ( f ) ⎩⎪σ = 0 0 Re 2 4 ζs + ζa K

where σF is the rms generalized force; K is the generalized stiffness which can be determined from the natural frequency and the generalized mass; ζs is the structural damping ratio; ζa is the aerodynamic damping ratio; and SF ( f0) is the power spectrum of the generalized force at the natural frequency f0. Since the force balance test results can be used to determine several parameters mentioned above directly, such as the rms generalized force σF and its normalized spectrum ( )/σ 2 σ Fig. 5. Coordinates and force notations. f0 SF f0 F , then the rms response R can be obtained by the following equation [16] ◦ ◦ ◦ from 0 to 360 with increments of 15 ,asshowninFig. 3;and σ π 1 f S ( f ) the coordinates and force notations are illustrated in Fig. 5.Data σ = σ 2 + σ 2 = F 1 + 0 F 0 . (7) R B Re ζ + ζ σ 2 sampling frequency was about 312.5 Hz with data sampling K 4 s a F length of 20 480. The aerodynamic damping ratio ζa is structural-motion dependent, and cannot be measured by the force balance model 2.2. Theoretical formulas and definitions of parameters test. Nevertheless, it was reported [17] that the value of the aerodynamic damping ratio is usually small and positive for Aerodynamic forces on tall buildings are usually described typical tall buildings in the drag direction, and is also positive in in terms of mean force coefficients and fluctuating force the lift direction up to the velocity where vortex shedding has coefficients with incident wind direction as a variable. Mean a major contribution to the response. This velocity is usually force coefficients are defined as follows: higher than typical design wind speeds, which is indicated in μ the force spectra by a narrow-band peak. Therefore, in this = Fx CFxmean (1) study, ζ = 0 was used, and the results from Eq. (7) give 1 ρV 2 BH a 2 H slightly conservative results, except for the lift forces at high μFy C = (2) velocities. Fymean 1 ρ 2 2 VH BH The acceleration response can be estimated in a straight- forward manner based on the above descriptions by noting where μFx and μFy are the mean shear forces along x-direction that acceleration = ω2× displacement. This frequency-squared and y-direction, respectively; ρ is the air mass density; VH is the mean wind speed at the height, H , of the building, and B is weighting implies that the background response contributes al- the width of the building. Here, B = 55.5mandH = 365 m. most nothing to the root-mean-square acceleration which can ω2σ Fluctuating force coefficients are defined similarly to the then be reduced to Re. mean force coefficients σ 3. Wind tunnel experimental results C = Fx (3) Fxrms 1 ρ 2 2 VH BH 3.1. Force coefficients σFy C = (4) Fyrms 1 ρ 2 2 VH BH Before the experimental results obtained in the wind tunnel test are presented and discussed, it is necessary to assess the σ σ where Fx and Fy are the rms shear forces along x-direction accuracy of the wind tunnel test results by comparing the and y-direction, respectively. present measurements with the available existing experimental Utilizing the “gust loading factor” method, the linear data [1,2]. Table 1 shows comparison of the peak base bending response of an elastic system can be expressed in the following moments obtained by Ho et al. [1], Gu et al. [2] and this study general form [15]: for the case of the wind speed of 40 m/s at a height equivalent to ˆ that at the top of the building and the structural damping ratio of R(t) = R + g(t)σR (5) 2.5%. It can be seen from Table 1 that obviously, the agreement where R is the mean response; σR is the rms response, and g(t) between the three sets of data is satisfactory for this case, even is a dimensionless time varying gust factor. The peak response though there were certain differences in the modelling of the Rˆ is of particular interest in engineering practice. incident turbulence and terrain characteristics in the three wind Q.S. Li et al. / Engineering Structures 28 (2006) 1745–1758 1749

(a) Mean force coefﬁcients along x-direction as a function of the approaching (b) Mean force coefﬁcients along y-direction as a function of the approaching wind direction. wind direction.

