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CMU Question

CMU Question

CMU Question

(OP)
When I design CMU, I never take advantage of the allowable stress increase that ACI 530 allows, because IBC requires you to use the "alternate" load combinations in order to take advantage of any allowable stress increase that comes from a material standard.  

I'm working some questions and it looks like (when determining a maximum allowable moment on a CMU wall that is subject to wind/seismic) that the question expects you to use the 1/3 increase.  There are answers that correspond to the values with and without it.  I guess it makes sense based on the question to use the stress increase, because is the maximum allowable moment of the section.  The moment demand will change based on IBC, but that's not really the question.  I guess I've answered my own question just typing this post.   

RE: CMU Question

In that case, you deserve a star.

BA

RE: CMU Question

Is the book you are working from based on the latest code?  I think that the requirement to use the alternate load combinations for material codes that allow a 1/3 increase in the resistance for any wind/seismic combinations is a fairly recent provision.  Someone older can verify.

RE: CMU Question

(OP)
The book is from NCEES.  It's a sample problem book from last year, which uses IBC 2006 which has the alternate load combinations in order to take advantage of the allowable stress increase that may be allowed in specific material standards.

RE: CMU Question

Use the 1/3 increase if they tell you to for an exam question, but I'd never use it in practice.

RE: CMU Question

(OP)
That's the thing, the problem explicitly state to use it. It says to find the maximum allowable moment, which, per ACI 530, would include it.  I'd just be a little concerned on the exam as there will probably be an answer that includes it and one that doesn't.  In the absence of explicit direction I'll include it where applicable.

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