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Anchor Bolt Design with respect to Petrochemical Facilities

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  • 1.  Anchor Bolt Design with respect to Petrochemical Facilities

    Posted 06-23-2020 06:41 PM
    Hi,

    I am facing a challenge in the current project i am working on. We are designing the Pedestal and the Anchor bolt for the Steel Column to Pedestal Connection and we are using Anchor rods with tack welded Heavy Hex Nut at the bottom with washer Plate. Since the forces are quite Huge we have used Anchor Reinforcement for the Tension and Shear Breakouts. The problem we are facing is with regards to "Pry Out" failure under shear loads. We are not able to satisfy the Pry Out Capacity.
    Now reading a little literature and the code commentary i understand that PRY OUT failure mainly happens for  Short and Stiff anchors around 4 to 6 times diameter. The code treats the failure as a pseudo Tension failure and uses the same capacity as that of tension cone break out, since the failure cone for pry out and tension breakout are both very similar and start from the head of the anchor bolt.
    The anchor bolts that we typically use have a minimum 12d embedment and mostly much more than this to provide sufficient development length to rebar above and below the failure plane. My Question is :

    1.) Is the same clause applicable for such long anchors, since pryout seams improbable in such a circumstance. Should we rally check Pry out for anchor bolts around 12 times diameter.
    2.) Since the capacity for the Pry out is a step function based on the Tension cone breakout capacity varying from 1 times to 2 times the Breakout capacity, can we use the capacity of  Anchor reinforcement instead of concrete, since the same reinforcement which prevents  the tension cone breakout will also tie the pry out failure crack.

    Will really appreciate your feedback.

    Thanks




    ------------------------------
    Mandeep Singh Kohli CP, M.ASCE
    Senior Engineer
    India
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  • 2.  RE: Anchor Bolt Design with respect to Petrochemical Facilities

    Posted 06-24-2020 12:32 PM
    Check this paper: https://www.pci.org/PCI_Docs/Publications/PCI%20Journal/2005/March-April/Pryout%20Capacity%20of%20Cast-in%20Headed%20Stud%20Anchors.pdf

    ------------------------------
    Subramanian Narayanan, Mentor, Consultant and Author
    Chief Exec
    Computer Design Consultants
    Gaithersburg, MD
    ------------------------------



  • 3.  RE: Anchor Bolt Design with respect to Petrochemical Facilities

    Posted 06-24-2020 01:28 PM
    Do not tack weld a nut to a high strength threaded rod.  It can result in brittle failure.  I recommend a double nut sandwiching the washer and upsetting the threads or a headed stud.  Try a design software like Hilti Profis and see if you can match its results with your analysis.

    https://collaborate.asce.org/integratedstructures/communities/community-home/digestviewer/viewthread?GroupId=9289&MessageKey=d5938fbb-d120-414e-9f09-629a9bf1a851&CommunityKey=6d0d80c2-458a-49ad-aa81-212c38ccf106&tab=digestviewer


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    Chad Morrison P.E., M.ASCE
    Professional Engineer
    Greenville RI
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  • 4.  RE: Anchor Bolt Design with respect to Petrochemical Facilities

    Posted 06-25-2020 09:04 AM
    Generally I would suggest one follows ASCE's Anchorage Design for Petrochemical Facilities, in conjunction with PIP STE05121. Both are specifically aligned to petrochemical plant type projects. If you're working to US codes & standards, then ACI 318 will likely be the code of record. Which specific version (-05, 08, -11, -14, -19) etc will determine the specific code requirements to be followed. Within the ASCE and PIP there are subsequent references. In respect to your specific problem, its a mix of anchorage problems both in the bolts and reinforcement. If you could argue you have a bond / anchorage problem with the anchor bolts lapping onto the top-hat reinforcement and then use standard L-bars, one can look to use the full pedestal cross-section to resist pull-out.

    ------------------------------
    Chris Evans
    Chief Civil & Structural Engineer
    Wood plc
    Reading, UK
    0118 913 3483
    ------------------------------



  • 5.  RE: Anchor Bolt Design with respect to Petrochemical Facilities

    Posted 06-28-2020 09:16 AM
    Hi Mandeep,

    For the Rods as anchor bolt, please see the AISC publication (available on their website) named:

    design-guide-1-base-plate-and-anchor-rod-design

    There is a table there and the formula in conjunction with the ACI for this purpose.

