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RE: spreading wheel load on a single span slab next to isolation joint.

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Scott,
 
The AASHTO Standard Specifications for Highway Bridges does provide for a distribution width as you described.  But a few articles later, it also says,
 
Edges beams shall be provided for all slabs having main reinforcement parrallel to traffic.
 
and
 
The design assumptions of this article do not provide for the effect of loads near unsupported edges.  Therefore, at the ends of bridges and at intermediate points where the continuity of the slab is broken, the edges shall be supported by diaphragms or other suitable means.  The diaphragms shall be designed to resist the full moment and shear produced by the wheel loads which can come on them.
 
FWIW, that is the "old" LDF code.  The distribution for the current code (LRFD) is of course different.
 
HTH,
 
David Finley
M. David Finley, P.E., P.A.
2086 SW Main Boulevard - Suite 111
Lake City, FL  32025
386-752-6400
-----Original Message-----
From: Haan, Scott M POA [mailto:Scott.M.Haan(--nospam--at)poa02.usace.army.mil]
Sent: Tuesday, August 08, 2006 4:04 PM
To: seaint(--nospam--at)seaint.org
Subject: spreading wheel load on a single span slab next to isolation joint.

I have to respond to a question by a contractor's engineer whom is reviewing someone else's work.  The question is about a removable lid spanning over a utilidor under a road having adequate reinforcement.
 
I found in a text book where it said AASHTO allows you to spread a wheel load out perpendicular to a slab span the lesser of 7' or 4+.06*SPAN.  Does this apply even when a wheel load occurs directly adjacent to an isolation joint in a slab?  The slab in question works if you can spread the wheel load over this distance.