Progressive Collapse - Enhaced Local Resistance

[MattJM]

Can anyone shed light on the use of the factor used in the UFC (as follows) for enhanced local resistanc of columns?

The purpose is to guard against shear failure below the flexural capacity of a column, so the provisions require that the column be designed for the shear resulting from uniform lateral load at the three-hinge formation condition in the column. For a pin(base)-fixed(top) column, the examples use
V = 7.5 * Mp/h,
where h is the column height. Not much explanation is given.

A lower factor can be derived for this condition (V=6.83*Mp/h).

Does anybody else have an explanation for the increased value? Is the extra 10 percent for any of the following reasons:
Column not actually pinned at base? (Fix-Fix has factor of 8)
Overstrength?
Something else I have probably missed?

Note: The progressive collapse seminar I attended way back also indicated the use of the 7.5 factor.

Thanks

 

[MattJM]

How about this reason:
Per ASCE 41 - Flexural capacities (deformation controlled action) must consider the likely strength, which carries a factor of 1.10. Therefore, Mp must be multiplied by 1.10 when I compare this to the shear capacity (a strength controlled action), which uses the lower bound strength.

6.83*1.10 approx equals 7.5.

Reasonable?