Fig. 6. Mean force coefﬁcients.

Table 1 function of the approaching wind direction, respectively. It can Comparison of the peak base bending moments (damping ratio of 2.5%) be seen from Fig. 7(a) and (b) that the interference effects on The cases of an isolated Jin Mao Building Peak base bending moment the fluctuating wind loads are very similar to those on the mean (kN m) wind loads, as discussed previously. The Jin Mao Building x-direction y-direction actually experiences significant reductions in fluctuating wind The present test 5.65 × 106 5.36 × 106 loads when it is sheltered by upwind buildings. Gu et al.’s test [1]5.12 × 106 5.12 × 106 Fig. 7(a) and (b) also reveal an important fact, i.e., the results Ho et al.’s test [2]5.37 × 106 5.09 × 106 for BL2-1 in the along-wind direction are much larger than those for BL1-1. The observed phenomenon can be explained tunnel tests. The comparison thus verifies the reliability of the as follows. The aerodynamic loading on a tall building usually present wind tunnel test. results from the atmospheric turbulence and wake excitation Mean force coefficients CFxmean along x-direction and due to vortex shedding. The atmospheric turbulence in the approach flow causes fluctuating along-wind loading and CFymean along y-direction as a function of the approaching wind direction are shown in Fig. 6(a) and (b), respectively. wake excitation induces fluctuating across-wind loads [18,19]. In this paper, BL1-1, BL1-2, BL2-1 and BL2-2 denote the This means that the fluctuating along-wind force coefficients measurement results for the isolated building case in BL1, increase as the atmospheric turbulence intensity increases. As a for the existing surrounding conditions in BL1, for the result, the increase of turbulence intensity from BL1-1 to BL2- isolated building case in BL2 and for the existing surrounding 1 makes the results for BL2-1 in the along-wind direction much conditions in BL2, respectively. larger than those for BL1-1. It can be seen from the results presented in Fig. 6(a) and It can be also seen from Fig. 7(a) and (b) that the fluctuating (b) for BL2-1 and BL2-2 that the interference effects from the force coefficients in the along-wind direction are slightly surrounding buildings which generally have building heights smaller than those in the across-wind direction for BL1-1; about half of the Jin Mao Building are significantly dependent but for BL2-1, the fluctuating force coefficients in the along- on the incident wind direction, which mainly leads to a wind direction are much larger than those in the across-wind reduction in mean wind loads when the Jin Mao Building is direction. The observed phenomenon will be explained in sheltered by upwind buildings; and the interference effects are Section 3.2. relatively smaller when these surrounding buildings are far 3.2. Force spectra away from the super tall building. Fig. 6(a) and (b) also show that the absolute results for BL1- Spectral characteristics of fluctuating force components are 1 are larger than those for BL2-1; this means that the mean force examined herein with the emphasis on the turbulence effects coefficients decrease as the ground roughness increases. It can of the incident winds. The measured spectra of Fx (along-wind ◦ also be seen from Fig. 6(a) and (b) that the magnitudes of the force spectrum) and Fy (across-wind force spectrum) at β = 0 mean force coefficients in the along-wind direction are much are shown in non-dimensional forms in Fig. 8(a) and (b) for larger than those in the across-wind direction. BL1-1 and BL2-1, respectively. Fluctuating force coefficients CFxrms along x-direction and The along-wind force spectra in Fig. 8(a) are similar to CFyrms along y-direction are shown in Fig. 7(a) and (b) as a the approaching wind speed spectra obtained above the test 1750 Q.S. Li et al. / Engineering Structures 28 (2006) 1745–1758

(a) Fluctuating force coefﬁcients along x-direction as a function of the (b) Fluctuating force coefﬁcients along y-direction as a function of the approaching wind direction. approaching wind direction.

Fig. 7. Fluctuating force coefﬁcients.

(a) Along-wind force spectra. (b) Across-wind force spectra.

