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RE: Bridge Live Load Distribution

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A track vehicle should distribute its dead weight for the front to the back
track guide wheels and across the width of the track; however, on a hard
surface such as concrete you may have trouble with punching shear.  I
suggest you contact the manufacturer for specifics.  Also, I highly
recommend you specify using heavy dimensioned timber runners to run the
tracks over.  Usually the girder strength is sufficient for construction
loads such as this; however, the deck strength between the girders is
usually inadequate.  It is a good idea once you determine the strength
capacities of the bridge members and components, that you develop a site
specific work plan (SSWP) for the contractor to follow.  For example, the
tracks may need to follow the girder lines, or timber planking of a specific
thickness may be needed to span across girder lines to distribute loads.
These things need to be spelled out.

And most importantly, make sure you are following AASHTO standard spec. for
highway bridges when performing your analysis.  You will have to supplement
the spec. with good engineering judgement to develop representative models
of the worst anticipated load configurations to analyze.  I would suggest
adding 30% for impact due to loads imposed on the structure from sudden
stopping and/or jerking of the crane, track vehicles typically aren't the

> -----Original Message-----
> From:	Kipp.A.Martin(--nospam--at) [SMTP:Kipp.A.Martin(--nospam--at)]
> Sent:	Tuesday, February 27, 2001 11:51 AM
> To:	seaint(--nospam--at)
> Subject:	Bridge Live Load Distribution
> I need to evaluate a bridge to determine if a large track hoe can safely
> cross
> without having to be put on a truck.  I have the track hoe weight and
> ground
> contact area.  How do I distribute the live load in order to analyse the
> deck
> and girders?  All my references deal with distributing wheel and axle
> loads, not
> loads from tracked vehicles.  Can any one point me in the right direction?
> Kipp A. Martin, S. E.
> Portland, Oregon