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OT: Wood board load limit

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  • OT: Wood board load limit

    Anyone have a copy of Beam Check or something similar?

    I'd like to know if I take a 2" x 6" - 48" long, Southern Yellow Pine, laid flat (the much weaker way), how much weight will that board support with a concentrated load in the center of the board.

    Obviously span tables are of no help since they are based on using the board vertically oriented and based on acceptable deflection, not failure.

    Thanks.
    Steve

  • #2
    You'll probably need to specify which way the grain is running such as quarter sawn, etc. How many knots and what size are allowed?

    Comment


    • #3
      See if this will help, you'll have to know the grade. If I had an idea of what you were doing I could probably help but I have to leave in an hour. http://www.southernpine.com/span-tables/

      Here's the section on scaffolding which may help but I don't think 2x6 will be listed http://www.southernpine.com/using-so...design-values/
      Last edited by flylo; 04-25-2017, 04:16 PM.
      "Let me recommend the best medicine in the
      world: a long journey, at a mild season, through a pleasant
      country, in easy stages."
      ~ James Madison

      Comment


      • #4
        I use this formula for thumbnail calculations:

        Max Load = (fiber stress x width x depth^2)/(9 x length)

        width & depth in inches, length in feet

        fiber stress is species dependent. I think SYP is around 2000, but you should look it up

        I forget, but the formula is probably based on a specific deflection.

        It's for rule of thumb, and not a final design spec.

        Ed
        For just a little more, you can do it yourself!

        Comment


        • #5
          I normally calculate acceptable loads on flats using 1/3rd of the 'strong' way, then overbuild. Haven't had anything break yet.
          Had broken ribs, jaw and wrist from relying on published load capacity, always willing to accept a +/- 10 or even 20%, but when something rated at 1200lbs breaks with a 140lb load it kinda shakes your confidence

          Comment


          • #6
            if the board is "laid flat", you still need to specify where it is supported. If I lay it flat on a hard flat surface, it will support a lot more weight than if i is only supported at the ends....

            Comment


            • #7
              Originally posted by kendall View Post
              I normally calculate acceptable loads on flats using 1/3rd of the 'strong' way, then overbuild.
              The 1/3 rule works well for 2 x 4, marginally for 2 x 6, and not very well for larger sizes.

              The strength of a beam is proportional to the width and the square of the depth, so the beam gets disproportionately more strength with increasing depth. Swap depth and width for a 2 x 4, and the difference isn't that great. Do it for a 2 x 12, and the difference is pretty big.

              Ed
              For just a little more, you can do it yourself!

              Comment


              • #8
                Originally posted by ed_h View Post
                The 1/3 rule works well for 2 x 4, marginally for 2 x 6, and not very well for larger sizes.

                The strength of a beam is proportional to the width and the square of the depth, so the beam gets disproportionately more strength with increasing depth. Swap depth and width for a 2 x 4, and the difference isn't that great. Do it for a 2 x 12, and the difference is pretty big.

                Ed
                true, but OP did specify a 2x6, which with a clear grain will normally work with the 1/3rd fine. Wood has far too many variables to adhere to a concrete rule, which is why I overbuild.
                If you're limited to a 2x, pick grain and crown, also explore the possibility of using angle iron on each side.

                Also, what are you building?

                Comment


                • #9
                  Originally posted by kendall View Post
                  true, but OP did specify a 2x6, which with a clear grain will normally work with the 1/3rd fine. Wood has far too many variables to adhere to a concrete rule, which is why I overbuild.
                  If you're limited to a 2x, pick grain and crown, also explore the possibility of using angle iron on each side.

                  Also, what are you building?
                  Yup, overbuilding a little is a good idea if you can.

                  I built the house I live in, and some other assorted smaller structures on the property. Only building a car at the moment.

                  Ed
                  For just a little more, you can do it yourself!

                  Comment


                  • #10
                    You need the Sagulator, designed for just this situation.

                    http://www.woodbin.com/calcs/sagulator/

                    Dennis

                    Comment


                    • #11
                      The inherent problem with materials, you have to actually break them to know how strong they are, otherwise how much they can take is a guess, it seems actual timber is completely unaware of the codes, tables and formulas, if your using the timber on flat like a plank then a good guide is the scaffholding plank regs, then use an actual scaffholding plank as they get deflection tested instead of visual knots and shakes.
                      Mark

                      Comment


                      • #12
                        Couldn't you take the rating for a 2x2 and multiply by about 3.5?



                        Originally posted by SteveF View Post
                        Anyone have a copy of Beam Check or something similar?

                        I'd like to know if I take a 2" x 6" - 48" long, Southern Yellow Pine, laid flat (the much weaker way), how much weight will that board support with a concentrated load in the center of the board.

                        Obviously span tables are of no help since they are based on using the board vertically oriented and based on acceptable deflection, not failure.

                        Thanks.
                        Steve
                        Paul A.

                        Make it fit.
                        You can't win and there is a penalty for trying!

                        Comment


                        • #13
                          If you have more than one & can tie them with a cross board it will highly increase the strength. There was a scaffolding chart in the link I provided. Really need a little more info before finding the right answer to your question.
                          "Let me recommend the best medicine in the
                          world: a long journey, at a mild season, through a pleasant
                          country, in easy stages."
                          ~ James Madison

                          Comment


                          • #14
                            You can find calculators on line for this. Here is one, but there are others.

                            https://courses.cit.cornell.edu/arch...rs/example8.1/

                            They seem to be aimed at finding the size of lumber that you need for a given load, not finding the load for a given size of lumber. So you may have to do some trial and error with the numbers until it starts to show your size.

                            I searched for:

                            wood beam load span chart
                            Paul A.

                            Make it fit.
                            You can't win and there is a penalty for trying!

                            Comment


                            • #15
                              Originally posted by ed_h View Post
                              I use this formula for thumbnail calculations:

                              Max Load = (fiber stress x width x depth^2)/(9 x length)

                              ......................
                              Ed
                              Thanks, Ed. That give me about 700 lbs which sounds reasonable, although the fiber stress numbers seem to be all over the place. Probably from folks "being on the safe side" regarding knots and poor grain orientation. I think I'm just going to take some concrete blocks (always handy to have a stack sitting around) and run a test tomorrow to confirm that number.

                              Steve

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