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ACROSS-WIND DYNAMIC RESPONSE OF HIGH-RISE

BUILDING UNDER WIND ACTION WITH INTERFERENCEEFFECTS FROM ONE AND TWO TALL BUILDINGS

Z. N. XIE1,2 AND M. GU1*1 State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai, Peoples Republic of China

2Department of Civil Engineering, Shantou University, Shantou, Peoples Republic of China

SUMMARY

Systematic studies on the across-wind dynamic interference effects on two and three tall buildings are presentedin this paper. It is found that surrounding and upstream interfering building(s) can significantly affect the across-wind load on the interfered principal building. Generally speaking, two interfering buildings can cause more

adverse dynamic effects on the principal building than a single one does. The results show that the maximuminterference factor (IF) among three buildings increases 80% over that between two buildings in terrain categoryB which has been defined in Chinese load code for design of building structures; a noticeable difference of 29%of IF is also observed in terrain category D. Vortex shedding from the upstream buildings can lead to vortex-induced resonance, resulting in excessive across-wind loads on the downstream building. Although interferenceeffects in terrain category D are much smaller than those in exposure category B, the maximum IF is found tobe 183 in the case of three buildings with the same size in terrain category D and 227 in other configurations.Copyright 2007 John Wiley & Sons, Ltd.

1. INTRODUCTION

In structural design, the evaluation of the wind loads on buildings is mainly based on industrial codes

and standards. These specifications are generally obtained from wind tunnel tests performed on iso-

lated structures in an open terrain. However, wind loads on buildings in realistic environments may

be quite different from those measured on isolated buildings. Surrounding or upstream buildings can

significantly increase or decrease the flow-induced forces on a building, depending mainly on the

arrangement and geometry of these buildings, wind velocity and direction, type of upstream terrain,

etc. The phenomenon is commonly known as interference effect and must be evaluated properly

(Kwok, 1995; Khanduri et al., 1998).

There are two main kinds of effects involved in the above-mentioned problems, namely the static

interference effects and the dynamic interference effects. Previous studies have shown that the dynamic

interference effects are more significant and more severe than the static effects. There are many

key factors, as mentioned above, affecting the dynamic wind loads on the buildings. However, due to

the huge amount of experimental workload, it is too difficult to deal with all these parameters indetail. Moreover, most previous investigations have focused on the interference effects between two

buildings (Bailey and Kwok, 1985; Kareem, 1987; Sakamoto and Haniu, 1988; Taniike, 1992), since

the inclusion of another building into the twin-building configuration makes the problem much more

THE STRUCTURAL DESIGN OF TALL AND SPECIAL BUILDINGSStruct. Design Tall Spec. Build. 18, 3757 (2009)Published online 17 August 2007 in Wiley Interscience (www.interscience.wiley.com). DOI: 10.1002/tal.393

Copyright 2007 John Wiley & Sons, Ltd.

*Correspondence to: Ming Gu, State Key Laboratory for Disaster Reduction in Civil Engineering, Tonji University, Shanghai200092, Peoples Republic of China. E-mail: [email protected]

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complicated. The interference effects on three or more buildings have not been studied in detail

so far.

This paper presents a detailed investigation on the across-wind dynamic interference effects on two

and three tall buildings on the basis of the high-frequency force balance technique. In order to compare

the present study with the previous results, detailed analyses of the interference effects between two

buildings are also carried out. A Windows-based software platform, integrating artificial neural

network, statistics and spectrum computations, is developed to analyze the huge amount of sampling

data from the tests, model the interference characteristics, and draw different interference factor con-

tours. Database technique is also employed to manage the experiment results.

2. DESCRIPTION OF EXPERIMENTS

2.1 Wind tunnel

The wind tunnel tests are conducted in the STDX-1 boundary layer wind tunnel of the Department of

Civil Engineering at Shantou University. The main test section of STDX-1 for the building model is

20m long, 3m wide, and 2m high. The test section has an adjustable roof, which provides a negligi-

ble pressure gradient in the downstream direction. The maximum wind speed can reach 45 m/s. Accord-ing to the Chinese load code (GB50009-2001, 2002), the terrain categories B and D, which have been

defined in Chinese load code for design of building structures (2001), are simulated in the test section

by means of spires, barriers and roughness elements. The simulated wind profiles V/Vg and turbulence

intensity distributionsIu (%) for the two categories are shown in Figure 1, where Vg is the wind speed

at the gradient wind height.

