A new buckling theory for curved beams of solid cross sections derived from rigid body and force equilibrium considerations

A new method is proposed for deriving the instability potential of initially stressed curved beams based on the rigid body and equilibrium considerations using the updated Lagrangian formulation. Starting from the rigid body rule, the virtual instability potential was derived for a spatially curved beam under real rigid displacements. Next, utilising the equilibrium equations for the boundary forces at the C₁ and C₂ states, another virtual instability potential was derived for the curved beam under virtual rigid displacements. Comparing the two potentials yields the one in total form for the curved beam. The present approach requires only simple integrations and analogical comparison of related virtual works, thereby avoiding the physically unclear, complicated derivations involved in previous procedures. Based on the first principles of rigid body rule and equilibrium, the derived potential energy is more concise than the conventional approach that requires the consideration of six stress components in the formulation. As an illustration, the present theory was successfully adopted in the buckling analysis of helical curved beams under radial loads.