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Grout Bases for Columns

  • 1.  Grout Bases for Columns

    Posted 06-12-2019 06:50 PM
    Edited by Tirza Austin 06-12-2019 06:50 PM
    I am working in CA on a project far from my office.  In browsing some incidental photos of a subgrade pipe installation, I noticed what appears to be a gap opening between the fresh grout base and column base plate.  The resolution of the images I have is not adequate to make out where the leveling plate is located relative to the gap (top of grout or bottom of base plate).  Unfortunately, the base plates are now cast into the slab on grade and no longer visible.  The special inspector was apparently not on site between the installation of the grout base and the slab on grade pour.

    I have been trying to puzzle through the consequences of what intuitively seems like a pretty severe issue.  Some posters on the following Eng-Tips forum seem to believe the grout base is extraneous:
    https://www.eng-tips.com/viewthread.cfm?qid=300734

    I expect cracking at service load at the joints around the column.  However, when fully loaded, the column will close the gap and bear on the concrete (albeit unevenly) rather than the anchor bolts, so the load path seems credible for gravity at ultimate.  The only columns subject to uplift are connected to HSS braces and further reinforced by concrete grade beams (tied directly to the gusset via embed plates).  Is proper installation of grout essential when using a leveling plate?  What might be some other consequences of a small gap?

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    Christian Parker EIT,A.M.ASCE
    Structural Project Engineer
    Washington DC
    (202)628-1600 EXT 190
    ------------------------------


  • 2.  RE: Grout Bases for Columns

    Posted 06-13-2019 10:04 AM
    Christian, having a complete grout base under a column base plate does not necessarily mean that the base plate installation is inadequate for the imposed loads.  It is highly doubtful that the loading of the column will close the gap between the base plate and grout as the leveling plate and/or anchor rods were installed with leveling nuts on the rods.  The leveling nuts will prevent the baseplate from moving downward to close the gap. 

    Have you ever noticed base plates on light poles?  Sometimes there is no grout between the base plate and the concrete pier.  The loads from the light pole is transferred to the pier through only the anchor rods with no assistance from a grout base.

    ------------------------------
    Dennis Young M.ASCE
    Owner/principle
    Young Engineering, LLC
    Omaha NE
    (402)983-1154
    ------------------------------

    Original Message


  • 3.  RE: Grout Bases for Columns

    Posted 06-13-2019 11:51 AM
    Thanks Dennis.  The leveling plates were installed with the grout; they do not bear on leveling nuts.

    ------------------------------
    Christian Parker EIT,A.M.ASCE
    Structural Project Engineer
    Washington DC
    (202)628-1600 EXT 190
    ------------------------------

    Original Message


  • 4.  RE: Grout Bases for Columns

    Posted 06-15-2019 09:57 PM
    Edited by Tirza Austin 06-15-2019 09:56 PM
    Dennis:

    Did you ever see a standard Specification of any kind give you the parameters for calculating the bearing capacity of anchor bolts, let alone the  means for handling combined vertical load (+/-), shear and bending action?  I assume that the "pole people" have demonstrated their bold capacity by uniquique, specific.testing. 

    I have been in the design field since 1960 and have never come across a code that provided the means for using bolts for other than tension above the foundations.  We always had to come up with out own design for anchorage capacity.  This was always an issue with "Pre-engineered" rigid frames whereby the base shears were given to the bottom of the base plates, usually without shear lugs, and we were (probably still are) responsible to come up with some approach, not including friction, to accommodate the building shear forces.

    Maybe things have changes and slipped past me.  This old dog is certainly open for correction and new solid ideas.


    ------------------------------
    Allen Hulshizer P.E.,F.ASCE
    Consulting Structural Engineer
    Chalfont PA
    (215)8872838
    ------------------------------

    Original Message


  • 5.  RE: Grout Bases for Columns

    Posted 06-13-2019 10:04 AM
    Edited by Tirza Austin 06-13-2019 10:03 AM
    Christian:

    I have been in the design and construction since 1960 and in all the practices for grouting major column bases we stayed away from using leveling plates because experience showed that the end results were not always what we were after.  Leveling nuts on the anchor bolts also raise questions about the final load bearing mechanism.

    Our practice in all cases, industrial, commercial, nuclear ws to use shim plated on the out side edges and after the grout was set requires the removal of the shims and the grout patched with non-shrink material.  This is also the way we required major equipment to be placed and grouted.  

    Proper placing of flowable, non shrink grout, if placed by flowing it under head from one side to the other can be achieved with almost 100& contact.  On large BP's some time we used "air holes" to watch the  grout flow across the plate as the grout came up thru the hole (also let air escape) while under the proper placing/flowin head.

