Opening in structural steel roof

[OAP]

Hi,
I'm designing the house which has 8.0m.x8.0m. (width x length) roof without the intermediate support and the client want to have the opening about 2.0m.x 2.0m. at the middle of the roof for the skylight (it looks like a pyramid with cut the top part of pyramid off). I plan to use the compression ring dia. 2.0m which built from CHS tube to allow for the opening at the middle of the roof because the compression ring will give the clear opening if I use square shape, it will have a diagonal member cross the opening,right? But I'm not familiar with this kind of structure. If anybody have any comment, please help me.
Thanks
OAP

 

[DaveAtkins]

You can certainly engineer a truncated pyramid roof without diagonals across the upper opening or the base. By statics, the force induced by the corner diagonal member is resisted by two perpendicular members at the compression ring or the base. Roof sheathing of some sort should be used to carry wind loads to the base AND to prevent racking of the entire truncated pyramid roof.

 

[Ron]

I agree with Dave...you can create a square "compression" block in the center, with the hip ridges of the roof coming off the corners of the square. The stiffness of the square can be such that all forces are resisted. Not a big issue.