Seismosoft | Earthquake Engineering Solutions

Hi,
I am trying to model a composite steel-concrete column. But, I am not sure whether to use con tl or con_frp for modeling the concrete core. The concrete should be confined by the steel tube, but there is no frp jacket.
Thanks in advance for your help.

Just a thought - I'm not intimatley familiar with frp modeling, but the frp would seem to be a good choice. You could set the elastic properties and ultimate strains of the frp to correspond to steel.

Another idea off the top of my head - you could also try com_ma with transverse reinforcement area and spacing (for confinement factor calculation) parameters set to give the area of steel shell per unit length equal to the actual shell area.

I believe using FRP_confined model for steel confined concrete might not be the best idea, since the confinement provided by these two different types of materials are different (FRP=Linear-Elastic behavior with ultimate sudden brittle rupture VS steel = Yielding plateau and exhibiting plastic strains). Because, unlike steel-encased concrete, response of FRP-encased concrete is almost bilinear with no descending branch. This difference is due to the elastic behavior of FRP composites. That's why I strongly don't recommend using FRP-confined for your case.

This is what I suggest:

1) For material properties:
Define stl_mn for your steel jacketing material to capture post-elastic behavior of your steel.
Define con_ma for your concrete core column.

2) For sections:
Define a hollow cross section for your steel jacketing and assign your stl_mn material to it.
Define a solid concrete cross section for your concrete.

3) In your element connectivity, connect these elements using same nodes (i.e. sharing same nodes in this way concrete will be in center and your jacket will be around it, since it's got a hollow cross section).

Hope it could help.