ReverenceEng
Structural
- Feb 18, 2016
- 81
I have a similar post just before this, but it's fundamentally a different question.
Per Chapter 29 of ASCE, we have Case B for freestanding signs that calls for a 0.2B offset, which generally makes sense since it will add some torsion to a pole sign with one pole, for example, or at least require a little "beefing up" of the support system. But I have always struggled with the application for the design of two poles. The chapter doesn't seem to make specific mention of it, but the offset on a flexible sign face will usually throw 70%-90% of the total load to one of the two poles depending on pole spacing relative to the sign width. This seems a little unnecessary and unrealistic.
Now, there are some reductions for enclosed signs with the Rmin and Rmax factors, but those apply to single pole signs too (because the chapter is blind to the number of poles)...so in the case of two poles...it doesn't really do much.
In the commentary, it specifically states how, for enclosed signs, this 0.2B is overly conservative. It makes the 0.2B seem antiquated.
So, is there a way around applying 0.2B for structures with two-poles or some way to mitigate having to design each of two poles for 70%-90% of the total load?
I've been applying the Case B offset for years...but I can't wrap my head around how the Commentary basically says "yea, this is overly conservative and not supported by current modeling, we know"...and yet we are still using it.
Thoughts?
Per Chapter 29 of ASCE, we have Case B for freestanding signs that calls for a 0.2B offset, which generally makes sense since it will add some torsion to a pole sign with one pole, for example, or at least require a little "beefing up" of the support system. But I have always struggled with the application for the design of two poles. The chapter doesn't seem to make specific mention of it, but the offset on a flexible sign face will usually throw 70%-90% of the total load to one of the two poles depending on pole spacing relative to the sign width. This seems a little unnecessary and unrealistic.
Now, there are some reductions for enclosed signs with the Rmin and Rmax factors, but those apply to single pole signs too (because the chapter is blind to the number of poles)...so in the case of two poles...it doesn't really do much.
In the commentary, it specifically states how, for enclosed signs, this 0.2B is overly conservative. It makes the 0.2B seem antiquated.
So, is there a way around applying 0.2B for structures with two-poles or some way to mitigate having to design each of two poles for 70%-90% of the total load?
I've been applying the Case B offset for years...but I can't wrap my head around how the Commentary basically says "yea, this is overly conservative and not supported by current modeling, we know"...and yet we are still using it.
Thoughts?