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  • ball screw anchor bolt

    I crossed an Arizona creek on a pedestrian suspension bridge this morning. The cables anchor into concrete footings, held by these steep-pitch bolts. They resemble ball screws but have hex nuts.

    What kind of threads are these, and what's the advantage for this application?



    Allan Ostling

  • #2
    It's called coil threaded rod and it's very tough.Picture a 3/4" OD rod roll threaded down to 5/8" od,all those fibers mashed and formed into a tight bundle almost like a cable,but solid instead of stranded.

    Add to that the incresed strength in tension from the large radius thread root and a secondary advantage of being able to be chopped and re-threaded on the job in seconds and you have some versitle threaded rod for use on the construction site.

    It's also used for form assembly,ground rod anchors(bulk head dead men) and post tensioning concrete structures.

    Used to fool with tons of it in construction.I used a lot of it to pull masonary structure back together.The rods could be drilled through a masonary wall,tensioned up in series until the required tension was reached and then the nuts would be tack welded so they wouldn't back off and the excess rod cut off.

    Forgot the link-

    http://www.williamsform.com/Threaded...aded_bars.html
    Last edited by wierdscience; 05-06-2008, 10:22 PM.
    I just need one more tool,just one!

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    • #3
      Thanks. How are those nuts made, with a special tap?
      Allan Ostling

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      • #4
        Along the same line the construction industry also uses a lot of acme all thread rod for large bolts.
        Free software for calculating bolt circles and similar: Click Here

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        • #5
          Originally posted by aostling
          Thanks. How are those nuts made, with a special tap?
          I was told by a saleman that they are "hot tapped" which he described as a spiral tool that was forced into a small hole in hex slug twisting as it's pushed in while the blank is red hot.Dunno if that's accurate or not,but from the looks of the nuts interior finish it looked almost smeared rather that smooth like you see in a tapped hole.

          This page gives you an idea of the uses in forming-

          http://www.williamsform.com/Concrete..._hardware.html



          This page lists the sizes of the more common grade75,

          http://www.williamsform.com/Threaded...ead_rebar.html

          we used to use a lot of this stuff.Had one foundation job that used 40' lengths of the #18 size.You know it's a big job when getting some all-thread requires a Lull forklift
          I just need one more tool,just one!

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          • #6
            Pretty hard to find a stress riser in a thread like that.
            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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            • #7
              Any reason it's left hand? or have you flipped the pic?
              Just got my head together
              now my body's falling apart

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              • #8
                Originally posted by Swarf&Sparks
                Any reason it's left hand? or have you flipped the pic?
                It very well could be lefthand,it's sold in both LH and RH commonly since it's also used as a turnbuckle arrangement.
                I just need one more tool,just one!

                Comment


                • #9
                  OK, thanks Weird, I'll file that one.
                  Just got my head together
                  now my body's falling apart

                  Comment


                  • #10
                    Been in construction for years, and if I ever left an anchor sticking out that far I wouldn't pass inspection!

                    Used a few similar to those, as stated they are surprisingly strong, but due to the steepness of the pitch need serious leverage to torque them down. Not good in tension as they tend to work loose.

                    ken

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                    • #11
                      Kendall---------That threaded rebar, left hand whatchamacallett caught my eye, also. Would hate to trip/fall face down on that thing. Hard to believe that may be fairly new construction, but WTH? Looks like the bracket itself may be heavy galvanized, to meet spec????????

                      A better learning experience among my many, was a six month project, where the inspector was a retired 20 year Corps of Engineers man. Plan docs called for warehouse hardware to be installed using brass screws, NOT brass plated screws, or whatever the devil they were. And, the builtup roof work got shut down: One too many 'fishmouths', try it again when the weather warms.

                      G

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                      • #12
                        I noticed the base plate connections myself,not to good of a job.The plates themselves aren't big enough and the anchor count and size is wrong.It's probably adequate,but just barely.

                        Four coil rods on each base would have been better with the proper spherical seat washers underneath.The rods should have been tacked off and then cut off if for no other reason but looks.
                        I just need one more tool,just one!

                        Comment


                        • #13
                          I'm not a construction expert, but I would bet it is a lot easier to clean off any concrete splashes on that kind of thread as opposed to a regular Vee or even an acme.
                          Paul A.

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

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                          • #14
                            I have to agree, the anchoring looks rather crude. The carpentry on the bridge itself seemed okay.

                            Allan Ostling

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                            • #15
                              Unless there's some sway bracing (diagonal) under that deck, it's another "Galloping Gertie".

                              Google "millenium bridge london"

                              Some engineers still don't get it!
                              Just got my head together
                              now my body's falling apart

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