38 Z. N. XIE AND M. GU

Copyright 2007 John Wiley & Sons, Ltd. Struct. Design Tall Spec. Build. 18, 3757 (2009)

DOI: 10.1002/tal

0 0.2 0.4 0.6 0.8 10

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.00 4 8 12 16 20

z/Z

g

V/Vg

(%)

Category B

Category D

V/Vg

=0.16

=0.30

Iu

Iu

Figure 1. Wind velocity profiles and turbulence intensity distributions

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In order to assure the reliability of the experiment, a standard CAARC (Commonwealth Advisory

Aeronautical Research Council of Canada) tall building model of a 1/300 scale is first tested. Figure

2 shows the comparison between the power spectrum density (PSD) of the across-wind overturning

moment from the present test and the result given by Obasaju (1992). It can be seen from the figure

that the agreement is reasonably good.

2.2 Equipment, models, experimental arrangements

The measurements in this paper are carried out by means of a Nitta universal forcemoment sensor

model No. UFS-4515A100 and the attached signal conditioner and amplifier. The technical specifica-

tions for the sensor are shown in Table 1.

The conditioned and amplified analog signal from the sensor is filtered by the low-pass filters in

the system, transmitted to a Scanivalve Zoc/EIM-16 module, and eventually converted quickly by the

Scanivalve sampling platform. The lowest natural frequency of the model-balance system is 112Hz,

which is much higher than the concerned frequency range of the aerodynamic forces acting on the

building models.

ACROSS-WIND DYNAMIC RESPONSE 39


DOI: 10.1002/tal

fS(f)/2

f D/VH

10-3

10-2

10-1

100

10-4

10-3

10-2

10-1

100

101

Obasaju (1992)

This paper

Figure 2. Normalized across-wind overturning moment spectra for a CAARC tall building model

Table 1. Specifications of Nitta UFS-4515A100 sensor

Component Full-scale range Accuracy

Fx, Fy 440N Linearity: 02% full scaleFz 880N Hysteresis: 02% full scale

Mx,My,Mz 51Nm

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A 600mm tall and 100mm wide square model, made of light foam and skinned with lightweight

wood, is used for the tested or principal building. The other relevant parameters of the prototypal prin-

cipal building are: height 240m; breadth 40m; structural damping 2% of critical damping; and natural

frequency 02Hz for both sway base modes. Five other types of square building models are used as

the interfering buildings. These interfering buildings have the same height h as the principal building

but different breadths of 05b, 075b, 10b, 15b and 20b, where b (=100mm) is the breadth of theprincipal building model. All building models are oriented with one face normal to the wind, while

the centre-to-centre spacing among them varies in the along-wind direction (x) and the across-wind

direction (y) in a coordinate grid shown in Figure 3.

2.3 Formulation

According to the theory of high-frequency base force balance (Tschanz and Davenport, 1983), the

PSD and the RMS value of the dynamic base moment response of the principal building, SMD(f) and

sMD, may be written as

(1)

(2)

in which

s sp

z

c c

sM M M

M

M

D S s

S

S

H f S f df S

= ( ) ( ) +( )

2

00

0 0

21

4

1

S f H f S f M MD S( ) = ( ) ( )2



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-0.8b

-1.6b

-2.4b

-3.2b

B

C

3.2b

2.4b

1.6b

0.8b

x

1.1b2.1b10.1b 9.1b 8.1b

A

7.1b 6.1b 5.1b 4.1b 3.1b

y

x

y

bWind

A,B: Interfering buildings

C: Principal building

is at (x,y)=(0,0)

Figure 3. XYcoordinate grid for positions of interfering buildings

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(3)

is the mechanical admittance of the principal building; denotes the dimensionless PSD of

the base moment;MS(t) is the base bending moment or the first generalized wind force on the build-

ing assuming a linear mode, which can be directly measured by the high-frequency base force balance;

sMS is the RMS value ofMS(t); is the reduced natural frequency; D is the characteristic

breadth of the structure; and VH is the mean velocity at the top of the structure. The reciprocal of the

reduced frequency c0 is the reduced velocity, i.e.

(4)

Thus one can find that the response dynamic base moment varies with the reduced velocity. Con-

sidering the effects of the nearby buildings, the across-wind interference effects on the principal build-

ing are commonly expressed in terms of an interference factor (IF) given by

(5)

where sMD is the RMS of the dynamic response of the across-wind base moment as defined in Equa-tion (2).

