Discussion: View Thread

  • 1.  Base plate connection

    Posted 01-12-2018 04:45 PM
    Edited by Tirza Austin 01-15-2018 09:17 AM
    Hi All,

    We are upgrading a compression testing machine from 1250 kN capacity to 5000 kN. The reaction frame consists of four W12x87 columns. The column is welded to a 1 1/4" base plate and attached to the footings using two 2" anchor rods. Now after increasing the tensile load on the column, four times, the base plate and the fillet weld between the column and the plate are unsafe. What I am asking is there any option rather than cutting the existing base plate and weld a new thicker one using groove weld? 
    Please find attached the detail dimensions. Thanks in advance for your input


    ------------------------------
    Ahmed Ashour P.Eng, Ph.D., M.ASCE
    St-Laurent QC
    ------------------------------


  • 2.  RE: Base plate connection

    Posted 01-18-2018 09:33 AM
    Just because you've increased the tension on the columns 4X does not mean you have overstressed the welds that much. First, see how overstressed the welds are and then, if there is sufficient space you could transfer the loads to the baseplate through stiffeners designed for the difference in forces.
    The stiffeners would also change the force distribution in the baseplate possibly making them strong enough for the additional loads.

    ------------------------------
    Nathan Smith P.E., M.ASCE
    Engineer
    Engineered Steel Products, Inc.
    Randleman NC
    ------------------------------

    Original Message


  • 3.  RE: Base plate connection

    Posted 01-18-2018 09:34 AM
    Easy fix may be to fit plates 11" by 7 1/4" by (say)1 1/4" thick, with appropriate drilled hole, each side of the web of the column. Drilled to match existing hole, chamfer lower side of plates to clear existing welds. Then weld new plate all round with 8mm weld. Could be done in situ but protect 2" rods from weld spatter or currents.
    Cheers       Ian Simpson, MASCE, FIEAust

    ------------------------------
    Ian Simpson P.E., M.ASCE
    Engineering Manager
    Austral Construction
    Dandenong
    Victoria
    Australia
    ------------------------------

    Original Message


  • 4.  RE: Base plate connection

    Posted 01-18-2018 09:34 AM
    Regarding my previous suggestion of adding a plate above that existing, hopefully there is enough HD bolt projection to allow full engagement of the nut if the overall plate thickness is increased? 
    Of course the HD bolts and anchorage into the footing would also need re-evaluation.
    Best regards

    ------------------------------
    Ian Simpson P.E., M.ASCE
    Engineering Manager
    Austral Construction
    ------------------------------

    Original Message


  • 5.  RE: Base plate connection

    Posted 01-18-2018 09:34 AM

    I could not see the attachment. I assume your anchor bolts are also inadequate; although this option would work even if they are OK. Assuming the anchor bolts are typical and in the corners of the base plate, you could add angles to the flanges and web (4 total), either welded or bolted, and then post install new anchors to the foundation; adhesive or undercut anchors. You would still have to grind some weld to get a tight fit for the angles against the column. Welding would probably be more feasible than bolting to the column also. I haven't run the numbers to see what sizing would be needed, but I don't think it would be astronomical. With the new connection, you basically have just turned the baseplate into a large shim plate. Depending on the size of the plate and the angles, you may also need to add additional shim outside the baseplate if the angle overhangs, and weld in place.

    Might not be the prettiest fix, but just a thought - and not have to lift anything!



    ------------------------------
    Jeff Teagarden P.E., M.ASCE
    Structural Project Manager
    ADTEK Engineers, Inc.
    Frederick MD
    ------------------------------

    Original Message


  • 6.  RE: Base plate connection

    Posted 01-18-2018 09:34 AM
    Edited by Tirza Austin 01-18-2018 09:33 AM
    ​I wasn't able to find a sketch attached but here are some options I think you could consider.

    1. Depending on the strength that needs to be made up in the weld you could increase the fillet weld size by adding more passes. This might depend on knowing the original weld material specs
    2. Add stiffeners around the anchor bolts to reduce the span of the base plate so that it works in bending. You need to get all the load into the stiffeners that you are depending on to reduce the plate span.
    3. It would seem that the bolts themselves may not have the tension capacity needed for the new uplift. In that case you need to add bolts along with stiffeners around the column face.

    There are probably a large variety of ways to develop a solution.


    ------------------------------
    Brett King P.E., M.ASCE
    Senior Structural Engineer
    GHD Inc.
    Lake Oswego OR
    ------------------------------

    Original Message


  • 7.  RE: Base plate connection

    Posted 01-18-2018 02:45 PM
    Thank you all for your reply. I would like to thank also Dr. Ronald Cook and Debu Bhaumik for replying by email. I think now I have so many options to consider. I am not concerned about the footing, the lab strong floor is well detailed so that each rod can resist up to 1000 kN.
    Using Abaqus model, I will try first adding vertical stiffeners between the column's web and the base plate, it might be interesting also to consider doubling the base plate as suggested by Ian. 

    Thanks again, I do appreciate all your constructive comments.


    ------------------------------
    Ahmed Ashour P.Eng, Ph.D., M.ASCE
    St-Laurent QC
    ------------------------------

    Original Message


Related Content