Wind Loading Analysis MWFRS and Components/Cladding
Per ASCE 7-02 Code for Low-Rise, Enclosed Buildings with h <= 60' and Roof q <= 45°
Using Method 1: Simplified Procedure (Section 6.4)

Civil Engineering Resources
WIND LOADING ANALYSIS - MWFRS and Components/Cladding
Per ASCE 7-02 Code for Low-Rise, Enclosed Buildings with h <= 60' and Roof q <= 45o
Using Method 1: Simplified Procedure (Section 6.4)
Input Data:
Wind Speed, V =
The Basic Design Wind Speed, V (mph), corresponds to a 3-second gust speed at 33' above ground in Exposure Category "C" and is associated with an annual probability of 0.02 of being equalled or exceeded (50-year mean recurrence interval).
For Basic Wind Speed Map (Fig. 6-1) see 'Wind Map' webpage.
mph?? (Wind Map, Figure 6-1)
Bldg. Classification =
TABLE 1-1
Classification of Buildings and Other Structures for Flood, Wind, Snow, Earthquake, and Ice Loads
Nature of Occupancy Category
Buildings and structures that represent a low hazard to human life in the event of failure including, I
but not limited to:
- Agriculture facilities
- Certain temporary facilities
- Minor storage facilities
Buildings and other structures except those listed in Categories I, III and IV II
Buildings and other structures that represent a substantial hazard to human life in the event of III
failure including, but not limited to:
- Buildings and other structures where more than 300 people congregate in one area
- Buildings and other structures with day-care facilities with capacity greater than 150
- Elementary or secondary school facilities with capacity greater than 250
- Colleges & adult education facilities with a capacity greater than 500
- Health care facilities with a capacity greater than 50 resident patients but not having surgery
or emergency treatment facilities
- Jails and detention facilities
- Any other occupancy with an occupant load greater than 5000
- Power generating stations and other public utility facilities not included in Category IV
- Buildings and structures not included in Category IV containing sufficient quantities of toxic,
explosive, or other hazardous materials dangerous to the public if released
Buildings and other structures designated as essential facilities including, but not limited to: IV
- Hospitals and health care facilities having surgery or emergency treatment facilities
- Fire, rescue and police stations and emergency vehicle garages
- Designated earthquake, hurricane or other emergency shelters
- Designated emergency preparedness, communication, and operation centers and
other facilities required for emergency response
- Power-generating stations and other public utility facilities required in an emergency
- Ancillary structures required foroperation of Category IV structures during an emergency
- Aviation control towers, air traffic control centers and emergency aircraft hangars
- Water storage facilities and pump structures required to maintain water pressure for fire
suppression
- Buildings and other structures having critical national defense functions
- Buildings and structures containing extremelyhazardous materials where quantity of material
exceeds a threshhold quantity established by authority having jusisdiction
(Table 1-1)
Exposure Category =
Surface Roughness Categories for the purpose of assigning Exposure Category are defined as follows:
Surface Roughness "B":
Urban and suburban areas, wooded areas or other terrain with numerous closely spaced obstructions having the size of single family dwellings or larger.
Surface Roughness "C":
Open terrain with scattered obstructions having heights generally < 30 ft. This category includes flat open country, grass lands, and all water surfaces in hurricane-prone regions.
Surface Roughness "D":
Flat, unobstructed areas and water surfaces outside hurricane-prone regions. This category includes smooth mud flats, salt flats, and unbroken ice.

Exposure Categories are defined as follows:
Exposure "B":
Exposure B shall apply where the ground surface roughness condition, as defined by Surface Roughness B, prevails in the upwind direction for a distance of at least 2630 ft. or 10 times the building height, whichever is greater.
(Exception: For buildings whose mean roof height <= 30 ft., the upwind distance may be reduced to 1500 ft.)
Exposure "C":
Exposure C shall apply for all cases where exposures B and D do not apply.
Exposure "D":
Exposure D shall apply where the ground surface roughness, as defined by Surface Roughness D, prevails in the upwind diection for a distance >= 5,000 ft. or 10 times the building height, whichever is greater.
(Sect. 6.5.6)
Ridge Height, hr = ft. (hr >= he)
Eave Height, he = ft. (he <= hr)
Building Width, W = ft. (Normal to Building Ridge)
Building Length, L = ft. (Parallel to Building Ridge)
Roof Type =
This program assumes that a Gable roof is symmetrical, as the ridge line is assumed in the center of the building width.