◦ Fig. 8. Fluctuating force spectra at β = 0 in two typical boundary layer flows. section before the models were moved into the wind tunnel, 0.1, which is near the Strouhal number of a square prism. The suggesting that buffeting due to incident turbulence is the main value of the peak frequency is consistent with a frequency of cause of the along-wind force component. This also confirms vortex shedding, indicating the across-wind forces acting on the the observations of previous research [18–20]. It can be seen Jin Mao Building were mainly caused by vortex shedding [18, from Fig. 8(a) that as the turbulence intensity increases, the 19,21]. magnitudes of spectral peaks increase accordingly. Fig. 8(a) It can be seen from Fig. 8(b) that the spectral peak is also shows that due to the differences in the incident flow lower and the spectral shape around the Strouhal number of characteristics, the overall spectral distributions are different, the reduced frequency becomes broadened as the turbulence especially in the range corresponding to higher spectral intensity increases; i.e., the spectral peak magnitude for BL1- amplitude where most of the energy lies. This implies that the 1 is much larger than that for BL2-1, and the bandwidth for turbulence intensity can significantly affect the fluctuating force BL1-1 around the Strouhal number of the reduced frequency coefficients in the along-wind direction, which are consistent is more narrow banded than that for BL2-1, which indicates with the observation made in Section 3.1. that the energy is more concentrated near the vortex shedding As shown in Fig. 8(b) for the across-wind force spectra, a frequency. This phenomenon may be related to the reattachment spectral peak appears at reduced frequency of approximately of separated shear flow. That is, at higher turbulence levels, Q.S. Li et al. / Engineering Structures 28 (2006) 1745–1758 1751

Table 2 Structural and modal parameters of the Jin Mao Building

Width (m) Depth (m) Height (m) Generalized stiffness (kN/m) Natural frequencies (Hz) Along x-direction 3.1399 × 107 Along x-direction 0.1465 55.5 55.5 365 Along y-direction 3.1399 × 107 Along y-direction 0.1465

(a) Rms displacement along x-direction as a function of the approaching wind (b) Rms displacement along y-direction as a function of the approaching wind direction. direction.

Fig. 9. Rms displacements. the entrainment into the shear layer is increased, and the Mao Building, wind-induced responses of the building, such shear layer becomes thicker, causing an earlier reattachment. as rms displacement and rms acceleration, etc. were estimated. As a result, the increase of turbulence intensity interrupts the The structural and modal parameters of the Jin Mao Building regular vortex shedding in some ways and the spectral shape is are listed in Table 2. It should be mentioned that unlike the broadened [8–10]. previous wind tunnel studies for the Jin Mao Building [1, Comparison between Fig. 8(a) and (b) indicates that the 2], the fundamental natural frequencies along x-direction and energies of the across-wind force spectra in the interested y-direction, which were used in the estimation of wind- frequency region are greater than those of the along-wind force induced vibrations of the building, were obtained from the field spectra. However, for BL1-1, the turbulence intensity is lower measurements to be described in Section 4 of this paper. and the spectral magnitudes are relatively lower in the along- The design wind speeds with 50-year return period for wind direction but relatively larger in the across-wind direction, Shanghai were used in evaluation of the dynamic responses of then σF determined from the along-wind force spectrum may the building, which were 53.48 m/s for BL1 and 50.21 m/s be smaller than that obtained from the across-wind force for BL2, respectively, at the elevation of 365 m (atop the main spectrum, which results in that the fluctuating across-wind structure of the Jin Mao Building). In the wind tunnel tests at load may be larger than the fluctuating along-wind force. But, the design stage [1,2], structural damping ratios were assumed for BL2-1, the turbulence intensity is higher and the spectral to be 1.5%, 2.0% and 2.5% for the estimations of wind-induced magnitudes are relatively large in the along-wind direction responses of the building. Therefore, the damping ratio of the but are relatively small in the across-wind direction, then σF Jin Mao Building was taken as 2.5% for the displacement obtained from the along-wind force spectrum may be larger responses presented in this section. Rms displacements along than that determined from the across-wind force spectrum. As x-direction and y-direction are shown in Fig. 9(a) and (b), a result, the fluctuating along-wind force may be larger than respectively as a function of the approaching wind direction the fluctuating across-wind load. These are consistent with the for the cases of BL1-1, BL2-1 and BL2-2. Fig. 10 presents observations made in Section 3.1. the relationship between the rms-displacement response and the wind speed at β = 0◦ for BL1-1 and BL2-1. 3.3. Displacement responses It can be seen from the results shown in Fig. 9(a) and (b) that the interference effects from the surrounding buildings varied Based on the results from the high-frequency force balance with the approaching wind direction when the Jin Mao Building model test and the associated theoretical formulas presented was sheltered by upwind buildings. Fig. 9(a) and (b) also show in Section 2.2 as well as the modal parameters of the Jin that the rms displacements may increase as the turbulence 1752 Q.S. Li et al. / Engineering Structures 28 (2006) 1745–1758

