steel rafter laterally restrain - AS4100
steel rafter laterally restrain - AS4100
(OP)
Hi
I have a case which the rafter has webside plate (weld to the web of the rafter, the length of the plate is approximate half of the depth of the web from the bottom of the top rafter) bolt (two bolts) to the purlin at 0.9m spacing. the bolt hole is slot hole (2.5 x the bolt dia) instead of the normal bolt hole (2mm + bolt dia).
My question is, for this case, can I consider the purlin can provide laterally restrain to the rafter so that the segment length is 0.9m?
If to consider the segment length is to be the distance between the column support (which is about 5m), is it little bit conservative?
Thanks for your comments.
Cheers
Saygoodday!!!
I have a case which the rafter has webside plate (weld to the web of the rafter, the length of the plate is approximate half of the depth of the web from the bottom of the top rafter) bolt (two bolts) to the purlin at 0.9m spacing. the bolt hole is slot hole (2.5 x the bolt dia) instead of the normal bolt hole (2mm + bolt dia).
My question is, for this case, can I consider the purlin can provide laterally restrain to the rafter so that the segment length is 0.9m?
If to consider the segment length is to be the distance between the column support (which is about 5m), is it little bit conservative?
Thanks for your comments.
Cheers
Saygoodday!!!






RE: steel rafter laterally restrain - AS4100
In some cases, full depth stiffeners combined with purlin connections can be considered as flange bracing, but the method which you described is not adequate.
RE: steel rafter laterally restrain - AS4100
My question is, does the slot hole arrangement good enough to provide the top flange laterally restrain?
Thanks.
RE: steel rafter laterally restrain - AS4100
I assume your purlins are bolted to cleats above the top flange. We do assume the purlins brace the top flange, even with the short slotted holes which are for tolerance. However, these holes are typically not as long as you described. Refer page 17 of the attached reference.
http://www.bluescopesteel.com.au/files/dmfile/Lysa...
RE: steel rafter laterally restrain - AS4100
It is not a new design, and engineering judgement is need for the consideration of the laterally restain. My feeling is, by using the slot hole (2.5 x dia), it is not ok to be considered to provide full laterally restain to the top flange, not there should have some laterally restain. Instead of considering the rafter segment length is 5m between support, there may be a factor to consider the benefit from the purlins.
RE: steel rafter laterally restrain - AS4100
RE: steel rafter laterally restrain - AS4100
BA
RE: steel rafter laterally restrain - AS4100
Restraint force should be significantly less than the 2.5% of flange force due to the close centres.