AISC truss unbraced length
AISC truss unbraced length
(OP)
Hi all,
For truss top chords under compression, does AISC-360 allow that the purlins be considered as a braced point for out of plane buckling? so that the out of plane buckling length is equal to the spacing of the purlins? or AISC leaves it for the engineer's judgement?
I used to design using AISC-ASD 89 and I remember that AISC leaves a lot for the engineer's judgement (which caused alot of argument among engineers).
thanks for the help
For truss top chords under compression, does AISC-360 allow that the purlins be considered as a braced point for out of plane buckling? so that the out of plane buckling length is equal to the spacing of the purlins? or AISC leaves it for the engineer's judgement?
I used to design using AISC-ASD 89 and I remember that AISC leaves a lot for the engineer's judgement (which caused alot of argument among engineers).
thanks for the help






RE: AISC truss unbraced length
RE: AISC truss unbraced length
BA
RE: AISC truss unbraced length
RE: AISC truss unbraced length
If you have no properly secured deck diaphragm but only a light metal roofing and the building diaphragm is developed via rod X braces or similar, then you probably might not want to depend on the purlins as brace points.
RE: AISC truss unbraced length
RE: AISC truss unbraced length
BA - Actually I am using it as a braced point of the top chord.
The term "braced" is at times too wide or too narrow for some people. Problem is some engineers wont accept that purlins can act as a braced point to the top chord of a roof truss, even after explaining the reasons you consider it as a braced point. My encounter with one such engineer will only accept that purlins can be used as a braced point if the code says "purlins are braced point". Its really a pain if that engineer is in a position of power to approve your plans & calculations.
RE: AISC truss unbraced length
BA
RE: AISC truss unbraced length
RE: AISC truss unbraced length
I hope the link is able to be opened by non ASCE members.
RE: AISC truss unbraced length
For a brace to work you need BOTH strength and stiffness. The PEMB metal roofing may not have the adequate stiffness and thus, the purlins would be too "LOOSE" to be effective braces for a large truss.