Loading

(Revised:  05/08/13)

The Loading screen describes the appropriate Building Code, Live Load, Wind Load, Snow Load, and Seismic Load for the Building.

„  Warning:

Compliance with a required 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. 

An order will not be processed with loading that is less than the MBMA Minimum County Loadings without written direction from the owner, unless allowed by Local code Requirements.

 

The system uses standard deflection criteria defined as below:

Building Code:

Building Code

This drop list is used to describe the Building Code for the building.  Information input at this level will be applied to all shapes within a project file.

If you do not know the correct Building Code, contact the local code officials or local code department.  This information is critical in the design of the building.

„  Note:

Depending on the Building Code selected, options on the other Design Loads and Codes fields will be enabled or disabled as required by the Code.

Building Use

This drop list is used to describe the general purpose of the building.  These options vary depending on the Building Code.

Live Load:

The Live Load defines design related information regarding the Building's Roof Live Loads.  The roof live load is a temporary load that must be applied to the entire roof area.  An example of roof Live load might be the weight of workers and equipment on the roof.  Live load is specified by the building code and the building specifications.  If these two documents differ, the higher value should be used unless clarification is requested and received from a Customer, or Engineer.

Depending on the Building Code, the Reducible Live Load option may be disabled if not permitted.  Some building codes will permit the Live load to be reduced for some design members.  The amount of reduction allowed depends on the tributary area that a member supports, and is automatically determined.

Additional Collateral Gravity and Collateral Uplift Loads can be added to the Building or Shape if required.

Live Load

In this edit box, enter the applicable Live Load for the State, County, and Local Codes; the maximum Live Load required for most US codes is 20 psf.

Reducible

This checkbox is enabled with most Building Codes.  It allows the design to reduce the Roof Live Load based on the Tributary Area.

The actual Tributary Load Area will be calculated and the appropriate reduction in the Live Load [considering the roof slope(s) and the Tributary Area] will be applied to all applicable structural members.

Collateral Load (Cg/Cu)

This edit box is used to apply additional collateral load for materials attached to the roof structure.  The collateral load is measured in Pounds per Square Foot and is applied to the entire footprint of the Building or Shape.

 

Collateral loads are additional dead loads, other than the weight of the building system itself, such as sprinklers, mechanical and electrical systems, and ceilings.  Collateral loads may be either uniformly distributed or concentrated loads, and may be present or planned for a future addition to the building.  Concentrated loads may be included in the uniformly applied Cg load magnitude providing these loads are ≤ 400 lbs. each.

Wind Load:

The Wind Load defines design related information regarding the Building's (or Shape's) Wind Load.  Wind causes pressures and suctions on wall and roof areas 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.

Wind Speed

This edit box is used to define the Wind Speed for the Building or Shape. 

Wind causes pressures and suctions on wall and roof areas 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.  Sometimes 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.

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 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.

„  Notes:

The Wind Enclosure must be set; the system will NOT determine this condition.

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

Hurricane Prone Region

This Check Box should be selected when the project is located in a Hurricane Prone Region.  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 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 “Impact Resistant Covering”

Impact Resistant Covering

If project is located in a Windborne Debris Region, building shall be designed as a Partially Enclosed structure unless this checkbox is selected to indicate that the covering, windows and doors meet criteria to be considered enclosed. 

 

Snow Load

The Snow Load defines design related information regarding the Building's (or Shape's) Roof Snow Loads.  This is the load induced by the weight of snow on the structure and may be expressed as Ground Snow, Roof Snow, or Both.  Snow load is not the same as live load, and requires a separate input to design the structure correctly.  Some building codes specify Ground Snow and define the snow load to be applied to the roof as a reduced percentage of the ground snow.  In many cases, especially in mountainous areas, it will be necessary to ask the local building department for the required roof or ground snow load.

„  Notes:

Snow Drifting/Sliding conditions are automatically recognized and added to the Building Shape's Load Cases.  Building input that will automatically generate Snow Drifting/Sliding loads are step conditions such as Below Eave Canopy conditions.

