Lumped Mass Parameters in 2D RC Frame Modeling

[burakduran]

Dear All Users of Seismostruct and Admin,

I have one-bay and one-story 2D RC bare frame model in SeismoStruct and I am applying Dynamic Time History Analysis. In settings, I only select X, Z, RY and also W for mass directions. However, I assigned lumped-mass at column top ends only X direction. I think this is not true because whatever the mass value in X direction, the total calculated mass of the frame can not change at the end of the analysis.

Would you please tell me whether I have to put for numerical values for the lumped mass parameters in all X, Z and RY ? If so, how can I calculate rotational mass in Y direction (Myy)? Since I am using 2D model, what should be a and b parameters in rotational mass inertia formula ; (M*(a^2+b^2))/12? L makes sense, but what about a and b? If I do not enter these inputs, is this a problematic issue?

[seismosoft]

It is not problematic, as regards the program and the analysis carried out. The program will accept mass values only in selected DOFs of the node.
However, we are not sure what you are trying to model. This is something that should better be discussed with your supervisor.
Seismosoft Support