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Re:Steel Bar Joists as Bridge Beams

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David:

I'd be wary of using bar joists if there is any danger that the bridge could
be overtopped by flood waters accompanied by logs or other flood borne
debris which might very possibly seriously  damage the relatively light
bottom chord and web members.

At the very least, I'd recommend  a horizontal bracing truss in the plane of
the bottom chords.

Frank Hartzell
frank.hartzell(--nospam--at)jacobs.com

>  -----Original Message-----
>  From: PEC - Lake City [mailto:pec(--nospam--at)isgroup.net]
>  Sent: Monday, December 04, 2000 2:06 PM
>  To: Seaint
>  Subject: Steel Bar Joists as Bridge Beams
>  
>  
>  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.





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