Upload
rahul-babu
View
237
Download
1
Embed Size (px)
Citation preview
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 1/39
i
SEMINAR REPORT
on
WIND-INDUCES RESPONSES OF SUPER-TALLBUILDINGS WITH VARIOUS AERODYNAMIC SHAPES.
Submitted in Partial Fulfillment of the Requirements for the Degree of
MASTER OF TECHNOLOGYin
CIVIL ENGINEERING by
NAME : RAHUL BABU
(Roll no ) - 15
DEPARTMENT OF CIVIL ENGINEERING
FEDERAL INSTITUTE OF SCIENCE AND TECHNOLOGY
MOOKANOOR P O, ANGAMALY
YEAR 2015
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 2/39
ii
CERTIFICATE
Certified that seminar work entitled “WIND-INDUCES RESPONSES OF SUPER-TALL
BUILDINGS WITH VARIOUS AERODYNAMIC SHAPES” is a bonafide work carried out in
the I semester by “RAHUL BABU ” in partial fulfillment for the award of Master of Technology
in Civil Engineering during the academic year 2015 who carried out the seminar work under the
guidance and no part of this work has been submitted earlier for the award of any degree.
Dr. Praseeda K I Mrs. Lidiya P. M
SEMINAR CO_ORDINATOR SEMINAR GUIDE
Mr. Unni Kartha G
HEAD OF THE DEPARTMENT
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 3/39
iii
ACKNOWLEDGEMENT
First of all, I am grateful to God Almighty, for showering his blessings upon me for
enabling me to complete this seminar work on time. I am deeply indebted to Dr. George Issac
(Principal) for his vital support and encouragement. I wish to express my sincere gratitude to
Mr. Unni Kartha G (HOD, CE) who has been a source of inspiration and for his much needed
motivation. I would also like to extend my heartfelt thanks to my guide Mrs. Lidiya P. M (Asst.
Professor, CE), for his able guidance and useful suggestions without which this seminar would
not have been successful. I am also grateful to all the teaching and non teaching staff for their
valuable assistance. Finally, I am thankful to my parents for their blessings and support, my
friends for their help and encouragement.
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 4/39
iv
ABSTRACT
Modern tall buildings go higher and higher with the advance in structural
design and high strength materials. As the height and slenderness increase, buildings
suffer from increased flexibility which has negative effects in wind loading. Flexible
structures are affected by vibration under the action of wind which cause building
motion and plays an important role in the structural and architectural design.
Understandably, contemporary tall buildings are much more vulnerable to wind
excitation than their predecessors. Hence different design methods and modifications
are possible in order to ensure the functional performance of flexible stuctures and
control the wind induced motion of tall building. An extremely important and effective
design approach among these methods is Aerodynamic Modification.
Keywords : Super-tall buildings; Wind load; Aerodynamic modification;
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 5/39
v
CONTENTS
Chapter No TITLE Page no.
CERTIFICATE ii
ACKNOWLEDGEMENT iii
ABSTRACT iv
LIST OF FIGURES vii
LIST OF TABLES ix
ABBREVIATIONS x
1 INTRODUCTION 1
2 BACKGROUND 2
2.1 Wind Exitation 2
2.1.1 Along Wind motion 3
2.1.2 Across wind motion 3
2.1.3 Vortex-Shedding phenomenon 4
2.2 Aerodynamic modifications against wind excitation 5
2.3 Shaping Strategies 9
3 OUTLINES OF EXPERIMENTS 11
3.1 Test Model 11
3.2 Wind Pressure measurements 15
3.3 Frame model for time history analysis 16
4 RESULTS AND DISCUSSIONS 18
4.1 Variation of peak and normal stresses with wind 18
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 6/39
vi
direction
4.2 Effect of damping ratio on peak normal stresses 22
4.3 Effect of various loading conditions 26
5 CONCLUSIONS 28
6 REFERENCES 29
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 7/39
vii
LIST OF FIGURES
Fig no. Description Page no.
1 Wind response direction 2
2 Effect of Vortex shedding on response 4
3 Vortices in different wind speed 5
4 The examples of tapering effect utilization 6
5 The examples of setbacks and sculpted building top utilization 7
6
6(a) The Burj Dubai 7
6(b) The Sears Tower 7
7
7(a) The Marina City Towers 8
7(b) The Millenium Tower 8
7(c) Toronto City Hall 8
7(d) The U.S Steel Building 8
8
8(a) Taipei 9
8(b) The Shanghai World Financial Centre 9
9 Shaping Strategies 10
10 Test Models 14
11 Profiles of mean wind speed and turbulance intensity 16
12 Schematic view of frame model and 3 mode shapes 17
13 Ratio of largest peak tensile stress 19
14 Peak tensile stress for various wind directions 20
15Peak normal stress for various bending moments and axialforces 21
16 Effect of damping ratio on peak tensile stresses 22
17
Variation of largest peak compressive stresses with damping
ratio 22
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 8/39
viii
18 Effect of damping ratio on normal stress 24
19 Effect of damping ratio on bending moments 25
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 9/39
ix
LIST OF TABLES
Table no Description Page no.