these figures are very similar to those for the rms-displacement responses, as discussed previously. For modern flexible super tall buildings, such as the Jin Mao Building, wind-related serviceability issues due to excessive wind-induced motion during strong windstorms, which may influence occupant comfort, is 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. Only the criterion of occupancy comfort for the case of design wind speed with 10-year return period is given in the Chinese code for the design of tall buildings (the technical specification JGJ3-2002 [22]). Therefore, it is decided to conduct the serviceability analysis of the Jin Mao Building for this case. It can be seen from Fig. 11(a) and (b) that the maximum rms-acceleration responses of the building subjected to the design wind speed with 10-year return period along x- Fig. 10. Relationship between the rms-displacement responses and the wind direction and y-direction for all incident wind directions are ◦ ◦ speed at β = 0 . 15.22 gal and 14.86 gal, which occurred at β = 270 and β = 15◦ for BL2-2, respectively. To evaluate the serviceability of the intensity increases, i.e., the responses for BL2-1 are much larger building more properly, it is needed to consider the relationship than those for BL1-1, even though the design wind speed for among the resultant acceleration responses and the mean wind BL1-1 is larger than that for BL2-1. This may be attributed speeds as well as the occupancy comfort criteria with different to the different distributions of the normalized power spectral return periods [23]. The simplest way to determine the resultant ( )/σ 2 density function f0 SF f0 F for the two cases. It can be seen responses by combining the accelerations from two sway from Fig. 8(a) and (b) that the magnitudes of the normalized motions is to take the square root of the sum of the squares. power spectral density function for BL2-1 are much larger The largest rms resultant acceleration was thus found to be than those for BL1-1 at higher frequency range which is most 16.54 gal, which occurred at β = 15◦ for BL2-2. The peak relevant for the response prediction, as shown in Eq. (7). factor for acceleration√ response was taken to be 3.0, which It can be seen from Fig. 10 that the rms-displacement was determined by 2ln(nT) [23], here n is the fundamental responses increase as the wind speed increases. It is evident that natural frequency of the building (0.1465 Hz), and T is the the rms-displacement responses depend on both the wind speed duration in seconds (600 s). Thus, the maximum peak resultant and the turbulence intensity. It is shown through this figure acceleration atop the building was 49.62 gal. This value has that at the same wind speed, the rms-displacement responses largely exceeded 25 gal which is the limit of the occupancy increase as the turbulence intensity increases. comfort criterion for office or hotel tall buildings specified Figs. 9 and 10 also show that the rms-displacement by “Technical Specification for Concrete Structures of Tall responses in the across-wind direction are much larger than Building (JGJ3-2002) of China” [22]. those in the along-wind direction at the same wind speed However, it was discussed by Li and Li [24] that the and turbulence intensity. This tendency may be explained design wind speeds for Shanghai given in the design codes as follows. Fig. 8(a) and (b) clearly show that the spectral and standards of China [14] are too conservative. Ho et al. [2] magnitudes in the across-wind direction are larger than those conducted an analysis of the wind climate of the Shanghai in the along-wind direction at higher frequency range which is area on the basis of the historical wind speed records at most relevant for the response prediction, as shown in Eq. (7). the Longhua weather station in Shanghai and a Monte Carlo simulation of tropical cyclones passing Shanghai, including the 3.4. Acceleration responses and serviceability analysis effects of the typhoons and the non-typhoon or extratropical winds. A statistical model of the “rational” wind speed The design wind speed with 10-year return period for and direction climate was developed for the design of the Shanghai was determined by the design codes and standards Jin Mao Building [2]. Results of their analysis for the of China [14]as45.60 m/s for BL1 and 42.82 m/sfor Shanghai “combined” climate (including extratropical climate BL2, respectively, at the elevation of 365 m. Rms-acceleration and typhoon climate) indicate 10-year return period 10-minute responses along x-direction and y-direction under the design average wind speed of 33 m/s at the reference height of 365 m wind speed action are shown in Fig. 11(a) and (b), respectively, above ground which corresponds to the height at the top of as a function of the approaching wind direction for the cases of the main structure of the Jin Mao Building. It is the authors’ BL1-1, BL2-1 and BL2-2 and structural damping ratio of 2.5%. opinion that the design wind speed for Shanghai determined Fig. 12 shows the relationship between the rms-acceleration by Ho et al. [2] is more reasonable and realistic than that response and the wind speed at β = 0◦ for BL1-1 and specified in the design codes and standards of China [14]. BL2-1. The observations for the acceleration results shown in Therefore, it was decided to adopt the design wind speed Q.S. Li et al. / Engineering Structures 28 (2006) 1745–1758 1753

