When to Include Special Seismic Load according to ASCE 7-16?

ASCE 7-16 §12.4.2.2 & §12.4.2.3

These sections define how vertical seismic effects (Ev) are added to load combinations.

✅ Summary:

Seismic Design Category (SDC)	Require Ev=0.2SDSDE_v = 0.2S_{DS}D?
A, B	❌ Not required
C, D, E, F	✅ Required

🔍 Clarifying Definitions:

• Ev=0.2Sds is used to represent the vertical component of ground shaking, not gravity loads.

• It is added to dead load (D) in load combinations involving seismic effects.

Example load combo:

(1.2D +0.2Sds)D +1.0L+ρQE

💡 Hint

In ETABS 9.7 the special seismic force is a separate menu which will apply to the default load combinations of ACI codes

However, this input menu is removed in the latest version 22. The user must manually input the right value if needed.

So even though SDC C is considered moderate risk, ASCE 7-16 mandates inclusion of Ev to ensure vertical shaking is accounted for in design.