1 Effects of various loading conditions on peak compressive stress of SQ model 26
2 Effects of various loading conditions on peak compressive stress of SB model 27
3
Effects of various loading conditions on peak compressive stress of SB+45RT
model 27
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 10/39
x
ABBREVIATIONS
1.
CC - Corner Cut
2. TP - Taper
3. SQ - Square
4. CF - Chamfered
5. SB - Setback
6. Hel - Helical
7. CV - Cross-void
8.
RT - Rotation
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 11/39
1
1 INTRODUCTION
Super tall buildings are those buildings whose height is more than 300m. As
buildings become higher, wind loads become more important than earthquake loads in
safety design as well as in serviceability design including occupants‟ vibration
perception. Thus many attempts have been made to suppress wind-induced responses
on a building by changing building shapes: so called aerodynamic modification. As
wind forces largely depend on building shape regardless of structural system, studies
on various aerodynamic modifications have been one of the most challenging issues in
wind-resistant design. Aerodynamic modifications include taper, set-back, helical
twist, openings and combinations of them, and a comprehensive study on these
aerodynamic characteristics was recently made. These typical and unconventional
building shapes are a resurrection of an old characteristic, but they have the advantage
of suppressing across-wind responses, which is a major factor in safety and
serviceability design of super- tall buildings. The effectiveness of aerodynamic
modification in reducing wind forces has been widely reported since the late 1980s.
Wind pressure measurements were conducted on super-tall building models,
which showed superior aerodynamic characteristics. Models tested included corner
modifications, taper, setback , helical, cross-void, and combinations of them. Time
history analyses were conducted in the present study using wind pressures. First, time
histories of local wind forces were obtained from the wind pressures, and the time
histories of local wind forces were input at the centre of each floor of the frame model
to investigate the wind load effects. The purpose of the present study was to directly
compare the wind load effects on super-tall buildings with various atypical building
shapes, focusing on peak normal stresses in columns. These comparisons can advise
the structural designers regarding the effectiveness of each aerodynamic
modification and provide them with comprehensive information that can be used in
the preliminary design stage. Also, it would be helpful to evaluate the most effective
structural shape in wind-resistant design of a typical super-tall building.
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 12/39
2
2. BACKGROUND
2.1 Wind Excitation
The motion of tall buildings occurs primarily in three modes of action: along
wind, across wind, and torsional modes. For a rectangular building with one face
nearly perpendicular to the mean flow, the motion is measured in the along wind and
across wind directions as well as in the torsional mode. The effects occurring on the
building due to along wind motion, across wind motion, and vortex-shedding
phenomenon of wind is discussed and aerodynamic modifications against these
motions are studied.
Wind approaching a building a complex phenomenon, but the flow pattern
generated around a building is equally complicated by the distortion of the mean flow,
flow separation, the formation of vortices. Large wind pressure fluctuations due to
these effects can occur on the surface of a building. As a result, large aerodynamic
loads are imposed on the structural system and intense localised fluctuating forces act
on the facade of such structures. Under the collective influence of these fluctuating
forces, a building tends to vibrate in rectilinear and torsional modes, as illustrated in
Fig.1. The amplitude of such oscillations is dependent on the nature of the
aerodynamic forces and the dynamic characteristics of the building.
Fig.1: Wind response directions
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 13/39
3
2.1.1 Along wind motion
Along wind or simply wind is the term used to refer to drag forces. Under the
action of the wind flow, structures experience aerodynamic forces including the drag
(along wind) force acting in the direction of the mean wind shown in Figure 1. The
structural response induced by the wind drag is commonly referred to as the along
wind response. The along wind motion primarily results from pressure fluctuations on
windward (building‟s frontal face that wind hits) and leeward face (back f ace of the
building).
2.1.2 Across wind motion
The term across wind shown in Figure1 is used to refer to transverse wind.
The across wind response, is a motion in a plane perpendicular to the direction of
wind. In the design of most modern tall buildings, the across wind response often
dominates over the along wind response. Buildings are very sensitive to across wind
motion, and this sensitivity may be particularly apparent as the wind speed increases.
Wind induced instabilities of modern tower-like structures with excess slenderness,
flexibility and lightly-damped (insufficient mechanical preventions against side sway
such as use of tuned mass dampers) features could cause considerably larger across
wind responses. Besides, while the maximum lateral wind loading and deflection are
usually observed in the along wind direction, the maximum acceleration of a building
loading to possible human perception of motion or even discomfort may occur in
across wind direction.
The well-known expression of Strouhal gives the frequency N at which
vortices are shed from the side of the building, causing oscillatory across-wind forces
at this frequency.
