effective modulus steel-concrete box girder section

huangyhg

effective modulus steel-concrete box girder section
dear all.
iam trying to model a steel open box girder section with a concrete deck slab in nastran. i need to perform nonlinear analysis for the box girder.
we are aware that modulus of concrete in p-delta behavior and m-phi behaviour are different. from this prespective please let me know what modulus and thickness of deck slab i need to use to get my nonlinear results properly.
do i have to use any effective modulus and effective thickness for concrete deck slab? in which case how do i compute them?
thanks in adv
regds
raj