Steel deck moment formula

[vmirat80]

The Vulcraft catalog for steel deck has two negative moment formulas. If the length is less than or equal to 10 feet, the formula is 1/12WL^2. If the length is more than 10 feet, the formula is 1/10WL^2. I understand the 1/10 factor is for a three-span condition. It also seems that they are using the 1/12 factor for a single beam with fixed ends and uniform load. How did they come up with the length of 10 feet to switch formulas?

 

[KootK]

You may ultimately have to ask Vulcraft to determine the answer with any certainty.

The switch may be occurring where limitations on individual deck sheet lengths would trigger a change to the number of flexurally continuous spans.