1. Wind Loads Calculation (ASCE 7)
Henry Kurniadi

2. Structure Loads
• Dead Loads: from the weight of the structure
itself.
• Wind Loads: could be determined based on
ASCE 7 (US Standard), Eurocode 1 (EU Code),
Wind Code 2004 (Hong Kong Code), GB 50009
(China PR Standard), AS/NZS 1170.2
(Australia/NZ Standard) or other
national/international standards/codes.

3. WIND LOADS

4. Wind Loads According to ASCE 7
• Wind loads are randomly
applied dynamic loads.
• They are depend on the
wind speed, shape, height
and topographic location
of the structure.
• Calculations using US
customary units (Metric
units also available in
ASCE 7-05).

5. Wind Speed Curve in Different Region
Sea-side Open area Built-up area Big city (Currently not used)

6. Surface Roughness and Exposure
Surface Definitions Examples
Roughness and
Exposure
B Urban and suburban areas,
wooded areas,
or other terrain with numerous
closely spaced obstructions
having the size of single-family
dwellings or larger.
C Open terrain with scattered obstructions
having heights generally less than 30 ft
(9.1 m). This category
includes flat open country, grasslands,
and all water surfaces in
hurricane prone regions.
D Flat, unobstructed areas and water
surfaces
outside hurricane prone regions.
This category includes
smooth mud flats, salt flats, and
unbroken ice.

7. Basic Wind Speed, V
• Basic wind speed, V, based
on 3-second gusts, 33 ft (10
m) above ground in a
Ground Roughness
Exposure C (defined in mph
or m/s).
• Some regions, such as:
Taiwan, coastal China,
coastal USA and Japan have
very high wind speed;
others such as: Indonesia,
India and inland USA have
lower wind speed.

8. Air Flow
• The more the air is streamed, the less the reaction
force exerted by the structure.
• Wind force highly depends on the shape of the
structure.

9. Wind Directionality Factor, Kd
• Wind Directionality
Factor, Kd shall be
determined from Table
6-4.
• This factor to
accommodate the
cross-sectional shape of
the structure.

10. Importance Factor, I
• An importance
factor, I, for the building
or other structure shall
be determined from
Table 6-1 based on
building and structure
categories listed in
Table 1-1.
• This factor to
accommodate the
importance of the
structure.

11. Velocity Pressure Coefficient Kz
• Velocity pressure exponent,
Kz, depends on the site
relative height to the
ground, z.
• This means for rooftop
structure, z, would be the
total height of the
component and the building
its installed.
• This factor to accommodate
the absolute height of the
structure from ground level.

12. Topographic Factor, Kzt
• Local abrupt topography affects wind near the ground.
• Wind speed depends on shape of hill, location of building, and height above ground.
• The value of Kzt was taken as 1 with assumption flat region environment.
• This factor to accommodate the topographic area of the structure location.

13. Force Coefficient, Cf
For chimneys, tanks &
• Force coefficient, Cf other similar structures:
determined based on
the shape of the
structure.
• This factor to
accommodate the
wind-facing area of the
For trussed towers:
structure.

14. Velocity Pressure, qz
• From Bernoulli’s equation of flow, the wind
pressure: (q in psf, V in mph)
• The velocity pressure, qz, evaluated at height z
shall be calculated by:

15. Gust Effect Factor, G
• Factor accounting for:
– Gustiness and turbulence
– Gust frequency
– Gust size
– Frequency of structure
– Structural damping
– Aerodynamic admittance
– Gust correlation
• Gust effect factor, G, could be calculated by
• In general, gust more likely to occur at lower altitude.

16. Wind Loads According to ASCE 7
FWT
• Design wind force for
each component shall
be determined by:
d
FSP FCT FL
e
FAC
c
• Moment because of
wind force calculated
b
FBF as:
a M FSF a FBF b FAC c FSP FCT FL d FWT e
FSF