infrlFBPH element and the use of an effective flexural stiffness (EI_eff)

[Doudine]

Dear SeismoStruct community,

In the context of my research, I am using concentrated plasticity models with the infrmFBPH element in SeismoStruct. I am comparing my results with the recommendations of Berry et al. (2008) for the seismic modelling of reinforced concrete bridge columns.

Berry et al. (2008) recommend the use of an effective flexural stiffness (EI_eff) for the elastic segment of concentrated plasticity models (based on Scott & Fenves formulation) to account for concrete cracking. I am wondering how this effective stiffness can be incorporated in SeismoStruct with the infrmFBPH element.

I have noticed that the "Cracked/Uncracked Stiffness" menu is available only for linear analyses (modal, response spectrum and static analyses). However, I am performing nonlinear analyses (pushover and time‑history) where this menu is not accessible.

I would appreciate any insights or suggestions from users who have addressed similar issues.

Thank you in advance for your help.

[seismosoft]

The infrmFBPH frame model employs the elastic, uncracked stiffness for the internal part of the element. Unfortunately, this cannot be changed because the stiffness is automatically calculated by the program.
An alternative would be the elastic element with hinges elfrmH, however in this model the plastic hinges are not fiber-based as in the case of infrmFBPH and the plastic hinge curve parameters need to be calculated with section analysis.
Seismosoft Support