mass rotational moment of inertia

[alaa]

In my model, masses are concentrated at the nodes where columns and beams meet according to the tributary mass per node. I use rigid diaphragm constraint to each floor and each floor has three freedoms: UX, UY and RZ.
So I define mass as follow:
mass $node $m $m 0 0 0 0

my questions are

1- is opensees can calculate the rotational inertia of mass automatic.
2- if not so how can i define the rotational inertia of mass
3-if i use a uniform mass (distributed) like example 5.1 . the rotational mass inertia will be m(bx*bx+by*by)/12 . it is mean i will use all ,masses as a lumbed mass at master point. ( is it mean that the displacement at master point ux,uy,Rz will be the same if the masses are concentrated at corner nodes)

[silvia]

1-2
OpenSees does not calculate rotational inertia automatically from the translational values, you specify it as the rotational degree-of-freedom mass.

3- OpenSees uses a lumped-mass matrix, so it would concentrate the mass at the end nodes. In this situation, I believe, OpenSees does calculate the inertial mass for all necessary dofs.

[Boris]

It can use both lumped (good for very large models) and consistent mass matrix (good in any case...). It depends what you supply.

Boris

[seddighi]

dr Silvia Mazzoni
in example of 7 for Wsection, you have not assigned any rotational mass component, you have used for example mass 1 $Mtop 0 $Mtop 0 0 0??




silvia wrote:

> 1-2
> OpenSees does not calculate rotational inertia automatically from the
> translational values, you specify it as the rotational degree-of-freedom
> mass.
>
> 3- OpenSees uses a lumped-mass matrix, so it would concentrate the mass at
> the end nodes. In this situation, I believe, OpenSees does calculate the
> inertial mass for all necessary dofs.