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RE: CALTran Loading combination

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Fire truck loading will be significantly higher than HS-20.  The normal fire
truck axle and wheel loading will be within AASHTO HS 20 when it is
traveling from point A to point B.  But when they set up and set the
outriggers, all bets are off.

The punching shear must be considered and will drive the thickness of the
slab.  The outrigger loading on aerial platforms is huge.  The last time I
checked Pierce, Seagrave, Sutphen, and E-1.  A Pierce aerial  had the
largest outrigger loads at about 60,000 pounds (HS-20 wheel loads are 16,000
pounds).  The only thing that NFPA says is that the outriggers are limited
to 75 psi maximum bearing pressure under the outrigger.

There is NOTHING in any code on this.  Fire apparatus manufactures are very
tight lipped on maximum outrigger loading.

Specifically to your question on distribution for HS 20.  The axle load is
distributed across a 10' lane.  The wheel load is distributed over a width
of 1 inch per ton of loaded weight.  You really need to get the AASHTO to
see all of the permutations of load distribution.

Harold O. Sprague

> -----Original Message-----
> From:	Samir Ghosn [SMTP:sghosn(--nospam--at)]
> Sent:	Thursday, July 12, 2001 3:02 PM
> To:	Seaint(--nospam--at)
> Subject:	CALTran Loading combination
> Fellow engineers,
> I have been asked to check a slab section subjected to HS-20 Loading.  I
> don't have CalTran manual since I don't generally do this type of work.
> Can some one point  me in the right direction as how to distribute the
> wheel loading on  a one foot strip.  The slab will be formed and poured on
> site, no post tension work.  This is only a segment that will support fire
> truck or trash truck.  My assumptions are, since the UBC allows the wheel
> load distribution on a specified area, there could be some thing parallel
> to that.  Thanks in advance.
> Samir y. Ghosn, P.E.
> Harris & Associates
> (800) 827-4900 XT 360
> "sghosn(--nospam--at)"
> Fax(949) 655-3995

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