this is a ppt for finding out wind load of any building by static method.............................

1. VARIATION OF WIND
LOAD WITH HEIGHT
& ASPECT RATIO

2. What Is Wind & Wind Load ?
 Wind is one of the nature’s greatest hazards to life on our planet. The
impact of this natural phenomenon is sudden, with little or no
warning to make preparations against damages and collapse of
buildings/structures.
 Wind load is produced due to change in momentum of air current
striking the surface of building. A building is less likely to experience the
other design loads in its life but it is almost certain that the building is likely
to be subjected to the design wind loads.

3. Types of Wind Flow
Wind is caused by airs from high pressure to low pressure. The Wind flow
generation is on account of atmospheric pressure differentials itself into various
forms, such as,
 Gales and monsoonal winds
 Cyclones/Hurricanes/Typhoons
 Tornados
 Thunderstorms
 Localised storms

4. Some Definitions…
 Angle of Attack : It is the angle between the direction of wind and a
reference axis of the structure.
 Developed Height :Developed height is the height of upward penetration of
the velocity profile in a new terrain.
 Effective Frontal Area :It is the projected area of the structure normal to the
direction of the wind.
 Element of Surface Area :It is the area of surface over which the pressure
coefficient is taken to be constant.
 Force Coefficient :A non-dimensional coefficient such that the total wind
force on a body is the product of the force coefficient.
 Ground Roughness: the nature of the earth’s surface as influenced by small
scale obstructions such as trees and buildings is called ground roughness.

5.  Gust: a positive or negative departure of wind speed from its mean value,
lasting for not more than, say, 2 minutes over a specified interval of time.
 Gradient Height: It is the height above the mean ground level at which the
gradient wind blows.
 Mean Ground Level :The mean ground level is the average horizontal plane
of the area enclosed by the boundaries of the structure.
 Pressure Coefficient :It is the ratio of the difference between the pressure
acting at a point on a surface and the static pressure of the incident wind to
the design wind pressure.
 Velocity Profile :The variation of the horizontal component of the
atmospheric wind speed at different heights above the mean ground level is
termed as velocity profile.

6. EFFECTS OF WIND
 1.General Wind Effects
 Direct Positive Pressure
 Aerodynamic Drag
 Negative Pressure
 Rocking Effects
 Harmonic Effects
 Clean-Off Effect

7.  2.Critical Wind Effects On Buildings
 Inward Pressure On Exterior Walls
 Overturn Effect
 Suction On Exterior Walls
 Torsional Effect
 Vortex shedding

8. Variation of wind speed across India

9. variation of wind velocity with height
Near the Earth surface the motion is opposed and wind speed reduced by
the surface friction .At the surface wind speed reduces to zero and than
begin to increase with height .A graph of wind velocity vs height above
ground given below.

10. LITERATURE REVIEW
 Peter A. Irwin, 2007, proposed that a Bluff body may be defined as an object
whose dimension perpendicular to the wind flow is almost equal to the
dimension parallel to the wind flow. Most man-made object s are bluff bodies.
Hence the study of bluff bodies is an important aspect of wind analysis.
 Kenny C.S. Kwok, Peter A. Hitchcock, and Melissa D. Burton, nowadays all
high rise exceeding 1000 m are faced with the challenge of wind vibrations
which interfere with the comfort of the occupants. But perception of
vibration is totally based on and varies from person to person. Hence no single
standard could be set up which defines the maximum limit of human
tolerance

11. About the project
 We have started our project taking 9 buildings as example.
 We have considered the aspect ratios of0.5,1.5 and 3 for buildings. And in
each aspect ratio there are three different types of building having 3
storeys,10storeys and 20 storeys.
 The height of each storey is 3 meters.
 The breadth of the building in the direction of wind is 20 meters. The
Columns of the building are at 5 meters interval.