(a) Rms acceleration along x-direction as a function of the approaching wind direction.

(b) Rms acceleration along y-direction as a function of the approaching wind direction.

Fig. 11. Rms accelerations. obtained by Ho et al. [2] for the serviceability analysis of the Jin Figs. 12 and 13 shows the relationship between the rms- ◦ Mao Building. For the design wind speed with 10-year return acceleration responses and the wind speeds at β = 0 for the period and structural damping ratio of 2.5%, the maximum rms- damping ratios of 1.5% and 2.5%, respectively. Damping ratio acceleration responses along x-direction and y-direction and is regarded as being an important parameter in the estimation of the maximum resultant rms-acceleration value were predicted dynamic responses of a structure. There is a need to investigate based on the wind tunnel test results, which were 5.82 gal, the effect of damping on the wind-induced vibrations of the 5.56 gal and 6.27 gal, respectively. For the damping ratio of Jin Mao Building. It can be seen from Fig. 12 (damping ratio = 2.5%) and Fig. 13 (damping ratio = 1.5%) that as the 1.5%, the corresponding results were 6.55 gal, 6.28 gal and damping ratio decreases, the rms-acceleration values in both 7.07 gal. If the peak factor for acceleration response is also the along-wind direction and across-wind direction increase taken to be 3.0, the maximum peak resultant accelerations signiﬁcantly. atop the building are 18.81 gal and 21.21 gal for the damping ratios of 2.5% and 1.5%, respectively. Both values are smaller 4. Field measurements than the occupancy comfort criterion speciﬁed in the China 4.1. Measurement instrumentation design code [22]. Therefore, the wind-induced response of this building satisfactorily meets the occupancy comfort criterion Two accelerometers were orthogonally installed along the for this case. two main axes (x-direction and y-direction, see Fig. 3)of 1754 Q.S. Li et al. / Engineering Structures 28 (2006) 1745–1758

◦ Fig. 12. Relationship between the rms-acceleration responses and the wind speed at β = 0 (damping ratio = 2.5%).