For flat roofs (roof angle = 0 degrees), either Gable or Monoslope may be used.
(Gable or Monoslope)
Wall C&C Name =
(Girt, Siding, Wall, or Fastener)
Wall C&C Eff. Area =
The Effective Area, for a component or cladding panel equals the span length times the effective width that need not be less than 1/3 of the span length; however, for a fastener it is the area tributary to an individual fastener.
Note: Major structural components supporting tributary areas > 700
sq ft shall be permitted to be designed using the provisions for
main wind-force resisting systems (MWFRS).
ft.^2 (for Component/Cladding)
Roof C&C Name =
(Purlin, Joist, Decking, or Fastener)
Roof C&C Eff. Area =
The Effective Area, for a component or cladding panel equals the span length times the effective width that need not be less than 1/3 of the span length; however, for a fastener it is the area tributary to an individual fastener.
Note: Major structural components supporting tributary areas > 700
sq ft shall be permitted to be designed using the provisions for
main wind-force resisting systems (MWFRS).
ft.^2 (for Component/Cladding)
Overhang Eff. Area =
The Effective Area, for a component or cladding panel equals the span length times the effective width that need not be less than 1/3 of the span length; however, for a fastener it is the area tributary to an individual fastener.
Note: Major structural components supporting tributary areas > 700
sq ft shall be permitted to be designed using the provisions for
main wind-force resisting systems (MWFRS).
ft.^2 (for Component/Cladding)
Hurricane Region?
Resulting Parameters and Net Design Pressures:
For Transverse Direction: (wind perpendicular to ridge)
Roof Angle, q = deg.
Mean Roof?? Ht., h =
For buildings with roof angle <= 10 degrees:
h = he (per Sect. 6-3).
ft.?? (h = he for q < 10 deg.)
Adjustment Factor, l =
Adustment Factor
for Building Height and Exposure, l
Mean Roof Exposure
Height (ft.) B C D
15 1.00 1.21 1.47
20 1.00 1.29 1.55
25 1.00 1.35 1.61
30 1.00 1.40 1.66
35 1.05 1.45 1.70
40 1.09 1.49 1.74
45 1.12 1.53 1.78
50 1.16 1.56 1.81
55 1.19 1.59 1.84
60 1.22 1.62 1.87
(adjusts for height and exposure)
Importance Factor, I =
Importance Factor, I (Table 6-1):

Non-Hurricane Prone Regions Hurricane Prone Regions
Category and Hurricane Prone Regions with V > 100 mph
with V = 85-100 mph and Alaska
I 0.87 0.77
II 1.00 1.00
III 1.15 1.15
IV 1.15 1.15
(Table 6-1)
Wall & Roof End Zone Width, a =
Width 'a' is equal to 10% of least horizontal dimension or 0.4*h, whichever is smaller, but not less than either 4% of least horizontal dimension or 3'.
ft.?? (use: "2*a"?? for MWFRS,?? "a"?? for C&C)
Transverse MWFRS Net Pressures (psf)
Location Direction Zone Load Case 1
Both load cases 1 and 2 are be checked for roof angle, 25 degrees < q <= 45 degrees.
Load Case 2
A = end zone of wall Horizontal A
B = end zone of roof Horizontal B
C = interior zone of wall Horizontal C
D = interior zone of roof Horizontal D
E = end zone of windward roof Vertical E
F = end zone of leeward roof Vertical F
G = interior zone of windward roof Vertical G
H = interior zone of leeward roof Vertical H
For Longitudinal Direction: (wind parallel to ridge)
Roof Angle, q =
For wind in longitudinal direction,
use q = 0 degrees (assumed).
deg.?? (assumed)
Mean Roof?? Ht., h =
For wind in longitudinal direction,
h = he+(hr-he)/2
ft.?? (h = (hr+he)/2)
Adjustment Factor, l =
Adustment Factor
for Building Height and Exposure, l
Mean Roof Exposure
Height (ft.) B C D
15 1.00 1.21 1.47
20 1.00 1.29 1.55
25 1.00 1.35 1.61
30 1.00 1.40 1.66
35 1.05 1.45 1.70
40 1.09 1.49 1.74
45 1.12 1.53 1.78
50 1.16 1.56 1.81
55 1.19 1.59 1.84
60 1.22 1.62 1.87
(adjusts for height and exposure)
Longitudinal MWFRS Net Pressures (psf)
Location Direction Zone Load Case 1
Both load cases 1 and 2 are be checked for roof angle, 25 degrees < q <= 45 degrees.
