Seismosoft | Earthquake Engineering Solutions

Hi,
I’m a engineering student and I’m doing a thesis in Dynamic of Structures.
I would do a 3D Modal Pushover Analisys (MPA) but I have some problems to define the point of forces application.
I would to apply forces in the centre of mass of each floor of the structure. If this point is a non structural point, how could define it?

Hi,

You should notice that the non-structural nodes, as the name indicates, can't be used for structural purposes but instead to define the orientation on your elements (see better in the help system).

If you are interested in apply the load only at the centre of mass (CM), and this is not coincident with a structural node, you should define a rigid element (e.g. rigid link) to connect one structural node of your floor to the CM node.

Cheers,
Romain

PS: In this particular case (force only at the CM), it is also recommended to model a stiff slab (e.g rigid diaphragm) in order to distribute the lateral load through all the vertical elements.

Hi Romain,

Thanks for your answer.

In my particular case the problem is the application of the force in the CM where I have a rigid diaphragm.

With this Nodal Constraint I can’t apply the force in a non-structural point.

I have already tried using the nodal constraint "Rigid Link" but the structural modal behavior is different from that of the structure with rigid diaphragm.

Bye
Annamaria

Hi Anna,

I recall that you should apply your load(s) at structural nodes.
If I understand well your issue, you should define a structural node at the coordinates of your CM and then link it (e.g.rigid link) to other structural node of your structure in the same plan.
Also, in order to distribute the force through the vertical elements you should define a rigid plan, for instance making use of the rigid diaphragm constraint, were the master node is your CM and the salve nodes the other structural nodes of the same plan.

Cheers,
Romain