3. EXPERIMENTAL RESULTS AND DISCUSSION

3.1 Configuration of two buildings of equal size

The across-wind dynamic interference effects between two identical buildings are measured and com-

pared with those obtained by Bailey and Kwok (1985) at a reduced velocity of 6. It can be found that

there is a good general consistency between the two studies, as shown in Figure 4.

Figure 5 shows the IF distribution of the same configuration in uniform flow and terrain category

D. From the contours one can find that the across-wind dynamic interference effects are strongly

affected by the upstream terrain. The interference factors decrease rapidly with increase in terrain

roughness. The maximum IF decreases from 65 in uniform flow to about 18 in terrain category B

and then to about 12 in terrain category D at a reduced velocity of 6. Figure 6 presents the distribu-tions of the interference factor contours for different reduced velocities. The list of contours shows

both the common behaviours and the differences. It can be seen that the critical upstream location of

the interfering building is in region (4b, 2b)(10b, 35b), where interference factors are tested up to22 in terrain category B and about 12 in terrain category D.

Since the shielding and the high-speed shedding wake depress the vortex shedding of the down-

stream building, interference factors of less than 10 are measured when the upstream interfering build-

ing is located at the region (referred to as shielding region) near the principal building. The strongest

IFof the principal building under interference

of the isolated pricipal building=

s

s

M

M

D

D

VV

f Dr

H= =

1

0 0c

c00=

f D

VH

c c

s

SM

M

S

S

( )2

H f

f

f

f

f

( ) =

+

2

0

22

0

0

2

1

1 2z



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-3

-2

-10.6

1.4

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1.34

C12345678910

x/b

-3.5

-2.5

-1.5

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012345678910

0

x/b

0.4

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1

1

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1.6

1.8

-3

-2.5

-2

-1.5

-1

y/b

C

-3.5

-4

(a)

(b)

Figure 4. Comparison of the across-wind interference factor for twin buildings with previous studies (Vr = 6): (a)Bailey and Kwok (1984) in open country with a= 015; (b) Present result in terrain category B with a= 016

12345678910

x/b

0.5

1

1

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1

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x/b

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0.90.9

1

1

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1

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-2.5

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-1

y/b

C

(a)

(b)

Figure 5. Interference factor contours of twin-building configurations in other terrains (Vr = 6): (a) uniform flow;(b) terrain category D

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DOI: 10.1002/tal

shielding location is found at (11b, 16b), where the minimum value of the interference factor isrecorded to be 02. The strongest shielded effects are found at a reduced velocity of 10 because it is

the critical velocity for an isolated building. The shedding wake from an existing nearby building dis-

turbs the vortex shedding of the principal building and reduces the across-wind response, resulting in

a much lesser effect compared with the isolated case.

A new significant interfering location, which has not been reported in the previous studies, is found

in the side-by-side building arranged at (0, 24b) at which the interference factor is recorded as 256at a reduced velocity of 8. The reason may be that the existing side-by-side building speeds up the

velocity of incidence flow that hits at the principal building. This phenomenon will be discussed in

detail in the following sections.

3.2 Configuration of three buildings with equal size

3.2.1 Side-by-side arrangements

For the three-equal-building configuration in terrain category B, the critical positions for the across-

wind dynamic interference effects are also found in the side-by-side arrangement of three buildings

like the twin-building configuration mentioned above. In this case, the critical locations are found at(0, 32b) and (0, 32b), where a maximum interference factor is found at a reduced velocity of 7 inuniform flow field and at 8 in the other two shear flow fields. The results are listed in Table 2.

A maximum interference factor of 455 is recorded in terrain category B, while the factor is 253

in the side-by-side twin-building arrangements. Figure 7 gives the typical normalized spectra of the

across-wind overturning moments of the principal building with and without the presence of the two

side-by-side arranged interfering buildings. It can be seen that the spectrum changes noticeably with

the presence of the interfering buildings. The peak of the spectrum rises significantly and shifts to the

right, indicating that the shedding frequency of the principal building becomes higher than that in the

isolated case and the vortex-induced resonance will occur at a smaller reduced velocity. The results

also show that, due to the narrow pipe effect, the mean along-wind overturning moment with inter-

fering buildings at the above-mentioned critical locations is increased by 10% over that without inter-

fering buildings. This increase of the mean along-wind overturning moment indicates the increase ofthe equivalent wind speed that approaches the principal building. The speeding up of the incidence

flow will enhance the strength of the shedding vortices and the vortex shedding frequency and, even-

tually, leads to a pronounced across-wind resonance at a smaller reduced velocity. Figure 8 shows the

variation of the across-wind dynamic interference factor with the reduced velocity for the two inter-

fering buildings located at the critical positions of (0, 32b). It can be seen that the critical reducedvelocity is 8 and the corresponding interference factor is 455.

