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 ASCE 7'16 Eqn13.5-3

  • ASCE Standards
  • ASCE7-16
David Van Volkinburg's profile image
David Van Volkinburg posted 07-21-2022 05:28 PM
It seems that for any I value greater than 1 Dclr is being amplified twice. I’m trying to find out if that is the authors’ intent.
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Christian Parker's profile image
Christian Parker posted 07-22-2022 08:26 AM
Hello David,

It strikes me that these separate amplifications are doing different things and therefore not redundant.  The I_e factor in eq. 13.3-6 reflects the occupancy of the building, while the 1.25 factor in eq. 13.5-3 corrects for epistemic uncertainty in the analysis.  I don't read this commentary section as being about using Dp rather than DpI, it seems to be about a failure of Dp to accurately predict drifts observed in actual seismic events.

D_pI is the code-calculated drift demand, adjusted for risk tolerance the same way design wind loads are higher for a nuclear waste storage facility than a single-family home.  1.25*D_pI is an adjusted drift demand based on research showing that code-calculated seismic drifts can be unconservative.

I suspect the intent is to push more high-importance projects towards safety glazing by propagating the importance factor to this component check.  It's more consistent this way.  Although, it's an open question whether the code should be applying importance factors to only the LFRS or to components like this as well.