IBC 2012 load Combinations

[SteelPE]

I was recently looking at the load combination equations of IBC 2012 and noticed load factors for both wind and seismic are 1.0 for the strength Design combinations. However, when design using Allowable Stress Design the load combinations are 0.6W and 0.7E. Why are they both not the same (0.7E & 0.7W)?

I understand that wind loads are calculated at strength level in IBC 2012 so I understand why the switch from IBC 2009. I just don’t understand why the different factors when considering Allowable combinations. Given the same loads for both wind and seismic, neither would really control a design carried out using strength level combinations, but seismic will control when using Allowable combinations.

 

[wannabeSE]

Maybe the ASCE 7 committee want to throw a bone to the old ASD guys . Just kidding. However, the old strength load factor for wind is 1.6 and 1/1.6 = 0.625. So you may need to look further back than the latest change.