I am looking at an assembly of Two Round Hollow Tubes running parallel next to each other. The tubes are 2.5in Diameter and 0.125in Thick.
I would like to see how the separation between the tubes impacts the bending and torsional rigidity of the system. Clicking on a single tube's cross section surface and looking at the section properties, the Area moment of inertia in the y-direction is 0.66in^4 and the Polar Moment of inertia is 1.32in^4, as expected when looking at the formula for moment of inertia of a hollow tube:
Increasing the separation of the tubes to 200mm drastically increases the area moment of inertia in the y-direction to 30.23in^4 and the Polar Moment of Inertia to 31.55in^4:
Can these results be trusted? I am having a hard time understanding how the bending resistance in the y-direction could increase by increasing the distance between the two members?