LRFD CONCRETE FILLED STEEL GRID BRIDGE DECK DESIGN

[jbasto]

Accoring to LRFD AASHTO 4.6.2.1.8 you have to calculate the live load moment with the equations provided in that section.
They specify the "D" value as EIx / EIy where Ix and Iy are the unit moments of intertia in the main and perpendicular to main directions respectively. These moments of intertia have to be computed for the cracked section using the transformed area method.
I asked a steel grid manufacturer (IDSI) and they say they don't provide the Iy value in their propety tables but there are some AASHTO recommended D values.

Question: Does anybody know where to find those recommended "D" values or another manufacturer that provide Ix and Iy, or how to go around this problem?

 

[wiktor]

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.