◦ Fig. 13. Relationship between the rms-acceleration responses and the wind speed at β = 0 (damping ratio = 1.5%). the building on the 76th floor corresponding to a height of over Wenzhou at night of 12 August and dissipated over land about 300 m above ground to provide measurement of the the next day. Typhoon Rananim was regarded as the strongest accelerations. Fig. 3 shows the definition of the wind attack typhoon to attack the eastern coastline of Mainland China in angle. Acceleration responses were continuously acquired and the last several decades [25]. The smallest distance from the digitized at 20 Hz. In order to provide detailed information on center of Typhoon Rananim to Shanghai was about 350 km. The the local wind regime, an anemometer which was specifically measurements of wind action and wind-induced vibration of the made for this study was installed at the top of a tall building Jin Mao Building during the passage of Typhoon Rananim were near the Jin Mao Building. The height of the location of the made on 12–13 August, 2004. The field data recorded during anemometer was about 220 m from ground. The anemometer Typhoon Rananim was analyzed and some selected results are produced analogue voltage outputs proportional to wind speeds presented and compared with the wind tunnel experimental and wind directions that were sampled continuously at 20 Hz. results.

4.2. Introduction to Typhoon Rananim 4.3. Wind speed and wind direction

As reported by Shanghai Typhoon Research Institute [25], The location of the anemometer installed atop a tall building Rananim developed as a tropical depression over the western near the Jin Mao Building was calibrated in the wind tunnel test North Pacific on 8 August 2004, about 1100 km east-northeast described previously in this paper. This is an essential part for of Manila. It intensified over water on the East China Sea and comparing the model test results with the field measurements. attained typhoon strength on 11 August. Rananim made landfall Based on the field measurements of wind speed, wind direction Q.S. Li et al. / Engineering Structures 28 (2006) 1745–1758 1755

(a) 10 min mean wind speed during Typhoon Rananim. (b) 10 min mean wind direction during Typhoon Rananim.

Fig. 14. Variations of the 10 min mean wind speed and mean wind direction during Typhoon Rananim.

(a) Power spectral density of acceleration along x-direction. (b) Power spectral density of acceleration along y-direction.

Fig. 15. Power spectral density of acceleration. and the wind tunnel calibration results, variations of the mean frequencies for the first mode of vibration along x-direction and wind speed and mean wind direction at the top of the Jin Mao y-direction are presented in Table 2, which were actually used Building (at a height of 365 m) in each 10 min period are in the wind tunnel test to estimate the wind-induced responses shown in Fig. 14(a) and (b), respectively. The maximum mean of the building. wind speed was found to be 15.6m/s during the typhoon. The measured acceleration data can also be used to obtain Fig. 14(b) shows that the 10-minute mean wind direction during the damping ratio of the Jin Mao Building. In fact, field the whole typhoon process was relatively stabilized at 260◦. measurements of damping have seldom been conducted for The mean wind direction during the 15-hour data recording super tall buildings (building height > 400 m) in the past. In was found to be 259.5◦. Therefore, the mean wind direction order to obtain the damping ratio of each mode, the measured can be regarded as constant during the whole passage of the signals of acceleration responses were band-pass filtered before typhoon. So, the typhoon was blowing approximately parallel processing the random decrement to remove the components to one accelerometer axis (y-direction, as shown in Fig. 3), not concerned with the mode under consideration. In the wind i.e. the measurement axes of acceleration responses were along- tunnel tests at the design stage [2], structural damping ratios wind (in y-direction) and across-wind (in x-direction). This were assumed to be 1.5%, 2.0% and 2.5% for the estimations of provided an excellent opportunity to investigate the along- wind-induced responses of the building. In order to evaluate the wind and across-wind vibration characteristics of the Jin Mao adequacy of current design practices, the overall damping ratios Building. along the two orthogonal directions (x-and y-direction) were determined using the random decrement technique [26–28] 4.4. Acceleration response spectra and damping ratio based on the field data measured during the whole passage of the typhoon, which were found to be 0.55% and 0.57%, Fig. 15(a) and (b) present the acceleration response spectra respectively. From the measurements of damping, it appears measured from the Jin Mao Building along x-direction and that the assumptions at the design stage may overestimate the y-direction, respectively. These spectra were obtained from damping ratios of the Jin Mao Building at least as far as an a direct analysis of the accelerometer output data that were amplitude appropriate to the serviceability criterion for the measured simultaneously. In order to examine the participation building is concerned. of the various modes of vibration, logarithmic plots of the acceleration spectra along the two directions are both used 5. Comparison between the field measurements and the in Fig. 15(a) and (b). The spectra of acceleration responses wind tunnel results illustrate that the wind-induced responses of the building along the two directions were primarily in the two fundamental Fig. 16(a) and (b) show the variations of 10-minute rms- translational modes of vibration, but higher translational modes acceleration responses with time along x-direction and y- and torsional modes were also clearly present. The natural direction, respectively, which were measured on the 76th 1756 Q.S. Li et al. / Engineering Structures 28 (2006) 1745–1758