3.2.2 Distribution of the critical positions

Table 3 shows the first five maximum interference factors and the corresponding critical locations of

interfering buildings for the three-building configuration. The recorded maximum interference factor

is found to be 455. Meanwhile, the first three critical locations of the interfering buildings are foundin the side-by-side arrangement and the other two in staggered arrangement. The critical locations

mentioned here are quite different from those in the conclusion drawn by Saunders and Melbourne

(1980), in which the positions of two interfering buildings were simplified and confined to the side-

by-side arrangement and were symmetrical to the longitudinal x-axis.

The results show that the interference effects for the three-building configuration are indeed more

complex than the twin-building configuration. Compared with the results for the twin-building con-

figuration in Figure 6, the first maximum interference factor of the three-building configuration has

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an increase of 79% over that of the twin-building configuration, and 72% for the second maximum

value. The results indicate that at the strongest interference position in the twin-building configura-

tion another equal-sized interfering building can produce more significant across-wind dynamic wind

load on the principal building. These results show that the interference effects of three buildings aremore significant than two buildings and should be carefully considered.

3.2.3 Typical distributions of the interference factor

Four contour plots in Figure 9 show the variation of the across-wind dynamic interference factor with

the relative positions of one of the interfering buildings (hereafter referred to as model B), while the

other interfering building (hereafter referred to as model A) is fixed at (0, 24b), (31b, 32b), (51b,08b) and (21b, 0), respectively.



DOI: 10.1002/tal

(c)

(b)012345678910

x/b

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0.8

0.8

11

11.2

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1.4

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1.

8

-3

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-1.5

-1

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C

(a)012345678910

x/b

0.4

0.6

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1

1 1.2

1.2

1.4

1.4

1.41.4

1.6

1.6

1.8

1.8

2

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/b

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1

1.2

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DOI: 10.1002/tal

Table 2. Maximum across-wind dynamic interference factor of three side-by-sidearranged buildings

Terrain category Maximum IF Critical reduced velocity

Uniform flow 653 7B 455 8D 166 8

Figure 6. Interference effects of twin-building configurations at different reduced velocities in terrain categoryB: (a) Vr = 2; (b) Vr = 5; (c) Vr = 8; (d) Vr = 10; (e) Vr = 12

(d)

(e)

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1.8

2

2.2

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-2.5

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y/b

C

Figure 9(a) shows the distribution of the interference factor with model A fixed at (0, 24b). It canbe seen that the interference effects of the other upstream building are similar to those of the twin-

building configuration shown in Figure 6(c). But, in general, interference effects of the three-building

configuration are more significant than those of the twin-building configuration. In particular, the inter-

ference factor of 435 recorded in side-by-side arrangement of three buildings is much greater than

that of 253 recorded in twin building configurations shown in Figure 6(c).When model A is fixed at (21b, 0), Figure 9(b) shows that the across-wind dynamic wind load of

the well-shielded principal building can also be significantly affected by another laterally located build-

ing. However, the interference effects in this case are smaller than the case shown in Figure 9(a). The

interference shows shielding effects and the interference factor is less than 1 when the three buildings

are arranged in tandem.

Figure 9(c) presents another critical distribution in which interfering building A is fixed at the other

critical location (31b, 32b) listed in Table 3. The maximum IF of 373 is recorded when model B

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10-3

10-2

10-1

100

10-6

10-5

10-4

10-3

10-2

10-1

100

fD/VH

fSMx(

f)/q

H2

Isolated buildingInterfering buildings

at (0,3.2b), (0, -3.2b)

Figure 7. Normalized across overturning moment spectra of the principal building with and without the presenceof the two interfering buildings at (0, 32b), (0, 32b)

2 4 6 8 10 120

1

2

3

4

5

V

IF

r

Figure 8. Across-wind dynamic interference factor with the two interfering buildings situated at (0, 32b),(0, 32b)

is located at (51b, 08b). Fixing the interfering building A at (51b, 08b), we get another criticaldistribution as shown in Figure 9(d).

