P-delta setting in ETABS

[Eva Wang]

Hi everyone, I have a problem with p-delta in ETABS.
In ETABS, there are two ways to consider p-delta effect: based on mass & based on loads, respectively.

I tried to use two ways to see what will happen in diaphragm center displacements of my 15-story isolation building model.
Compared with the model without considering the p-delta effect, using the "based on mass method" will make the displacement of the seismic isolation level become much larger, and using the "based on load method" will make the displacement of isolation level smaller.

I have no idea about the difference between these two ways.
Can someone help me figure out?

Appreciate it!

 

[JoshPlumSE]

https://wiki.csiamerica.com/display/etabs/P-Delta+analysis+parameters

I personally always use the iterative based on loads option. The non-iterative based on math method is good for high rise structures that have a rigid diaphragm at each floor level. It's also good as a first approximation. But, for my final design, I'd use the iterative based on loads method.