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- Jerry Grana - Chicago, IL
- Jerry Grana - Chicago, IL
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A Discussion of Snow and Rain Loads on Steel Buildings
Any discussion of steel buildings, especially in the northern climates, requires a full understanding of snow and rain loads and their applications.
Design Snow Load is a number that portrays the maximum probable weight of snow that can be present on a roof at a given time. The expression of live load is very dependant on building on building occupancy, but snow load correlates specifically to location on the building. The design snow load number is impacted by the given ground snow quantity in any area. There are certain coefficients applied a given ground
Design Snow Load is a number that portrays the maximum probable weight of snow that can be present on a roof at a given time. The expression of live load is very dependant on building on building occupancy, but snow load correlates specifically to location on the building. The design snow load number is impacted by the given ground snow quantity in any area. There are certain coefficients applied a given ground
snow number to engineer a specific steel structure to achieve its correct design snow load. These factors include flat roof snow load, the ground snow load number, and thermal and exposure indications. Factors are then adjusted for higher pitches of roofs.
Generally, the roof snow load number will be less than the ground snow load number because there is some snow removed from any roof by the actions of wind and melting. Other weather related circumstances that occur such as snow sliding and snow drift have to be accounted for if they are applicable. Snow will slide down a pitched roof and gather on a lower roof, thus increasing the snow load on the lower roof. Snow drifts can accumulate against building walls and parapets. Additional snow load needs to be factored into this scenario by taking total roof square footage and wall and parapet heights into account. For example, some of the snow load calculations for a flat roof abutting a building wall towered over by a higher roof that is steeply pitched and adds sliding snow to the lower roof can be four times the amount of the snow load for the pitched roof.
There is also need to be aware of, for design considerations, the factor of unbalanced snow on gabled or hip roofs. Specific calculations for the correct loading of this design are a result of the building area, roof pitch, and the flat and pitched roof snow loading numbers applied to a very complicated formula.
Another term to consider when discussing snow load is that of partial loading . Partial loading is, in general, specified in the design of structural supports such as purlins or frames that use multi-span rather than clear-span construction. Some spans of the building, then, have less of a level of snow load applied while others are at a maximum level. Engineering for this type of snow load balancing needs to be scrupulous.
Rain-on-snow and rain loads have also been reintroduced into the calculations for proper roof loading. This is important because in some areas of the country a snow storm can quickly change to rain - thus, the rain on snow load. If the pitch on the roof is negligible the water cannot drain away readily and it is absorbed by the existing snow. Exaggerated roof pitches or more structural support are the answers to this heavier load. Rain load is the weight of the water on a roof that can exist due to the drainage system being compromised. Quick rain water flow off of a roof guarantees the entire structure's integrity. The popularity of exterior gutters, rather than interior drains is a remedy for potential roof failure due to water weight.
Generally, the roof snow load number will be less than the ground snow load number because there is some snow removed from any roof by the actions of wind and melting. Other weather related circumstances that occur such as snow sliding and snow drift have to be accounted for if they are applicable. Snow will slide down a pitched roof and gather on a lower roof, thus increasing the snow load on the lower roof. Snow drifts can accumulate against building walls and parapets. Additional snow load needs to be factored into this scenario by taking total roof square footage and wall and parapet heights into account. For example, some of the snow load calculations for a flat roof abutting a building wall towered over by a higher roof that is steeply pitched and adds sliding snow to the lower roof can be four times the amount of the snow load for the pitched roof.
There is also need to be aware of, for design considerations, the factor of unbalanced snow on gabled or hip roofs. Specific calculations for the correct loading of this design are a result of the building area, roof pitch, and the flat and pitched roof snow loading numbers applied to a very complicated formula.
Another term to consider when discussing snow load is that of partial loading . Partial loading is, in general, specified in the design of structural supports such as purlins or frames that use multi-span rather than clear-span construction. Some spans of the building, then, have less of a level of snow load applied while others are at a maximum level. Engineering for this type of snow load balancing needs to be scrupulous.
Rain-on-snow and rain loads have also been reintroduced into the calculations for proper roof loading. This is important because in some areas of the country a snow storm can quickly change to rain - thus, the rain on snow load. If the pitch on the roof is negligible the water cannot drain away readily and it is absorbed by the existing snow. Exaggerated roof pitches or more structural support are the answers to this heavier load. Rain load is the weight of the water on a roof that can exist due to the drainage system being compromised. Quick rain water flow off of a roof guarantees the entire structure's integrity. The popularity of exterior gutters, rather than interior drains is a remedy for potential roof failure due to water weight.