Q: What deck thickness can I use for computing the effective flange width? A: In accordance with AASHTO LRFD, Section 4.6.2.6.1, for filled grids, partially filled grids, and unfilled grids composite with reinforced concrete slab (Exodermic™ deck), the “slab depth” used should be the full depth of grid and concrete slab, less a sacrificial depth for grinding, grooving, and wear (typically 0.5”).