ESWA Catalog 241C:ESWA Catalog 241 final copy - EVAPCO.com

8
Wind Load Calculations
The data required to calculate the wind load are:
Basic Wind Speed (V) – Numerical value, in miles per
hour (mph) found in ASCE 7-05 Figures 6-1 (A,B,C).
Wind Directionality Factor (Kd) – 0.85 for building
components and cladding. Table 6-4 of ASCE 7-05 provides
additional information.
Occupancy Category – I, II, III or IV depending on the
nature of the building occupancy. Table 1604.5 in the
IBC 2006 Code Book defines each of the categories in
detail. This is the same Occupancy Category used in
Seismic calculations.
Importance Factor (I) – Numerical value between 0.77
and 1.15 based on the Basic Wind Speed and the
Occupancy Category. These values are found in Table 6-1
of ASCE 7-05.
Exposure Category – B, C or D as defined in Section
6.5.6.3 of ASCE 7-05.
Component Elevation (z) – The anchorage height of
the unit in feet.
Nominal Height of the Atmospheric Boundary Layer
(zg) - Numerical value based on Exposure Category. These
values are found in Table 6-2 of ASCE 7-05.
3 second Gust-Speed power Law Exponent (α) -
Numerical value based on Exposure Category. These
values are found in Table 6-2 of ASCE 7-05.
Velocity Pressure Exposure Coefficient (Kz) – A
calculated value using the values for zg and α.
KZ = 2.01
z
( zg)
2
( a )
Topographic Factor (Kzt) – 1.0 default when
topographic effects are not a factor. ASCE 7-05 Section
6.5.7 provides additional detail on topographic factors.
Velocity Pressure (qz) – This number in pounds per
square foot (psf) is calculated using the factors described
above. The ESWA is offered with a choice of two
structural design packages, consisting of:
– Standard Design - up to 60 psf
– Upgraded Structural Design - up to 145 psf
IBC COMPLIANCE
Wind Load Sample Calculation
The following example demonstrates the procedure to
determine which structural design package a
Condominium Building located in Miami, FL (zip code
33101) would require under the latest version of IBC. In
this example, the closed circuit cooler will be installed on
the top of the 60 foot tall building.
Step 1: Calculate the Exposure Category Coefficient (Kz)
Where:
z = 60; Installation Height
zg = 700; from ASCE 7-05 Table 2 using an Exposure
Category of D.
α = 11.5; from ASCE 7-05 Table 2 using an Exposure
Category of D.
Step 2: Calculate the Velocity Pressure (qz)
Where:
( a )
qz = 0.00256(Kz)(Kzt)(Kd)(V 2 )(I) =
0.00256(1.31)(1.0)(0.85)(145 2 )(1.0) = 59.93psf
Kz = 1.31; as calculated above.
( )
( 11.5)
KZ = 2 2
z
60
2.01
= ( zg)
2.01 =
700
1.31
Kzt = 1.0; default when topographic effects are not a
factor.
Kd = 0.85; default for building components and
cladding.
V = 145; wind speed from ASCE 7-05 Figure 6-1.
I = 1.0; Based on an Occupancy Category of II.
In order to meet Code requirements, the unit and its
attachments must be designed and constructed to
withstand 59.93 psf.