Base Moment

[Gholamreza]

Hello Engineers,

I was wondering if there is a recorder to get the seismic base moment of structure similar to base shear ? if element recorder does so, please explain or give me the example!!

[mhscott]

Not that I'm aware of, but should be easy enough to post-process overturning moment from recorders of node reactions at the base.

[Gholamreza]

Can you give me a hint ?

[selimgunay]

If you are doing pushover analysis, in each step, you compute it as (the sum of the applied lateral forces) x (the distance from the centroid of lateral forces to the base of the structure. If you are using time history, you should record all reactions at the base of the structure and take the moments of axial forces and base moments with respect to a point at the base.

[Gholamreza]

I am doing time history. So, then I should use element recorders (globalForce) to record the forces (axial forces, Fy) in elements (columns) connected to boundary conditions (supports) at base and also get the base moment (Mz) in those elemnets and take the moment about a point !
OR
I can use the node recorder to get support reactions in dof 1 ,2 and 2 (in 2D problem) and then use forces in dof 2 as axial forces and dof 3 as base moments ?

[selimgunay]

You can do either way. Doing both would be good for double checking your calculations.