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Re: Cracked Concrete Sections

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Ec is calculated per Section 1908.5.1.

Essentially all researchers and most practicing engineers who think 
about it use Ae = Agross for members in compression.  For members in 
tension, it probably makes sense to reduce AE, but this is not 
usually a significant consideration for most moment resisting frames.

Many researchers and practictioners use Ie = 0.5 Igross.  There is 
support for this approach in FEMA 273 and ATC 40 as well as in 
past research.  FEMA 273 indicates that Ie = 0.5 Igross for beams and 
columns in tension; Ie = 0.7 Igross for columns in compression.

The calculation procedure outlined in Section 1910.12.3 can be used 
for stability analyses, so you could argue that it is reasonable for 
general lateral analysis, where beta_d = 0 for transient loading.  An 
even simpler approach (with the same rationale) would be to use the 
values in Section 1910.11.1 (0.35Ig for beams, 0.70Ig for columns).


**********
> Date:          Tue, 21 Dec 1999 17:21:28 -0800 (PST)
> From:          James Lin <se3949(--nospam--at)yahoo.com>
> Subject:       Cracked Concrete Sections

> What are the effective I, E, & A for cracked concrete
> moment-frame members (beams & columns) while
> calculating the lateral drift per UBC97?

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Michael Valley                                   E-mail: mtv(--nospam--at)skilling.com
Skilling Ward Magnusson Barkshire Inc.                  Tel:(206)292-1200
1301 Fifth Ave, #3200,  Seattle  WA 98101-2699          Fax:        -1201