Eq. (1)
where, S = Strouhal number, U = wind speed, b = building width.
The Strouhal number is a constant with a value typically in the range 0.1 to
0.3. For a square cross-section it is around 0.14 and for a rough circular cylinder it is
about 0.20. When N matches one of the natural frequencies Nr of the building,
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 14/39
4
resonance occurs which results in amplified crosswind response, as illustrated in
Figure 2. From Equation 1 this will happen when the wind speed is given by
U= Eq. (2)
Fig.2: Effect of Vortex Shedding on Response
The peak response in Figure 2 can be moved to the right on this plot if the
building natural frequency is increased and if it can be moved far enough to the right
the wind speed where the peak occurs will be high enough that it is not a concern.
This is the traditional approach of adding stiffness but this approach can become
extremely expensive if the peak has to be moved a long way to the right. However,
the height of the peak is sensitive to the building shape and, with astute aerodynamicshaping, the peak can be substantially reduced or even eliminated. There are many
examples of slender structures that are susceptible to dynamic motion perpendicular
to the direction of the wind. Tall chimneys, street lighting standards, towers and
cables frequently exhibit this form of oscillation which can be very significant
especially if the structural damping is small.
2.1.3 Vortex-shedding phenomenon
When a building is subjected to a wind flow, the originally parallel wind
stream lines are displaced on both transverse sides of the building shown in Figure 3.
and the forces produced on these sides are called vortices. At low wind speeds, the
vortices are shed symmetrically (at the same instant) on either transverse side of the
building shown in Figure 3a. and building does not vibrate in the across wind
direction. On the other hand, at higher wind speeds, the vortices are shed alternately
first from one and then from the other side. When this occurs, there is an impulse both
in the along wind and across wind directions. The across wind impulses are, however,
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 15/39
5
applied alternatively to the left and then to the right. This kind of shedding which
causes structural vibrations in the flow and the across wind direct ion is called „vortex-
shedding‟. This phenomenon of alternate shedding of vortices for a rectangular tall
building is shown schematically in Figure 3b.
(a) (b)
Fig.3: Vortices in different wind speed conditions: (a) vortices in low speed of wind
(there is no vibration in the across wind direction); (b) vortices in high speed of wind
– vortex-shedding phenomenon (there is vibration in the across wind direction).
2.2 Aerodynamic Modifications against Wind Excitation
Many studies show that from the wind engineer‟s point of view, aerodynamic
modifications of tall building‟s form and cross-sectional shape are very effective
design dimensions to be considered to control wind excitation and many of the most
elegant and notable buildings utilize these approaches. The aerodynamic
modifications of tall buildings against wind excitation are classified into two:
1. Major architectural modifications: Modifications having effect on the architectural
concept such as tapering, setbacks, sculptured building tops, varying the shape,
openings.
2. Minor architectural modifications: Modifications having no effect on architectural
concept such as corner modifications and orientation of building in relation to the
most frequent strong wind direction.
Some examples are: The John Hancock Centre (Chicago, 1969), Chase Tower
(Chicago, 1969) and the Transamerica Pyramid (San Francisco, 1972) shown in
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 16/39
6
Figure 4. are the examples of the „tapering‟ effect utilization by creating smaller
surface areas at higher levels and reducing the upper level plans, and thus mitigating
the wind load. The Jin Mao Building (Shanghai, 1998) and the Petronas Towers
(Kuala Lumpur, 1998) shown in Figure 5. use „setbacks‟ to slightly taper the building
shape, and „sculptured building tops‟ highlighting the height of the structure, but also
serving for the practical aerodynamic purposes such as reduction in the wind response
of the building . The more sculptured a building‟s top, the better it can minimize the
along wind and across wind responses.
Fig.4: The examples of tapering effect utilization;
(a)
The John Hancock Center, (b) Chase Tower, (c) The Transamerica Pyramid
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 17/39
7
Fig.5. The examples of setbacks and sculptured building top utilization;
(a) The Jin Mao Building, (b) The Petronas Towers
Fig.6: (a) The Burj Khalifa (b) the Sears Tower (Chicago, 1974).
While reducing the plan areas at the upper level by „varying the shape‟ of the
building along its height, minimizes the wind forces by causing the wind to behave
differently, preventing it becoming organized as in the Burj Khalifa Tower (UAE,
2008) shown in Figure 6(a). The Sears Tower (Chicago, 1974) is also a good example
for this effect shown in Figure 6(b). It is a well-known fact that the shape of structures
has a considerable effect on maintaining the lateral resistance. If the form of a tall
building is limited to rectangular prisms, from geometrical point of view, this form is
rather susceptible to lateral drift. Other building shapes such as cylindrical, elliptical,
crescent, triangular and like, are not as vulnerable to lateral force action as a
rectangular prism. Since these shapes have inherent strength in their geometrical
form, they provide higher structural efficiency or allow greater building height at
lower cost. Building codes permit a reduction of the wind pressure design loads for
circular or elliptical buildings by 20 to 40% of the usual values for comparably sized
rectangular buildings. Hence, in many of the most famous buildings, these
aerodynamically favourable forms are preferred. The Marina City Towers (Chicago,1964) shown in Figure 7(a) with its cylindrical form, the Millennium Tower (Tokyo,
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 18/39
8
2009) shown in Figure 7(b) with tapered circular plan, Toronto City Hall (Toronto,
1965) shown in Figure 7(c) with its crescent form, and the U.S. Steel Building
(Pittsburgh, 1970) shown in Figure 7(d) with its triangular plan are among these
buildings.
