Live Load Reduction Roof

The commentary in asce 7 05 c4 about roof live load reductions explains the anticipated difference in use of roof areas vs.

Live load reduction roof.

For uses other than storage where approved additional live load reductions shall be permitted where shown by the registered design professional that a rational approach has been used and that such reductions are warranted. One for the tributary area supported by the structural element r 1 and the other for the slope of the roof surface r 2. The live load on a roof is the weight of any temporary objects on the roof. R 1 1 for a t less than or equal to 200 psf r 1 1 2 0 001 a t for between 200 psf and 600 psf.

The reduction formula has two reduction terms. In some building codes the live load reduction is a function of the number of stories carried by a member or is dependent on whether the load is coming from a single level or from more than one level. The live loads for members supporting two or more floors are permitted to be reduced by a maximum of 20 percent but the live load shall not be less than l as calculated in section 1607 10 1. Where l r shall not be less than 12 psf and not more than 20 psf.

If the roof design load is 20psf and you are considering the compression in a web member that is located near the mid span than i would not use live load reduction for the compression in that member. Where uniform roof live loads are reduced to less than 20 psf 0 96 kn m 2 in accordance with section 1607 13 2 1 and are applied to the design of structural members arranged so as to create continuity the reduced roof live load shall be applied to adjacent spans or to alternate spans whichever produces the most unfavorable load effect. Live load reduction is a reduction in live load that contributes to the actions on a member. L r l o r 1 r 2.

Roof live load reduction. Where snow isn t a problem the live load can come from people working on the roof and any equipment they take on to the.