overhead sign support angle top and bottom chord

[delagina]

i design pipebridge (not an actual bridge see pic attached) from time to time and in all cases i had to use wide flange beam for bottom and top chord because of bending.

i'm confused because i see these sign supports all the time in freeway some even around 100' and angles are working fine.

can someone link me the analysis of these supports. are the bottom and top chord assumed as axial only because i cant see these angles passing if it were to take bending.

 

[hokie66]

Did you paint them? All the ones I have done have been hot dipped.

 

[KootK]

Can this be analyze as one built up shape basically just one member?

Yes. That's essentaially what a truss model is, with some shear flexibility thrown in, right?

should it be modeled as continuous beam, shear connection at the ends?

That is what I would do for physically continuous chords. Hopefully the shear stiffness of the truss is high enough that it wouldn't matter much either way.

I believe that sign structures are allowed to be designed rather aggressively with regard to their flexibility. Perhaps that accounts for some of the difference. Locally, we've had some issues with resonant vibration.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[hokie66]

Amazing that folks continued to drive under that dancing sign. And then, one fell off. Looks like they used a lighter section for the horizontal than for the vertical. The advantage for this type support is that, as chicopee said, they are simple to make, and they are also simple to erect. But it is not wise to skimp on the size of tube selected. I hadn't previously considered resonance as a problem, similar to what has been experienced with footbridges.

 

[KootK]

It seems to have been a one off affair. We've got zillions of the things and the rest have been performing admirably to my knowledge.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.