ASD Load Combinations - IBC 2015 1

[Tim_B]

IBC 2015, chapter 16, section 1602, under "Notations" the code defines "L" as "Roof live load greater than 20 psf and floor live load". It defines "Lr" as "Roof live load of 20 psf or less". How do you interpret "L"? If I have a roof live load of Lr=25 psf am I to treat all 25 psf as "L" since it is greater than 20psf? Or, am I to only treat the 5 psf above the 20 psf threshold as "L" and still have an "Lr" of 20psf?

Let me know if this question doesn't make sense. Thanks!

 

[JAE]

The types of roof live loads that are more than 20 psf are shown in Table 1607.1. These typically are occupiable roofs such as roofs with decks, assembly areas, roof gardens, etc.

When the roof live load then gets higher than 20 psf, the code assumes that this is now really just a "plain" live load...so all of it would be an L load.
If the load is 20 psf or less, then you would have an Lr load for the combinations.

You wouldn't split the load into a 20 and a 5 psf per your example above.




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