    We found it important to have the grout placed under the dead load, when the grout has set then remove the shim plates before tightening the anchor bolts. I have seen cases where the anchor bolts where torqued down with out the grout in place with the result that the "local" load on the small shim area produce a high force enough to break off the edge of the walls and columns.



    ------------------------------
    Allen Hulshizer P.E.,F.ASCE
    Consulting Structural Engineer
    Chalfont PA
    (215)8872838
    ------------------------------

    Original Message


  • 6.  RE: Grout Bases for Columns

    Posted 06-14-2019 07:41 AM
    Edited by Tirza Austin 06-14-2019 07:41 AM
    Shim plates are essentially wedges to preserve a gap prior to grouting.... The Grout itself then holds the base plate and column at the correct level, therefore this grout does augment the long-term structural role of the holding down bolts and needs to be free of voids with air holes vented out. Thanks for mentioning this Allen.

    ------------------------------
    Tim Clark, FRAS, R.A., M.ASCE,
    President Emeritus RIBA-USA,
    Deutsche Bahn Engineering,
    Bavaria, Germany.
    ------------------------------

    Original Message


  • 7.  RE: Grout Bases for Columns

    Posted 06-13-2019 04:47 PM
    Edited by Tirza Austin 06-13-2019 04:47 PM
    This might be similar to a typical Precast column base detail. But before commenting any further, would you kindly provide a sketch of what you described?

    ------------------------------
    Neil Kazen, M.Eng., M.Sc., P.Eng.
    FASCE, FCPCI, FEC,
    Retired Structural Engineering Manager, Transportation Division, SNC-Lavalin
    Toronto, Ontario, Canada
    ------------------------------

    Original Message


  • 8.  RE: Grout Bases for Columns

    Posted 06-15-2019 09:27 AM
    Edited by Tirza Austin 06-15-2019 09:27 AM

    What's described might appear to be a typical column. More structural detail and a sketch is required. In this typical case, if the column is designed to be a gravity column, nuts are bearing vertical loads and thus far, the nuts should be designed to be adequate.  However, in the case of a firm base plate on the grout, the nuts and level base plate bond with the grout to provide a strong foundation. There are a few reasons for the gaps in between the column and the base plate; first, the column you seen might be a tension seismic column. Second, the column might be designed to fail right at the gap. This usually a design method for poles. If you design a pole column that's firm to the grout, the impact is either to the column or into the grout which  both replacing the column or pour in grouts are cost effective, so, in order to save the column and the grout, let the joint to bear the impact and that's the reason there's a gap between the column and base plate.   


    ------------------------------
    Sayed Maqsood S.M.ASCE
    Alameda CA
    (510)830-6285
    ------------------------------

    Original Message


  • 9.  RE: Grout Bases for Columns

    Posted 06-16-2019 08:50 AM
    Edited by Tirza Austin 06-16-2019 08:49 AM
    I'd double check your details for the job and ask around the office. If you still think the base plates are not built to detail call the contractor. If no resolution is met a progress report to the client may be needed.

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    Elliot House P.E.,S.M.ASCE
    W.B. Clausen Structural Engineers
    Emeryville CA
    (415)444-4144
    ------------------------------

    Original Message


  • 10.  RE: Grout Bases for Columns

    Posted 06-16-2019 08:48 AM
    Columns for structural columns are generally grouted.

    I suggest that you check the project drawings and specifications, and talk with the special inspector to determine the actual condition.

    You may need to cut the slab to expose the condition to verify that the base plates are or not grouted.

    You may have a serious condition that requires repair.

    Notify the EOR about your concerns imeadiately.



    ------------------------------
    William Scott M.ASCE
    Scott Engineering
    Port Townsend WA
    (907)952-6019
    ------------------------------

    Original Message


  • 11.  RE: Grout Bases for Columns

    Posted 06-17-2019 01:56 PM
    Edited by Tirza Austin 06-17-2019 01:56 PM
      |   view attached
    Thank you all for your help.  Here is a sketch of the as-built condition, based on photos.  I do not know whether they used temporary shims, but my working assumption is that they leveled the plate with the wet grout, which was the design intent.  To clarify, my firm is the EOR on this project.

    ------------------------------
    Christian Parker EIT,A.M.ASCE
    Structural Project Engineer
    Washington DC
    (202)628-1600 EXT 190
    ------------------------------

    Attachment(s)

    pdf
    BPSketch.pdf   962 KB 1 version
    Original Message


  • 12.  RE: Grout Bases for Columns

    Posted 06-17-2019 06:22 PM
    Edited by Tirza Austin 06-17-2019 06:21 PM
    Christian:

    Not a good situation if there is actually a gap between the leveling plate and the base plate.  Of course it will eventually drop to make up the gap.  For over 50 years I have always been specifying the use of shim plates and their removal after the grout sets and the shim hole grouted.

