Rotational mass

[Sanjeema]

A super mediocre question - how does the rotational mass work in OpenSees?

[fmk]

users have the option of specifying the mass coefficients directly at a node .. they only have option of specifying a diagonal mass matrix .. if one of the doc ir a rotational doc they are providing a rotational mass .. OpenSees itself asks nodes and elements for the mass matrix, not special treatment is given if mass term is for a rotational or rotational dof.

[Sanjeema]

I have a diagonal matrix with masses along local x-and y-directions and a rotational mass about the local z-axis. I am trying to model an eccentric bridge (and compare my results with the previous). I checked my model using eigenvalue analysis. The three natural frequencies of my numerical model tally. However, the rotational response of the model under bidirectional excitations is totally different. I'm not sure what is wrong with my model.