(a) Rms acceleration atop the building along x-direction. (b) Rms acceleration atop the building along y-direction.

Fig. 16. Variation of rms-acceleration responses atop the building.

(a) Rms acceleration along (b) Rms acceleration along x-direction. y-direction.

Fig. 17. Comparison between the full-scale measurements and the model test results.

floor of the Jin Mao Building during the passage of smooth curves plotted in Fig. 17 were obtained by curve fitting Typhoon Rananim. It was found from the field acceleration to the field measurements and the wind tunnel test results. measurements that the acceleration responses in the across- It can be seen from Fig. 17 that at the same wind speed, wind direction (along x-direction) were generally larger that the field data are larger than those from the wind tunnel test those in the along-wind direction (along y-direction) during the for the damping ratio of 1%, but are smaller than the model typhoon. This is consistent with the observations from the wind test data for the damping ratio of 0.5%. The wind tunnel test tunnel tests. results plotted in Fig. 17 also show that the damping ratio has It is always useful to compare model test results with actual significant effects on the acceleration responses. Obviously, the performance, in particular, for a super tall building, such as determination of damping ratios is very important in exactly the Jin Mao Building. Fig. 17(a) and (b) show the comparison estimating responses of high-rise structures at the design stage. between the full-scale measurements and the model test results The necessity of carrying out further full-scale measurements for the rms-acceleration responses along x-direction and y- of damping from super tall buildings should thus be stressed. direction at different wind speeds for the approaching wind It can also be seen from Fig. 17 that the measured field ◦ direction which was about 260 .InFig. 17, the field data were acceleration data along x-direction and y-direction are both recorded during the passage of Typhoon Rananim and the consistent with those obtained in the model tests, although the wind tunnel data were obtained from the present model test wind tunnel results for the case of the damping ratio of 0.5% for the case of BL2-2. As mentioned previously, the overall are larger than the field measurements by 19.1% and 11.8% damping ratio values determined from the field measurements in x-direction and y-direction, respectively. Considering that during the passage of Typhoon Rananim were 0.55% and 0.57% there were many uncertainties in the wind tunnel test such as in x-direction and y-direction, respectively. Therefore, wind- properly modeling of incident turbulence, terrain characteristics induced vibrations obtained in the wind tunnel test for the cases and Reynolds number as well as reasonable estimation of of damping ratio of 0.5% and 1.0% are presented in Fig. 17 for the damping ratio of the tall building etc., the agreement the purpose of comparison with the field measurements. The between the field measurements and the model test data is Q.S. Li et al. / Engineering Structures 28 (2006) 1745–1758 1757 satisfactory, thus illustrating that the wind tunnel test can (6) The interference effects from the surrounding buildings provide satisfactory predictions of wind-induced vibrations of varied with the incident wind directions, which mainly the super tall building under typhoon conditions. led to a reduction in wind loads and wind-induced responses when the Jin Mao Building was sheltered by 6. Conclusions upwind buildings. It was observed from the wind tunnel measurements that the influences of incident turbulence and The objective of this study is to investigate wind effects on terrain roughness on the wind loading and wind-induced the Jin Mao Building under strong winds by means of wind vibration of the Jin Mao Building were generally more tunnel tests and full-scale field measurements. In the wind tunnel experiments, wind loads and wind-induced responses significant than the interference effects. of this super tall building, such as force coefficients, power (7) Based on the spectral analysis of the data measured spectral densities, rms displacements and rms accelerations during Typhoon Rananim, it was found that the wind- were