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Calculating defelction of concrete

  1. Oct 9, 2014 #1

    Ranger Mike

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    I have a large machine that must be installed on concrete foundation. It can have no more than 20 micron deflection. Are there different types of concrete?
    The specs i have from the manufacturer recommend Foundation block reinforced concrete C30/37.
    this is 1500 mm deep foundation that is 7730 mm long and 6000 mm wide.
    i have a 34,000 pound granite plate on the concrete and 30,000 pound part resting on it. The gantry machine surrounds the part and plate and weighs less than 30,000 per side
    Any tips of links that will assist are much appreciated.
  2. jcsd
  3. Oct 10, 2014 #2


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    Most assuredly, yes.

    It's not clear where your foundation is located or if it's built yet. Either way, you should talk to a civil engineer about this foundation. It's not something you're going to mix up in a wheelbarrow using a couple bags of Sak-crete and pour yourself. It's also probably not going to set overnite either, so you'll want to have the setting monitored to make sure the concrete has reached its maximum strength. The concrete probably should be tested before installing your machine.

    If your foundation is a solid block, your pour is going to be almost 91 cu. yards of material, and a single cement mixing truck might be able to carry about 8 yards of wet cement. You can expect to pay in the range of $120-$200/yd. of cement delivered, so I would call around to several suppliers and get estimates for a job this size. IDK how much arranging and installing the necessary re-bar will run you.
  4. Oct 13, 2014 #3


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    Sounds like a BIG coordinate measuring machine... Is it realistic to expect less than 20 microns of deflection out of such a large structure?
  5. Oct 14, 2014 #4
    Could probably use a laser tracker instead of a CMM. However, 20 micron deviation over 7.7m does seem rather tight.
  6. Oct 14, 2014 #5

    Ranger Mike

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    acutally a big CMM with 4 meter x 5 meter x 2 meter travel
    spec is 6.9 + L/350 per ISO 10360-2/4 with SP25 scan probe
    laser not that accurate
  7. Oct 14, 2014 #6
    Well yes, a CMM is more accurate compared to a laser tracker.
  8. Oct 14, 2014 #7

    Ranger Mike

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    i been selling cmms since 1980...lol
  9. Oct 14, 2014 #8
    That is a long time. For my previous project at work, I had to research various 3d measurement system. CMMs were excluded because they aren't very mobile, which was one of the requirements.

    Just out of curiosity, what is the accuracy of the CMM you will use to measure the deflection?
  10. Oct 14, 2014 #9

    Ranger Mike

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    the customer is responsible for the foundation..we recommend Euro spec C 30/37 for the concrete and if it is met the cmm will be good to go.
    A laser plane scanner is probably best to find the deflection i would think.

    FYI- we use the ISO standard 10360 to measure the machines uncertainty. Basically a series of bi directional measurements of gage step bar that is up to 2000 mm long and is certified by calibration lab. there are about 105 measurements taken in three directions and the procedure is repeated three times. The calculations are made and the accuracy or degree of uncertainty is determined for the volume.
  11. Oct 15, 2014 #10

    Ranger Mike

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    Weight of complete machine is approx.. 17000 kg * 2.204623 lbs/kg = 37500 lbs.

    - weight of the bridge/portal (dynamic mass) is approx.. 4000 kg * 2.204623 lbs/kg = 8820 lbs

    - weight of the right rail is approx.. 7000 kg * 2.204623 lbs/kg = 15450 lbs

    - weight of the left rail is approx.. 6000 kg * 2.204623 lbs/kg = 13230 lbs

    Granite Table

    - 3500 x 4500 x 355.6 mm

    - Grade AA, 0-Ledge Black Granite Surface Plate with (50) ¼-20 threaded inserts

    - 33,643 lbs

    - (3) pedestals and leveling jacks 14” x 14” and thickness specified by customer depending upon working height needed.

    - <image002.jpg>


    - Size of foundation and tub as specified on the attached drawing, R20.

    - Foam lining per the attached drawings, though substitutions are allowed; i.e. an Owen Corning product of similar characteristics which is locally available.

    - Foundation concrete type could be Portland Cement, Class A with modifications to meet the European Specification C30/37, as noted in the drawing, R20.

    - Tub concrete type could be Portland Cement, Class A with modifications to meet the European Specification C20/25, as noted in the drawing, R20.

    - Foundation should be reinforced with rebar as appropriate to meet the requirements noted above. For example, Mk606 bars on 12” O.C. spacing, in all directions may be appropriate and adequate to meet current standards and local codes.

    I am having difficulty with what the rebar Mk606 specs are? When going for a quotation for the foundation contractor i need to have this foundation not deflect when i put a 33,000 part on the granite plate.
    How much rebar do i need to prevent deflection over 20 micron when the part is loaded on to the plate?

    do i need nitrogen sprayed while pouring concrete to reduce heat build up?
    Last edited: Oct 15, 2014
  12. Oct 15, 2014 #11


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    There's no drawing attached to your post.

    Again, for such a critical function as this foundation serves, and the small tolerances allowed, soliciting advice thru an anonymous forum is not recommended. You need to talk to an experienced foundation engineer, one who can review your drawings, inspect the equipment to be installed, and evaluate the site where the installation is to take place. I don't think you can just turnkey this process without some first-hand knowledge of what's going on and where this machine is supposed to go.

    It appears that the manufacturer of the machine has specified a lot of European standards to follow, which standards may not be familiar to engineers practicing outside of Europe, but it's not clear if this machine is being installed in Europe. There seems to be a mixture of metric items and USCS items being used, which could present complications if not carefully managed.

    I'm not familiar enough with concrete construction to know if it is even technically feasible to engineer a foundation which won't deflect 20 microns under load. I suspect anchoring a steel foundation in concrete might be an alternative, but that's why you should consult with a foundation engineer.
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