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RE: Steel Bar Joists as Bridge Beams

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Be careful with what you think KCS joists can do!  All concentrated
loads must still occur at panel points.  Therefore, if the location of
the concentrated load can vary (as for moving loads) the "constant
shear" is meaningless.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Michael Valley, P.E., S.E.                   E-mail: mtv(--nospam--at)skilling.com
Skilling Ward Magnusson Barkshire Inc.              Tel:(206)292-1200
1301 Fifth Ave, #3200,  Seattle  WA 98101-2699      Fax:        -1201

-----Original Message-----
From: Effland, Greg [mailto:geeffland(--nospam--at)butlermfg.com]
Sent: Tuesday, December 05, 2000 8:28 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: Steel Bar Joists as Bridge Beams


David,

One joist that might be of interest is the KCS series of bar joists.
These
joists are designed to allow a specific joist to handle a specific
shear
value at any point along the length of the joist.  This could be handy
in
dealing with moving loads such as on a bridge.  The KCS series should
be
available from any supplier that supplies SJI Joists.  Vulcraft, SMI
Joist,
and Canam Steel are 3 examples of suppliers.  These are available in
lengths
up to 60 ft long.  Typically the span should not exceed 24x the depth
of the
joist.  If you need longer than 60 ft you should look at LH or DLH
joists.
If you are unconfortable designing the joists from a table then most
suppliers will design the joists based upon loading diagrams supplied
by
yourself.

As far as cross-bridging I would use the SJI recommendations as
minimums and
possibly increase as desired since the bridge will have moving loads.

I would provide some sort of lateral bracing, such as rods, or
diaphragm
deck (using the bar joists as struts) and not count on the bar joists
for
lateral loads through weak-axis bending.

One thing you might consider is serviceability to keep the bridge from
bouncing as the truck moves over it.  The KCS joist table provides a
gross
moment of inertia that could be used for the deflection calcs.  Not
sure
what deflection and vibration limits apply to bridges though.

Not sure where you are located but here are a few contacts if you need
them.
If the locations are not close you could contact the manufacturer of
your
choice and obtain an address/phone for a closer location.

Vulcraft
PO Box 637
Brigham City, Utah 84302
(801) 734-9433

SMI Joist Company
Highway 32 North
PO Box 2000
Hope, Arkansas 71802
(501) 777-8777
(800) 643-1577

Canam Steel Corporation
2000 W. Main St.
Washington, MO 63090
(314) 239-6716
if for some reason the area code has changed on this one it might be
473.

Hope this helps,
Greg Effland, P.E.


-----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.