    Thanks,
    Amin Ghafooripoour, Ph.D., PE, M.ASCE

    ------------------------------
    Amin Ghafooripour Ph.D., P.E., M.ASCE
    Padir Consulting Eng.
    Padir Consulting Engineers
    San Jose CA
    ------------------------------



  • 6.  RE: Anchor Bolt Design with respect to Petrochemical Facilities

    Posted 06-24-2020 03:59 PM
    I did go through  the reference and it also recommends the same that Pryout failure mainly concerns short and stocky studs with embedment less than 4.5 dia. It also mentions that anchor bolts due to semi fixed or pinned connection at top have lower capacity in general but tend to show the same change in failure mode at hef/d of around 4 (hawkins)

    Still is their any Codal or INDUSTRY SPECIFICATION which i can use as a reference in calculation ?

    From the paper 
    CONCLUSIONS AND DESIGN RECOMMENDATIONS Based on this study, the following conclusions and recommendations are offered:
    1. Headed studs in normal weight concrete with a hef/d less than 4.5 may invoke a failure mode known as pryout. This failure mode produces an ultimate capacity less than that predicted by Eq. (1), that is, Vu = 1.0 nAs Fut(design) .
    2. When headed studs are embedded in lightweight aggregate concrete, the hef/d limit is not as well defined because of the nature of lightweight aggregate concrete. From the literature, it was found that this ratio varies from about 5.4 to 7.4.
    3. Eqs. (6), (7), and (8) are proposed to predict the capacity for short, stocky studs having hef/d ratios less than 4.5.
    4. Proposed Eqs. (6), (7), and (8) provide good correlation to predicting the pryout capacity. The equations are based on a database of 225 tests, presented in Appendix B of this paper.
    5. The ACI 318-05 Appendix D provisions for predicting pryout capacity are overly conservative and reflect poor prediction statistics. The ACI model, based on a pseudo-tension breakout, is not appropriate for predicting pryout capacity.

    ------------------------------
    Mandeep Singh Kohli CP, M.ASCE
    Senior Engineer
    India
    ------------------------------



  • 7.  RE: Anchor Bolt Design with respect to Petrochemical Facilities

    Posted 06-24-2020 01:28 PM
    Great information!

    ------------------------------
    John Jamanca M.ASCE
    FONDEPES
    Lima
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  • 8.  RE: Anchor Bolt Design with respect to Petrochemical Facilities

    Posted 06-24-2020 03:04 PM
    Dear Sir,

    Thank you for the reference i will go through it. My intention was actually to find out if their is some codal provision or some mention in a commentary to a regulatory code like ACI, ASCE, some task committee report which i can refer to get a sort of waiver form this requirement of ACI. If not that iw ould still like to know how the general community tackle,s this issue.

    Thanks & regards

    ------------------------------
    Mandeep Singh Kohli CP, M.ASCE
    Senior Engineer
    India
    ------------------------------



  • 9.  RE: Anchor Bolt Design with respect to Petrochemical Facilities

    Posted 06-24-2020 03:34 PM
    Hi

    I totally understand the reservations mentioned in  the above discussion and know that they are totally valid, we also do have an additional detail wherein we use two nuts instead of one and a plate washer instead of normal one for Gr 55 and 105 bolts and bolts with large diameter. But for normal bolts i have seen and used the tack weld detail all too very often. its not a structural  the tack welds we use are very minor tack welds, just few small tack welds at the bottom of the nut and top of washer plate, just to keep the nuts in place during concreting.

    Thanks for sharing.

    ------------------------------
    Mandeep Singh Kohli CP, M.ASCE
    Senior Engineer
    India
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  • 10.  RE: Anchor Bolt Design with respect to Petrochemical Facilities
    Best Answer

    Posted 06-25-2020 09:03 AM
    I think you are referring to very old version of ACI 318. ACI 318-2019 version gives following information which may be useful to you:
    Pryout failure of cast in anchors longer than 65mm is double of tension breakout failure (Cl 17.7.3). Tension breakout failure capacity of anchor group Ncbg may be found by clause 17.6.2.1 (b).
    If the strength is still less than what you need then code allows you to provide reinforcement in lieu of this check. Please see footnote 3 under table 17.5.2 and explanations given in commentary clause R17.5.2.1(b). Code has also given figures R17.5.2.1b(i) and (ii) explaining how to place the reinforcement. From these figures you will also notice the shear cone actually starts from the underside of base plate and not from bolt head that is why reinforcement is shown close to base plate and code has also written a remark "as small as possible observing cover requirements" for the location of reinforcement from top of pedestal.
    Please check above  and it should solve your problem. Alternatively, I suggest you to use shear key for shear forces and design bolts only for tensile forces . 2019 version of ACI has also included an exclusive new section on shear key related checks for concrete design. See section 17.11 for details

