huangyhg

allowable reinforcing steel stress increases
in designing a concrete grade beam resisting live and dead loads as well as wind/seismic otm...can i take any stress increases for the reinforcing steel? codes are aci 318, 2006 ibc. thank you.
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in ultimate strength design, there are not "stress increases." the various load combinations accomplish what you are looking for.
daveatkins
dave is correct. in concrete you are dealing with strengths, not stresses. the only time you can consider a stress increase is using asd, you can't when using lrfd. additionally, ibc doesn't allow the use of the 1/3 stress increase unless you use the "alternate" load combinations (which essentially increase certain load cases by roughly 1/3).
daveatkins and structuraleit. thank you both for answering my question. in california we are still sorting out the icc, and as an architect i am less familiar with concrete strength design as i am with asd wood design. haven't tried lrfd for wood yet.
are you designing concrete using asd? i don't believe aci 318-05 even recognizes asd.
either way, you can only use the 1/3 increase if the following two conditions exist:
1. you use the alternate load combinations out of ibc for asd.
2. the material specification specifically permits its use.
aci 318 does recognize asd - just in a very indirect way - see chapter 1, commentary section r1.1 - 5th paragraph.

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