effective EI for concrete members

[Ahil_Anand]

Dear seismosoft,
Please let me to know how can define effective EI for a RC member in seismostruct? It seems that the EI only define in section modulus by the program automatically and the users do not allow to change it. I want to apply a 0.5 coefficient to EI which is calculated by the program, but this value is lock in the section modulus.

[Ahil_Anand]

I use infrFB for a RC member. According to FEMA 356, i should be use the effective stiffeness instead of common stiffeness.

[huffte]

FEMA 356 requires the use of effective stiffness if you are performing a linear analysis. For nonlinear analysis, FEMA directs the engineer to adopt "nonlinear load-deformation relations", which is precisely what SeismoStruct offers.

So, if you are doing a nonlinear analysis, I believe you may have misinterpreted FEMA 356.

If you are, however, doing a linear analysis, then you could specify an artificial material having E = 0.5 times the actual value. This strategy, however, will also render EA equal to 0.5 times the gross value, which is not required by FEMA.

So, if you are doing a linear analysis, your best option might be to input the properties manually using the "elastic frame element" element class, for which you may directly enter the desired values of EA, EI, etc. . .