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    Neeraj Agrawal
    Gurgaon
    India
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  • 11.  RE: Anchor Bolt Design with respect to Petrochemical Facilities

    Posted 06-25-2020 11:46 AM
    Dear Er Mandeep Singh
    I think Er Neeraj Agrawal has given the right answer to your question of which code or document to refer. He has also given proper quotes from the latest version of the ACI 318, which I think is the only code that gives provisions for anchor bolts. These provisions were largely based on the work of Prof. Eligahausen of the University of Stuttgart, who has published numerous papers on anchor design in English and German.  Hope there is some German code on anchors.

    All the best
    Subramanian

    ------------------------------
    Subramanian Narayanan Mentor, Consultant and Author
    Chief Exec
    Computer Design Consultants
    Gaithersburg, MD
    Phone
    ------------------------------



  • 12.  RE: Anchor Bolt Design with respect to Petrochemical Facilities

    Posted 06-25-2020 11:49 AM
    Hi,
    The figure you are referring to is for shear breakout, which is a different life of failure than Pry out.
    I am well aware of the anchor reinforcement and the code allows us to use anchor reinforcement for both shear cone breakout and tension come breakout.

    Pryout is a little different in that the failure plane starts from the bottom head and radiates backward away from the anchor bolt to the top surface of the concrete it is more like a half tension breakout cone which also originated from the anchor bolt.

    The code does not specifically mentions to use anchor reinforcement capacity in place of concrete breakout for Pry Out Failure mode. and that is my question, can we consider the reinforcement capacity instead of concrete breakout to preclude PryOut Failure?


    thanks.

    ------------------------------
    Mandeep Singh Kohli CP, M.ASCE
    Senior Engineer
    India
    ------------------------------



  • 13.  RE: Anchor Bolt Design with respect to Petrochemical Facilities

    Posted 06-25-2020 11:47 AM
    Hi,
    Thanks for your  response
    I have gone through all the documents and they do not mention anything that might address the My question of Pry-out Failure mode, weather we can ignore it for long anchors or we can use anchor reinforcement to preclude it?

    Thanks

    ------------------------------
    Mandeep Singh Kohli CP, M.ASCE
    Senior Engineer
    India
    ------------------------------



  • 14.  RE: Anchor Bolt Design with respect to Petrochemical Facilities

    Posted 06-26-2020 06:59 AM

    Sir,

    Thank You so much for your response. So that means that the beneficial effects of Tension anchor reinforcement can be used to preclude pry out failure.  That clears my doubt.

    Much thanks to all for chipping in!



    ------------------------------
    Mandeep Singh Kohli CP, M.ASCE
    Senior Engineer
    India
    ------------------------------



  • 15.  RE: Anchor Bolt Design with respect to Petrochemical Facilities

    Posted 06-26-2020 01:58 PM
    Yes now there is also a German code DIN EN 1992-4: 2019 dedicated to anchors in concrete

    ------------------------------
    Neeraj Agrawal
    Gurgaon
    India
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  • 16.  RE: Anchor Bolt Design with respect to Petrochemical Facilities

    Posted 06-26-2020 06:58 AM
    Yes, code  explicitly does not mention that in lieu of pry out check, reinforcement may be provided but my interpretation is that once I ignore breakout and provide reinforcement close to base plate, pry out can also be ignored since pry out is the result of bolt's tendency to rotate due to shear forces acting on its top (see fig R17.5.1.2b(ii)). Once all shear is arrested by the reinforcement on its top, there is no question of bolt rotation hence no pry out action.
    However, if you want to stick to code, I would advice you to use a shear key because in clause 17.11.1.1.2 code clearly says that shear relate checks including pry out need not be checked for anchor bolts if entire shear is taken by the key. Note that in this case you will have to use bigger holes in base plate to ensure that no shear is transferred to anchor bolts. Also minimum 4 anchors are required to qualify in this clause.

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    Neeraj Agrawal
    Gurgaon
    India
    ------------------------------



  • 17.  RE: Anchor Bolt Design with respect to Petrochemical Facilities

    Posted 06-27-2020 04:07 AM
    Dear Sir,

    Much thanks and appreciate your response. Your response cleared my doubts.

    Thanks.

    ------------------------------
    Mandeep Singh Kohli CP, M.ASCE
    Senior Engineer
    India
    ------------------------------