Pedestrian Bridge Design
Pedestrian Bridge Design
(OP)
I am designing a pedestrian bridge (only 30 ft span but over a small creek) and I have initially designed it with ASD since its timber. But in doing some more research it appears that the bridge code makes you use LRFD (since 07) even for timber.
This is behind a proposed apartment complex in the woods but will provide access to a greenway at some point. Currently using 100psf for LL, also a 4000lb vehicle, and 1000lb (over 2.5ftx2.5ft area) for deck loading.
But I guess the main question is what governs. Also its 6ft wide. Main members are treated V4 1.7E 5.125x20.625 glulams (three of them). Planning to meet building code railing and ADA ramp requirements on approach. Interesting the bridge code uses a 6 inch sphere still for railing openings while building code uses 4 inch sphere.
This is behind a proposed apartment complex in the woods but will provide access to a greenway at some point. Currently using 100psf for LL, also a 4000lb vehicle, and 1000lb (over 2.5ftx2.5ft area) for deck loading.
But I guess the main question is what governs. Also its 6ft wide. Main members are treated V4 1.7E 5.125x20.625 glulams (three of them). Planning to meet building code railing and ADA ramp requirements on approach. Interesting the bridge code uses a 6 inch sphere still for railing openings while building code uses 4 inch sphere.






RE: Pedestrian Bridge Design
Otherwise I'm not sure your question. I would bet the wheel load for the vehicle (or the 1000lb) will govern the decking design. For the other members, we'd need to know more of the framing plan in order to comment further.
RE: Pedestrian Bridge Design
RE: Pedestrian Bridge Design
It really boils down to what jurisdiction will be approving the design (if any), and what they want to see.
Even if the plan reviewer or project specs nominally call for an LRFD design, a reasonable person would possibly still accept an ASD equivalent. As Jayrod points out, you should end up with the same physical bridge in the end. Your luck finding a reasonable reviewer may vary though.
RE: Pedestrian Bridge Design
South of the border however, I believe you are required to submit calculations, therefore I would say yes you likely would have to. There are some slight nuances that may result in slightly different sizing but if you were conservative enough with your design I can't see anything changing drastically.
RE: Pedestrian Bridge Design
RE: Pedestrian Bridge Design
Its funny-the contractor who hired me wants "a simple wood bridge". That's an oxymoron.
RE: Pedestrian Bridge Design
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.
RE: Pedestrian Bridge Design
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.
RE: Pedestrian Bridge Design
I am actually quite interested in pedestrian bridge design after my unfortunate experience with a previous renovation project that went south. Is the AASHTO Pedestrian Bridge Guide the definitive (best) reference? Where should one start to get more education on the subject?
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Pedestrian Bridge Design
RE: Pedestrian Bridge Design
Regarding the glulam widths: the 1/2-widths are unfinished, i.e., suitable for conditions where the member is hidden by finishes (or the rough look is desired), whereas the 1/4-widths are finished. It is recommended to check with local suppliers to determine the availability of both "flavors", but I would suggest using the 1/4-widths for design. Then it is usually not a big deal if the contractor asks if he can substitute for the larger member.