Using proper Drift Value in ASCE 7-16 Seismic Design

The table below summarizes the drift value used for different seismic design purposes. We have 2 drift values

• Elastic drift from reduced seismic load Ie/R

• Inelastic or (actual) drift obtained from multiplying elastic drift by Cd

In most cases, we use actual drift for all design purposes with the exception of P-Delta analysis, which relies on linear analysis. Think like this, since P-Delta analysis must be embedded into the linear analysis (via second-order analysis), the displacement used for updating the model geometry is obtained from linear analysis without any scaling. This is practical and straightforward.