Here is a very simple technique for making effective looking Rib & Infill look correct in section
First create your your slab composite, with 2 skins.
set the bottom skin to show the thickness and sectional fill of your timber and the top skin to show the thickness and sectional fill of the concrete topping slab.
Next create a custom profile shape for you ribs. Ensure that the central concrete fill uses the same pens and fills as the concrete fill in the composite slab. Stretch the top of the concrete fill up to the same height as the timber infill
Then simply move the ribs/beams so that the top of the shell touches the underside of the composite slab