Wind Load Calculator

In order for a structure to be sound and secure, the foundation, roof, and walls must be strong and wind resistant. When building a structure it is important to calculate wind load to ensure that the structure can withstand high winds, especially if the building is located in an area known for inclement weather. The main wind force resisting system of a building is a vital component. While wind load calculations can be difficult to figure out because the wind is unpredictable, some standard calculations can give you a good idea of what a building can withstand. Wind loading analysis is an essential part of the building process. If wind loading analysis is not done correctly the resulting effects could include collapsed windows and doors, ripped off roofing, and more. Contact BuildingsGuide for quotes on safe and durable prefabricated steel buildings.

Types of Wind Load Forces on Buildings:

To assist in your wind loading analysis, use the following wind load calc to get the necessary wind load calculations. Accurate wind load calculations will that a safe, durable structure is assembled.

Wind Loading Analysis - Main Wind-Force Resisting System, per ASCE 7-05 Code [wind loads on structures 2005] for Enclosed or Partially Enclosed Buildings
Using Method 2: Analytical Procedure (Section 6.5) for Low-Rise Buildings

Input Data

Wind Speed, V = mph  (Wind Map, Figure 6-1)
Bldg. Classification = [?] (Table 1-1 Occupancy Cat.)
Exposure Category = (Sect. 6.5.6)
Ridge Height, hr = ft. (hr >= he)
Eave Height, he = ft. (he <= hr)
Building Width = ft. (Normal to Building Ridge)
Building Length = ft. (Parallel to Building Ridge)
Roof Type = (Gable or Monoslope)
Topo. Factor, Kzt = (Sect. 6.5.7 & Figure 6-4)
Direct. Factor, Kd = (Table 6-4)
Enclosed? (Y/N) (Sect. 6.2 & Figure 6-5)
Hurricane Region?

Resulting Parameters and Coefficients:

Member Properties for :
Roof Angle, q = deg.  
Mean Roof  Ht., h = ft. (h = (hr+he)/2, for angle >10 deg.)
 
Check Criteria for a Low-Rise Building:
1.  Is h <= 60' ?   2. Is h <= Lesser of L or B?Table 10-1  
       
External Pressure Coeff's., GCpf (Fig. 6-10):
(For values, see following wind load tabulations.)
Positive & Negative Internal Pressure Coefficients, GCpi (Figure 6-5):
+GCpi Coef. = (positive internal pressure)
-GCpi Coef. = (negative internal pressure)
 
If h < 15 then: Kh = 2.01*(15/zg)^(2/a) (Table 6-3, Case 1b)
If h >= 15 then: Kh = 2.01*(z/zg)^(2/a) (Table 6-3, Case 1b)
a = (Table 6-2)
zg = (Table 6-2)
Kh = (Kh = Kz evaluated at z = h)
I = (Table 6-1)
 
Velocity Pressure: qz = 0.00256*Kz*Kzt*Kd*V^2*I (Sect. 6.5.10, Eq. 6-15)
qh = psf qh = 0.00256*Kh*Kzt*Kd*V^2*I (qz evaluated at z = h)
Design Net External Wind Pressures (Sect. 6.5.12.2.2):
p = qh*[(GCpf) - (+/-GCpi)] (psf, Eq. 6-18)

Wall and Roof End Zone Widths 'a' and '2*a' (Fig. 6-10):
a = ft.  
2*a = ft.  
   
MWFRS Wind Load for Transverse Direction MWFRS Wind Load for Longitudinal Direction
Surface GCpf p = Net Pressures (psf) Surface *GCpf p = Net Pressures (psf)
    (w/ +GCpi) (w/ -GCpi)     (w/ +GCpi) (w/ -GCpi)
Zone 1       Zone 1      
Zone 2       Zone 2      
Zone 3       Zone 3      
Zone 4       Zone 4      
Zone 5       Zone 5      
Zone 6       Zone 6      
Zone 1E       Zone 1E      
Zone 2E       Zone 2E      
Zone 3E       Zone 3E      
Zone 4E       Zone 4E      
 
*Note: Use roof angle q = 0 degrees for Longitudinal Direction.
For Trans. when GCpf is neg. in Zones 2/2E:
For Trans. when GCpf is neg. in Zones 2/2E:   For Long. when GCpf is neg. in Zones 2/2E:
Zones 2/2E dist. = ft.   Zones 2/2E dist. = ft.
Remainder of roof Zones 2/2E extending to ridge line shall use roof Zones 3/3E pressure coefficients.
       
