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(OP)
I am checking the design of a temporary roof structure and am having trouble getting the design to perform against uplift.  I have problems in both the capacity of my connections as well as simply not having enough dead load to resist the applied uplift forces.

I believe I will be able to make the numbers work by going to a shorter MRI and possibly a lower importance factor based on the fact that this is a short term installation (covered deck for a construction office trailer), however I get completely blown out of the water when I consider the load combination of 0.6D + W.

My question is this:  Is it necessary to apply the 0.6 factor to my dead load when my only DL is the self weight of the structure?  I can understand taking a reduction in DL if I had a higher degree of uncertainty in my loads (such as superimposed dead loads) but in this case I have a high level of confidence in my dead load as I am only considering the self weight of the actual structure.  Is there any case when it would not be necessary to consider the 0.6 reduction factor?

No - the 0.6 factor is not ONLY to account for uncertainty in the amount of dead load, but also to provide an inherent factor of safety against uplift and overturning.

No need for a Factor of Safety when using 0.6DL.  1.0 is sufficient, resistance/applied load.

(OP)
Thanks all, that is kind of what I was thinking as well, and I appreciate the lesson in the legacy codes, it's a little easier to swallow knowing the how the load combinations were developed.

I agree with your comment WillisV on the unintended consequences of this load combination, seems that it is appropriate to use 0.6D + W when considering overall stability of the structure but for individual members/connections this would introduce an over-conservative design by effectively doubling up on the factor of safety as the various material specifications already include a F.S.

To further illustrate this, consider section 2.4.4 of ASCE 7-95 that WillisV refers to - this section required a 1.5 F.S. (2/3 DL) for checking structures for sliding or overturning unless the structure was anchored to resist excess movement.  Presumably this exception considered that the anchor would be designed with a factor of safety and that it was unnecessary to double up.

I think ASCE 7-95 and its associated 1.5 overturning safety factor was out before the 0.6D+W combination occurred in the codes.  The 1.5 SF was replaced by the 0.6D+W combination.

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