There are two primary ways to include P-Delta effect:
- Create a nonlinear analysis case for each load combination including the P-Delta geometric nonlinearity parameter.
- Create an Initial P-Delta Analysis case including the P-Delta geometric nonlinearity parameter for the anticipated gravity loads, and consider all other analyses as linear using the stiffness matrix developed for this one set of P-delta loads.
You may find it useful to take a look at the video “P-Delta Analysis” from our “Watch and Learn Series” available at http://www.csiberkeley.com/sap2000/watch-and-learn.