Firstly, thanks to everyone who corroborated the opinion that I expressed at the top. And thanks to those who expressed dissenting opinions as well. Those are required for meaningful discourse.
bisandcan said:
koot,In the design that was in discussion, it was simple 3' wide elevated walkways with no equipment or other loads on the beams. I used a HSS3x2 tube, and was told that I was crazy and needed to use a 5" tube, no matter what the deflections were, they came up to be L/1347 for LL deflection. There are several of these platforms on the site and would you really double your steel weight to control deflections more than L/1347?
While I still don't feel that I understand your situation well enough to comment with any certainty, I
would be inclined to question your choice of stringer size. I'm imagining your walkway to be HSS stringers with something like bar grate spanning in between. Things that might concern me include:
1) I sketched this system to scale and do find that the proportions draw the eye.
2) If this is an elevated walkway, will there be handrail mounted to the stringers?
3) If it would take 5" to satisfy L/24, that implies that 3" is around L/40. This could put you in vibration issue territory for footfall traffic. If you get three big guys walking along in lockstep on your 1.5ft trib structure, there might be some bounce. I'm feeling industrial structure here, however, so it may well be that nobody would care.
4) It's actually the members with small tributary areas that I often worry about. They will be more susceptible to problems related to unanticipated point loads than members supporting larger tributary areas. Could you end up with shoveled snow piled up somewhere along the walkway? Might a moose attempt to use it as a thoroughfare and leave the thing demolished? Will vehicle be running into the walkways?
5) Given your slenderness, could you get wind induced resonance as wind passes above and below your walkways? I know that sounds pretty extreme. That said, I'm sure that the guy who designed this keeps a tight on things now:
Link. Be sure to watch the video.
6) If this is an industrial application, those folks tend to prefer spending a few extra dollar rather than deal with problems later.
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.