Large Displacement Problems?

[seu]

I intend to use Opensees tcl scripts to do some research about progressive collapse of steel structures.

I'm confused how does Opensees deal with the problem with large displacement ,large strain and large rotation?
I find the "large displacement" option in sap,and "nlgeom,on" option in ansys.
But the only command I can find in the Opensees Manual Page 286 is "geomtransf",without any large displacement option.
Anyone who knows the answer please tell me,thanks a lot.

[fmk]

it is possible to use the beam coumn elements in situations with large displacement small strain.. to do so use the corotational transformation