The fourth and fifth critical locations listed in Table 3 are in staggered arrangements. The variations

of the spectra of the principal building with and without the presence of the interfering buildings in

the staggered arrangement are similar to those for the side-by-side arrangement in Figure 7. The cor-

responding variation of the interference factor with the reduced velocity for the interfering buildings

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DOI: 10.1002/tal

located at the fourth critical positions of (31b, 32b) and (51b, 08b) is shown in Figure 10, wherea critical reduced velocity of 8 can be found.

3.2.4 Effects of upstream terrain and number of interfering buildings

This section is devoted to the discussion of the effect of different terrain on the across-wind dynamicinterference effects. Table 4 presents the measured maximum dynamic interference factors and the

corresponding critical positions in different upstream terrain, where the figures in parentheses in the

second column denote the maximum interference factors of the twin-building configuration. All inter-

ference factors of the two configurations decrease rapidly with the increase in turbulence of the inci-

dence flow, but in terrain category D the maximum interference factor is still found to be up to 183

in the three-building configuration and 142 in the twin-building configuration, respectively. The most

significant interference effect is found in uniform flow in the three-building configuration, where

the largest recorded interference factor is 2819, which is much greater than that of 124 in the twin-

building configuration. The corresponding differences between the two configurations in terrain

categories B and D are found to be 80% and 29%. The results suggest that two interfering buildings

could produce more significant interference effects on the principal building than a single one.

3.3 Effects of relative section size

3.3.1 Twin-building configurations

When vortices that shed from the upstream buildings hit the side face of the downstream building, a

pronounced across-wind response could be induced. In particular, if the shedding frequency coincides

with the natural frequency in the across-wind direction of the principal building, resonance will occur.

The dimensionless ratio of the vortex shedding frequency from the upstream building to the natural

frequency of the downstream building with the same height is

(6)

wherefis the vortex shedding frequency,fs is the natural frequency of the principal building, St is the

Strouhal number of the upstream building, Vr is the reduced velocity (Equation (4)), andBr is the ratio

of the breadth of the across-section of the interfering buildings to the principal building. When the

ratio of the two frequencies is equal to 1, i.e. when the vortex shedding frequency of the upstream

structure coincides with the natural frequency of the principal downstream building, resonance occurs.

The Strouhal number of the square-section buildings discussed above is about 01 in terrain category

B and this leads to the critical reduced velocity for the downstream building as

(7)

According to Equation (7), with the interfering building having a breadth ratio of 05, 075 and 1,

respectively, the critical reduced velocity of the principal building will be correspondingly 5, 75 (8

is selected approximately) and 10. The corresponding contributions of the interference factor for the

three critical velocities are shown in Figure 11. Since the reduced velocity of 10 is the resonant veloc-

ity of the principal building in the isolated case, the interference effects of the two smaller breadth

ratios of interfering buildings, as shown in Figure 11(a) and (b), are more pronounced than those of

the equal-sized interfering building shown in Figure 11(c).

V B S B Br r r r r= = =0 1 10.

f

f

S V

Bs

t r

r

=

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With regard to the critical location of (31b, 16b) and (41b, 16b) shown in Figure 11(a) and(b), Figure 12 shows the normalized across-wind overturning moment spectra of the principal build-

ing with and without the presence of the interfering building for the two cases. The dominant fre-quency in the incidence flow that sheds from the upstream building is registered in the across-wind

overturning moment spectra as a peak shown in Figure 12. The figure shows that the dominant peaks

of the two cases are approximately centred at the reduced frequencies of 02 and 0125, respectively.

This leads to the principal building being probably excited at a resonant frequency and produces a

higher interference factor at the corresponding reduced velocities of 5 and 8.

