Building Loading - Wind Load

(Revised:  12/09/13)

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 code.  Some building codes specify wind 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).  Note, 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.

  Warning:

Compliance with a selected Building Code is the Responsibility of the Builder (Customer).

Please consult the Job Specifications and/or the Building Department having jurisdiction for specific loading requirements.

The Metal Building Manufacturer will not process an order with less loading then the MBMA Minimum County Loadings without written direction from the owner, unless allowed by Local code Requirements.

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 Pounds per Square Foot (English - Pressure) or Miles per Hour (English - Speed or Velocity) 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 code.  Some building codes specify wind velocity in MPH, while others specify the resulting wind pressure in PSF.  Sometime specifications or local building departments will require more severe wind loads than those given in the code.

  Notes:

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 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.

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 (Low-rise by default unless All Heights is required).  A switch can be made manually from Low-rise to All Heights, but the All Heights box cannot be unchecked if determined that it is required.  Buildings using 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 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

%!JumpId(IDC_CODES_USE_1)   ASCE 7-05, 2006 IBC, 2009 IBC

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

%!JumpId(IDC_CODES_USE_1)   2005 NBCC, 2010 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, 2001 FL, 2001 FL (HVHZ), 2000 IBC

%!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), MAST (7th)

%!JumpId(IDC_CODES_USE_1)   1995 ASCE

NA:  MBMA, SBC, MUBC, 1991 NCST, NYST, WIST, 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.

 

   Levels of Wind Enclosure IBC / ASCE Codes

   Levels of Wind Enclosure 2005 NBCC, 2010 NBCC

  Notes:

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

Each building code has its own definition; please refer to your building code.

Regional Information:

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.

  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.  (ASCE 7-05, Table 6-1).

Windborne Debris Region

Coastal region defined by the Building Code, verify with your local building code official if applicable to your project.

  Note:

If applicable, see option for “All ext. doors, windows, skylights, etc.”

All Exterior Doors, Windows, etc.

If project is located in a Windborne Debris Region, building shall be designed as a Partially Exposed structure unless this radio button is activated.  Checking this box indicates that doors and windows meet the design code criteria to still be considered Enclosed.

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.

Samples:

1) Specify a floor elevation change between building shapes.

2) A penthouse that is on top of a building.

3) The building or shape actually sits on a concrete wall.  Example is a truck dock terminal where ground elevation is several feet lower than the base of columns (finish floor).

  Note:

This is not the actual (nor the nominal 100'-0'') elevation from sea level.  This Building Base Elevation dimension is commonly or normally thought of as 0'-0''.

Topographic Factor

A topographic factor (Kzt) is a wind load related coefficient, used with IBC or other standards where wind loads are calculated in accordance with ASCE 7.

This coefficient will increase the design wind loads (basic wind pressure) for the localized, job-site topographic features, such as isolated hills, escarpments or ridges, in cases where local terrain configuration may cause 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.

This effect must be included for rare cases only, where all five requirements listed below (Section 6.5.7 of ASCE 7) 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. 6-4 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 Figure 6-4 in the ASCE 7-05 Standard.  In all other cases the value of Kzt coefficient is unity (1.0).

Step Height

This edit box is intended for use by Joint Ventures only.

Regional Information:

Typhoon

This edit box is intended for use by Joint Ventures only.

Normal

This edit box is intended for use by Joint Ventures only.

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