2. Introduction
Wind is essentially the large scale Horizontal
movement of free air. It plays an important role in
design of tall structures because it exerts loads on
Building.
High Rise Building-
A building Having height more then
15m As per National Building Code 2005 of India is
called High Rise Building.
Imperial Tower 1(254m)
Ref- Wikipedia
3. What is Wind?
Wind means the motion of air in the atmosphere.
The response of structures to wind depends on
the
characteristics of the wind.
4. Causes of Wind-
Wind is caused by air
flowing from high
pressure to low pressure.
Since the Earth is rotating,
however, the air does not
flow directly from high to
low pressure, but it is
deflected to the right (in the
Northern Hemisphere; to
the left in the Southern
Hemisphere), so that the
wind flows
mostly around the high and
low pressure areas.
5. Variation of Wind Velocity with
Height-
Near the earth’s surface, the motion is
opposed, and the wind speed reduced,
by the surface friction. At the surface,
the wind speed reduces to zero and
then begins to increase with height,
and at some height, known as the
gradient height, the motion may be
considered to be free of the earth’s
frictional influence and will attain
its ‘gradient velocity’.
Gradient Height 300 m for flat ground
& 550 m for very rough terrain
6. How wind force governing for tall structure?
with increase height of building
•Construction cost per unit area decrease
•Increasing lightness in weight per unit area
•More danger against high velocity of wind force
at high level.
8. Wind Effects on Structures
Wind effects on structures can be classified as
‘Static’ and ‘Dynamic’.
Static-
Static wind effect primarily causes
elastic bending and twisting of structure.
Dynamic
For tall, long span and slender structures a
‘dynamic analysis’ of the structure is essential.
Wind gusts cause fluctuating forces on the
structure which induce large dynamic motions,
including oscillations.
11. Determination of Wind Loads as per IS 875 (Part 3)
Physical parameters-
•Length : 17m
•Width : 13m
•Height : 20.5m
•Height of each storey : 3m
Wind Data-
•Wind Zone : 2(Basic wind Speed= 39m/s For
Raipur)
•Terrain Category : 3
•Class of Structure : A (Since Max. Dimension is less
then 20m)
•Topography : Flat that is upwind slope <3 °
•Life of Structure : 100 Years
3d Model By
12. Design wind speed –
Vz=Vb.K1.K2.K3
Vz = Design wind speed at any height z in
m/s;
K1= Probability Factor (K1=1.06 For
Important Buildings of Life 100 years)
K2= Terrain, Height and Structure size
factor (Varies for Height)
K3= Topography Factor)
27. Main Conclusions
In the Static Analysis of the RCC Building the
comparison has been made in two cases in first case without
considering the wind load and Considering the wind load in
second case. Results from SAP2000 Shown that the Bending
moment and shear Force increase due to wind load hence
wind load governing factor for design of High rise building .
