Allowable Foot Bridge Deflection 1

[Atops]

Hello Everyone,

My company recently designed and built a stainless Footbridge/gangway for the NY Department of Environmental Protection. We have Signed & Stamped calculations showing that over a 65' span the max deflection is 4.25". This was originally approved by the project engineer at the DEP, except now they are saying that the deflection is too much. Is there a bridge standard that I can show them that this deflection is within acceptable parameters? Preferably with another NY agency or the state. I haven't found anything as of yet, & this bridge seems a bit small to apply ASSHTO standards.

Thanks!

 

[TDIengineer]

@ a2mfk--
I have also seen the handrail used as a truss element to stiffen the walkway..

However, I caution this approach for any walkway that has people walking side by side. Not sure if you saw the footage of the footbridge that collapsed (I think in China) that was overloaded. When I watched the video... it appears that the top chord of the truss buckled outward, and it had a sudden failure. Possibly from the combination of vertical load plus outward hand rail load (albeit not 200#, but something significant).

So, my point being, make sure your handrail has very little deflection from out of plane loads if you're using it as a compression member in a truss!!

Buckling = BAD.

 

[msquared48]

That gets into bracing the top of the handrail with outrigger struts to the transverse walkway beams.

You know, I've been resisting the impulse for four days now, and feel I've done pretty good, but I have to capitulate here... The answer to the OP's question lies in the name of the bridge. It's a foot bridge, so the maximum deflection allowed due for the load of a foot, is a foot. It's just that simple... It's also Friday.

Mike McCann
MMC Engineering

 

[a2mfk]

Good point TDI, you sure had better add in the lateral handrail load and consider all the forces in designing that truss.

 

[Lion06]

I'm with mijowe and StructSU10 - I have a hard time believing that this checks out for vibrations per AISC DG #11.