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Re: 5 Ton Golf Course Bridges

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Steve:
 
I appreciate your response regarding the loads to timber vehicle bridges.  I looked at the Continental site and note that they use a 60 - 40 split of total vehicle weight.
 
AASHTO and the UBC require design wheel load to be 40 percent of the gross vehicle weight.  This is where we have the problem.  Continental uses 30 percent for design wheel load.  The reduced wheel load can make a big difference in designing short spans.
 
I was hoping that someone on the list could give me a justification for using the smaller loads.  In my opinion, the design wheel load for a 5 ton loading should be 4000 pounds.
----- Original Message -----
From: S. Gordin
Sent: Thursday, May 12, 2005 3:28 PM
Subject: Re: 5 Ton Golf Course Bridges

Dave,
 
What your specs most probably meant was a 10000-lbs vehicle, with 60-40% weight distribution.  It is a pretty standard loading for 12' wide pedestrian bridges.  You may want to look at the Continental Bridge Standard Specification (available on their website).
 
V. Steve Gordin, PhD
Registered Structural Engineer
Irvine CA
 
  
----- Original Message -----
Sent: Thursday, May 12, 2005 11:34 AM
Subject: 5 Ton Golf Course Bridges

I have an interesting problem.  I am looking at the design of several timber golf course bridges.  Specifications say "12'-0" wide, 3-inch plank deck, and 5-Ton capacity.
 
The contractor bid based upon his normal business of constructing golf cart bridges for golf courses.  He "sort of" follows the pictures and layout shown on page 8 of "Southern Pine Pedestrian Bridges & Walkways".
 
Designing the timber bridges by AASHTO leads to much larger members than he thought he was going to have to use.  The problem seems to be the use of the term "5-Ton Capacity".  A wheel load for a 5 ton truck will cause much larger stresses in the stringers than a uniform load that will add up to 5 tons.
 
I would appreciate any comments on what others have done in this situation.
 
Dave Smith
 
David G. Smith & Associates, Inc.
Gainesville, GA