Modified Stability Equations for Pre-Twisted Columns

Abstract

It is shown that the theory of pre-twisted bars used in all existing publications on the subject violates the traction boundary conditions on the side surfaces of those bars. A simple modification is proposed to satisfy those conditions without changing anything in the basic kinematic structure of the theories currently in use. Stability of pre-twisted bars is used in this work to present and illustrate the new, modified theory. There are two specific outcomes of that new formulation, one is emergence of torque as an additional internal force generated by the axial load, and the other is the reduction of the bending stiffness in pre-twisted bars. Of the two, the former turns out to be rather negligible, but the latter is quite significant and, comparing to the current theory, changes the buckling load of pre-twisted bars rather significantly. This is illustrated by a number of numerical examples.