The Forestry Forum

General Forestry => General Board => Topic started by: Patrick NC on October 16, 2021, 06:03:42 PM

Title: Wooden bridge
Post 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..
Title: Re: Wooden bridge
Post by: moodnacreek on October 16, 2021, 06:29:33 PM
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.
Title: Re: Wooden bridge
Post by: Larry on October 16, 2021, 09:50:00 PM
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)




Title: Re: Wooden bridge
Post by: Mooseherder on October 16, 2021, 10:03:52 PM
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.
Title: Re: Wooden bridge
Post by: Resonator on October 16, 2021, 10:29:00 PM
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.
Title: Re: Wooden bridge
Post by: woodroe on October 17, 2021, 04:48:20 AM
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)