Steel portal frames

[PeterP121]

Hi, I am designing a portal frame and understand that the dead load and self-weight deflection of the rafters can be ignored as this can be taken out by the steel frame fabricators 'pre-setting' the rafter. How is this done, what does pre-setting involve? Is it cambering the rafter?

 

[rowingengineer]

Preset means that the fabricated ridge connection is constructed a set amount above the required point. However this still allows the rafter to deflect between this point and the eaves, so can be ineffective on long span portals.

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

 

[PeterP121]

Thanks, so effectively I have to make the angle of the roof very slightly steeper to allow for it dropping under its self-weight and after the roof sheeting has been installed?

 

[hokie66]

If you are that worried about the roof deflection affecting drainage, then the roof is too flat.

 

[rowingengineer]

Yes, it is an effective way to control the slope from the first portal to the end portal which is genrllly propped by mullions.

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."