ASCE 7-22 Chapter 12 | Seismic Design Requirements
During an earthquake, the building's own mass generates inertial forces against acceleration. The total force at the base of the building (v) depends on its spectral acceleration and its ability to absorb energy (R factor).
Governing Formula
Variables
Quick Example
Determine spectral acceleration
Look up SDS and SD1 from mapped site parameters.
Calculate the coefficient Cs
Compute Cs using SDS, R, and Ie. Make sure to check the upper limits (T-dependent) and lower limits.
Compute Base Shear
Multiply the response coefficient by the effective seismic weight of the structure.
When does this govern?
Seismic controls the lateral design of heavy concrete or masonry structures, or any structures specifically located along major fault lines in California or the PNW.
Common Mistake
Calculating the seismic weight (W) incorrectly. Engineers often forget to include 20% of the snow load if it exceeds 30psf, or the partition loading.