Elastic softening from fiber hinges

[Fahimeh]

Hello,

In SAP2000, softening of the frames modeled with fiber hinges occurs due to calculation of the fiber-hinge response curve, "which proceeds directly from the axial response of individual section fibers. During linear response, fiber elasticity is added to element elasticity, causing softening". Are the same formulations used here in OpenSees? If not, how did you eliminate that additional softening?
Thanks in advance ...

[fmk]

if you stay within the linear response range, whether you model the frame with elastic, displacement based or force based elements (including the beam with hinges element) using fiber sections you will get exactly the same response if you use at least 3 integration points for the non elastic elements. now if you add hinges at the end of an elastic element you indeed muck up the stiffness of the system .. but that is something you as the modeler control as it is something you have introduced through your modeling choice.