Analysis of "Voided slab" (as shown in attached Fig.), especially analysing for live load - what should be the stiffness properties of the transverse members in the grillage model?
Is it worth considering the top slab and bottom slab properties together as stiffness for transverse members of the grillage model?
When analysing the voided slab for live load, as the transverse stiffness increases, the load get distributed to the wider width of the bridge resulting in lesser effects on the longitudinal members of the grillage. I am not confident to use this approach as it may result in the effects on the longitudinal members of the grillage model on the unsafe side. Please correct me if I am wrong.
Shall we consider the stiffness of the transverse members equivalent to the top slab only, in order to obtain the effects on the longitudinal members on a little conservative side?
The cross section shown in the drawing is of a box section bridge and stiffness of this is calculated automatically in the software. Whereas you are asking for voided slab. Seems somewhat mismatch between the diagram and question?