Restrained/unrestrained beam
Restrained/unrestrained beam
(OP)
I have the folowing situation, and I am not sure if the beam I am designing is prone to LTB;
If I have a pin jointed truss, with a back to back channel section upper chord. To the web of this top chord I have a fin plate to which a secondary beam is connected (pinned).
On this secondary beam's flange lies 5 equidistant purlins (also pinned).
Lateral stability is provided with two horizontal wind girders at each side of the structure.
I am concerned about the secondary beam connected to the top chord (pinned)... is it restrained against LTB by the purlins? should I check LTB, for every span between purlins?
Thankyou, help much appreciated
If I have a pin jointed truss, with a back to back channel section upper chord. To the web of this top chord I have a fin plate to which a secondary beam is connected (pinned).
On this secondary beam's flange lies 5 equidistant purlins (also pinned).
Lateral stability is provided with two horizontal wind girders at each side of the structure.
I am concerned about the secondary beam connected to the top chord (pinned)... is it restrained against LTB by the purlins? should I check LTB, for every span between purlins?
Thankyou, help much appreciated






RE: Restrained/unrestrained beam
RE: Restrained/unrestrained beam
BA
RE: Restrained/unrestrained beam
Another thing I wanted to ask, is it safe to choose a purlin from load tables and specifications?
I have a table stating that for 2Kn/m2 of imposed load and 10m span an IPE 140 would suffice... Not sure if I should still design as a beam (i.e make the checks we do for simply supported beams with UDL roof sheet)
Thanks for your kind help... (not very familiar with long span steel structures)
RE: Restrained/unrestrained beam
If purlins do not provide adequate bracing to the top flange of the beam, you would have to check LTB with an unbraced length of 6*Sp, a completely different proposition. The sensible approach is to ensure that the purlins do provide adequate bracing to the beam.
Not sure what you are asking in your second question. Perhaps a framing plan would be helpful.
BA
RE: Restrained/unrestrained beam
RE: Restrained/unrestrained beam
www.metaalchristiaens.be/wordpress-christiaens/pdf...
RE: Restrained/unrestrained beam
RE: Restrained/unrestrained beam
Last question, if you don't mid ,
As a top and bottom chord, I am using double channel sections back to back, with a gusset 12mm in between, and battened along the 5 mm span between gussets.
When doing the checks, the thickness of flange (tf) and web (tw), are the summation of both sections and gusset.... or just the thickness of one C- section?
and any guideline on the amount of battens required between gussets provided at each node of truss?
Thank you, for all feedback
RE: Restrained/unrestrained beam
Doesn't matter...you've gotten good answers otherwise, just wanted to clarify!
RE: Restrained/unrestrained beam
RE: Restrained/unrestrained beam
Am I right to take thickness of web (tw), of the welded built section ]|[ as ;
tw of Channel (9) + Gusset thickness (12) + tw of channel (9) = 30mm
Thanks hokie66
RE: Restrained/unrestrained beam
RE: Restrained/unrestrained beam
However, I was in doubt about tw, for section web classification. Since I have always made use of rolled sections.
RE: Restrained/unrestrained beam