Allowable Reinforcing Steel Stress Increases 3

[surfer08]

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.

 

[DaveAtkins]

In ultimate strength design, there are not "stress increases." The various load combinations accomplish what you are looking for.

DaveAtkins

 

[Lion06]

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).

 

[surfer08]

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.

 

[Lion06]

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.

 

[JAE]

ACI 318 does recognize ASD - just in a very indirect way - see chapter 1, commentary section R1.1 - 5th paragraph.