For the interfering building with a Br of 05, a maximum interference factor of 709 is found at a

reduced velocity of 6 in terrain category B when it is located at (31b, 0) and the significant interfer-



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2

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2

Mode lA

CA

(a)

(b)

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Figure 9. Typical distributions of across-wind dynamic interference factors in terrain category B (Vr = 8): (a)interfering building model A fixed at (0, 24b); (b) interfering building model A fixed at (21b, 0); (c) interfering

building model A fixed at (31b, 32b); (d) interfering building model A fixed at (51b, 08b)

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y/b

0.4

0.4

0.4

0.6

0.6

0.60.8

0.8

0.8

0.8

0.8

0.8

0.8

0.8

0.8

1

1

11

1

1

1

1

1

1

1.2

1.2

1.2

1.2

1.2

1.2

1.2

1.4

1.4

1.4

1.4

1.4

1.4

1.4

1.61.6

1.6

1.6

1.8

1.8

22.2

Mode lA

C

A

2.63

3.43.6

(c)

(d)

Table 3. Distribution of the critical locations for the three-building configuration

(terrain category B, Vr = 8)

Interference factor Critical locations Arrangement

455 (0, 32b) (0, 32b) Side-by-side435 (0, 32b) (0, 24b) Side-by-side373 (0, 24b) (0, 24b) Side-by-side339 (31b, 32b) (51b, 08b) Staggered311 (21b, 32b) (41b, 08b) Staggered

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DOI: 10.1002/tal

ence effect, with an IF of 25 recorded, still can be found in terrain category D. The distributions of

the interference factor in the two types of terrain are shown in Figure 13. These observed results show

similar trends to the results obtained by Taniike and Inaoka (1988), where a much higher interference

factor of 20 in the across-wind direction was found when an interfering building with a smaller Br of

04 was located at (3b, 0) in a smoother terrain of open country. Figure 14 compares the normalized

spectra of the across-wind overturning moment of the principal building with and without the pres-

ence of the interfering building at the critical location of (31b, 0) in terrain category B. It can be seen

that the spectrum of the across-wind load of the principal building is completely changed by the inter-fering building, in which the dominated frequencies, due to vortices shedding from the upstream build-

ing, are registered clearly on the spectrum distribution. Since the principal building is submerged

completely in the low speed wake of the upstream building, the registered peak of the reduced fre-

quency is slightly smaller than that of the principal building located at the high-speed wake boundary

of the upstream building. This leads to possible resonance occurring at a higher critical reduced veloc-

ity of 6, which is greater than the critical reduced velocity of 5 when the interfering buildings are stag-

gered as shown in Figure 12(a).

2 4 6 8 10 120.5

1

1.5

2

2.5

3

3.5

4

V

IF

r

Figure 10. IF of the principal building with the presence of the interfering buildings at (31b, 32b) and(51b, 08b)

Table 4. Maximum interference factor in different terrains

Critical

Terrain category Maximum interference factor Reduced velocity Locations

Uniform flow 2819(124)a 8 (41b, 32b) and (61b, 0)B 455(253) 8 (0, 32b) and (0, 32b)

D 183(142) 8 (0, 32b) and (101b, 32b)a Maximum IF of twin-building configuration.

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3.3.2 Three-building configurations

For three-building configurations, the statistical characteristics of the distributions of the across-wind

interference factors at different reduced velocities are shown in Figure 15, wherep represents the per-

centage of the positions of the corresponding interference factor over the whole test positions of the

configuration. From those figures one can clearly find the existence of the wake vortex-induced reso-nance. It can be seen that the relationship between the critical reduced velocity andBr is also the same

as that predicted by Equation (7). In the listed figures for different reduced velocities, the reduced

velocity of 3 corresponds to a non-resonance case, while the values of 5 and 8 are the critical reduced

velocities of configurations ofBr = 05 and 075, respectively. Since the two larger interfering build-ings have higher critical reduced velocities, the interference effects of the interfering buildings with

Br > 1 would be smaller than those of the smaller interfering buildings at the lower reduced velocitieswhich are frequently encountered in the real building structures.



DOI: 10.1002/tal

012345678910

x/b

0.20.40.6

0.8

0.8

1

1

1.2

1.2

1.

4

1.6

1.6

1.8

22.2

2.4

2.4

2.6

2.62.6

2.6

2.8

2.8

2.8

2.8 3

3

3

3.2

3.2

3.2

3.4

3.4

3.6

3.6

3.6

3.8

3.8

4 4.2

-3

-2.5

-2

-1.5

-1

y/b

C

012345678910

x/b

0.2

0.4

0.40.6

0.6

0.8

0.8

1

1

1

1.2

1.2

1

.21

.2

1.4

1.4

1.4

1.6

1.6 1.8

1.8

222.2

-3

-2.5

-2

-1.5

-1

y/b

C

(a)

(b)

(c)

