Sign Wind Importance Factor

[SteelPE]

I am working on a project for a client that requires me to design a sign in front of his building. The sign will be freestanding. The sign is to be designed in accordance with IBC 2009 and ASCE 7-05 (V=100mph). I am wondering what importance factor you would use with the design of the sign? This type of structure seems like something that you would use I=0.87 in accordance with table 6-1.

 

[azcats]

I typically use 0.87 for our sign structures. I know other engineers that use 1.0 because 'what if it fails and a lawyer looks at the calcs'.

Although with Risk Category base wind speeds in ASCE 7-10, I see more and more municipalities kicking back my stuff looking for the Risk Category II based wind speeds. They don't even understand the risk categories. Well they didn't understand importance factors either - but those were buried in the calcs and they quit looking when they saw the wind speed they needed.

Why do you have 100 mph winds?

 

[SteelPE]

I'm on the east coast.

I currently have I set to 1.0 but the owner has some existing tubes he would like to use for this sign and they are 14% overstressed in my initial calculations. I told the owner to reduce the height of the sign by a foot and raise the foundations by a 1 and we should be all set, but we are so close.

100mph is required by the building code, I'm on the east coast.

 

[EngineeringEric]

2009 IBC Still really? I typically have always used 1.0 for my signs, but they have always been near buildings and have been new construction.

Depending on sizes, the new ASCE7-10 usually produces some smaller wind loads... minor difference, but a little something?

 

[steellion]

If not in a heavily-trafficked area and/or 20 feet tall, I think you could justify Risk Category I for your sign. I'd rather go with what is there than play around with reinforcing footings if not needed. Does it "represent a low risk to human life in the event of failure"?

 

[SteelPE]

steellion

It is next to a heavily traveled road.

I'm not sure I conveyed the situation correctly. The sign is completely new using some old steel columns the owner has in storage. So, I told him that if he wanted to use the columns then he needed to reduce the height of the sign. I am just wondering if using I=1.0 is too conservative and if I actually should have used I=0.87.

Of course, the owner thinks whatever I need to do is overkill, but I'm willing to entertain the idea of reducing the loads slightly if needed.

 

[Lomarandil]

I would use I=1.0

I had a similar circumstance (rebar cage next to heavily traveled road) that led me to decide that I=0.87 wasn't appropriate due to the risk to human life (even if not the sign/cage falling itself, the likelyhood of an auto accident afterward). I would however seriously consider using 0.87 for a rebar cage in the middle of a field.