MWFRS Wind Load for Transverse, Torsional Case MWFRS Wind Load for Long., Torsional Case
Surface GCpf p = Net Pressure (psf) Surface GCpf p = Net Pressure (psf)
    (w/ +GCpi) (w/ -GCpi)     (w/ +GCpi) (w/ -GCpi)
Zone 1T ---     Zone 1T ---    
Zone 2T ---     Zone 2T ---    
Zone 3T ---     Zone 3T ---    
Zone 4T ---     Zone 4T ---    
Notes:
  1. For Transverse, Longitudinal, and Torsional Cases:
    Zone 1 is windward wall for interior zone. Zone 1E is windward wall for end zone.
    Zone 2 is windward roof for interior zone. Zone 2E is windward roof for end zone.
    Zone 3 is leeward roof for interior zone. Zone 3E is leeward roof for end zone.
    Zone 4 is leeward wall for interior zone. Zone 4E is leeward wall for end zone.
    Zones 5 and 6 are sidewalls.  
    Zone 1T is windward wall for torsional case Zone 2T is windward roof for torsional case.
    Zone 3T is leeward roof for torsional case Zone 4T is leeward wall for torsional case.
  2. (+) and (-) signs signify wind pressures acting toward & away from respective surfaces.
  3. Building must be designed for all wind directions using the 8 load cases shown below. The load cases are applied to each building corner in turn as the reference corner.
  4. Wind loads for torsional cases are 25% of respective transverse or longitudinal zone load values. Torsional loading shall apply to all 8 basic load cases applied at each reference corner. Exception: One-story buildings with "h" <= 30', buildings <= 2 stories framed with light frame construction, and buildings <=2 stories designed with flexible diaphragms need not be designed for torsional load cases.
  5. Per Code Section 6.1.4.1, the minimum wind load for MWFRS shall not be less than 10 psf.
  6. References :
    • ASCE 7-02, "Minimum Design Loads for Buildings and Other Structures".
    • "Guide to the Use of the Wind Load Provisions of ASCE 7-02" by: Kishor C. Mehta and James M. Delahay (2004).




x
TABLE 1-1
Occupancy Category of Buildings and Other Structures for Flood, Wind, Snow, Earthquake, and Ice Loads
Nature of Occupancy
Occupancy Category
Buildings and structures that represent a low hazard to human life in the event of failure including, but not limited to:
- Agriculture facilities
- Certain temporary facilities
- Minor storage facilities
 I
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 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
Buildings and other structures, not includes in Occupancy Category IV, with potential to cause substantial economic impact and/or mass disruption of day-to-day civilian life in event of failure, including, but not limited to:
- Power generating stations, water treatment facilities, sewage treatment facilities, and telecommunication centers
- Buildings and structures not included in Category IV containing sufficient quantities of toxic, explosive, or other hazardous materials dangerous to the public if released
 III
Buildings and other structures designated as essential facilities including, but not limited to:
- 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 jurisdiction
 IV
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' worksheet of this workbook.

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 2600 ft. or 20 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 20 times the building height, whichever is greater. Exposure D shall extend into downwind areas of Surface Roughness B or C for a distance of 600 ft. or 20 times the height of the building, whichever is greater.

The eave height, 'he', is the distance from the ground surface adjacent to the building to the roof eave line at a particular wall. If the height of the eave varies along the wall, the average height shall be used.
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.
The Topographic Factor, Kzt, accounts for effect of wind speed-up over isolated hills and escarpments (Sect. 6.5.7 and Fig. 6-4).

Kzt = (1+K1*K2*K3)^2 (Eq. 6-3), where:
H = height of hill or escarpment relative to the upwind terrain, in feet.
Lh = Distance upwind of crest to where the difference in ground elevation is half the height of hill or escarpment, in feet.
K1 = factor to account for shape of topographic feature and maximum speed-up effect.
K2 = factor to account for reduction in speed-up with distance upwind or downwind of crest.
K3 = factor to account for reduction in speed-up with height above local terrain.
x = distance (upwind or downwind) from the crest to the building site, in feet.
z = height above local ground level, in feet.

