LRFD CONCRETE FILLED STEEL GRID BRIDGE DECK DESIGN

The simplest way to solve this problem will be to calculate moment of inertia for the composite steel/concrete in x and y directions, using the known section properties, i.e. detailed sections dimensions. You have to neglect the concrete in the cracked tension zone, so you have to find the depth of the compression zone first. As your LL moment is dependant on the D factor, I would assume LL moment by some other method (simple supported or continuous beam under partial length uniform loading by truck tire), calculate compression depth and determine D. Later you have to adjust your compression depth based on the moment computed using AASHTO 4.6.2.1.8 formulas, and repeat the process if necessary.