Steel structure for digital billboard on 120 year old wood balloon-framed building 2

[enginerding]

I have a client who wants to support the steel structure for a digital billboard on the roof of an old wood balloon-framed building. There is currently a billboard on the roof, but this new structure will weigh much more.

What are your thoughts about supporting a heavy steel structure on wood framing?

I know that the codes speak very specifically against supporting masonry on wood for fire considerations, but I am not familiar with anything that addresses steel supported by wood.

 

[SteelPE]

While I have some weird phobia against it, there is nothing I have ever seen that says steel can't be supported by wood.

Now, from doing a bunch of solar panel renovations, I find it very hard to believe that you are going to support a large billboard on top of an existing wood structure with out some major modifications. Would it be possible to have the billboard frame independently from the existing structure?

 

[msquared48]

Aside from the vertical forces, resisting the lateral forces would be a big concern to me, especially the existing wood roof diaphragm.

Just inspected an old two story structure a month ago with a amall triangular steel antenna structure on top. The north side of the diaphragm had separated from the north brick wall, apparently in the Nisqually quake of 2001. The structure was added before that, and the roof never reinforced for it. Now they have problems.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[Ron]

The tail will wag the dog in this case...be careful and analyze conservatively.

 

[enginerding]

Thanks guys. I apparently have the same weird phobia. Supporting the thing independently was my original recommendation.

I completely agree with the lateral load issues too - even in the walls. The client is telling me it shouldn't be an issue since the existing billboard has been there for 50 years. So they say we are not adding any lateral loads. And they would be right. But my gut still is not satisfied on this issue yet...

 

[woodman88]

There are probability locations on the building that a sign would have a minimal cost to upgrade the structure. Not that any of these locations would be where they want to place the billboard. But you may offer to calculate these locations, for a fee, for their review.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[MiketheEngineer]

Ask the client where he got his engineering degree?? off a match book??

 

[shobroco]

Unlike masonry, our code has no prohibition against supporting steel on wood other than meeting the structural requirements. It should be fairly straightforward to analyze it and decide if it is reasonable or not; my gut feeling like everyone else's is that a billboard ain't gonna cut it.

 

[msquared48]

On the contrary, the billboard WILL cut it...

... the wood that is...

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com