Wooden bridge span question

[tommu56]

RobA

Here are a couple of links

Timber Bridges


and

http://www.fpl.fs.fed.us/documnts/pdf1996/taylo96b.pdf

and

http://www.masterlogger.org/logjam/issues/portablebridges73.pdf


the last one is the type loggers use in my area

edit

here is another

http://www.umass.edu/nrec/pdf_files/skidder_bridge.pdf

tom

 

[mboulais]

another link

http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr125.pdf

 

[Wayne_H]

We just finished our fifth wooden bridge this fall. It spans 24 feet. I used two 2x12 glued and bolted together for the trusses, and used a total of four trusses. I used three concrete piers on each side 30 inches deep and about 12 inches diameter. I did not use tubes. I did frame out a sqaure with 2x4's on the top to get it level to I could put steel across the three concrete posts. For the steel I welded two five foot "lentils" that were 3/8" thick. The decking is 2x6. The mule weighs about 1000 pounds, and we have had it loaded with about another 1000, and the bridge does not move.

I'll try to post a pic, hope it works.

wayne

 

[MadJack]

How about 4 telephone poles with 4" hemlock decking? The snowmobile clubs up here use these poles with 2x4 pressure treated and have no problems with three crossing at a time over a 40+ foot span.
The poles aren't even noticed! With the decking spaced at one to 1 1/2" apart, no one gets a foot caught either.

Just a suggestion.


Wayne, awesome bridge!

 

[RobA]

.... It spans 24 feet. I used two 2x12 glued and bolted together for the trusses, and used a total of four trusses. .....

I haven't shopped for lumber for the project yet. Did you have trouble finding 24' long 2x12's? Expensive? Are your joists 16" on center?

I like your overall design. That's exactly what I was thinking. If I could safely use 24' beams it sure would make the pier placement easier.

 

[RobA]

I haven't shopped for lumber for the project yet. Did you have trouble finding 24' long 2x12's?

I called a few local lumber stores. I can easily get 2x10's and 2x12's in 20 foot lengths. That's the longest I could find.

 

[Wayne_H]

No, the best I could find was 20 foot lengths, and they were 8 foot longer than my trailer... So I bought 16 footers, and spliced them with an offset. I used 1/2 inch galvanized bolts every foot, and glued it. The spacing is odd, its about 20 inches, just worked out that way! 0,20,40 and 60 inches.

I have been watching a bunch of almost new telephone poles getting ready to come down, but that's been a four months now, and while the electric company did their thing, the phone company is dragging, so the poles are still up.

But, the 2x12's are nice to work with. Yes, they are expensive, but I have a few sponsors helping with the money on the material.

Wayne

 

[RobA]

Splicing sure would make things easier and a little cheaper. Longer boards are more expensive per foot. Even if I don't splice I was going to use construction adhesive and galvanized bolts to join boards together. Maybe I'll consider splicing. Thanks.

 

[MAYOR8020]

i built a bridge that spans 6-7' w/ 3ply 4x4 @ wheel spacing then decked w/ 2x material. bridge is 12' wide 2-3' off ground i drive tc40a w/ ballast and
pallet box of fire wood over it w/ no problem i built this w/ what i had around
i also drove a 5000lb mini vator over it w/ no prob
bridge has been in svc for 6 yrs. also i just laid it on ground
dws

 

[RobA]

i built a bridge that spans 6-7' w/ 3ply 4x4 @ wheel spacing then decked w/ 2x material. bridge is 12' wide 2-3' off ground i drive tc40a w/ ballast and
pallet box of fire wood over it w/ no problem i built this w/ what i had around
i also drove a 5000lb mini vator over it w/ no prob
bridge has been in svc for 6 yrs. also i just laid it on ground
dws

Any pictures?

