2006 IBC Conc. Load Factors

[OldPaperMaker]

1. Did ACI 318-05 change the Live Load factor from 1.7 to 1.6?
2. When designing reinf. concrete retaining walls for a seismic load, E, in addition to the lateral soil loads does the E get a load factor? Since E comes from ASCE 7-05 and is a Strength level load it seems to be overkill to tack on a load factor.

I suspect that the commentary of chapter 9 of ACI 318-05 answers this question. I only have ACI 318-99.

Thanks for your thinking on this subject.

 

[JAE]

With 05, you have different load factors which are now consistent with ASCE7 and with AISC. Also - and very important, the [φ] factors have changed as well.

So no more 1.4D and 1.7L....now 1.2D + 1.6L

 

[JedClampett]

1) Technically, the change was made in ACI 318-02. Note that the strength reduction factor, phi, also changed appropriately. There's an Appendix C that still has the old load factors and phi factors.
2) I don't have ACI with me at home, but I'm used to putting a 1.1 factor on seismic loads. As far as that being an overkill, I'll leave that to some of my California brethern to answer.

 

[JAE]

JedC - not sure where you got the 1.1 factor on E. I always use 1.0.

 

[OldPaperMaker]

JAE & JedClampett,
Thanks for the update. I have noticed that at least since the 97 UBC that the Strength Design & LRFD factors were 1.2D + 1.6L but the ACI 318-99 was still 1.4D +1.7L. I guess that it makes sense to "effect alignment" between IBC, ASCE 7, ACI & AISC.
JAE,
I think that the 1.1E was called for in paragraph 9.2.3 of the ACI 318-99 & I don't know what happened to this in ACI 318-05.

OldPaperMaker

 

[VTPE]

Please also note that to officially use the new load factors and resistance factors, you have to perform a compatibility analysis, not the old balanced reinforcing analysis. The determination of whether a member is compression or tension controlled will affect your choice of factors.