The present report covers a series of torsional tests on stiffened D-tubes of alclad 24S-T3 aluminum alloy having a cross section similar to the NACA 0012 airfoil section and a closing web at 30 percent of the chord. The stiffeners consisted of ribs and stringers. An average strength chart has been developed for this type of structure that takes into account the skin thickness, rib spacing, and stringer spacing. This chart may also be used for unstiffened D-tubes.nMeasurements of unit twist and unit strain were made at a number of points on most of the specimens. The unit-twist measurements indicated substantial agreement between this type of structure and Bredt’s theory below the buckling point. The unit-strain measurements did not provide data that could be verified by theoretical analysis except for the strains measured in the webs.
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