Add bodyforce

[Lei Lei]

Dear STKO Team,

I noticed various body force settings in multiple places within STKO, such as the density of some materials (e.g., PressureDependentMultiYield), the body force in the elements (e.g., quad), and the mass or load in Conditions.

Could you please explain the differences between these settings? Do they impact calculations?

Looking forward to your reply!

[kesavapraba]

Density and mass are associated with dynamics analysis, they will not add any static structural loads, as the other (body force and load) do. If you specify density of the material, the equivalent mass at nodes for the elements are internally calculated and assigned. Otherwise, you should manually calculate the mass and assign at the nodes. So, density option for material adds a layer of sophistication.

[Lei Lei]

If you specify density of the material, the equivalent mass at nodes for the elements are internally calculated and assigned. Otherwise, you should manually calculate the mass and assign at the nodes. So, density option for material adds a layer of sophistication.

It seems that the body force within the element also contributes to this sophistication.

[STKO Team]

Yes some elements have the body force as input.
But not all of them, that's why in STKO we developed utilities such as VoulumeForce, FaceForce, EdgeForce... to provide for distributed forces where not available in OpenSees

[Lei Lei]

So, for face force, should I consider the thickness of the quad element？

[STKO Team]

A FaceForce is a pressure F/L^2, so yes, you can compute it as self-weight (F/L^3) times the thickness

[Lei Lei]

Alright, I think Opensees will time the thickness automatically.

Thanks for your reply!

[kesavapraba]

You need to multiply the self-weight (either in N/m3 or kN/m3) with the corresponding thickness and apply it as face force (STKO automation) along the inplane direction of the quad element.

[Lei Lei]

Thanks for your reply!

Best wishes!

[STKO Team]

You're welcome