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  • 1.  R and Cd Factors

    Posted 11-30-2018 04:59 PM
    Edited by Tirza Austin 11-30-2018 04:58 PM
    Can anyone explain the relation between the R and Cd factors?  Where does the Cd factor come from? I understand that the R factor is the force reduction factor due to the ductility of the system, and the Cd factor is the way to return up to the real deformation of the system. However, I still have questions about the relation between theses two factors, and how the Cd factor came to be lower than the R factor?

    Thank you


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    Elizabeth Davalos A.M.ASCE
    Constructora Cautin SA de CV
    Zapopan
    5233 36820633
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  • 2.  RE: R and Cd Factors

    Posted 12-01-2018 10:46 AM
    Edited by Tirza Austin 12-01-2018 10:46 AM
    Read the commentary in ASCE 7.  In reality it is a little more complex but this is a starting point.

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    Mark Gilligan P.E., M.ASCE
    Berkeley CA
    (510) 548-8029
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  • 3.  RE: R and Cd Factors

    Posted 12-01-2018 10:47 AM
    Edited by Tirza Austin 12-01-2018 10:46 AM
      |   view attached
    In order to answer your question, I recommend the attached link provides a good background on these factors and their relationships

     https://www.structuremag.org/wp-content/uploads/2014/08/C-GuestCol-SeismicDesign-SEAOC-Sept081.pdf

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    J.M. Albaine P.E., M.ASCE
    Consulting Engr
    JM Albaine Engineering, LLC
    Waterford CT
    (203) 447-0235
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  • 4.  RE: R and Cd Factors

    Posted 12-14-2018 03:25 PM
    Edited by Tirza Austin 12-14-2018 03:25 PM
    ​What about Chapter 13? I am looking at seismic separation between two non structural components. Eqn 13.3-8 directs me to Chapter 12 and there's no case in Table 12.2-1 that exactly defines my non structural components. Do I use the same Rp/I value as Cd/I value to amplify my displacement?

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    Anami Bingi EIT, A.M.ASCE
    Staff Professional II
    Kleinfelder
    San Diego CA
    (424)402-7067
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    Original Message


  • 5.  RE: R and Cd Factors

    Posted 12-15-2018 11:13 PM
    Edited by Tirza Austin 12-15-2018 11:13 PM
    ​Rp, ap, and omega-zero are determined for non-structural components using the tables in Chapter 13.  Displacements for non-structural components are calculated using EQ 13.3-6 in Section 13.3.2 and has no Cd factor. The reference in EQ 13.3-8 for displacements using Chapter 12 is used when determining relative displacements between structures in which case you'd use the appropriate factors for the structures themselves. Since the component being considered is non-structural, it is assumed that it "goes along for the ride" being forced to deform to meet the displacements of the structures to which it's attached.  It's a bit confusing, but in effect, you're not considering the deformation behavior of the non-structural component itself.  Rather, you are just looking at the displacement that it would undergo to remain attached to the structural systems supporting it.  Hope this helps.

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    Cliff Jones P.E., S.E., M.ASCE
    Jensen Hughes
    Portland OR
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    Original Message


  • 6.  RE: R and Cd Factors

    Posted 12-01-2018 02:16 PM
    Edited by Tirza Austin 12-01-2018 02:16 PM
    From Thornburg's book. Hi,

    Hope this picture answers that (or sparks your imagination further). You can check ASCE 7-16 Chapter C12 as well.

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    Richard Wanjala
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