Wind Deflection of Pulins and Girts

[sybie99]

Hi Guys,

When designing roof purlins and side rails (girts) using cold formed lip channels, what deflection limits do you use. For normal live loading it would generally be 1/360 (British Standards) and span/250 total deflection (dead plus live). As wind loading is greater than my imposed live loading, in even more so for the side rails where wind loading is the only imposed load, what do you use as deflection limits?

The structure has been checked on a basis of height/300 to which it complies. But I find it a bit of a waste to over size purlins and girts to be within normal deflection limits as a wind deflection is such an instantaneous load. What are your thoughts?

 

[DST148]

The deflection criterion would depend on the type of cladding / finishes attached to the purlins or girts. For guidance, you may Google AISC Design Guide No. 3 - Serviceability design considerations for steel buildings.

 

[MiketheEngineer]

IBC allows much higher deflections based on building use. An AG building allows much higher deflections. Who cares what the horses and cows think?? I even push those a bit from time to time - because - who cares??

 

[demayeng]

span/150 for wind, most of the time.

 

[DST148]

@sybie99: Try thread176-153232 and thread507-207611

 

[apsix]

As per demayeng: span/150 for wind, most of the time.