Calculate Torsional Constant for tubular truss

[qbrasco]

Am trying to calculate Torsional Constant for an aluminium tubular truss. The truss is made up of 4 50dia tubes setout in square shape 470mm apart. Tubes are separated by bracing struts. Can anyone provide advice?

 

[youngstructural]

To be honest I can't get a very clear picture of your layout. However, if you're looking for how to calculate torsion section properties, you may get a head start looking at this paper from CISC...

http://cisc-icca.ca/resources/tech/updates/torsionprop/

Post more detail, or just a simpler (perhaps just longer and more wordy) version for me...

Good luck,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[qbrasco]

The structure is an aluminium truss used at exhibitions. Their are 4 50dia tubes forming the beam/truss separated by lattice bracing. Tubes are spaced at 470mm thus forming a square shaped truss. I have read the paper suggested but it only provides J for an individual CHS. I'm looking for J for the combined beam shape i.e. J for 4 CHS working together. I have checked the beam for individual section capacities but would like to check the overall member capacity as the truss may span up to 24m. Would like to know if the compression flange will buckle at some stage.

 

[pappyirl]

Try this software which is on a free trial.

http://www.softpedia.com/progDownload/ShapeCAD-Download-48948.html

 

[vonlueke]

qbrasco: Assuming a tube wall thickness of 2 mm, and generic, minimal lattice bracing, I got a very rough estimate for torsional constant of K = 3617300 mm^4 corresponding to using typical aluminum shear modulus G in the torsional deflection equation, theta = T*L/(K*G).