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RE: STAAD-Concrete sectional properties

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Here's my best attempt to provide some input to your questions:

1.  Is it usual practice to use the member properties in ACI 10.11.1?

Be careful when using the member properties, if using service loads as
input be sure to increase the moments of inertia by 1.43 as the ACI
commentary recommends.  It's hard to say if it's "usual" or not because
that depends on what your modeling and the degree of analysis you want
to use.

2.  Section R8.6.1 talks about using gross section properties for all
members in braced frames. My building has two parallel shear walls in
east-west direction (in combination with moment resisting frame) and
only a
moment resisting frame in north-south direction. Can I use gross section

Use of the gross section properties versus reduced properties is a
function of the degree of cracking thus really dependent on the overall
setup of your model in the east-west direction.

3.	STAAD PDelta analysis has been performed. The engineer who done
analysis informed me that the PDelta analysis in STAAD takes into
(automatically) reduced section properties due to cracking, therefore it
acceptable to input gross section properties. Is this correct?

Answered previously in a separate e-mail..... I believe the engineer's
statement to be incorrect.

4.	I reviewed the UCB on this subject. Section 1633.2.4 states that
and shear properties shall not exceed one half of the gross section
properties unless a rational cracked-section analysis is performed.
someone explain to me what a rational cracked-section analysis is.

Check out Wang & Salmon's Reinforced Concrete Design book (I'm looking
at the third edition Chapter 15.  A more accurate EI relationship is
established based on the loads (i.e., a member that has a DL that
creates constant compression in the member reduces the flexural
stiffness of the member and could be accounted for.......) and based on
the nonlinear stress-strain curve of concrete. 

5.	Section 1910.11.1 of the UCB gives similar member properties as
10.11.1 but seems to contradict the requirements of UCB Section 1633.2.4
i.e. using 50% of gross. Can someone clarify this for me.

I use BOCA more than UBC so I'll leave this up to someone else.......

Hope this helps.....

Robert C. Rogers, PE
Senior Structural Engineer
A.M. Kinney, Inc. 
Consulting Engineers / Architects
150 East Fourth Street, 6th Floor
Cincinnati, Ohio 45202
PH: 513-421-2265, ext. 125
FX: 513-345-1318

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