# Phi Discrepancy



## Bigwolf (Sep 1, 2008)

I think I have found a discrepancy in a phi value for LRFD between ACI 318-05 and Steel Construction Manual 13th Edition.

With regard to the bearing strength of concrete, the Steel Construction Manual says to use phi = 0.60 (Section J8, Pg 16.1-115)

I believe that in ACI 318-05 for Section 10.17.1 for the bearing strength of concrete, that phi = 0.65 per Section 9.3.2.2b (without spiral reinforcement) would be used.

I understand that phi = 0.60 would be slightly more conservative, but I am thinking that ACI 318-05's recommendation should be used when determining the concrete bearing strength as opposed to the Steel Construction Manual's recommendation.

Thoughts? Anybody else encounter this?


----------



## MA_PE (Sep 1, 2008)

Bigwolf said:


> I think I have found a discrepancy in a phi value for LRFD between ACI 318-05 and Steel Construction Manual 13th Edition.
> With regard to the bearing strength of concrete, the Steel Construction Manual says to use phi = 0.60 (Section J8, Pg 16.1-115)
> 
> I believe that in ACI 318-05 for Section 10.17.1 for the bearing strength of concrete, that phi = 0.65 per Section 9.3.2.2b (without spiral reinforcement) would be used.
> ...


I'm not too familiar with the steel code, but if you're designing a steel connection and referencing the steel code you use the value from the steel code. If you're designing a concrete beam for bearing and referencing the the ACI code then you use the ACI 318 value. This is not a "discrepancy" (difference between facts) so much as it is an "inconsistency" (things not being consistent or the same).

As long as your methods and values follow one code and you can provide the appropriate references you're OK. In your example, the steel beam would be designed to resist a bearing pressure from the concrete of .65, and then the concrete support should is designed at a bearing capacity of .6. There is no mandate for the codes to be equal.

my :2cents:


----------



## Casey (Sep 1, 2008)

I ran into this a few weeks ago and rationalized that for all intents and purposes of the SEII exam, that as long as I reference the applicable code, then I should be fine. Also, if the question was primarily a steel design question, then I would tend to go with the AISC phi value. Which is pretty much what MA said... Thanks MA for confirming my thoughts.


----------



## kevo_55 (Sep 2, 2008)

^^ Great rationale Casey!

I think you're ready for the exam!


----------



## Casey (Sep 2, 2008)

kevo_55 said:


> ^^ Great rationale Casey!
> I think you're ready for the exam!


Oh god no....

I'm more or less through concrete, steel, and timber and am now working on masonry. I hope there isn't much to masonry on the exam. It seems to me that it mostly focuses on beams, columns, walls, and shear walls... which is ok by me.

And, I got questions about plastic analysis that I will post when I revisit it in a week or two... unless someone is working on it now and wants to go over it together...

I'm not really freaking out yet, but my wife has been since the day I signed up!


----------



## Bigwolf (Sep 2, 2008)

Thanks for the replies, sounds like we're all on the same page.

7 1/2 weeks and counting........next month........... 10940623:


----------



## kevo_55 (Sep 2, 2008)

Ha ha! Well, keep that confidence level up!! arty-smiley-048:

Keep it up guys!

7.5 weeks left!!


----------

