Building a long bridge

[paintman161]

Okay,

I am getting ready to build my bridge across my creek. I have about half the telephone poles that i will be using for the piers, I plan on burying the poles 4-5' into the ground and have about 7'-8' above the lowest point of the creek. I will put two 2x12x5' across the pole for the beams, the beams will be 20'-0" center to center and the joist will be 12" O.C. and have 2x8 laid across for the decking. During the spring or heavy rain fall this creek likes to flood onto the side banks (which are only 1-2' above the normal level), So this is why i plan on making the bridge about 100'-0 in total. So my concern is in the center of the creek at normal creek levels it is about 30'-0" across to clear the water. I am just not sure 2x12 @ 12" o.c. would span that, I was thinking about doubling up the joist in the center to span it?? Would this work??

I do plan on using an ATV or UTV to cross this bridge, which is about 2500 pounds.

 

[oosik]

I don't know, but it appears to me that you are entering an arena where you will want sound engineering advice not some home-spun tales. I would suggest you contact a civil/mechanical engineer or engineering company. A project of this size might also require permits from various agencies. Just MHO.

 

[paintman161]

I don't know, but it appears to me that you are entering an arena where you will want sound engineering advice not some home-spun tales. I would suggest you contact a civil/mechanical engineer or engineering company. A project of this size might also require permits from various agencies. Just MHO.

No money for engineering, I did do a little engineering anyways, permits will not be needed, and will never been seen by anyone other then me

 

[newbury]

The Army has some engineering manuals for hasty bridge construction on line in pdf form. I provided a link to one a while back and it might have some specs.
I just don't have the time to dig it up now.

 

[Streetcar]

No money for engineering, I did do a little engineering anyways, permits will not be needed, and will never been seen by anyone other then me

The size of the creek would require a permit for the work in Ohio. For that amount of water, you also need to be aware of scour at the piers

 

[s219]

Over a 30' span, a double 2x12 of pressure treated SYP is good for supporting a uniform load of 55-65 lbs per foot (that includes weight of the lumber and what it supports). That assumes the two boards are properly sistered together.

If you haven't already, start by calculating the loads that the span needs to support. Only then can you properly determine what size and quantity of beams are needed.

 

[hslogger]

For starters, see'in you are asking, I would lay down concrete, or at the least compacted rock that has been inserted on either side of the crossing. I would dig it out, lay lots of crushed rock and compact it, then lay your telephone poles on top of 'er.

 

[joecoin]

Here's some good info:

FM 3-34.343 Chapter 4

 

[EddieWalker]

If I understand your plan, you are basically building a pier across the creek. Two post with a pair of 2x12's across the top of the posts to support the joists. Then decking across the joists.

Then is sounds like you are planning on putting the pair of posts every 20 feet. Is that right? So you will have a 20 foot span from your posts? To me, this is where you will run into trouble. I'm not aware of 2x12 PT lumber longer then 16 feet. What are you going to use for your joists? The span tables I'm looking at online have 20 feet at the extreme limits for 2x12's with 40 psf at 12 inch on center spacing.

Then there is the real issue of diagonal bracing. With the posts just being 5 feet apart, you will need some very serious diagonal bracing at that height just to make it stable. Adding water to this makes it very questionable to how safe it will be.

While it might work at first, and for a period of time, my thinking is that you will spend a lot of money and time on something that is going to fail rather quickly. If you are lucky, it will just fall down on it's own. If not, something or somebody is going to go down with it.

I wouldn't do it.

Eddie

 

[boggen]

any pictures / diagrams to show what you have more in mind?

paint, comes with all Microsoft computers, mac's have simuliar program. it is slap stick drawing. much like taking a piece of paper and some markers / pens / pencils, and not using any sort of straight edge, measurements, etc... but it works to rough out the details. and quick and cheap. due to details most likely change quickly.

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a tip, look at very bottom of this thread a "simliar thread" listings of other folks asking about a bridge show up.