12. Working On It
 We have done our project by FORCE COEFFICIENT METHOD.
 The project has been undergone in DURGAPUR, WEST BENGAL.
 Basic wind speed (Vb) at this region = 47 m/s.
 Let’s assume all buildings belong to terrain category 1.
 Taking mean probable design life of structure is 50 years.
 Also taking the upwind slope of the buildings is below than 3.

13. Design Wind Speed ( Vz )
 Design Wind Speed for any site is depend on :
a) Risk level;
b) Terrain roughness, height and size of structure and
c) Local topography.
 It can be mathematically expressed as follows:
Vz = Vb k1 k2 k3
where
Vz = design wind speed at any height z in m/s
k1 = probability factor ( risk coefficient)
k2 = terrain, height and structure size factor and
k3 = topography factor

14.  Risk Coefficient (k1 Factor):This factor is taken as 1.0 at 10 m above ground
level based
 Height and structural size factor (K2): It vary due to variation of height by
which the basic wind speed shall be multiplied to obtain the wind speed at
different heights, in each terrain category for different sizes of buildings on
50 years mean return period.
 Topography (k3 Factor ) :This factor is generally taken as 1.0
 Storey shears are also changing due to variation of K2
 Design wind speed, Vz =Vb*K1*K2*K3
=47*1*K2*1
=47*K2

15. Design Wind pressure
 The design wind pressure at any height above mean ground level shall be
obtained by the following relationship between wind pressure and wind
velocity.
 Wind pressure on the building
Pz =0.6*Vz
2
Where
Pz =design wind pressure in N/m2 at height z, and
Vz= design wind velocity in m/s at height z.

16. Storey Shear
 The wind force acting on the building is called wind load or storey shear.
 It is given by
F = Cf Ae pd
Where
Cf is the force coefficient for the building .It is depend upon aspect ratio.
Ae of the building or structure and by design wind pressure
pd is the total wind load on that particular building or structure

17. Variation of Force Coefficients vs Aspect ratio
Variation of Force Coefficients vs Aspect ratio is given below

18. Example
We consider For the 3 stores building having aspect ratio 0.5
A table is given below..
NO. OF
STOREY
HEIGHT (m) K2 Vz Cf Aeinter
(m2)
Ae end (m2) Pz(KNm2) F inter (KN) F end
(KN)
STOREY SHEAR
(KN)
1 3 1.05 49.35 1.19 15 7.5 1.4613 26.084205 13.0421025 260.84205
2 6 1.05 49.35 1.19 15 7.5 1.4613 26.084205 13.0421025 156.50523
3 9 1.05 49.35 1.19 7.5 3.75 1.4613 13.0421025 6.52105125 52.16841

