Seismosoft | Earthquake Engineering Solutions

Is it possible to capture the true biaxial moment-axial force
interaction when using fiber elements in IDA analyses?
In FEMA-P695 it is stated that currently due to limitations on fiber elements models (especially in capturing rebar buckling softening behavior), it is not recommended to use such method for modeling collapse behavior of RC structures. How do we think about the subject?

Hi,

Rebar buckling can be modelled either explicitly through the use of the 'steel_mn' material model or by changing one of the parameters of the 'steel_mp' material model (see notes in Help System). Hence, we do not feel that the limitation of fibre element models is on this front.

Instead, what current fibre beam-column elements cannot do is to model shear deformation and shear capacity degradation, as well as bond degradation and bar slippage, though these limitations can be (indirectly) overcome by the employment of link elements with an appropriate relationship.

Hence, in a nutshell, we do not necessarily agree fully with the FEMA-P695 statement you quote.

Seismosoft Support