Integrated Buildings & Structures

  • 1.  Welding Structural Nuts

    Posted 03-09-2020 02:19 PM
    A common question from the shop or field is, "Can we just weld the nut?"

    You are unlikely to get a "Yes" answer from the manufacturer, AWS, or AISC.  Most agree that it is a bad idea, but will stop short of saying no, leaving it up to engineer's judgment.

    Here are a couple of questions to get the discussion started:

    If welding of high strength bolts is prohibited, can A307 bolts be specified instead of A325 bolts?  Are the nuts the same A563 material for both bolts?

    If F1554 threaded anchors are installed to short and an A563 nut is only installed with half the thread engagement, can a plug weld be used as a field fix?

    Are there any cases where welding a nut is specifically allowed and desired?

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    Chad Morrison P.E., M.ASCE
    Professional Engineer
    Greenville RI
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  • 2.  RE: Welding Structural Nuts

    Posted 03-10-2020 10:03 AM
    What is the reason for welding the nuts? A563 is not listed as an approved base metal in either clause 3 or 4 of AWS D1.1 2015( I have not purchased my copy of the newly released edition). A563 is a medium carbon steel that is heat treated. The heat from welding will change the mechanical properties of the steel so the question becomes  will the resulting changes to the base metal meet the design requirements.  If there is a serious need to weld the nuts, which I don't  see now, determining the carbon equivalence would be a first step towards preparing the required weld procedure specification (WPS) and procedure qualification record (PQR) necessary for production welding. Hydrogen cracking is a big concern so pre heat and PWHT would most likely be included in the WPS. Post weld heat treatment is not necessarily easily accomplished in the field. Which leads me back to the beginning of my response "what is the reason for welding the nuts".

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    Matthew Beck P.E., M.ASCE
    Engr
    Beck Engineering Pc
    Bondville VT
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  • 3.  RE: Welding Structural Nuts

    Posted 03-10-2020 10:55 AM
    My understanding is that the amount of heat treatment applied to the A563 will determine if it can be welded or not.

    https://www.portlandbolt.com/technical/faqs/weldable-nut-grades/

    Thus, the grade needs to be specified and known.

    The application is also important.

    A blind field connection where a stringer channel is erected against a wall might require the nut to be tack welded in the shop.

    The other example I gave was a plug weld in a nut installed on an anchor rod.  These are requests from the shop and field, not ideas specified by an engineer or QC inspector.

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    Chad Morrison P.E., M.ASCE
    Professional Engineer
    Greenville RI
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  • 4.  RE: Welding Structural Nuts

    Posted 03-10-2020 10:43 AM
    My answer would be "You know better than that!"

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    Stacey Morris P.E., M.ASCE
    ETI Corporation
    West Memphis AR
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  • 5.  RE: Welding Structural Nuts

    Posted 03-10-2020 10:46 AM
    Never weld nuts is a good answer!  But it may not satisfy the shop or field, the question does persist which is an indication that more awareness of the dangers is needed.

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    Chad Morrison P.E., M.ASCE
    Professional Engineer
    Greenville RI
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  • 6.  RE: Welding Structural Nuts

    Posted 03-10-2020 08:47 PM
    Never weld high strength nuts, due to the potential loss of strength on the nut. A tack weld is possible, as it is around the perimeter of the nut and can neither be on the bearing surface, nor affect the threaded portion of the nut. The tack weld is not structural and should only be large enough to hold the nut in place for the blind assembly. But note also that there are proprietary bolt assemblies that can be inserted through a blind hole and tightened from one side only, and these assemblies are AISC/ICC accepted, so you can say no.

    Never on anchor bolts where the nut does not totally engage the threads. The GC must have been sloppy in setting the embedded bolts and there is no reason to believe that they will get more careful during the welding process. Best to replace the embedded bolt with an epoxy anchor. (I had a project where we specified 1/2" epoxy bolts. The GC used 1/2" wedge anchors and then asked for approval. I told the GC to drill it out and replace it with the specified bolt. The GC moved the anchor plate, ground off the bad bolt and used an epoxy anchor half the length specified. This went on for a while, ending with a 1" diameter rod embedded 36 inches into a pile cap. This was part of the lateral force resisting system for a huge building, thus was critical to be adequate. All because they could not (or would not) put in the originally specified 1/2" bolt.)


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    William Kirkham Ph.D. Ph.D., P.E., M.ASCE
    Director MCE Program
    The University of Kansas
    Overland Park KS
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  • 7.  RE: Welding Structural Nuts

    Posted 03-10-2020 10:50 PM
    My understanding, we can see weldability by the carbon equivalent of the steel. there some formula to calculated CEV.
    after calculated that we can define the weldability of the steel material.

    https://en.wikipedia.org/wiki/Equivalent_carbon_content

    in BS EN 1090-2-2018, Clause  8.2.1 Bolts and nuts shall not be welded,unless otherwise specified. This restriction does not
    apply to special weld nuts according to e.g. EN ISO 21670 or weldable studs

    https://www.portlandbolt.com/technical/faqs/bolt-welding-guidelines/

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    Hendi Hendi Aff.M.ASCE
    Field Design Manager
    Bogor
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  • 8.  RE: Welding Structural Nuts

    Posted 03-11-2020 01:09 PM
    As a retired civil engineer and AWS welding inspector from California Do Not weld or tack weld HSB.  It will destroy the connection.

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    Clifford Craig P.E.,M.ASCE
    VP Technical Operations
    Walnut Creek CA
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  • 9.  RE: Welding Structural Nuts

    Posted 03-12-2020 06:17 AM
    ​Hello,

    AISC Design Guide 17 Section 5.4.11 discusses this topic in detail. Table 5-2 summarizes weldability of different grades and only A307 Grade A or B with Supplementary requirements S1 offers better control compared to all other grades based on CE limit. An indication of 'Relative Weldability' is also provided in the same table which is 0 for A307 Grade A/B (S1) whereas 5 for A325.

    When serviceability of connection depends on welded nut itself, alternatives should be worked out.

    Regarding your question on Field Fix for anchors installed too short, Flare groove weld can be used for Gr 36 or Gr 55 with S1. Gr 55 without S1 is not weldable. You may also think of using a coupling Nut.

    Regards,

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    Rushikesh Trivedi
    P. Eng. (India), C. Eng, MASCE
    Lead Engineer
    Fluor India
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