Outputs for damping forces

[dgale]

Hi,
I'm trying to obtain in a concentrated plasticity model the damping forces aiming at obtaining the damping energy by integration of damping forces and nodal displacements. I've used the model for damping "modalDamping" and the recorders "rayleighForces" and "rayleighForces!". With the first recorder, I obtained damping force equal to 0 in all nodes in each step and, with the second recorder, I obtained a line of data for each mode that I understand that they are the forces obtained for each mode and node in each step.

Could I use the recorder “rayleighForces” in "modalDamping" or it is only valid for rayleigh command?

Could someone explain me how I can obtain the total damping energy dissipated by the model along an earthquake? I mean the outputs that I would need to compute it.

I really appreciate any comment

Best regards and thanks in advance

[dgale]

Is there any recorder to obtain energies dissipated in the model such as plastic energy, input energy, damping energy, etc? It'd be very useful for energy based seismic design of structures.

Thanks again!

[fmk]

the only way to determine damping forces when using modal damping is to determine from global equilibrium .. it is a pain to do but you need to record the ground motion, all nodal accelerations for which there is a mass, and the element end forces .. create a free body diagram and then utilize the fact that equilibirum that is being satisfied, i.e.
-M * 1 * Ag = Ele Forces + Damping Forces + M * accel recorded

NOTE this assumes that convergence has been achieved (which is not gaurenteed if you are using Norm of the displacement increment, so make sure you are using NormUnbalance as the convergence criterim).`