Composite Beam w/Formed Steel deck 1

[sigma1]

According to AISC 9th edition (ASD) section "I5" concrete below the top of the steel deck shall be neglected when determining section properties and in calculating "Ac" for Equation (I4-1).However, the manual is not clear about the location of the concrete NA. In other words, is the rib height ignored or used in determining the "NA" and "I" of the composite beam.

Thank you

 

[Lion06]

The rib height is used, you just ignore the concrete in the ribs. This only applies when the flutes are perpendicular to the beam span. If the flutes are parallel you can take advantage of the concrete in the flutes.