Wagner Hypothesis in Beam and Column Theory

A examination is made on the underlying assumptions on which the flexural-torsional theory of thin-walled members is based. One of them, the Wagner hypothesis, is found not to be needed for the development of a comprehensive theory of rods. Use of the hypothesis is found to lead to the production of behavioral anomalies for axially loaded thin-walled members. A theory not using the hypothesis is found to be possible when it is recognized that the axis of torsional moments passes through the shear center but is directed parallel to the axis of displaced centroids. Results under the two theories are compared for the buckling of angle structs and monosymmetric I-beams. Physical tests capable of identifying the preferred theory are identified.