Fig.7.(a). The Marina City Towers (Chicago, 1964), (b) The Millennium Tower
(Tokyo, 2009), (c) Toronto City Hall (Toronto, 1965), (d) The U.S. Steel Building
(Pittsburgh, 1970).
Some modifications on cross-sectional shape such as slotted, chamfered,
rounded corners, and corner cuts on a rectangular building can have significant
effects on both along wind and across wind responses of the building to wind as in
Taipei 101 (Taipei, 2005) shown in Figure 8(a). Corner modifications in Taipei 101
provide 25% reduction in base moment when compared to the original square section.
Chamfers of the order of 10% of the building width, makes 40% reduction in the
along wind response, and 30% reduction in the across wind response when compared
to the rectangular cross sectional shape without corner cuts. Excessive rounding of
corners of the cross section, approaching a circular shape in the cross section, and
cylindrical form in the building, significantly improve the response against wind.
Addition of openings completely through the building, particularly near the top, is
another very useful way of improving the aerodynamic response of that structure
against wind by reducing the effect of vortex shedding forces which cause across
wind motion. The Shanghai World Financial Centre (Shanghai, 2008) shown in
Figure 8(b) is a good example for this modification.
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 19/39
9
Fig 8.(a) Taipei 101 (Taipei, 2005),(b) The Shanghai World Financial Center
(Shanghai, 2008).
2.3 Shaping Strategies
Softened Corners: - Square or rectangular shapes are very common for
buildings and experience relatively strong vortex shedding forces. However, it
is found that if the corners can be “softened” through chamfering, rounding or
stepping them inwards, the excitation forces can be substantially reduced. The
softening should extend about 10% of the building width in from the corner.
The corners on Taipei 101 where stepped in order to reduce crosswind respond
and drag, resulting in a 25% reduction in base moment.
Tapering and Setbacks: - As indicated in Equation 1, at a given wind speed,
the vortex shedding frequency varies depending on the Strouhal number S and
width b. If the width b can be varied up the height of the building, through
tapering or setbacks, then the vortices will try to shed at different frequencies
at different heights. They become “confused” and incoherent, which can
dramatically reduce the associated fluctuating forces. Burj Dubai shown in
Figure 6(a), is a classic example of this strategy.
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 20/39
10
Fig 9: Shaping strategies
Varying Cross-Section Shape: - A similar effect can be achieved by varying
the cross-section shape with height, e.g. going from square to round. In this
case the Strouhal number S varies with height, which again, in accordance
with Equation 1 causes the shedding frequency to be different at different
heights. This again results in “confused” vortices.
Spoilers: - One can also reduce vortex shedding by adding spoilers to the
outside of the building. The most well known form of spoilers is the spiral
Scruton strake used on circular chimneystacks. Architecturally and practically,
the Scruton strake leaves something to be desired for circular buildings, but
other types of spoiler could be used that might be more acceptable, such as
vertical fins at intervals up the height.
Porosity or Openings: - Another approach is to allow air to bleed through the
building via openings or porous sections. The formation of the vortices
becomes weakened and disrupted by the flow of air through the structure.
3 EXPERIMENTAL STUDY
3.1 Test Model
The test models used for the pressure measurements are given below. The
width B of the square (SQ) model is 0.05 m, which is used as the representative
width in this work, and the height H is 0.4 m, giving an aspect ratio H/B of 8. The
geometric scale of the wind tunnel tests is 1/1000, so the height of the super-tall
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 21/39
11
buildings is 400 m in full scale. The total volumes of the super-tall buildings are set
to be the same: about 106 m3 in full scale.
