Loads and mass

[NabilBishtawi]

Hello everybody,

I have a simple frame with three cases:
First case with mass only
Second case with load only
Third case mass and load togather.

First case gives displacement only under earthquake, under static analysis its zero.
Second case gives only static displacement.
Third case gives static and earthquake displacement but the problem that its not the same as case one despite its the same mass!
If the loads are not transferred into mass in opensees which clearly proved in case 2 why case 3 and case 1 are different

[mhscott]

You don't provide enough information about your model, but you are applying both inertial and static forces in case 3, so generally there will be different response from case 1. https://portwooddigital.com/2020/11/20/mass-and-weight/