Building Loading - Wind Load

(Revised:  11/15/2016)

The Wind Load tab defines design related information regarding the Building's (or Shape's) Wind Load.  Wind causes pressures and suctions on wall and roof surfaces of buildings.  The Wind Load is specified in the required building code.  Some building codes specify wind speed/velocity in MPH (miles per hour in English units), while others specify the resulting wind pressure in PSF (pounds per square foot in English units).  Customer specifications or local building departments may require more severe wind loads than those given in the code.

The wind loads are applied to the entire Building or Shape, considering all of the applicable Wind Load options.

  Note to Builder/Customer:

The builder is responsible for contacting the local building official or project design professional to obtain and provide all code and loading information for the specific building site.  Data supplied is assumed to be accurate and is not verified.

 

Wind Load Information:

Wind Load

This edit box is used to define the Wind Load for the Building or Shape.  This Load can be measured in Miles per Hour (English - Speed or Velocity) or Pounds per Square Foot (English - Pressure) based on the corresponding radio button selected.

Wind causes pressures and suctions on wall and roof surfaces of buildings.  The wind load is specified in the required building code.  Some building codes specify wind velocity in MPH, while others specify the resulting wind pressure in PSF.  Sometimes specifications or local building departments will require more severe wind loads than those given in the code.

  Note:

The Canadian codes require input of the wind load as a Pressure.

Speed

Select the Speed option if entering the wind load as a wind velocity.  This option measures the Wind velocity in miles per hour (English).  The software converts the wind speed to an equivalent wind pressure based on the Building Code requirements.  External and internal wind coefficients are applied to the converted wind pressure loads depending on the Building Code selected.

Pressure

Select the Pressure option if entering the wind load as a wind pressure.  This option measures the Wind Pressure in Pounds per Square Foot (English units).  External and internal wind coefficients will be applied to the user entered wind pressure loads depending on the Building Code selected.

Use ‘All Heights’ Method

When the limits of Low-rise buildings given in ASCE 7-05 Section 6.2 (for 2006/2009 IBC) and in ASCE 7-10 Section 26.2 (for 2012/2015 IBC) are exceeded, or when user selected, wind loads will be calculated using the provisions for the rigid buildings of “All Heights”.  The “All Heights” method may be used for any building height or configuration. This check box is not active for NBCC codes.

 

The “All Heights” method is mandatory for Eave heights > 60 feet, and with buildings with an eave height > the least horizontal dimension of the building.  The wind load method will automatically be selected by the software based on the building geometry. (The “Low-rise” method is the default unless “All Heights” is required.)  A switch can be made manually from Low-rise to All Heights; however, the “All Heights” box cannot be unchecked if the software determines that “All Heights” is required.  Buildings using Wind Enclosure of “Open – All Heights” will inherently be loaded with the “All Heights” method.

 

Wind Exposure

    

This drop list defines the surrounding terrain of the Building or Shape.  Depending on the Building Code, the Wind Exposure option may be disabled if it is not required by the Code.

The Wind Exposure is used to recognize the impact of the surrounding terrain during the calculation of the wind pressure applied to the Building or Shape for the specified Wind velocity.

 

Wind Exposure Descriptions:

%!JumpId(IDC_CODES_USE_1)   ASCE 7-10, 2012 IBC, IBC2015, 2015 MNBC, 2014 FL–HVHZ (5th)

%!JumpId(IDC_CODES_USE_1)   ASCE 7-05, 2006 IBC, 2009 IBC, MAST (7th), MAST (8th), 2014 WICBC

%!JumpId(IDC_CODES_USE_1)   ASCE 7-02, 2003 IBC

%!JumpId(IDC_CODES_USE_1)   2005 NBCC, 2010 NBCC, 2015 NBCC

%!JumpId(IDC_CODES_USE_1)   1982 ANSI, 1998 ASCE 7, 1999 BOCA, 1996 BOCA, 1993 BOCA, 1996 NCST, 1994 NCST, OBBC, 1994 SFL, JBSA, CONN, 2000 IBC, 2001 FL, 2001 FL (HVHZ)

%!JumpId(IDC_CODES_USE_1)   1987 BOCA, 1990 BOCA, OKC

%!JumpId(IDC_CODES_USE_1)   1988 UBC, LLB, SEA

%!JumpId(IDC_CODES_USE_1)   1991 UBC, 1994 UBC, 1997 UBC

%!JumpId(IDC_CODES_USE_1)   MAST (5th), KS, MAST (6th)

%!JumpId(IDC_CODES_USE_1)   1995 ASCE

NA:  MBMA, SBC, MUBC, 1991 NCST, NYST, WICBC, CHI, MSY, PHX, 1991 SFL, 1995 NBC

 

Wind Enclosure

 

From this drop list, select the Enclosure that best describes the Building or Shape.  This option determines the net wind loading on a building depending on the presence of permanent Framed Openings or Wall Openings.  Wind pressures for a Partially Enclosed building are higher than those for an Enclosed building. Since each building code has its own definitions for Wind Enclosure, reference the applicable building code.

 

   Levels of Wind Enclosure IBC, ASCE codes, MAST (7th), MAST (8th), 2014 WICBC, 2015 MNBC, 2014 FL–HVHZ (5th)

   Levels of Wind Enclosure 2005 NBCC, 2010 NBCC, 2015 NBCC

  Notes:

The User must set the Wind Enclosure as the system will NOT determine this condition.  Contact a Service Center for assistance.