Single Modification Models
Square (SQ)
Width=0.05m
Height=0.4 m
Aspect ratio= 8
Chamfered(CF)
Modification length = 0.1 times building
width
Corner-cut (CC)
Modification length = 0.1 times building
Taper(TP)
Taper ratio = 10%
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 22/39
12
width Area ratio of top to bottom floor= 1/6
Setback(SB)
4 layer setback with area ratio of roof floor to
base floor=1/6
90 Helical (90Hel)
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 23/39
13
180 helical (180Hel) Cross-void (CV)
Void size=5H/24
Multiple modification models
CC + 180Hel TP + 180Hel
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 24/39
14
CC + TP + 180Hel CC + TP + 360Hel
SB + 45RT
Setback model with 45◦
rotation
Fig.10:Test models
Eight different single modification models were used. For corner
modifications, chamfered (CF) and corner- cut (CC) were focused on, and the
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 25/39
15
modification length was set at 0.1B, where B is the building width. This modification
length was determined considering the previous result which showed that the
optimistic modification length is 0.1B. For the tapered model (TP), although models
with larger tapering ratios show better aerodynamic characteristics, a taper ratio of
about 10% was used considering practicality. Taper ratio is defined as (base width-
roof width)/height*100, and the taper ratio of the John Hancock Center on its long
side is about 9.1%. The taper ratio of 10% roughly corresponds to an area ratio of the
top floor to the bottom floor of 1/6. A 4-layer setback (SB) is used, and the area ratio
of the roof floor to the base floor is also set at 1/6. Two helical models were used,
whose helical angles between roof floor and base floor were 90◦(90Hel) and
180◦(180Hel). A cross-void model whose void was provided at the top-center was
used. The void size was set at 5H/24.
Five multiple modification models were also used, which combined the above
aerodynamic modifications, i.e. corner cut (CC), taper (TP), setback (SB), and two
helical angles (90Hel and 180Hel). Multiple modification models included corner-cut
+ 180 helical (CC + 180Hel), taper + 180 helical (TP + 180Hel), corner-cut + taper
+180 helical (CC+ TP+ 180Hel), and corner-cut+taper+180 helical (CC+TP+
360Hel). Besides, the effects of rotation of each portion of setback shape on load
effect characteristics were also examined (SB+45RT).
3.2 Wind Pressure Measurements
Wind tunnel experiments were performed in a closed-circuit boundary-layer
wind tunnel whose working section was 1.8 m high by 2.0 m wide. Fig 11 shows the
condition of the approaching turbulent boundary layer flow with a power -law index of
0.27, which represents an urban area flow. The wind speed and turbulence intensity at
the top of the model were about UH ≈11.8 m/s and Iu,H ≈ 0.09% respectively.
The fluctuating wind pressures of each pressure tap were measured and
recorded simultaneously using a vinyl tube 80 cm long through a multi-channel
pressure transducer. The sampling frequency was 1 kHz with a low- pass filter of 500
Hz. The total number of data was 32,768. The fluctuating wind pressures were revised
considering the transfer function of the vinyl tube. There were about 20 measurement
points on one level on four surfaces, and the measurement points were instrumented at
10 levels, giving about 200 measurement points. The local wind force coefficients
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 26/39
16
were obtained for the structural axes by considering the dynamic velocity at model
height qH and the building width of the square model B regardless of building shape.
Fig.11: Profiles of mean wind speed U/UH and turbulence intensity Iu.
3.3 Frame model for time history analyses
The frame model for the time history analyses and the fir st three mode shapes are
shown in Fig 12. Building dimensions (B*D*H) are 50*50*400 in common, and all
beams were assumed to be rigid shown in Fig 11(a). Square tube columns were used
and column sizes were adjusted such that the first translational natural period becomesabout H/50 assuming steel buildings. Local wind force coefficients were converted
into full-scale local wind forces, and input at the center of each floor. A design wind
speed of 70 m/s was used, corresponding to a 500 year return period wind speed in
Tokyo. In the frame model, no eccentricities were considered, and dead and live
loads were not applied, so that only the effects of various building shapes on load
effect were evaluated. For mode shapes, as no eccentricities were considered, there
was no coupled motion, as shown in Fig 12(b). The frame model was designed
approximately as bending type.
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 27/39
17
B× D× H =50m×50m×400 m
1st mode 2nd mode 3rd mode
Fig.12: Schematic view of frame model and first three mode shapes (a) Framemodel,(b) first three mode shapes.
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 28/39
18
4 RESULTS AND DISCUSSION
4.1 Variations of Peak Normal Stresses with Wind Direction
The variations of peak tensile stresses with wind direction for two single
modification models (square (SQ) and setback (SB)) and two multiple modification
models (CC+TP+360Hel and SB+45RT) are shown in Fig 13. For SQ, the largest
peak tensile stress was observed for wind directions of 0◦ and 90◦.The peak tensile
stresses of Col. 1 were generally large and those of Col.4 were generally small in the
ranges between 0◦ and 90◦. Col. 3, which was on the windward side, showed a large
peak tensile stress, but the peak tensile stresses decreased with increasing wind
directions because Col.3 was located on the leeward side for large wind directions.The opposite trend was found for Col. 2. One thing to be noted is that when the wind
direction ranged from 0◦ to about 20◦, the peak tensile stresses in Col.3 were larger
than those in Col.1. This seems to be because, for these wind directions, as the
separated shear layer approached the side surface of Col.1 and Col.2, relatively large
peak tensile stresses occurred at Col.3. Similarly, relatively large peak tensile stresses
were found in Col.2 for wind directions from 70◦ to 85◦. Similar discussions can be
made for SB, although the peak normal stresses were smaller than those for SQ for the
considered wind directions. For the multiple modification models, the peak tensile
stresses in Col.1 were the largest for the considered wind directions, and the
variations with wind direction for Col. 1 and Col.4 were small compared with those
for SQ and SB. One more difference was that there were no stress reversals between
Col. 1 and Col. 3, and between Col. 1 and Col. 2 with wind direction. The variations
of peak tensile stresses of the two helical models (90Hel and 180Hel) showed a quite
similar tendency to the multiple modifications models, showing less variation of peak
tensile stresses in Col.1 and Col.4 and not showing stress reversal for specific wind
directions.
