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[Jim Warne <jwarne(--nospam--at)shaw.ca>]

Re: "Unbraced Top Chord" Pedestrian Bridge Design Reference:

There were lots of good responses, yesterday, to Ken Peoples' query regarding "...through truss without top chord bracing."

A reference that I've used, that looks pretty good is: the AASHTO "Guideline for design of Pedestrian Bridges." Published in 1997, the ISBN Number is 1-56051-044-7.

Clause 1.3.6 under "Design Details" Says that vertical truss members and the floorbeams and their connections in half - through truss spanbs shall be proportioned to resist a lateral force applied at the top of the truss verticles that is not less than 0.01/K times the average design compressive force in the two adjacent top chord members . . ."

That sounds pretty close to the 2% rule that was mentioned by Matthew Stuart.

There are other things to check and evaluate, of course, so you should find a copy of the complete spec. It may be at your library, but it's only $20 ($32 for us Canadians) from AASTO. I think it includes shipping, for most of us. Try 1-800-525-5562, or www.transportation.org

It's a real good spec, with a commentary and design examples. One illustrated design example is for a "Half-Through Truss bridge with Tubular Members. Appendix "A" tabulates 1/K values for values of CI/Pc and n (whatever they are) for half-trusses.

The commentary on clause 1.3.6 refers to the work by "Holt and others," and to "T.V. Galambos' Guide to Stability Design Criteria for Metal Structures."

Give it a try.

Condensing his query, Ken had asked:

"Can any of you recommend a reference for the design of a through-truss  without top chord bracing? "
Ken

Kenneth S. Peoples, P. E.