Lipped Channel Cold-formed purlins design
Lipped Channel Cold-formed purlins design
(OP)
Hi everyone, I have a couple of questions regarding cold-formed design, (because the book that i have didn't address this questions)
1.Is there an easier method to design Cold-formed Lipped channels? Because using the reduced section properties of the lip, Flange, and stem of a section is quite tedious. I know DSM but i don't think it can be applied when bending occurs on both axis.
2. if there is a major and minor axis bending, can i use the reduced section properties (using the reduced section properties when bending is at the major axis) for both major and minor axis moments?
I wonder why AISI did not bother to make the analysis of the section simpler, I think using a certain factor to reduce the section capacity is more practical, rather spending so much time computing the effective properties of a section.
1.Is there an easier method to design Cold-formed Lipped channels? Because using the reduced section properties of the lip, Flange, and stem of a section is quite tedious. I know DSM but i don't think it can be applied when bending occurs on both axis.
2. if there is a major and minor axis bending, can i use the reduced section properties (using the reduced section properties when bending is at the major axis) for both major and minor axis moments?
I wonder why AISI did not bother to make the analysis of the section simpler, I think using a certain factor to reduce the section capacity is more practical, rather spending so much time computing the effective properties of a section.






RE: Lipped Channel Cold-formed purlins design
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RE: Lipped Channel Cold-formed purlins design
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RE: Lipped Channel Cold-formed purlins design
There is also another table located in the AISI manual which gives moment capacity based upon unbraced length of the compression flange. I believe it is Chart II-1b. I sometimes uses these tables.
There is also a computer program you can get which will give you the capacity of various sections. I metal building engineer I know swears by it..... and, oddly enough, you only need the part that is free (go figure)... but I can't remember the name at the moment.
I agree that is it very complicated, but the complications comes from the fact that the sections are so thin. You end up with local buckling before global buckling which really throws a wrench in things. Remember, most of the sections in the AISC manual comply with the buckling requirements.
RE: Lipped Channel Cold-formed purlins design
I had my company buy all the AISI books that apply. They work out a lot of examples, which gave me a lot of confidence that my approach was right.
RE: Lipped Channel Cold-formed purlins design
RE: Lipped Channel Cold-formed purlins design
RE: Lipped Channel Cold-formed purlins design
Sometimes I just reduced the Section modulus by 40% to avoid the lengthy effective section properties calculations.
Has anyone have another rule of thumb in quick calculations?
RE: Lipped Channel Cold-formed purlins design
http://www.ce.jhu.edu/bschafer/cufsm/
Mike Halloran
Pembroke Pines, FL, USA
RE: Lipped Channel Cold-formed purlins design
RE: Lipped Channel Cold-formed purlins design
Hookie66, since purlins cross-section are paralllel to the roof slope. The purlins are subjected to weak axis bending if the roof slope is large maybe 20 deg or more. if less the moment to be resisted at the weak axis is, in my judgement, insignificant.
RE: Lipped Channel Cold-formed purlins design
Same as for wall girts...they don't rely on bending to carry the gravity load of the cladding and self weight. You hang them from an eave strut or else support at the bottom.
The links I provided show how it is done in Australia.
RE: Lipped Channel Cold-formed purlins design
RE: Lipped Channel Cold-formed purlins design
Another factor in designing purlin systems is to load the purlin as closely as possible to the shear centre. So for C purlins or channels, where the shear centre is outside the web, the top flange should be up the slope. Z shape purlins are more efficient, as they can be lapped at the supports. Top flange up the slope for Z's as well, as the shear centre is at the section centroid.
RE: Lipped Channel Cold-formed purlins design
RE: Lipped Channel Cold-formed purlins design
thread507-266205: Sag Rod Support