Max Span of Portal Frame Rafter? 3

[civengzak]

Hello valuable eng-tippers,

I'm to design a 40m width, 115 m long and 10m heigh ( 12.25 to roof pitch)portal frame for a factory . I have experience with standard length portal frames using Eurocodes. So I'd really appreciate if you can help me on...
1- Can I use 20m long rafter? Whats the max allowed length of rafter/beam?
2- Whats the thermal expansion limit for steel structures? For concrete strucutres 30m max. Ambient temperature is 48 C (middle east).
3- Due to the length, would it be okay to give centred bracing in the middle and not at both ends?

Huge thanks in advance!

 

[BenAustralia]

Column in the middle is great for the Rafter size. Won't do much for your column size, as this stiff knee still needs to provide the bracing. It will also help with the footing sizes, greatly reducing the uplift on each.

As for frame spacing, this needs to be with consideration of the purlins as stated. A lot of the cost of a portal frame structure is in the purlins. At least here in Australia.

Depending on your loadings (wind/snow), I don't see many frames spaced past 10m. Most around 8m or so. We like to keep the purlins to 250mm deep or below, above this a few other aspects bump up, such as cleats and bolt sizes/grades.

12m is about the accepted maximum span for transport here too. We can certainly do greater, but 12m is a standard truck and helps a lot keeping costs down. A splice just after the haunch is common (either haunch, or a thicker/bigger member).

Good luck!