Page 1 of 2 12 LastLast
Results 1 to 15 of 20

Thread: Building a Bridge

  1. #1
    Join Date
    Dec 2005
    Location
    Pennsylvania
    Posts
    896

    Building a Bridge

    Since I'm using wood I figure it's ok to post this here...

    One of my summer projects is building a bridge across the creek that goes through my property. I'm looking to span about 20-24 feet. Does anyone know of a good calculator that I can use to determine the size of the beams that I should build for this thing?

  2. #2
    Join Date
    Dec 2005
    Location
    Northern Virginia
    Posts
    243
    Hi Rob,

    There are various tables here:

    http://www.globalsecurity.org/milita...ppc.htm#tabC-1

    This is from the US Army field manual FM 3-34.343 Military Nonstandard Fixed Bridging.

    The table of contents for the manual is here, there is probably more info elsewhere in the manual:

    http://www.globalsecurity.org/milita...343/index.html

    Maurice

  3. #3
    Join Date
    Mar 2003
    Location
    San Francisco, CA
    Posts
    10,304
    Unfettered by any knowledge of your project, I think you should build a covered bridge -- y'know, timber-framed, with a roof to keep the elements off the timber. For a woodworker, they are way, way cool!

    Pennsylvania is a hotbed of covered bridges. Google with "covered bridges pennsylvania" for scads of sites about them. You could have a real fun weekend driving around to look at a few.
    Last edited by Jamie Buxton; 06-08-2006 at 1:24 AM.

  4. #4
    Join Date
    Mar 2005
    Location
    Houston, TX
    Posts
    857
    My BIL bought some land very cheap b/c there was a small creek that had a very deep channel running in front of the property. Nobody was willing to pay for a bridge to be built just so that they could then build a house. BIL found a source for free/very cheap telephone poles. He used several set in concrete for the legs and then laid more across to form the base of the roadway. Cement trucks were driving over it to build the house with no problem. The county bridge inspector said that it was ridiculously overbuilt and that he would never have problems with it.

  5. #5
    Join Date
    Dec 2005
    Location
    Pennsylvania
    Posts
    896
    Maurice, I started to look at that manual and it made my head spin. Maybe I'll try again later.

    Jamie, yes, there are a lot of covered bridges in PA. In fact I drive across a few on my way to work. I like you're thinking and I may do that in the future. However, I wanna get something up quick so that'll have to remain in my dreams.

    Tom, I have looked into that but have not been able to locate any. I'll keep trying. If it's overkill for cement trucks, it's gotta be overkill for my three and five year olds to walk across.

    Let me throw this out there more clearly. I want to build a bridge that will only be used for walking, no cars or cement trucks. 24 feet long by 4-6 feet wide. It must span that length. No cover. Nothing fancy. I was going to bind together a bunch of 2XSomethings to make the spans and lay planks perpendicular across the top.
    Would 4"x8" be sufficient? What type of wood would you use?

  6. #6
    Join Date
    Feb 2006
    Location
    Kalamazoo, MI
    Posts
    781
    If I were to make such a structure, I might go to a house which has floor trusses, the kind that will clear span a 24' basement and reverse engineer three of them out of green treated lumber. Slap on some decking and enjoy....should hold foot traffic as long as you break your step instead of marching.

    Kyle in K'zoo

  7. #7
    Join Date
    Feb 2003
    Location
    Starkville, MS
    Posts
    172
    I would go with the telephone pole route. No worries about rotting, etc. I've seen several built this way. A tractor/loader or backhow would help moving and setting the poles.
    Doyle

  8. #8
    Join Date
    Nov 2003
    Location
    Northern California
    Posts
    28
    Here in the mountains of northern California where I live there are numerous creeks. When we need a bridge in a hurry we use a scrap railroad flatcar.
    Greg Jurrens

  9. #9
    Join Date
    Mar 2003
    Location
    San Francisco, CA
    Posts
    10,304
    Rob, I think you aren't going to find 4xsomethings which are 24 feet long at your local lumber emporium. To get beams that long, you may need to order engineered beams, like glu-lams. When I last looked at them (quite a few years ago now), the manufacturers didn't want to guarantee glued-up beams for exterior use. Timbers shorter than the span is one of the motivating factors in covered bridges. They built timber trusses from short lumber in order to span wide rivers.

    Telephone poles or railroad flatcars are expedient solutions, but they're sure inelegant compared to timber-framing!

  10. #10
    Join Date
    Feb 2003
    Location
    Collin County Texas
    Posts
    2,417
    A friend about 6 miles away had a gully to put a small bridge across so that he could access his auto workshop. He put a concrete retaining wall on each side, and then bought steel I-beams to span the gully using the walls as support piers. Across the beams he put 2x10s to form a road bed, and then came back with a wide wooden tread for car tires. I have been over the bridge in my pick-em-up, and it is steady as a rock.

    BTW, he will not have to replace the steel beams in his lifetime.
    Best Regards, Ken

  11. #11
    24 foot span, weather, cost effective= steel..02 tod
    TO WHOM IT MAY CONCERN; I ACCEPT FULL LEGAL RESPONSIBILITY FOR MY POSTS ON THIS FORUM, ALL POSTS ARE MADE IN GOOD FAITH CONTAINING FACTUAL INFORMATION AS I KNOW IT.

  12. #12
    Join Date
    Mar 2003
    Location
    Monroe, MI
    Posts
    11,896
    A house the next road over from us has a covered bridge on their driveway that crosses a small creek. It looks really cool.

    Personally, I think the pole idea sounds like a great one. It will be way overbuilt for a walking bridge but you won't have to worry about it. You could put some kind of a skirt on the sides to hide the poles if didn't want to see them.

  13. #13
    Join Date
    Feb 2003
    Location
    South Windsor, CT
    Posts
    3,304
    I did a quick search for floor span tables. Douglas fir 2"x14"s will span 24'+, assuming you're using #1 or better lumber. The only thing is does pressure-treating lumber change its load-carrying specs.

    Where you'd find 24'x2"x14" pressure treated lumber is a good question.

    As far as using PT lumber and building floor trusses - I'd want assurances from the truss manufacturer that the plates wouldn't rust. If they do, your trusses fall apart.

    I'd guess that the steel would have the advantage of producing a lower bridge deck.

  14. #14
    Join Date
    Mar 2003
    Location
    SE PA - Central Bucks County
    Posts
    65,685
    Three telephone poles...some side skirts as mentioned to "clean it up and...some 3/4" modified to make an even surface for walking and biking across. The skirts would also allow you to construct a rope railing for safety, too, if you want.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  15. #15
    Join Date
    Mar 2004
    Location
    Lacey, Washington
    Posts
    412
    I notice you're in Penn. If you get snow and ice and your only talking about foot traffic be sure you"re taking into account a snow and ice loading. It may be the heavist load you'll have. A 48" deck (walkway) can hold a lot of anow and ice. Dick B.

Similar Threads

  1. Building the new storage building day 2...pics...
    By Terry Hatfield in forum Off Topic Forum
    Replies: 4
    Last Post: 05-28-2005, 11:51 PM
  2. The long anticipated new storage building project...pics..long....
    By Terry Hatfield in forum Off Topic Forum
    Replies: 10
    Last Post: 05-28-2005, 7:44 AM
  3. Another Newbie building & outfitting a shop.
    By Mike Holbrook in forum General Woodworking and Power Tools
    Replies: 28
    Last Post: 01-29-2005, 6:52 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •