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Re: Story Drift - Cracked or Uncracked Section Properties

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Yep, cracked section properties, then amplify the drifts.


On Fri, Jun 6, 2008 at 1:32 PM, <Tom.Hunt(--nospam--at)> wrote:


I believe you have to use cracked section properties in accordance with ACI 318-05 Sections 10.10 and 10.11.

Thomas Hunt, S.E.

"Paul Blomberg" <paul.blomberg(--nospam--at)>
06/06/2008 01:24 PM
Please respond to seaint
seaint <seaint(--nospam--at)>
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?
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