Load Case 2
A = end zone of wall Horizontal A
B = end zone of roof Horizontal B
C = interior zone of wall Horizontal C
D = interior zone of roof Horizontal D
E = end zone of windward roof Vertical E
F = end zone of leeward roof Vertical F
G = interior zone of windward roof Vertical G
H = interior zone of leeward roof Vertical H
Total Design MWFRS Horizontal Load (kips)
Transverse Longitudinal
Load Case 1 Load Case 2 Min. Load Load Case 1 Load Case 2 Min. Load
Formulas:
Ph(Trans) = ((Pc*(L-4*a)+Pa*4*a)*he+(Pd*(L-4*a)+Pb*4*a)*(hr-he))/1000
Ph(Trans)(min) = P(min)*L*hr/1000?? ,?? where: P(min) = 10.0 psf on projected area
Ph(Long)(min) = P(min)*W*(hr+he)/2/1000?? ,?? where: P(min) = 10.0 psf on full area
Components & Cladding Net Pressures (psf)
Item Location Zone Pos. (+) Neg. (-)
4 = interior zone of wall 4
5 = end zone of wall 5
1 = interior zone of roof 1
2 = end zone of roof 2
3 = corner zone of roof 3
Roof Overhang 2 = end zone of o.h. 2 ---
3 = corner zone of o.h. 3 ---
Notes:???? 1. For Method 1: Simplified Procedure of Section 6.4 to be used for an enclosed low-rise building??
to determine the design wind loads, all of the following nine conditions of 6.4.1.1 must be met:
???? a. Building is a simple diaphragm building, in which wind loads are transmitted through floor??
???????????? and roof diaphragms to the vertical Main Wind-Force Resisting System (MWFRS).
???? b. Building is a low-rise building where mean roof height, h <= 60 ft., and h <= min. of L or W.
???? c. Building is enclosed and conforms to wind-borne debris provisions of Section 6.5.9.3.
???? d. Building is a regular shaped building, having no unusual geometrical irregularity.
?????? f. Building is not classified as a flexible building so it is considered "rigid".
???? g. Building is not subject to across-wind loading, vortex shedding, etc.
???? h. Building has no expansion joints or separations.
?????? i. Building is not subject to topographic effects, no abrupt topographic changes.
?????? j. Building has an approximately symmetrical cross section in each direction with either a??
???????????? flat roof, or gable roof with q <= 45 degrees.
Wind pressures (ps30) in Figures 6-2 and 6-3 were prepared based on following assumptions:
???? a. Mean roof height, h = 30 ft.?? ,?? Exposure category = B?? ,?? Importance factor, I =1.0
???? b. Velocity pressure exposure coefficient, Kz = 0.70
???? c. Directionality factor, Kd = 0.85?? ,?? Topographic factor, Kzt = 1.0
???? d. Internal pressure coefficients, GCpi = +0.18, -0.18 (enclosed building)
???? e. MWFRS pressure coeff's. from Figure 6-10, and C&C pressure coeff's. from Figure 6-11.
?????? f. Design wind pressure, Ps = l*I*ps30, in psf.
Design wind pressures are net pressures (sum of external and internal pressures).
Wall net pressure for MWFRS is total for both windward and leeward walls.
(+) and (-) signs signify wind pressures acting toward & away from respective surfaces.
If pressures for Zones "B" and "D" < 0, assume = 0.
For the design of the longitudinal MWFRS use roof angle, q = 0 degrees.
Both load cases 1 and 2 are be checked for roof angle, 25 degrees < q <= 45 degrees.
The total design MWFRS horizontal load is the total horizontal wind load on either the length (L)??
or the width (W) of the building respectively assuming one end zone of a width = 2*a.
Minimum wind load for MWFRS design shall be 10 psf applied on projected vertical plane.
Minimum wind load for C&C shall be 10 psf acting in either direction normal to surface.
References:??
???? a. ASCE 7-02 Standard, "Minimum Design Loads for Buildings and Other Structures".
???? b. "Guide to the Use of the Wind Load Provisions of ASCE 7-02"
???????????? by: Kishor C. Mehta and James M. Delahay (2004).
(continued)
Figure 6-2
MWFRS - Wind Zones
Figure 6-3
Components and Cladding - Wind Zones

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