The largest peak tensile stresses were selected for the considered wind
directions, and the ratios of stress for each model to that of SQ were calculated and
shown in Fig 13. The largest peak tensile stress in SQ was about 11kN/cm 2. The
largest peak tensile stresses for the multiple modification models were generally
smaller than those for the single modification models, and the largest peak tensilestresses for the single modification models were less than 90% of that of SQ, and
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 29/39
19
those for the multiple modification models were about 70 – 80%. The smallest value
was found for the CC + TP + 360Hel model. The corner modification models (CF
and CC) showed similar values, and it was found that setback was quite effective in
reducing peak normal stresses in columns, showing superior characteristics to taper
and helical shapes. The effects of corner cut and taper seemed to be negligible when
they were added to the 180Hel model, showing similar values to the 180Hel model.
Increasing helical angle resulted in smaller peak tensile stresses for single and
multiple modification models but, as pointed out by, the helical angle effect is small
when the helical angle is larger than 180◦. The ratios of peak tensile stresses of SB
and SB + 45RT were similar, showing that the effect of rotation of each setback
portion on peak normal stresses in the columns was very small.
Fig 13: Ratio of largest peak tensile stresses (The largest peak tensile stresses of SQ
is about 11 kN/cm2)
To examine the contributions of two bending moments (MY and MX) and
axial force (NZ) to peak normal stresses, peak normal stresses were evaluated
separately and the variations of peak normal stresses with MX, MY and NZ are
shown in Fig 14 for the square model (SQ) for a damping ratio of 1%. Peak normal
stresses by bending moments were relatively small and showed less variation with
wind direction and column position. But significant variations with wind direction and
column position were found for axial force, and it was found that the peak normal
stresses were greatly affected by axial force. The contributions of bending
moments were approximately 20% when the wind directions were 0◦ and 90◦, and
they increased when the wind directions were between 0◦ and 90◦ because the peak
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 30/39
20
normal stresses decreased for these wind directions, as shown in Fig 13(a). Similar
trends were found for the other models.
Fig 14: Peak tensile stresses for various wind directions for damping ratio of 1%(unit: kN/cm2). (a) SQ, (b) SB, (c) CC + TP + 360Hel, (d) SB+ 45RT.
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 31/39
21
Fig.15: Peak normal stresses for various bending moments and axial forces for SQ
wind damping ratio of 1%. (a) Peak normal stresses by bending moment MY, (b)
Peak normal stresses by bending moment MX, (c) Peak normal stresses by axial force
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 32/39
22
4.2 Effects of damping ratios on peak normal stresses
In the wind-resistant design of super-tall buildings, a damping ratio of 1% is
recommended for safety design, and 70 – 80% of that damping ratio is recommended
for serviceability design including habitability check. The results shown before were
for the damping ratio of 1%.
Fig 16: Effects of damping ratios on peak tensile stresses for square and 180 helical
models (Q.S. means quasi-static). (a) SQ (wind direction of 0◦), (b) 180Hel (wind
direction of 30◦)
Fig 17: Variations of largest peak compressive stresses with damping ratio(Q.S.
means quasi-static)
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 33/39
23
But examination of the effects of damping ratio on wind load effect is an
issue of interest, and variations of peak compressive stresses with damping ratio are
shown in Fig 16 for the SQ and 180 Hel models for the wind directions where the
largest peak normal stresses occur. Q.S. shown in Fig 16 indicates quasi- static
condition. As expected, peak compressive stresses decrease with increasing damping
ratios, approaching the quasi-static value. Decreasing ratios of peak compressive
stress also decrease with increasing damping ratios. But there are clear
discrepancies in trend for the SQ and 180Hel models. For the SQ model, the
differences among peak compressive stresses in columns are large for extremely
small damping ratios, even for columns located on the windward side (Col. 1 and
Col. 3) or leeward side (Col. 2 and Col. 4). As the damping ratios increase, these
differences for Col.1 and Col. 3 or Col. 2 and Col. 4 decrease, and when the
damping ratio is larger than approximately 3%, the difference is negligible. For the
180Hel model, the differences among peak compressive stresses in columns
remains for large damping ratios, and decreasing ratios of peak compressive stresses
with damping ratio are not significant compared with those for SQ. For the column
on the windward side, i.e. Col.1, the peak compressive stresses are negative when
the damping ratio is larger than about 3%, which means that tensile forces are
applied to Col. 1 at all time instants for these damping ratios.
