Portal Buildings

[leisure17]

Being nosey again.
What stops the "long" lengths of roof beams from buckling in portal frames. they seem quite a small depth relative to other structures.
Cheers
Mick

 

[hokie66]

Bracing prevents buckling. Some portal frames do appear very skinny. There can be a number of reasons, some related to the loading, some to design methods and assumptions, some to risk. Not all engineers are the same.

 

[csd72]

A lot of the bending goes into the outer columns therefore reducing the required strength and stiffness of the beam.

Also, loads and stiffness criteria are much less stringent for industrial roofs than they are for floor beams e.t.c.

 

[ToadJones]

beams may be braced often

 

[sdz]

Rafters are braced partly by the attached purlins themselves on the top flange and by fly bracing to the bottom flange. Fly braces are the angle braces from the bottom flange to the purlins.

 

[kieran1]

SDZ we call it lateral restraint bracing in the UK

Kieran

 

[rscassar]

I have always worked off the rule of thumb of span/25 for simply supported roof beams and span/40 for portal frame roof members. This due to the end fixity provided by the columns in the portal frames.

 

[kieran1]

The roof angle pitch is very important in the design of the rafters.

Kieran