The Forestry Forum
General Forestry => General Board => Topic started by: Patrick NC on October 16, 2021, 06:03:42 PM
I want to build a wooden bridge across a small creek on my property. It will be built from rough cut white oak. The span from bent to bent is 16 feet. Ideally I would like to drive my truck across it. (Ram 2500 crew cab 4x4) I've tried to find a calculator for timber size and spacing but no luck so far. Has anyone ever done this? Any advice would be greatly appreciated..
What they used to do was stretch cables under the beams with turn buckles . There would be a fulcrum at the half way point and the cable is trying to crown the beam up. The other way is an A frame truss top side with a pull up rod in the middle doing the same thing and easier to make. This is for people like me wo can't engineer things sometimes called the dumb way.
Back when I actually had to work for a living, I was a manager in the telephone company outside plant engineering office. I designed some pretty weird tunnels and supporting structures. I found I could get off the shelf designs from the state highway department engineering office...free. I remember seeing bridge designs made from wood in their library.
With that in mind I did a google search using the term "timber bridge design manual".
Very first hit looked promising with many others.
Timber Bridge Manual (http://www.dot.state.mn.us/bridge/pdf/insp/USFS-TimberBridgeManual/index.html)
You might want to consider 20 ft steel Beams and deck over with wood.
10 inch I-beams are about 500 each. 3 for 1500 bucks is money well spent.
X2 on adding steel beams, especially for something to support vehicle traffic and to get years of use. Some have used old semi flatbed trailers with the wheels removed for crossings.
Log loading calculator, insert species, length, total load in lbs... top 3 items upper left column
click on show result.
Use the minimum dia. log required for L/360 deflection to determine size of log needed.
Log Beam Calculator (http://www.timbertoolbox.com/Calcs/logbeamcalc.htm)