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bridge for Island
Sorry guys....I made a few errors in my post. First of all, I used 3 inch OD .25 wall square tubing for my lower rails....not 4 foot  My bridge is 24 feet long and 46 inches wide. The upper rails are made of 1.5 inch OD .1875 wall square tubing. The cross planks are made up of treated 2x6 wood. I looked for my original specs but couldn't find them so I went down to the pond and measured. I built it about 2 years ago and believe it cost around $1100 to build it.
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bridge for Island
Hey Beagle
check out this link and see if it makes any sense to you for my project.
Link:
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bridge for Island
Pretty good stuff, could be a solution, but also could be pricy, be carefull of a couple things when picking a bridge type:
Un-tied arch bridges rely heavily on their foundations for capacity. The foundation needs to be designed to accomodate the horizontal thrust from the arch. The bridge structure will be lighter and less expensive, but you will pay for it in foundation cost.
Tied arches are extremely efficient, and require less foundation work. There aren't horizontal reactions to worry about in tied arch bridges.
Pick a wood bridge with the least number of pieces in it. Connections of pieces in woof structures is where all the deterioration starts. The fewer the number of pieces, the less places for the structure to rot.
When picking a bridge type, make sure you know what kind of foundation you need for your span, you could end up putting a lot of money in the ground.
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bridge for Island
I see what you mean, where all the bolts hold the boards together will hold moisture and go down hill from there. I did notice the step type foundaions that they were using. Any way all those boards add up and will take some labor (several people).
I have priced several beams and trying to find the best for the cheapest. You and I had discussed using 12" by 12" beams I was going with the 35' span with a 20' brace. Would it make a great deal of difference if I used a 10" X 10" beam. The distance to span is 32' I was going with 35' as to have enough to set on the footing.
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bridge for Island
I had a situation like that a few years ago. I had to transverse a drainage ditch. I did it with a pair of used utility poles which I streched across the ditch. I think the distance for that one was 32 feet. Once I had them in place I screwed regular treated 5/4 decking across the entire span. Although this worked and I did drive my JD 212 across it, I decided to make one set of peers midway which really strengthened it. I did that with a pair of 4 X4s which I extended into the water then fastned to the bridge. It is still standing and I have not had to perform any maintenace. Best part it didn't cost me that much especially since all the decking I already had.
Gary
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bridge for Island
SG, I'll check the 10' x 10" if you can tell me what type of wood it is, (ie southern pine). THe allowble stresses vary quite a bit between species.
Remember we are doubling up the girders at the center, so we sould have a nominal 20" depth where we are doubled up.
The other problem with wood structures is "creep". Wood tends to "stretch" over time when under load, so we want to stay in a low stress range. Otherwise your bridge will have an ugly sag in it after a couple years.
Se if you can find out what type of wood the 10" x 10"'s are, and I'll check them. They will probably work.
Beagle
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bridge for Island
SOUTHERN PINE down here there are very few other kinds. 
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bridge for Island
Thanks, I'll check itr for southern pine. I trust you still have the sketch of the girders we drew a couple months ago.
I'll let you know on the 10x10's.
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bridge for Island
Beagle
The sketch is #20 on your pictures. I was going to make the support beam 24'. Is that correct?
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bridge for Island
That is what we needed with the 12x12 timbers. Give me until noon today and I'll let you know what you need for 10x10", southern pine.
Got a couple thingws we need to get out this morning, them I'll check the 10x10's.
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Gas Generator Weather Protecti
03-19-2006, 12:50 
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