Seismic Forces and LRFD Load Combinations 2

[Scoobo]

Apologies if this has been covered before, but I searched the forum before posting and couldn't find an answer. I'm a rookie engineer looking to get some help wrapping my head around how seismic loads are handled in the LRFD load combinations. Since there are separate horizontal and vertical components to seismic forces, are the horizontal and vertical components applied separately when considering load combinations for a particular direction/type of loading? For instance, when looking at the axial load on a column, would the combination of 1.2D + 1.0E + L + 0.2S actually end up becoming 1.2D + 1.0Ev + L + 0.2S? Or does the horizontal component from the seismic effect also get included in the vertical case as well? Similarly, in the case of looking at shear, would it just be the horizontal seismic force that needs to be included or does the vertical component need to be included?

Thanks in advance

 

[dauwerda]

Take a look at ASCE 7-16 Section 12.4.2:

 

[Roukkia]

I often see the Ev added to the dead load, with the factor for the dead load being modified. So if your Ev is .15D, this gets added to the 1.2 to make the dead load factor 1.35D.

If the column is not responsible for resisting any horizontal seismic load (aka not a part of your LFRS), you do not need to include the horizontal seismic load effects in the load combination to check axial load only, Eh would be 0. Side note, there is an L/500 out of plumb check per AISC that you must check though that induces bending moment on your “axial only” column

 

[MotorCity]

Roukkia - lumping the seismic load into the same load case as dead load is not correct. You need to maintain each as a separate load case. Combining them over estimates the dead load which could overestimate the resistance to sliding, overturning, uplift, etc

 

[JLNJ]

Adding to what MotorCity wrote, Ev can be either direction, so you need to account for both cases in you load combinations. Ev also has its own load factors.

 

[WinelandV]

If you use RISA's load combo generator, and tell it to include Ev, it will add Ev to the 1.2 DL LC's, and will subtract Ev from the 0.9 DL LC's:

Please note that is a "v" (as in Violin) not a "y".