19. FOR THE 20 STORES BUILDING HAVING ASPECT RATIO 3
NO. OF
STOREY
Ht.
(m)
K2 Vz Cf Ae inter
(m2)
Ae end
(m2)
Pz(kNm2) F inter(kN) F end(kN) STOREY SHEAR(kN)
1 3 0.99 46.53 1 15 7.5 1.29902454 19.4853681 9.74268405 1810.666353
2 6 0.99 46.53 1 15 7.5 1.29902454 19.4853681 9.74268405 1732.72488
3 9 0.99 46.53 1 15 7.5 1.29902454 19.4853681 9.74268405 1654.783408
4 12 1.006 47.282 1 15 7.5 1.341352514 20.12028772 10.06014386 1576.841935
5 15 1.03 48.41 1 15 7.5 1.40611686 21.0917529 10.54587645 1496.360785
6 18 1.042 48.974 1 15 7.5 1.439071606 21.58607408 10.79303704 1411.993773
7 21 1.054 49.538 1 15 7.5 1.472408066 22.086121 11.0430605 1325.649477
8 24 1.066 50.102 1 15 7.5 1.506126242 22.59189364 11.29594682 1237.304993
9 27 1.078 50.666 1 15 7.5 1.540226134 23.103392 11.551696 1146.937418
10 30 1.09 51.23 1 15 7.5 1.57470774 23.6206161 11.81030805 1054.52385
11 33 1.0975 51.5825 1 15 7.5 1.596452584 23.94678876 11.97339438 960.0413857
12 36 1.105 51.935 1 15 7.5 1.618346535 24.27519803 12.13759901 864.2542306
13 39 1.1125 52.2875 1 15 7.5 1.640389594 24.60584391 12.30292195 767.1534385
14 42 1.12 52.64 1 15 7.5 1.66258176 24.9387264 12.4693632 668.7300629
15 45 1.1275 52.9925 1 15 7.5 1.684923034 25.27384551 12.63692275 568.9751573
16 48 1.135 53.345 1 15 7.5 1.707413415 25.61120123 12.80560061 467.8797753
17 51 1.1412 53.6364 1 15 7.5 1.726118043 25.89177064 12.94588532 365.4349704
18 54 1.1448 53.8056 1 15 7.5 1.737025555 26.05538332 13.02769166 261.8678878
19 57 1.1484 53.9748 1 15 7.5 1.747967421 26.21951132 13.10975566 157.6463545
20 60 1.152 54.144 1 7.5 3.75 1.758943642 13.19207731 6.596038656 52.76830925

20. Graph of Storey Shear vs No. of storey
A graph is given of STOREY SHEAR VS NO. OF STOREY GRAPH FOR RA=0.5
0
500
1000
1500
2000
2500
3000
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
STOREYSHEAR
NO. OF STOREY
FOR 3 STOREY BUILDING
FOR 10 STOREY BUILDING
FOR 20 STOREY BUILDING

21. STOREY SHEAR VS NO. OF STOREY GRAPH FOR RA=1.5
0
500
1000
1500
2000
2500
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
STOREYSHEAR
NO.OF STOREY
FOR 3 STOREY BUILDING
FOR 10 STOREY BUILDING
FOR 20 STOREY BUILDING

22. STOREY SHEAR VS NO. OF STOREY GRAPH FOR RA=3
0
200
400
600
800
1000
1200
1400
1600
1800
2000
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
STOREYSHEAR
NO. OF STOREY
FOR 3 STOREY BUILDING
FOR 10 STOREY BUILDING
FOR 20 STOREY BUILDING

23. GRAPH FOR STOREY SHEAR VS NO. OF STOREY FOR 3 STOREY BUILDING
0
50
100
150
200
250
300
1 2 3
STOREYSHEAR
NO. OF STOREY
FOR a/b = 0.5
FOR a/b = 1.5
FOR a/b = 3

24. GRAPH FOR STOREY SHEAR VS NO. OF STOREY FOR 10 STOREY BUILDING
0
200
400
600
800
1000
1200
1 2 3 4 5 6 7 8 9 10
STOREYSHEAR
NO.OF STOREY
FOR a/b = 0.5
FOR a/b = 1.5
FOR a/b = 3

25. GRAPH FOR STOREY SHEAR VS NO. OF STOREY FOR 20 STOREY BUILDING
0
500
1000
1500
2000
2500
3000
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
STOREYSHEAR
NO. OF STOREY
FOR a/b =0.5
FOR a/b = 1.5
FOR a/b =3

26. CONCLUSION
We can analyse wind load by two method-Static method & Dynamic method. But in
this paper we have worked out through static method or force coefficient method.
 Storey shear at top store is minimum and maximum in bottom.
 Storey shear vary with top storey to bottom.
 Wind load depends on height.
 Storey shear is directly proportional to aspect ratio of the building.
 For tall buildings difference of storey shear at top is very less with respect to
various aspect ratio.
 For tall building difference of storey shear at bottom is very high with respect to
various aspect ratio.
 Wind load is also depends on risk coefficient & topography factor.
 It depends on terrain category of building. There are four types of terrain category.

27. THANK YOU