Discussion: View Thread

  • 1.  Limit of number of shim plates in connection

    Posted 03-12-2018 09:55 AM
    Edited by Tirza Austin 03-12-2018 09:54 AM
    Hi Steel Structural Engineers,

    In our project with huge steel truss structure for roofing and I noticed that the Contractor is using multiple shim plates between flanges of a joint connection.
    Is there a limit on number of shim plates allowed in connection especially in major connection be it on trusses or other steel structure?
    Can you give the details of any code if any?
    Thank you in advance.


    ------------------------------
    Angelo Alieto P.E., C.Eng, M.ASCE
    Site Engineer
    KEO International Consultants
    Doha
    ------------------------------


  • 2.  RE: Limit of number of shim plates in connection

    Posted 03-12-2018 11:19 AM
    Section J5 of Spec. AISC 360 discusses use of filler/shim plates up to 3/4" thick.  The shear value of the bolt is reduced by a factor given in J5.  The number of shim plates is irrelevant.  Once the total thickness of the filler plates exceeds 3/4" you need to use judgment.  Is the connection in bearing?  What kind of shear are the bolts subjected to?  For gaps exceeding 3/4", shim/reinforcement plates should be welded to the member.  The weld and the plate need to be designed for the forces it is expected to be subjected to: the full connection force or the shared force from the member element it is attached to.

    ------------------------------
    Chad Morrison P.E., M.ASCE
    Professional Engineer
    Greenville RI
    ------------------------------

    Original Message


  • 3.  RE: Limit of number of shim plates in connection

    Posted 03-13-2018 02:04 PM
    Good points by engineer Morrison.

    I have seen a cacophony of shimming and gusseting due to dimensioning, alignment, coping, etc. issues of steel (and aluminum) member connections in the field. Every case needs to be considered on its own merits. For any steel structure, assume some kind of welding at some point will be necessary. Almost always there will be more welding by the time the job is finished than you may have expected at the beginning. Then you come up against hot-dipped galvanized member connection problems; even if there is a metallizing rig available, it is still a challenge to layout the field weld so that it is accessible to the prep and finished blasting.

    It seems the structural engineer's job is not done until the keys are handed to the owner.

    ------------------------------
    Robert Bullard P.E., M.ASCE
    President
    Ahimsa Technic Inc
    Ponce Inlet FL
    ------------------------------

    Original Message


  • 4.  RE: Limit of number of shim plates in connection

    Posted 03-14-2018 09:57 AM
    Edited by Tirza Austin 03-14-2018 09:57 AM
    AISC 360 J5 states, "in welded construction, any filler 1/4 in. or more in thickness shall extend beyond the edges of the splice plate and shall be welded to the part on which it is fitted with sufficient weld to transmit the splice plate load....."
    For bolts through fillers adding up to 3/4 inch there is a reduction in bolt shear value. it appears that 3/4 inch is the maximum with fillers that are bolted.  You can check AWS and see if they have other conditions for thicker shims.

    ------------------------------
    Martin Fradua P.E., F.ASCE
    Vice President
    Huntington NY
    ------------------------------

    Original Message


  • 5.  RE: Limit of number of shim plates in connection

    Posted 03-16-2018 11:57 AM
    Hi,

    Thanks for your prompt response.
    Bolts are subjected to tension.
    Does allowed 3/4" on AISC 360 J5 also applicable if the joint connection is slip critical. Can the 3/4" thick of shimming be of multiple shim plates?




    ------------------------------
    Angelo Alieto P.E., C.Eng, M.ASCE
    Site Engineer
    KEO International Consultants
    Doha
    ------------------------------

    Original Message


  • 6.  RE: Limit of number of shim plates in connection

    Posted 03-17-2018 11:00 AM
    The filler reduction factor does not need to be applied to the slip critical bolt value.  The faying surface of the shims needs to match or be more slip resistant than the steel members.  The fillers should not impact the tensile performance of the bolts.  If they are installed as slip-critical, the specified pretension needs to be achieved upon installation.  The number of shims does not matter.  The number of bolts matters... is this a 2 bolt connection or 10 bolt connection?  How comfortable are you that the bolts are going to perform per the intended design?  More bolts can be used to account for some of the unknown factors of the design.

    ------------------------------
    Chad Morrison P.E., M.ASCE
    Professional Engineer
    Greenville RI
    ------------------------------

    Original Message


Related Content