presented and discussed in detail. On the other hand, full- induced response of the building was primarily in the scale measurements of wind effects on the Jin Mao Building two fundamental translational modes of vibration, but were carried out during the passage of Typhoon Rananim. higher translational modes and torsional modes were Field data such as wind speed, wind direction and acceleration also present. The overall values of damping ratio in the responses were simultaneously and continuously recorded along-wind direction and across-wind direction during during the typhoon. Furthermore, the full-scale measurements the passage of the typhoon were found to be 0.57% were compared with the wind tunnel results. Some conclusions and 0.55%, respectively. The measurement results implied from the combined wind tunnel and full-scale study are that damping values of 0.5%–1.0% of critical appeared summarized as follows. reasonable for wind-resistant design of super tall buildings for serviceability consideration and the damping ratios of (1) The comparison between the present wind tunnel test the building may be overestimated at the design stage for results with the available existing model test data [1,2]for serviceability analysis. the Jin Mao Building showed that the agreement between (8) Wind-induced acceleration responses of the Jin Mao the three sets of data was satisfactory, thus verifying the Building were found to be monotonically increasing with reliability of the present wind tunnel test. the measured wind speeds. It was found from the field (2) The mean force coefficients decreased as the ground measurements that the acceleration responses in the across- roughness increased; but the fluctuating along-wind force wind direction were generally larger that those in the along- coefficients increased with the turbulence intensity. (3) Along-wind force spectra were very similar to the wind direction during the typhoon, which was consistent approaching wind gust spectra, suggesting the turbulence with the observations from the wind tunnel tests. was the cause of fluctuating along-wind force. An apparent (9) The field measured acceleration responses have been peak appeared at a reduced frequency of approximately compared with the wind tunnel test results. The field 0.1 in the across-wind force spectra, indicating fluctuating measurements of acceleration data were consistent with across-wind force was mainly induced by vortex shedding. those obtained in the force balance model study. In fact, the As the turbulence intensity increased, the peak magnitudes agreement was satisfactory for engineering applications, of the along-wind spectra increased; but the peak thus verifying the accuracy of the model test results and magnitudes of the across-wind spectra decreased and the illustrating that the wind tunnel test can provide satisfactory spectral shape around the Strouhal number of the reduced predictions of the wind-induced vibrations of the super tall frequency became broadened. building under typhoon conditions. (4) The rms-displacement responses depended on both the incident wind speed and the turbulence intensity; the Acknowledgements rms-displacement responses increased as the turbulence intensity and wind speed increased. At the same wind speed The work described in this paper was fully supported and turbulence intensity, the rms-displacement responses by a grant from the Research Grants Council of the Hong in the across-wind direction were larger than those in the Kong Special Administrative Region, China (Project No: CityU along-wind direction. 1131/00E). The financial support is gratefully acknowledged. (5) As the damping ratio decreased, the rms-acceleration responses in both the along-wind and across-wind References directions all increased significantly. By utilizing the wind [1] Gu M, Zhou Y, Zhang F, Xiang HF. Dynamic responses and equivalent tunnel test results, the predicted acceleration responses at wind loads of the Jin Mao Building in Shanghai. In: Proceedings of the top of the building subjected to the design wind speed the tenth international conference on wind engineering vol. 3. 1999. p. with 10-year return period [2] were all lower than the 1497–504. acceleration comfort criterion. 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