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Steel Bar Joists as Bridge Beams

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I've been contacted by a local builder who wants to build a bridge
connecting two pastures separated by a stream.  This will be a private
bridge - no government controlled loading criteria, but almost certainly the
water management district has jurisdiction.

The span is 40', single lane to accommodate a loaded pickup truck (builder
says use 7000# total live load).  Structure is 2 bar joists @ 7'-0" with 4 x
4 decking - total width of about 12 feet.

I have designed a number of bridges, but none using bar joists.  In fact,
I've never used bar joists for anything since I don't normally do buildings.

With that ignorance in mind, can bar joists be successfully used in such an
application?  I'm concerned about the wheel loads that occur directly over
the bar joist - there would be pretty good concentrated loads between panel
points.  Also, without a rigid diaphragm deck (concrete, for example), I
don't see any load sharing for lateral loads.  I can see the need for some
pretty significant cross-bridging.

I've already tried to talk the guy into using precast double tees or even a
proprietary arch culvert, but he is stuck on the bar joist idea.

Any comments, suggestions, ideas?

David Finley, P.E.