012345678910

x/b

32

.5

2

1

.5

1

0 .5

0

0.5

0.5

0.5

1

1

1

1.5

1.5

1.5

1.5

2

2

2

2

2

2

2.5

2.52.5

2.53

3

3

3.5

3.5

4

4

4.5

4.5 5

5.5

-3

-2.5

-2

-1.5

-1y/b

C

Figure 11. The critical IF distributions for different breadth ratio interfering buildings in terrain category B; (a)Br = 05, Vr = 5; (b)Br = 075, Vr = 8; (c)Br = 10, Vr = 10

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DOI: 10.1002/tal

10-3

10-2

10-1

100

10-6

10-5

10-4

10-3

10-2

10-1

f D/VH

fSM

x(f)/q

H2

Isolated buildingInterfering building at (3.1b, -1.6b)

10-3

10-2

10-1

100

10-6

10-5

10-4

10-3

10-2

10-1

100

f D/VH

fSMx(

f)/q

H2

Isolated buildingInterfering building at (4.1b, -1.6b)

(a)

(b)

Figure 12. Normalized across-wind overturning moment spectra of the principal building with and withoutthe interfering building at the critical interfering location for twin building configuration in terrain categoryB: (a) interfering building ofBr = 05 located at (31b, 16b); (b) interfering building ofBr = 075 located

at (41b, 16b)

The distributions of the interference factor for the configuration ofBr = 1 at a critical reduced veloc-ity of 10, as shown in Figure 15(d) and (h), are not as significant as the critical distributions for the

configurations ofBr = 05 at Vr = 5 andBr = 075 at Vr = 8, as shown in Figure 15(b), (c), (f) and (g).However, the interference effects for the configuration ofBr = 1 at the reduced velocity of 10 are stillfound to be more significant than those of the other four types of configuration as shown in Figure

15(d) and (h). The distributions of the interference factors at higher reduced velocities are not given

here since the higher reduced velocity rarely occurs in concrete buildings.

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DOI: 10.1002/tal

012345678910

x/b

1

1

1

1

1

1.5

1.5

1.5

2

2

2.53

3.54

4.5

55.5

66.57

-3

-2.5

-2

-1.5

-1

y/

b

C

012345678910

x/b

0.

6

0.

7

0.8

0.9

1

1

1

1

11

1

1.1

1.1

1.1

1.1

1.1

1.2

1.

2

1.2

1.

3

1.4

1.6

1.8

22.22.4

-3

-2.5

-2

-1.5

-1

y/b

C

(a)

(b)

Figure 13. The critical distributions of the across-wind dynamic interference factors of twin-buildingconfigurations ofBr = 05 at a reduced velocity of 6: (a) terrain category B; (b) terrain category D

10-3

10-2

10-1

100

10-6

10-5

10-4

10-3

10-2

10-1

100

f D/VH

fSMx(

f)/q

H2

Isolated buildingInterfering building at (3.1b,0)

Figure 14. Normalized across-wind overturning moment spectra of the principal building with and without theinterfering building ofBr = 05 at (31b, 0) in terrain category B

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Variations of the maximum interference factors for different configurations of breadth ratios with

reduced velocity are shown in Figure 16. The figure shows an obvious peak in each curve correspon-

ding to the critical velocity, especially in the lower roughness terrain. However, only two cases with

smaller breadth ratios ofBr = 05 and 075 are related to the wake vortex-induced resonance. The crit-ical locations for other three cases with larger breadths are in the side-by-side arrangement and are

the same as that of the side-by-side arranged three-building configuration discussed in previous

sections.

Since higher turbulence depresses the generation of shedding vortices from the interfering build-

ings and the principal building, interference effects decrease rapidly in terrain category D. However,

the distinctive interference factors of 267 forBr = 05, 227 forBr = 075 and 183 forBr = 10 are stillrecorded.

4. CONCLUSIONS

Systematic studies for the across-wind dynamic interference effects on three tall buildings are con-

ducted on the basis of wind tunnel experiments in this study. The interference excitations can be from

of one or two adjacent buildings under various conditions. Some of the main results are summarized

as follows.