Ground Snow Load (Pg)

This edit box is used to define the Ground Snow Load for the Building or Shape.  This Load is measured in Pounds per Square Foot (English).  The Ground Snow Load data along with the Building Geometry will generate factors that convert this Load into the applied Roof Snow, Snow Drift or Sliding Snow Loads.  A non-negative value must be input in this field to be allowed to exit from the Loads and Codes dialog.  If the Local Code does not require snow load a value of zero can be input.

Specified Min. Roof Snow (SMS)

This edit box, when enabled by checking the box to the left of the description, is used to define a specified minimum roof snow load for the Building or Shape per the local Code Requirements.  This Load is measured in Pounds per Square Foot (English).  Values for the Specified Min. Roof Snow load and Ground snow may be different; however, the specified value is typically larger than the Calculated Sloped Roof Snow.  The loading defined in this edit box will only be combined with the dead and collateral gravity loads for the frame, purlin, and panel design; this load will not be combined with any other snow, wind, crane, or mezzanine loading.  This load cannot be entered if the ground snow load is 0 psf.

Exposure

If enabled, use this drop list to select the Snow Exposure options that describe the applicable surrounding terrain conditions that may impact the applied Snow Load.

The following defines the Snow Exposure options for each Building Code.

„  Warning:

The Snow Exposure options vary in descriptions for each Building Code.  Sample:  The description for ''All Other Structures'' for UBC, is Thermal Factor 3 and for NBC, it is Thermal Factor 1.

Snow Exposure Descriptions:

Thermal Factor

The Thermal Factor is used to adjust the applied Snow Load based on the relative climate and temperature of the Building.

Heated:                                         All structures except as indicated below.

Kept just above freezing:        Structures kept just above freezing and others with cold, ventilated roofs.

Unheated:                                    Unheated Structures.

Heated Greenhouse:                 Continuously heated greenhouses.

Surface Condition

This dropdown list defines whether you have an Unobstructed, Slippery Roof or an Obstructed or not Slippery roof. 

Unobstructed, Slippery             An unobstructed or slippery roof allows the free sliding of snow off the roof surface.  Unobstructed Slippery roof surfaces shall include metal, slate, glass, bituminous rubber and plastic membrane with smooth surfaces. 

Obstructed or Not Slippery      The Obstructed or Not Slippery option should be used for cases where movement of snow off the roof is restricted by the Non-slippery roof surfaces or objects located on or along the low eave.  The result may be a larger magnitude of system generated roof snow depending on conditions such as roof pitch and Thermal Factor.  Examples of Non-slippery roof surfaces are membrane roofs with embedded aggregate or mineral granules, asphalt shingles, wood shingles, and shakes.  Roof obstructions that qualify as “Obstructed” include, but are not limited to, roofs with Ice Damming, snow guards, Facades or Parapets along the low eave, and roof top units uniformly spread over the roof.

„  Note:

All BlueScope roofing systems satisfy the requirements of “slippery surfaces” per ASCE Section 7.4.

Metal buildings are typically not constructed with attics similar to those of residential structures, and therefore may be considered “Unobstructed” without consideration for the insulation R-Value used.

 

Rain Surcharge (RS)

This edit box defines the system generated weight of Rain that is required by the Code to be superimposed on the balanced roof snow.  This load is required for ground snow ≤ 20 psf when roof pitches are small in relationship to the width of the roof.  The Rain Surcharge (RS) value is measured in Pounds per Square Foot (English).

„  Note:

The Canadian codes require input of the Rain Surcharge field.  Values for this field can be found in the National Building Code of Canada 2005 Volume 2, Division B, Table C-2, Snow Load column Sr.

Seismic:

The Seismic Load defines related design information regarding the Building's Seismic Load.

The Seismic data defined will apply to the design of the Building's resistance to stress produced by earthquake loads.

