Force-Based Beam-Column Element to stiff?

[miranc]

I have modelled a 4 storey frame structure in 2D with shear walls in the different softwares, including OpenSees. In two of the programs, I have used Force-Based Beam-Column Elements. Both in OpenSees and in the other software I get a stiffer system using Force-Based Beam-Column Elements than do using elasitc beam-column elements. Does anyone have any experience with this problem?

[fmk]

Instead of a Fiber Section provide an Elastic Section to the force beam column. The elastic beam and force beam periods should be the same. Next go back to the fiber section and make all materials Elastic (if you have done a typical fiber model the result should be ever so slighly more flexible, i.e. longer period). If results are in poor agreement it means your section definition is incorrect. if ok, look to your nonlinear material models and the tangent.