Fig 17 shows the variations of the largest peak compressive stresses with
damping ratios of the square (SQ), corner cut (CC),180 helical (180Hel), and CC +
180Hel models. The largest peak compressive stresses were defined as the largest
value for considered wind directions. The largest peak compressive stresses for SQ
is the largest, and those for 180 Hel are the smallest. As mentioned before, the
effect of corner cut is negligible, and when the damping ratio is less than 1%,
corner cut has a negative effect on peak normal stresses, giving larger peak
compressive stresses for CC + 180Hel than for 180Hel.
The effects of damping ratio on phase-plane trajectories are shown in Fig 18
for square (SQ) and cross void (CV) models for wind directions of 0◦ and 85◦,
respectively. When the damping ratios are relatively small, the shapes of the
envelopes are elliptic or parallelogram, but as the damping ratio increases, decreases
of bending moments in the across-wind direction (MX for SQ and MY for CV) are
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 34/39
24
significant, and the shapes of the envelopes change to semi-circular or semi-elliptic.
The decreases of bending moments in the along-wind direction are not so
noticeable, and the mean value of along-wind bending moments is almost the same.
The envelopes of phase-plane trajectories in quasi-static conditions are similar to
those of the phase-plane trajectory of along- and across-wind forces. Fig 18 shows
time histories of normal stresses by bending moments (MX and MY) for the square
model (SQ) for wind direction 0° for different damping ratios. Fig 18(a) shows the
time histories with MX, which corresponds to across-wind direction. As damping
ratios increase, a decrease in the resonant component is clearly observed. Some
differences are admitted for the time histories with bending moments MY (Fig
18 (b)), which correspond to the along-wind direction, but the differences are not
significant compared with those in the across-wind direction.
Fig 18(a): Effect of damping ratio on Normal stress by MX for square (SQ) for wind
direction 0◦.
Fig.18(b): Effect of damping ratio normal stress by MY for square (SQ) for wind
direction 0◦.
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 35/39
25
The effects of damping ratio on phase-plane trajectories are shown in Fig 18
for square (SQ) and cross void (CV) models for wind directions of 0° and 85°,
respectively. When the damping ratios are relatively small, the shapes of the
envelopes are elliptic or parallelogram, but as the damping ratio increases, decreases
of bending moments in the across-wind direction (MX for SQ and MY for CV) are
significant, and the shapes of the envelopes change to semi-circular or semi-elliptic.
The decreases of bending moments in the along-wind direction are not so noticeable,
and the mean value of along-wind bending moments is almost the same. The
envelopes of phase-plane trajectories in quasi-static conditions are similar to those of
the phase-plane trajectory of along- and across- wind forces .
Fig.19: Effect of damping ratio on bending moments for square (SQ) and cross
void model (CV). (a) SQ when damping ratio is 0.3% (left),1% (center), and quasi-
static (right) when wind direction of 0◦, (b) CV when damping ratio is 0.3% (left),
1% (center), and quasi-static (right)when wind direction of 85◦.
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 36/39
26
4.3 Effects of Various Loading Conditions
For the wind directions where the largest peak normal stresses occurred, the
effects of various loading conditions were examined. Loading conditions included (i)
ALL loads (Fx+ Fy + Mz), (ii) Fx only, (iii) Fy only, (iv) Mz only, (v) Fx and Fy
(Fx + Fy), (vi) Fx and Mz (Fx+ Mz), and (vii) Fy and Mz (Fy + Mz), i.e. 7 cases in
total. The results are summarized in Tables 1 - 3 for the square model (SQ, wind
direction 0◦), setback model (SB, wind direction 85◦), and SB +45RT (wind direction
40◦). For SQ, the peak compressive stress in Col. 4 when Fx and Fy (Fx + Fy) are
applied is almost the same as that for the ALL loading condition. Under the (Fx +
Mz) loading condition, thestresses are slightly larger than those under the Fx only
loading condition, and under the (Fy + Mz) loading condition, they are slightly larger
than those under the Fy only loading condition. The results for the Mz only loading
condition are very small, and can thus be ignored only when there are no
eccentricities. For SB, the peak compressive stress under the Fy only loading
condition is larger than that under the Fx only loading condition for wind direction
85◦. For this wind direction, Fy roughly corresponds to along-wind force. Thus,
the trends are very similar to those for SQ, i.e. for Col. 3, the (Fx + Fy) loading
condition gives almost the same results as the ALL loading condition, and (Fy + Mz) gives slightly larger results than the Fy only loading condition. Also, the
results for the Mz only loading condition are negligible. For Col. 4 of SB + 45RT,
when the wind direction is 40◦, the contributions of the Fx only and the Fy only
loading conditions are similar.
