calculate torsional constant for tubular truss

huangyhg

calculate torsional constant for tubular truss
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?
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...
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   
try this software which is on a free trial.
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).