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RE: Golf Course Bridge

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Brian-
Actually finding the maximum moment without a computer is not all that difficult if one uses influence lines.  If you place the midpoint between your heaviest load and the center of gravity of all the loads that will be on the bridge at the maximum point on the moment influence line, that will produce the maximum moment in the girder.  Of course, since the EIT after your signature on a prior posts indicates that you have probably been educated since advent of the frequent use of the computer for structural analysis, you may not have learned influence lines.  Refer to most any text on indeterminate analysis such as Norris and Wilbur or Kinney for a discussion of this technique.  It will give you a much better feel for the structure than reams of computer printouts.
Regards,
Bill Cain, SE
Oakland CA
-----Original Message-----
From: Brian M. McMahon [mailto:brian(--nospam--at)ubsdesign.com]
Sent: Tuesday, June 05, 2001 9:43 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: Golf Course Bridge

Eric,
 
Finding the maximum moment for the girder(s) with the vehicle load is somewhat tricky, especially by hand (without computer software).  If you use a 10K vehicle you can check me with the follow equations:
 
Assumption: Back wheel = 4K and front wheel = 1K (Spacing between wheels is 5'-6" and wheel span is 11'-0")
 
Hint: The CG of the vehicle is 1.1 ft left of the center line of the span, L/2 (that would be the rear wheel)
 
M = 1.25*L + 6.05/L - 5.5 K*lbs
 
R (left support) = 5 - 5/X - 11/L
 
X is the distance from the left support to the center of the back wheel.
 
Make sure you prove these formulas before using them.  It's been a while since I derived them.  But, I had them written down.
 
Thanks to Bill he knew the word Bollards for those metal posts at the end of the bridge.  Space them as required.
 
Don't forget to buy your AASHTO manual.  You'll pay for it with your first bridge.
 
Good luck!
 
Brian McMahon
Timber Design
Universal Building Specialties, Inc.
Auburndale, Florida 33823
(863) 967-1131
 
 
 
 
 
 
 
----- Original Message -----
Sent: Monday, June 04, 2001 7:55 PM
Subject: Golf Course Bridge

I am designing two cart path bridges for a golf course.  First bridge is 3 span 70'+50'+50', second bridge has a single span of 70'.
 
Wonder of wonders, the owner and the contractor both want to minimize the cost on the structures, and are asking that I use the minimum live loading possible. 
 
The largest vehicle used on the golf course is a mower/utility vehicle with a gross weight of about 2 tons, well below H15 loading.  The bridges themselves are to be 10 feet wide, and the approaches are so hilly that it is unlikely that  a truck could even get to the bridges.
 
Soooo, my question is : Does anyone have experience regarding the use of loads substantially less than those required by AASHTO for the design of NON-highway bridges.  If so, are there standard loads?  I was thinking of using 5 tons as a minimum, and having the owner post a permanent sign showing the weight restriction.
 
Also, does the AASHTO manual govern the design of the bridges?  We are currently under UBC94, soon to switch to the IBC, but I am not all that familiar with AASHTO requirements (not much bridge work on Guam).  I would prefer to use UBC94, LRFD 2nd Ed for the girders, and refer to AASHTO for load distribution (based on 5 ton total weight) and seismic design.
 
Any suggestions?
 
 
T. Eric R. Gillham PE
PO Box 3207 Agana Guam 96932
Ph:   (671) 477-9224
Fax: (671) 477-3456
Cel  (671) 687-7115