 

Regional Information:

 

Distance to the Coast

This edit box is enabled when required by specific Building Codes.  Enter the actual mileage to the nearest coastline if less than 101 miles.  Enter 101 miles when the distance from project to the coast exceeds 100 miles.

Building Base Elevation

In this edit box, enter the height of the finished floor (typical base of columns) above the ground elevation.  This input DOES affect the net wind loading on the building. This Building Base Elevation dimension is commonly or normally thought of as 0'-0''. 

Sample Conditions where the Building Base Elevation might be revised:

1) To specify a floor elevation change between building shapes

2) For a penthouse or cupola shape that will actually be on top of another shape

3) When the building or shape actually sits on a concrete wall / elevated foundation, for example:  a truck dock terminal where the ground elevation is several feet lower than the base of columns (finish floor)

  Note:  This is NOT the actual (or the nominal 100'-0) elevation from sea level designated as Fin. Fl. Elev. on the Geometry / Shape tab.  If the 100/0/0 default elevation from sea level / ground elevation is revised on the Geometry / Shape tab, the wind load will NOT be affected.

 

Topographic Factor / MsMt

This box is dual purpose and will typically be used for the Topographic Factor as described below.  MsMt value is used by International Codes.

The Topographic Factor (Kzt for IBC/ASCE based codes; Ct for 2015 NBCC) is a wind load related coefficient that increases the design wind loads (basic wind pressure) to account for localized, job-site topographic features, such as isolated hills, ridges and escarpments (in any Exposure Category) where there is an abrupt change in the general topography that could cause a sudden change of the wind speed.  Contact a Service Center Engineer for help with the appropriate factor if the building is located on or near a hill, ridge or escarpment.

The default Topographic Factor in the software is 1.0000. Please see the following for rare conditions where this is unconservative. 

For IBC or other standards where wind loads are calculated in accordance with ASCE 7, (Kzt) must be evaluated and calculated for rare cases only, where all five requirements listed below (Section 26.8.1, ASCE 7-10) are satisfied:

1.     H is greater than or equal to 15 feet (4.5 m) for Exposures C and D and 60 feet (18 m) for Exposures A and B.

2.     H/Lh >= 0.2, where:

Lh is distance upwind of crest to where the difference in ground elevation is half the height of hill or escarpment, in feet (meters).

H = Height of hill or escarpment relative to the upwind terrain, in feet (meters).

3.     The hill, ridge, or escarpment is isolated and unobstructed upwind by other similar topographic features of comparable height for 100 times the height of the topographic feature (100*H) or 2 miles (3.22 km), whichever is less.  This distance shall be measured horizontally from the point at which the height H of the hill, ridge, or escarpment is determined.

4.     The hill, ridge, or escarpment protrudes above the height of upwind terrain features within a 2 mi (3.22 km) radius in any quadrant by a factor of two or more.

5.     The structure is located as shown in Fig. 26.8-1 (ASCE 7-10) in the upper one-half of a hill or ridge or near the crest of an escarpment.

When required, the Kzt factor is calculated per Equation 26.8-1 (ASCE 7-10).  In all other cases, Kzt = 1.0000.

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Note:

New in 2015 NBCC, the Topographic Factor, Ct, is defined per Article 4.1.7.4.  Similar to Kzt above, Ct must be evaluated and calculated for rare cases only for buildings situated at or near the tops of isolated hills, ridges, and escarpments. When required, the Ct factor is calculated per Article 4.1.7.4.  In all other cases, Ct = 1.0000.

 

Step Height

This edit box is intended for use with International Codes.

 

Hurricane Prone Region

This Check Box should be selected when the project is located in a Hurricane Prone Region as defined by the Building Code.  By clicking in the box, the system will use the appropriate Wind Importance Factor.  This check box is not active for NBCC codes.

  Note:

If Hurricane Prone Region / Cyclonic Region box is checked with a Building Use / Importance / Risk Category of Low Hazard:  Ag, Storage, Temp selected, then the Wind Importance factor, Iw, will be reduced to 0.87 for winds up to 100 mph, and reduced to 0.77 for winds greater than 100 mph when using ASCE 7-05 (Table 6-1).

 

Windborne Debris Region

Coastal region defined by the Building Code.  Verify with the local building code official, if applicable, for each project.  This check box is not active for NBCC codes.

  Notes:

If Windborne Debris Region is applicable, see option for “All ext. doors, windows, skylights, etc.” following.

Per 2014 FL–HVHZ (5th) for Broward and Miami-Dade counties in Florida, all buildings fall within the Windborne Debris Region.

All Exterior Doors, Windows, etc.

If project is located in a Windborne Debris Region, building shall be designed as a Partially Enclosed structure unless this radio button is activated.  Checking this box indicates that doors and windows meet the design code criteria for the building/shape to be considered Enclosed.  This check box is not active for NBCC codes.

 

Regional Information:

Temp Correction / Dom Opening Ratio

This edit box is intended for use with International Codes.

Typhoon

This edit box is intended for use with International Codes.

Normal

This edit box is intended for use by International Codes.

 

Standard Controls:

§ OK, Cancel, Apply, Help

 

See also:

§ Building Loading - Building Codes

§ Building Loading - Live Load

§ Building Loading - Snow Load

§ Building Loading - Seismic

§ Building Loading - Deflection Conditions