Spectral Response Acceleration (Ss) – IBC

Ss is a coefficient used to calculate the effect of the Maximum considered earthquake ground motion for the given geographical location.  It corresponds to the expected ground acceleration at the short period (0.2 sec.) with 5% critical damping included.  The Ss coefficient is commonly shown as a percentage of the ground acceleration (e.g., 47%g).  It is based on 2 percent probability of exceedance within a 50-year period.

Spectral Response Acceleration (S1) – IBC

S1 is a coefficient used to calculate the effect of the Maximum considered earthquake ground motion for the given geographical location.  It corresponds to the expected ground acceleration at the 1-second period with 5% critical damping included.

The S1 coefficient is commonly shown as a percentage of the ground acceleration (e.g., 24%g).  It is based on 2 percent probability of exceedance within a 50-year period.

Damped Spectral Response Acceleration [ Sa(T) ] – 2005 National Building Code of Canada (NBC)

Sa(T) = 5% damped spectral response acceleration, expressed as a ratio of gravitational acceleration for a period of T, as defined in sentence 4.1.8.4(1).  Sa(0.2), Sa(0.5), Sa(1.0) and Sa(2.0) are values that come directly from the Canadian Building Codes for a given location.

„  Notes:

In some areas of higher seismic susceptibility, the magnitude of this coefficient may change significantly within a short distance.  Therefore, one should use prudence when relying on the zip code since the zip code areas may be large or even discontinuous.

„  Notes:

There are several possible sources for this required input, Ss and S1, shown in the order of preference:

Local building department official.

Local or state building code (several states list county-specific minimum coefficients).

USGS web site – allows precise determination of the required parameters for 48 lower states based on:

    See < USGS Help Screen > explaining the use of the Seismic Calculator found on the USGS web site.

Acceleration (Av)

Av is a coefficient representing the effective peak velocity-related acceleration which is used to calculate the prescribed seismic forces for the given geographical location.  It is based upon a 90% chance of not being exceeded in a 50-year mean recurrence interval.

The Av coefficient is commonly shown as a rational number with minimum value of 0.0 (zero) and maximum value of 0.4.

Acceleration (Aa)

Aa is a coefficient representing the effective peak acceleration which is used to calculate the prescribed seismic forces for the given geographical location.  It is based upon a 90% chance of not being exceeded in a 50-year mean recurrence interval.

The Aa coefficient is commonly shown as a rational number with minimum value of 0.0 (zero) and maximum value of 0.4.

„  Notes:

There are several possible sources for these parameters, shown in the order of preference:

Local building department official.

Local or state building code (several states list county-specific minimum coefficients).

Seismic maps included in the seismic section of the relevant Building Code or seismic maps included with 1991 and 1994 edition of the NEHRP Recommendations.

Seismic Zone

From this drop list, select the Seismic Zone Code that is specified by the regional Building Code.

This option is enabled when the Building Code requires it.

Seismic Zone Descriptions:

Typical           UBC

Zone 0           Zone 1           Lowest probability of damaging seismic conditions.

Zone 1           Zone 2a         Relatively low probability of damaging seismic conditions.

Zone 2           Zone 2b         Greater probability of damaging seismic conditions.

Zone 3           Zone 3           Much greater probability of damaging seismic conditions.

Zone 4           Zone 4           Highest probability of damaging seismic conditions.

Zone NA        Zone NA        Not Applicable.

„  Notes:

Consult your Building Code Map for these values.

If the Seismic Zone is greater than 1, the Building (or Shape) will be designed to resist a minimum total lateral seismic force.

The Collateral Load is automatically included with the Gravity Loads in all Seismic calculations.  A percentage of the Snow Load is also included if required by the Building Code and snow conditions

Hazard Group

From this drop list, select the Seismic Zone Hazard Group that is specified by the regional Building Code.  This option is enabled when the Building Code requires it.

Hazard Group Descriptions
Only applicable for the following currently available Building Codes:

 

1999 SBC:

Seismic Hazard Exposure Group 1:  All buildings except those listed below.