DOI: 10.1002/tal

Br=0.50Br=0.75Br=1.0Br=1.5Br=2.0

0 0.5 1 1.5 2 2.5

30

20

10

0

IF

p/%

(a) (b)

(c) (d)

0 1 2 3 4

40

30

20

10

0

IF

p/%

Br=0.50Br=0.75Br=1.0Br=1.5Br=2.0

0 1 2 3

40

30

20

10

0

50

p/%

IF

Br=0.50Br=0.75Br=1.0Br=1.5Br=2.0

0 0.5 1 1.5 2

40

30

20

10

0

IF

p/%

Br=0.50Br=0.75Br=1.0Br=1.5Br=2.0

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A stronger across-wind dynamic response will occur when a tall building is located near the high-

speed wake boundary of upstream buildings. The tandem or side-by-side arranged interfering build-

ings could produce significant interference effects on the principal building.

Two interfering buildings could produce more significant across-wind interference effects than a

single one does. For configuration with three equal-sized buildings, the tested maximum interfer-

ence factor increases, respectively, 80% and 29% over those of the twin-building configuration in

terrain categories B and D.

Shedding vortices from upstream buildings, especially smaller buildings in some particular region,

could produce resonance on the downstream building at a predictable lower critical reduced veloc-

ity. The breadth ratio of the interfering and the principal buildings could significantly affect the inter-

ference factors due to vortex-induced resonance. Higher turbulence flow depresses the generation of shedding vortices from the interfering and the

principal buildings and, as a result, interference effects decrease rapidly with increase in roughness

of the upstream terrain. However, noticeable interference factors of 267 for Br = 05, 227 forBr =075 and 183 forBr = 10 are still recorded in terrain category D.

Owing to the complex nature of the problem, it is not easy to make some direct and general recom-

mendations from the up-to-date results for three-building configurations. More comprehensive

approaches and experiments are therefore needed for further studies.



DOI: 10.1002/tal

(e) (f)

(g) (h)

p/%

0 0.5 1 1.5

40

30

20

10

0

IF

Br=0.50Br=0.75Br=1.0Br=1.5Br=2.0

p/%

0 0.5 1 1.5

40

30

20

10

0

IF

Br=0.50Br=0.75Br=1.0Br=1.5Br=2.0

p /%

0 0.5 1 1.5 2

40

30

20

10

0

IF

50Br=0.50Br=0.75Br=1.0Br=1.5Br=2.0

p/%

0.5 1 1.5

40

30

20

10

IF

Br=0.50Br=0.75Br=1.0Br=1.5Br=2.0

0

0

Figure 15. The distributions of the across-wind dynamic interference factors of the three-building configurationwith different breadth ratios: (a) Vr = 3, terrain category B; (b) Vr = 5, terrain category B; (c) Vr = 8, terraincategory B; (d) Vr = 10, terrain category B; (e) Vr = 3, terrain category D; (f) Vr = 5, terrain category D; (g)

Vr = 8, terrain category D; (h) Vr = 10, terrain category D

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Kareem A. 1987. The effects of aerodynamic interference on the dynamic response of prismatic structures.Journalof Wind Engineering and Industrial Aerodynamics 25:365372.

Khanduri AC, Stathopoulos T, Bdard C. 1998. Wind-induced interference effects on buildings: a review of thestate-of-the-art.Engineering Structures 20(7): 617630.

Kwok KCS. 1995. Aerodynamics of the tall buildings: a state of the art in wind engineering. In Proceedings of9th International Conference on Wind Engineering, New Delhi, India; 180204.

Obasaju ED. 1992. Measurement of forces and base overturning moments on the CAARC tall building model ina simulated atmospheric boundary layer. Journal of Wind Engineering and Industrial Aerodynamics40:103126.

Sakamoto H, Haniu H. 1988. Aerodynamic forces acting on two square prisms placed vertically in a turbulentboundary layer.Journal of Wind Engineering and Industrial Aerodynamics 31: 4166.

Saunders JW and Melbourne WH. 1980. Buffeting effects of upstream buildings. In Proceedings of the5th International Conference on Wind Engineering, Fort Collins, CO. Pergamon Press: Oxford; 593605.

Taniike Y. 1992. Interference mechanism for enhanced wind forces on neighbouring tall buildings. Journal ofWind Engineering and Industrial Aerodynamics 41:10731083.

Taniike Y, Inaoka H. 1988. Aeroelastic behaviour of a tall building in wakes. Journal of Wind Engineering andIndustrial Aerodynamics 28(1): 317327.

Tschanz T, Davenport AG. 1983. The base balance technique for the determination of dynamic wind loads.Journalof Wind Engineering and Industrial Aerodynamics 13: 429439.



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