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Re: Story Drift - Cracked or Uncracked Section Properties

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For the question on when to use cracked vs non-cracked:

If I remember correctly, you can multiply the cracked section factors
given in ACI by 1.43 when checking service level drift. I don't
believe you are able to assume the moment frame sections are
completely uncracked in any case.


On Fri, Jun 6, 2008 at 5:06 PM, Scott Maxwell <smaxwell(--nospam--at)> wrote:
> Cd is purely the "switch" from an elastic deformation to an assumed
> inelastic (I say assumed as it is an approprimation...not an exact
> analysis).  When you do you elastic analysis, you should be using cracked
> section properties.
> Regards,
> Scott
> Adrian, MI
> -----Original Message-----
> From: Paul Blomberg [mailto:paul.blomberg(--nospam--at)]
> Sent: Friday, June 06, 2008 4:25 PM
> To: seaint
> Subject: Story Drift - Cracked or Uncracked Section Properties
> We are checking some concrete moment frame calcs and debating internally
> about using the cracked or uncracked concrete section properties for the
> structural analysis.  There is some discussion that Cd (deflection
> amplification factor) incorporates the loss of stiffness as the concrete
> cracks while most believe that Cd increases the elastic deflections (using
> cracked section properties) to to account for inelastic behavior and that
> the elastic deflection is based on a cracked section.  The code is a mix of
> a north African national code with incorporation of ACI 318-05 and ASCE 7-05
> just for fun.
> So on this fine Friday, anyone want to chime in on this debate.  When do you
> use the uncracked section properties of concrete versus the cracked section
> properties?
> Paul.

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