Seismic Hazard Exposure Group 2:  Buildings which have a substantial public hazard due to occupancy or use, including buildings containing any one or more of the indicated uses.

1.)     Group A in which more than 300 people congregate in one area.

2.)     Group E with an occupant load greater than 250.

3.)     Group B used for college or adult education with an occupant load greater than 500.

4.)     Group I-Unrestrained with an occupant load greater than 50, not having surgery or emergency treatment facilities.

5.)     Group I-Restrained

6.)     Power generating stations and other public utility facilities not included in Seismic Hazard Exposure Group 3.

7.)     Any other occupancy with an occupant load greater than 5000.

Seismic Hazard Exposure Group 3:  Essential facilities which are required for post-earthquake recovery, including buildings containing any one or more of the indicated uses.

1.)     Fire or rescue and police stations.

2.)     Group I-Unrestrained having surgery or emergency treatment facilities.

3.)     Earthquake emergency preparedness centers.

4.)     Post-earthquake recovery vehicle garages.

5.)     Power-generating stations and other utilities required as emergency back-up facilities.

6.)     Primary communication facilities.

7.)     Highly toxic materials as defined by 308.2.1 as H4 occupancy where the quantity of the material exceeds the exempt amounts of Table 308.2D.

 

1999 BOCA:

Seismic Hazard Exposure Group 1:  All occupancies except those listed below.

Seismic Hazard Exposure Group 2:  Buildings which have a substantial public hazard due to occupancy or use, including buildings containing any one or more of the indicated occupancies.

1.)     Use Group A in which more than 300 people congregate in one area.

2.)     Use Group E with an occupant load greater than 250.

3.)     Use Group B used for college or adult education with an occupant load greater than 500.

4.)     Use Group I-2 with an occupant load greater than 50, not having surgery or emergency treatment facilities.

5.)     Group I-3.

6.)     Power generating stations and other public utility facilities not included in Seismic Hazard Exposure Group 3.

7.)     Any other occupancy with an occupant load greater than 5000.

Seismic Hazard Exposure Group 3:  Buildings having essential facilities which are required for post-earthquake recovery, including buildings containing any one or more of the indicated occupancies.

1.)     Fire, rescue and police stations.

2.)     Use Group I-2 having surgery or emergency treatment facilities.

3.)     Emergency preparedness centers.

4.)     Post-earthquake recovery vehicle garages.

5.)     Power-generating stations and other utilities required as emergency backup facilities.

6.)     Primary communication facilities.

7.)     Highly toxic materials as defined by 307.0 where the quantity of the material exceeds the exempt amounts of Section 307.8.

 

MAST(6th):

Seismic Hazard Exposure Group 1:  All occupancies except those listed below.

Seismic Hazard Exposure Group 2:  Buildings are those, which have a substantial public hazard due to occupancy or use, including buildings containing any one or more of the indicated occupancies:

1.)     Use Group A in which more than 300 people congregate in one room.

2.)     Use Group E with an occupant load greater than 250.

3.)     Use Group B used for college or adult education with an occupant load greater than 500.

4.)     Use Group I-2 with an occupant load greater than 50, not having surgery or emergency treatment facilities.

5.)     Use Group I-3.

6.)     Power generating stations and other public utility facilities not included in Seismic Hazard Exposure Group 3.

7.)     Any other occupancy with an occupant load greater than 5000.

Seismic Hazard Exposure Group 3:  Buildings are those having essential facilities, which are required for post-earthquake recovery, including buildings containing any one or more of the indicated occupancies:

1.)     Fire or rescue and police stations.

2.)     Use Group I-2 having surgery or emergency treatment facilities.

3.)     Emergency preparedness centers.

4.)     Post-earthquake recovery vehicle garages.

5.)     Power-generating stations and other utilities required as emergency back-up facilities.

6.)     Primary Communication facilities.

7.)     Highly toxic materials as defined by 780 CMR 307.0 where the quantity of the material exceeds the exempt amounts of 780 CMR 307.8.