    Of course, if that gap really exists it gives you an idea of the kind of work you can expect in other parts of the job.


    ------------------------------
    Allen Hulshizer P.E.,F.ASCE, FACI
    Consulting Structural Engineer
    Chalfont PA
    (215)8872838
    ------------------------------

    Original Message


  • 13.  RE: Grout Bases for Columns

    Posted 06-18-2019 07:54 AM
    Edited by Tirza Austin 06-18-2019 07:54 AM

    For the typical it's ok. Thank you for providing the sketch. It's an uplift wide flung column braced to the hollow structural section. The uplift tension force would determine the number of anchors to be used to resist the uplift force due to bracing. It's often not a good situation to brace light influenced members, because it would cause to increase the uplift force. However, there are many ways to attach the column to the foundation to bear the uplift force. There's also a minor possibility that installation of the braces and the beams are prioritized that would left the column to be un-adjusted as well.



    ------------------------------
    Sayed Maqsood S.M.ASCE
    Alameda CA
    (510)830-6285
    ------------------------------

    Original Message


  • 14.  RE: Grout Bases for Columns

    Posted 06-18-2019 12:02 PM
    OSHA 1926 requires a minimum of four anchor bolts on all steel columns. Shims are needed to level the column unless leveling nuts are used. 

    The column base should be fully grouted to conform to the design of the base plate.

    ------------------------------
    William Scott M.ASCE
    Scott Engineering
    Port Townsend WA
    (907)952-6019
    ------------------------------

    Original Message


  • 15.  RE: Grout Bases for Columns

    Posted 06-19-2019 02:24 PM
    Sayed,

    Only a few columns on this job are subject to net uplift.  In any event, the top AB connections are fine for uplift; our concern is that the column is unsupported below the base plate, in the typical cases of net downwards loading.  We did consider the possibility that the braces are taking more of the gravity load than they're meant to, but the line containing three hovering columns (see my most recent comment) does not have any braces, so this would not explain the worst cases.  As for the possibility that the they are awaiting final adjustment for some other erection milestone, this does not appear to be the case as neither the GC nor the concrete sub even believed that there was a gap until we stuck a 1/8" feeler gauge in it.

    ------------------------------
    Christian Parker EIT,A.M.ASCE
    Structural Project Engineer
    Washington DC
    (202)628-1600 EXT 190
    ------------------------------

    Original Message


  • 16.  RE: Grout Bases for Columns

    Posted 06-19-2019 05:46 PM
    Edited by Tirza Austin 06-19-2019 05:45 PM
    How thick was the grout and did they use non-shrink grout?

    A properly installed base plate will have full grout contact, no gaps for any reason!!!

    ------------------------------
    Allen Hulshizer P.E.,F.ASCE, FACI
    Consulting Structural Engineer
    Chalfont PA
    (215)8872838
    ------------------------------

    Original Message


  • 17.  RE: Grout Bases for Columns

    Posted 06-19-2019 10:13 PM
    Edited by Tirza Austin 06-19-2019 10:12 PM
    Allen's comment is right on point. As far as the downward loading and the base plate are concerned. The grout might have shrinked with the shrinkage factor of 1-5%.

    ------------------------------
    Sayed Maqsood S.M.ASCE
    Currently Looking for Employment
    Alameda CA
    (510)830-6285
    ------------------------------

    Original Message


  • 18.  RE: Grout Bases for Columns

    Posted 06-19-2019 02:24 PM
    Edited by Tirza Austin 06-19-2019 02:23 PM
    I appreciate the feedback.  I will keep shim plates and different grouting techniques in mind in the future. 

    We visited the site yesterday and got a good look at the handful of columns that are still exposed to view.  It's much as we feared.  Most of the base plates have a measurable gap with the leveling plate on two or more sides.  Three columns are hovering with no contact whatsoever to the leveling plate. (We speculate that either there is some loose gravel or the rough edges of the plate holes are caught on the threads of the anchors.)  In at least one case, there is also delamination of the leveling plate from the grout.  The metal deck above is fastened to steel and the pour is scheduled for the end of this week.  It looks like we're going to get everything documented in a report, then write the architect and owner to see where we go from here.  My concerns at this point are:

     - Cracking in the slab
     - Noisy release under service load
     - Fatigue damage due to cyclic variation of bearing length
     - Impact to the grout upon release
     - Secondary moment in the columns under eccentric bearing, base rotation
     - Overstress in moment connections on upper floors under support settlement

    What are everyone's thoughts on these and other consequences?

    ------------------------------
    Christian Parker EIT, A.M.ASCE
    Structural Project Engineer
    Washington DC
    (202)628-1600 EXT 190
    ------------------------------

    Original Message


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