cover plates

[kwrohde]

I have am using a w30x124 section with a cover plate in STAAD. The cover plate dims. are 14"x0.75". The w30x124's area is 36.5in^2 and the cover plate's area is 10.5in^2 the sum of which is 47.0in^2. When I enter it into STAAD as a member with a cover plate STAAD returns an area of 46.619in^2. Through some simple calculations I figured that Staad was reducing the cover plate width by 0.508". But then I noticed by accident that if you enter a section with a cover plate and define the plate dims. as 0x0 Staad will reduce the section area. A w30x124 entered in Staad with a cover plate of 0x0 returns an area of 36.119in^2. So Staad reduces the area of the original section and then adds the full area of the plate. What is going on? Is STAAD reducing moments of Inertia as well? Does this reduction only affect stiffness of the section or does it reduce its dead load effects as well? Why is this redution happening? Thanks in advance.

Karl