The effect of wind speed-up shall not be required to be considered (Kzt = 1.0) when H/Lh < 0.2, or H < 15' for Exposures 'C' and 'D', or H < 60' for Exposure 'B'.
Wind Directionality Factor, Kd (Table 6-4)
Structure Type Kd
Buildings 
Main Wind-Force Resisting System 0.85
Components and Cladding 0.85

Note: this factor shall only be applied when used in conjunction with load combinations specified in Sect. 2.3 and 2.4. Otherwise, use Kd = 1.0.
This worksheet assumes either Enclosed or Partially Enclosed buildings, and does not consider open buildings.
  1. An enclosed building is a building that does not comply with the requirements
    for open or partially enclosed buildings.
  2. An open building is a structure having all walls at least 80% open.
  3. A partially enclosed building complies with both of the following conditions:
    • the total area of openings in a wall that receives positive external pressure exceeds the sum of the areas of the openings in the balance of the building envelope (walls and roof) by more than 10%; and
    • the total area of openings in a wall that receives positive external pressure exceeds 4 sq ft or 1% of the area of that wall, whichever is smaller, and the % of openings in balance of the building envelope does not exceed 20%.
The building Mean Roof Height, h, is determined as follows:
  For buildings with roof angle > 10 degrees: h = (hr+he)/2
  For buildings with roof angle <= 10 degrees: h = he
For an enclosed or partially enclosed building to be classified as a Low-Rise building, the following 2 conditions must both be met:
  1. The building mean roof height, h, must be <= 60 ft.
  2. The building mean roof height, h, does not exceed the least horizontal dimension, L or B.
External Pressure Coefficients, GCpf, for MWFRS ( Fig. 6-10):
Roof Angle,θ Building Surface (Zone)
(deg.) 1 2 3 4 5 6 1E 2E 3E 4E
0-5 0.40   -0.69  -0.37   -0.29  -0.45   -0.45   0.61  -1.07  -0.53  -0.43 
20 0.53  -0.69  -0.48   -0.43  -0.45   -0.45  0.80  -1.07  -0.69  -0.64 
30-45 0.56  0.21  -0.43  -0.37  -0.45  -0.45  0.69  0.27  -0.53  -0.48 
90 0.56  0.56  -0.37  -0.37  -0.45  -0.45  0.69  0.69  -0.48  -0.48 
Internal Pressure Coefficients, GCpi (Figure 6-5)
Condition (+/-) GCpi
Partially enclosed buildings +0.55, -0.55
dings +0.55, -0.55
 +0.18, -0.18
   
Per Sect. 6.5.11.1, for a partially enclosed building containing a single, unpartitioned large volume, the GCpi coefficients shall be multiplied by the following reduction factor, Ri:
Ri = 1.0 or Ri = 0.5*(1+(1/(1+Vi/(22800*Aog))^0.5)) <= 1.0
where: Aog = total area of openings in the building envelope
(walls and roof, ft.^2).
Vi = unpartitioned internal volume (ft.^3).
Note: This program assumes NO reduction of the GCpi coefficients for large volume buildings. Thus, Ri = 1.0.
Terrain Exposure Constants (Table 6-2)
Exposure Category αzg (ft)
B 7.0 1,200
C 9.5 900
D 11.5 700
Importance Factor, I (Table 6-1):
Category Non-Hurricane Prone Regions
and Hurricane Prone Regions
with V = 85-100 mph and Alaska 		Hurricane Prone Regions
with V > 100 mph
I 0.87 0.77
II 1.00 1.00
III 1.15 1.15
IV 1.15 1.15
Note: in the U.S. and its territories hurricane prone regions are defined as:
  1. U.S. Atlantic Ocean and Gulf of Mexico coasts where the basic wind speed is > 90 mph.
  2. Hawaii, Puerto Rico, Guam, Virgin Islands, and American Samoa.
Per Code Section 6.1.4.1, the minimum wind load to be used in the design of the Main Wind-Force Resisting System shall not be less than 10 psf.
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'.
Per Code Section 6.1.4.1, the minimum wind load to be used in the design of the MWFRS shall not be less than 10 psf multiplied by the area of the building or structure projected onto a vertical plane normal to the assumed wind direction.
For Transverse Load Case the roof pressure coefficient, GCpf, when negative in Zone 2 or 2E, shall be applied in Zone 2/2E for a distance from the edge of the roof equal to 0.5 times the horizontal dimension of the building parallel to the direction of the MWFRS being designed or 2.5*he at the windward wall, whichever is less; the remainder of Zone 2/2E extending to the ridge line shall use the pressure coefficient GCpf for Zone 3/3E.
For Longitudinal Load Case the roof pressure coefficient, GCpf, when negative in Zone 2 or 2E, shall be applied in Zone 2/2E for a distance from the edge of the roof equal to 0.5 times the horizontal dimension of the building parallel to the direction of the MWFRS being designed or 2.5*he at the windward wall, whichever is less; the remainder of Zone 2/2E extending to the ridge line shall use the pressure coefficient GCpf for Zone 3/3E.

 

 

 

Disclaimer: This calculator is not intended to be used for the design of actual structures, but only for schematic (preliminary) understanding of structural design principals. For the design of an actual structure, a competent professional should be consulted.

‘Calculations courtesy of Alex Tomanovich, PE ’