Similar results for three different beams

[nima178]

I model three simple-support RC beams with these properties:
a) Without any rebar (Just concrete)
b)Common RC beam with compressive and tensile reinforcement
c) RC beam with FRP (Full wrapping in shear span)
Dimension of beams :0.4 m width ,0.5 hieght, two F18 mm in top an 2 in bottom, Fc=30Ma,Fy=240Mpa
(Reinforced concrete asymmetric rectangular section – rcars)

and after push over analysis ,it was observed that all of the beams have a same ultimate deflection (deflection correspond to ultimate load, beneath the peak=15.5 mm) and there is have very negligible difference between ultimate loads of second and third beams(Respectively 880, 998 and 1000, only 2 KN difference between second and third).
If you wish, I will send you my files, and you can judge yourself.
Is this true that no difference exist between ultimate deflection of a beam with no longitudinal rebars and RC beam with frp ?

[seismosoft]

Your three 4-hinge beams do indeed feature similar behaviour, owing to the mechanical characteristics of such structure and to the displacement-controlled loading you have applied.
The material strains, however, are likely to be quite different, did you have a look at them? (define some strain-stress points to check this)
Further, if you consider different boundary conditions (e.g. fully restrained supports and/or ditributed loading), you should get much varied results.
You should also try a finer meshing, as recommended by the Help System.

Seismosoft Suppport

PS: we hope you will agree that the original title of your post ("A fatal error in SeismoStruct's results") was slightly unjustified, to say the least..