Table 1. Effects of various loading conditions on peak compressive stress of square
model (SQ) for ζ = 1% (wind direction of θ = 0◦, kN/cm2)
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 37/39
27
Table 2 Effects of various loading conditions on peak compressive stress of setback
model (SB) for ζ = 1% (wind direction of θ=85◦, kN/cm2)
Table 3 Effects of various loading conditions on peak compressive stress of SB +
45RT model for ζ = 1% (wind direction of θ=40◦, kN/cm2)
5 CONCLUSIONS
Using wind pressures applied to 13 super-tall building models with atypical
building shapes, time history analyses were conducted. Test models included 8 single
modification models, and 5 multiple modification models. The primary purpose was
to directly compare the peak normal stresses in columns of super-tall buildings.
Comparison and discussion led to the following concluding remarks.
The peak normal stresses for the square model were the largest among all the
models tested. The CC + TP + 360Hel model showed the smallest peak normal
stresses among the models tested, and the setback model showed the smallest peaknormal stresses among the single modification models tested. The peak normal
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 38/39
28
stresses of the two helical models and the multiple-modification models showed less
variation with wind direction. Also, it was found that the effects of corner-cut and
taper seemed to be negligible when they were added to the 180Hel model.
The peak normal stresses under bending moments Mx and My were almost
the same for the considered wind directions, and the contributions of bending
moments to total peak normal stresses were about 20% of the total. Most of the peak
normal stresses were affected by axial force. This was because the frame model
used in the present study was designed as bending type.
As the damping ratio increases, the peak normal stress decreases and
approaches the quasi-static value. The increase in bending moment for the across-
wind direction became significant as the damping ratios decreased, and the sensitivity
of the peak normal stresses for the helical and multiple modification models to
damping ratio as well as wind directions was smaller than for the other models. The
effects of damping ratio are also clearly seen in the time histories of normal stresses.
From the analyses for the various loading conditions, it was found that the
contribution of bending moment in the along-wind direction was larger than those of
the other loading conditions and that of torsional moment was almost negligible.
6 REFERENCES
[1] Amin J.A and A.K. Ahuja “aerodynamic modifications to the shape of the
buildings: a review of the state-of-the-art” Asian journal of civil engineering
(building and housing) vol. 11, no. 4 (2010) pages 433-450
[2] Ankit Mahajan, Puneet Sharma, Er. Ismit Pal Singh “Wind Effects on Isolated Buildings with Different Sizes through CFD Simulation” IOSR Journal of
Mechanical and Civil Engineering (IOSR-JMCE) e-ISSN: 2278-1684,p-ISSN: 2320-
334X, Volume 11,Issue 3 Ver. IV (May- Jun. 2014)
[3] Dutton, R., and Isyumov, N. (1990). “ Reduction of tall building motion by
aerodynamic treatments.” Journal of Wind Engineering and Industrial Aerodynamics,
36, 739-47.
7/24/2019 Wind induced response of super-tall buildings with various aerodynamic shapes
http://slidepdf.com/reader/full/wind-induced-response-of-super-tall-buildings-with-various-aerodynamic-shapes 39/39
[4] Irwin, P. A. (2009). “Wind engineering challenges of the new generation of super -
tall buildings.” Journal of Wind Engineering and Industrial Aerodynamics, 97, 328 –
334.
[5] Kawai .H, “Effect of corner modifications on aeroelastic instabilities of tall
buildings”. J. Wind Eng. Ind. Aerodyn, 1998, pp 74 – 76,719 – 729.
[6] Kim .Y.C, Kanda .J, Tamura .Y,” Wind-induced coupled motion of tall buildings
with varying square plan with height.” J. Wind Eng. Ind. Aerodyn. 99(5), 2011, pp
638 – 650.
[7] Ryan Merrick1 and Girma Bitsuamlak2 “shape effects on the wind-induced
response of high-rise buildings” Journal of Wind and Industrial Engineering , Vol. 6,
No. 2, July 2009, pp. 1-18
[8] Tamura.Y, Kim.Y.C., Kumar.B.E., Tanaka.H, Ohtake.K, “Aerodynamic
characteristics of tall building models with unconventional configurations”, Structures
Congress, 2012 ,pp 103-134
[9] Tanaka.H, Tamura.Y, Ohtake.K, Nakai.M, Kim.Y.C, “Aerodynamic and flow
characteristics of tall Buildings with various unconventional configurations.” Int. J.
High- Rise Buildings 2 (3), 2013, pp 213 – 288.
[10] Tanaka. H, Tamura .Y, Ohtake .K, Nakai .M, Kim Y.C, “Experimental
investigation of aerodynamic forces and wind pressures acting on tall buildings with
various unconventional configurations”. J. Wind Eng. Ind. Aerodyn, 2012, pp 107 –
108,179 – 191.