Building a bridge: PT or rough cut??

[/pine]

FWIW...generally speaking a white oak of worthy timber size is already 80 to 100 years old...many do not even produce acorns until they are that old...domesticated (potted) versions may produce fruit (mast) sooner...here in the forest many of the 30" or better white oaks clock out at over 200 years old...

 

[jymbee]

...

JMHO - I would build the bridge out of 8 x 8 timbers and wide enough to accommodate a larger utility tractor. At least 84" wide.

There's another bridge further up the same stream that we built with three 6x6 PT beams as the main deck support and the same 6x6s as a structure on each end to support the deck with sloped concrete ramps also at each end. At the time, friends thought the three 6x6s were "overkill" but that was many years ago and it's still standing strong. The 748 JD we have now is heavier than the 425 we had back then.

The whole idea for this build is to utilize the railroad railings we have now as they were basically free having come from a much older bridge even further down the same stream on the neighbor's property. That bridge had pretty impressive stone foundations built up on both sides and back in its day was a part of a main thoroughfare for farm equipment, cows, etc. When I salvaged that old bridge there were three of these steel railroad rails. Only fitting that they be resurrected and used again.

 

[jymbee]

Explain 'railings'. Track rails? Or some sort of bridge sides that have been removed?

Twenty foot sections of railroad tracks. See pic above.

 

[jymbee]

Not to be smart, But why go with such a temporary material anyway. Why not STEEL? Maybe Wood Decking.

?? Did you see the pic above of the steel, railroad track sections?

If I needed to build a small bridge, I would buy an old flat deck highway trailer.

Yikes-- I get where you're coming from but that just seems like overkill for a rather simple project.

 

[TnAndy]

FWIW...generally speaking a white oak of worthy timber size is already 80 to 100 years old...many do not even produce acorns until they are that old...domesticated (potted) versions may produce fruit (mast) sooner...here in the forest many of the 30" or better white oaks clock out at over 200 years old...

White oak/black locust are great choices for lumber due to another factor....they have tyloses cell structures that other hardwoods/softwoods don't have. These cell structures tend to make them watertight, which is why white oak is used in barrels and red oak is not. Comparing white oak to any pine is not an apples to apples comparison.

 

[BrokenTrack]

Longevity of wood is also dependant upon where the wood is.

In the case of my bridge, it will last a long time because the main part of the bridge is open to the air. Sure, during rain storms the wood gets wet, but as soon as the breeze kicks up, it is dried. I still made that out of Hemlock, but where it rests on the ground (ground contact) I used White Cedar. Still: the bridge cost me $12.50 and took a day to build. Even if it last 7 years, its not a big deal to replace it.

A lot of people do not know this but White Pine will last forever...as long as it is siding on a house. The air has to dry it out, then it will outlast cedar, but that does not apply to the bottom two feet of the siding because that stays wet. So it really depends on location.

I think the Orginal Poster should just build a cheap bridge and see how many times he uses the bridge. If he uses it a lot, then they can build a better one down the road. But who knows, maybe after it is built, they realize they almost never use it. My life motto is to build, and then refine.

Better a bridge that is mediocre and built, then the best bridge ever designed never made.

 

[fried1765]

Not to be smart, But why go with such a temporary material anyway. Why not STEEL? Maybe Wood Decking.

If I needed to build a small bridge, I would buy an old flat deck highway trailer.

130+ year old covered bridges, all built of wood, are "temporary"?

 

[fried1765]

When we first move here I cut my ancient Ponderosa pines for firewood. I cut a few( big mistake ) that were 38" to 42" on the butt. I soon learned - they were much more valuable for lumber and a 40" tree is a real ***** to manhandle the rounds & split.

Anyhow - it was very noticeable - the last 30 to 40 years of the trees growth had the growth rings much tighter together the the preceding years. Tighter growth rings equal - dryer years - more atmospheric pollution??

Twenty years ago I had the property selectively logged. Got a premium price for the old pines.

JMHO - I would build the bridge out of 8 x 8 timbers and wide enough to accommodate a larger utility tractor. At least 84" wide.

8x8 timbers are heavy, massive for posts, but equal dimension timber for a span is not the best idea.
The deeper the timber cross section, the stronger the span will be.
For a tractor potentially much heavier than the aforementioned 1200 lbs.,
Beams made up of 3-2x12s laminated (glued and spiked), would be a much better choice for bridge carrying beams.

 

[dougtrr2]

Interesting project. More questions than answers. I agree that if you space the rails to the width of your tractor the wood is a minor factor. Any idea how much deflection there will be? I would be tempted to make a temporary set up on dry ground to check the deflection. How do you attach the wood to the rails. My impression is that the rails are a pretty hard material, more that just run of the mill steel. Will you mount the rails in their normal orientation or upside down to have a wider mounting flange.



Doug in SW IA

 

[Industrial Toys]

I knew a German craftsman who never stopped working on his property. Built stuff of wood. Then he realized the stuff was falling apart before he ever got the whole place finished. He moved to concrete, masonry and steel and never looked back. In the right application, wood has it's place and can last hundreds of years. No one seems to care how short the life of stuff is anymore it seems. As long as no evil chemicals are employed. Imagine all that creosote that must have leached into rivers over the years on those huge timer tressle bridges?