Bridge

[SIHunter]

I have a creek on my property that is about 65'-70' from bank to bank. I would like to build an ATV bridge across the creek. Any ideas from some of you guys as to how to go about this project. Thanks for any and all input!

 

[firemanpat2910]

70 feet? thats one heck of a creek. How deep is it,and how
steep is it? can you dive a tractor through it to dig post holes?

 

[DANOCHEESE]

That is a large span. Smaller you could get away with power poles laced together. 60-70 feet would need some major design and construction.

 

[MikeD74T]

Our snowmobile club put in a bridge that is a 75' span. We got used beams from a salvage company. Just copied a nearby highway bridge. 36" tall, don't know the weight per foot. The bridge handles truck traffic from the landowners gravel pit. Far more than needed for an ATV, but doable even by amateurs. We planked the deck with 3"pt. yellow pine. A cable suspension bridge is far cheaper & easier to build for ATV traffic. Our club has a 100' span cable bridge.

 

[Mavrik02]

Without knowing much about the situation I agree 100% about the design/construction comments. My creek is 12 feet wide and the amount of flow calculations that went into that project was significant.

To have the bridge last a few years you will likely need to figure out how much water flows through the creek during heavy rain storms and how high up the banks it will get. Water is a destructive force and will destroy anything not built to handle it. /forums/images/graemlins/frown.gif

 

[valleydweller1]

That span sounds pretty close to ideal for an old railroad car bridge.

 

[SIHunter]

What do you mean by railroad car bridge.

Would it be possible to get a pic of the cabel suspension bridge used for ATV's.

Thanks for the inpu so far, much appreciated!

 

[MikeD74T]

I don't have a digital camera yet. I gave someone directions to the bridges a while back. RADAIR - did you visit the bridges in Jefferson & Lancaster? Pics? If Radair doesn't answer or have pics I'll pm you a description. A suspension bridge is really easy (uncomplicated) & fun to build. Just takes a little advice, confidence, ingenuity, & ability. It's also very satisfying to cross after it's done.
A railroad car bridge is simply a railroad flatcar spanning the gap. Junk railcars are very availible in some areas. Can be costly to transport to site & place but huge capacity. Same but shorter for over the road flatbed trailers. In northern NH there are a couple hundred railcars within 30 miles of our snowmobile club. Some of the track runs beside our trails. Moving a car 1 mile away from the track & lifting into place is another matter.

 

[radair]

Mike - no, I haven't made it up there yet. I will take pics when I do. I agree that a well-designed and constructed suspension bridge would be more economical than steel stringers.

I've design steel stringer bridges up to 50' span. 75' is doable, of course, but will require taller, heavier beams. A quick calculation for a 6' wide bridge with allowable deflection of 3.75" requires stringers consisting of W27 x 84 (27" tall, 84 lbs. per foot). Using an allowable deflection of 2.5" you'd need W30 x 99 beams. These assume bracing at 10' intervals and a live load of 85 psf. That's over 15,000 lb. of steel for the W30 beams, which would cost you a bundle.

I'd recommend you get a licensed engineer to look over whatever design you end up pursuing.

 

[MikeD74T]

SIHunter, Found a few small suspension bridges. They'll give you the general idea. http://www.bridgemeister.com/snapshots.php?type=F&pg=1
http://www.bridgemeister.com/pic.php?pid=1453
Pay attention to the general proportions, span, height, distance to anchors, cable angles over the towers.