 

[MikeD74T]

RobA, Have you looked at these bridges? Index A versatile and scaleable bridge design for spans up to 50 feet, build foot bridges, design construction of foot bridges, constructing footbridge design, free bridge design, gartenbrücke, how to build wooden bridge beams, instructions for wooden bridge design, pedestrian arch bridge plans, free plans for garden bridges, pond bridge plans, prefab bridges, rainbow bridge construction technique, the design of foot bridges, vehicular bridge plan, wooden arch bridge design, bach, baupläne, bridge kit, brücke, brückenbauplan sizes required constructing popsiclestick popsicle stick timber footbridge foot bridge fir hemlock cedar pine outdoor pressure treated lumber They have engineered specs & are load upgradable by adding more trusses. MikeD74t

 

[KSopocy]

Just remember your liability goes for scum bag trespassers too,if they get hurt crossing your bridge. Because if it is there, they will cross it by foot, quad, horse, snowmobile and even vehicle if they even think it might hold them. And some, lower than a snake, lawyer will gladly take their case if it is even remotely possible to sue your butt for every dime you have now or ever will have.

Now skip the wood understructure and go get a couple of old I-beam from maybe your county road commission and build your bridge.

Oh, check with your county drain commissioner before you place a bridge over a public drain. The fines and their charge for removing the structure can be astronomical.

Also if you are placing it near any wetlands, you could be going against federal wetland laws. This will surely bring out a tree huggin' bed-wetter or two.

Yes, sir I have been down a few rough roads with this sort stuff.

 

[MAYOR8020]

Any pictures?

yes i will take them today @ lunch and get them posted i dont know if i will have time to get tractor out and on it but ill try
dws

 

[okie350]

Just remember your liability goes for scum bag trespassers too,if they get hurt crossing your bridge. Because if it is there, they will cross it by foot, quad, horse, snowmobile and even vehicle if they even think it might hold them. And some, lower than a snake, lawyer will gladly take their case if it is even remotely possible to sue your butt for every dime you have now or ever will have.

Now skip the wood understructure and go get a couple of old I-beam from maybe your county road commission and build your bridge.

Some of you guys are so paranoid of something happening I dont know you function.

The original poster got some good advice and had a pretty sound plan to begin with. so build it and enjoy it. I'm about to build one myself

 

[chucko]

mboulais

You know that you should double all live loads before doing you math right?
for a horuse I would go more as they "could" be on two feet at any given time

 

[RobA]

You know that you should double all live loads before doing you math right?
for a horuse I would go more as they "could" be on two feet at any given time

I'm not an engineer but I thought to calculate live load I need maximum weight per sqaure foot of bridge. My latest design is 7'x16'. That's 112 square feet. So, 2,000 pounds on 112 sq fet of bridge is less than 20 pounds/sq ft, right?

 

[KSopocy]

Some of you guys are so paranoid of something happening I dont know you function.

The original poster got some good advice and had a pretty sound plan to begin with. so build it and enjoy it. I'm about to build one myself

Okie350,

I'm not paranoid. Just have seen the lawsuit happen in person. It was not a pleasant experience.

KSopocy

 

[chucko]

20 pounds/sq ft is more like a roof live load.(not total load)
Building I just did had a deck on the roof that area was 100 psf live load + any dead loads (weight of decking ect) and I don't think they were planing on a horse or a ATV on the roof.

Then you have to design hand rails . On a building you have to be able to pust at the top with 200 lbs in any driection. I am willing to be a bridge is much more in all cases

 

[Danno1]

.

Rob,

The horse is not spread out over the whole bridge. If he's on two feet that's what's called a point load. Or two point loads actually. Do a Google for "Beam calculations".

Simply Supported Beam Loading Options

.

 

[scgargoyle]

I've built one of the bridges suggested by MikeD74T. The website is pacifi.ca.
Very graceful bridges- look through the many pictures. The only problem I had is the the lumber size has to be exact or the drilled holes won't line up. The PT lumber I use was 1/8" oversize, and I had to re-drill the holes.