Stability of Guyed Towers

A method is presented for determining the lateral loading at which a multilevel guyed tower becomes unstable. The point in the load-displacement history at which a small increase in the applied load produces an inordinately large increase in displacements is interpreted as the point at which collapse occurs. The nonlinear algebraic equations governing the displacements of the tower are transformed into a set of nonlinear differential equations which are solved by matrix inversion and numerical integration. Instability occurs as the determinant of the stiffness matrix relating differentiated displacements approaches zero. Nonlinear effects considered include flexural contraction of the mast, continuous changes in the bending stiffness of the mast, and effects of wind on the cables. Numerical results are presented for the static stability analysis of a 1,100-ft, symmetrically loaded, three-level guyed tower. The effects of independently varying several parameters of the system, such as the moment of inertia of the mast and the pretensioning and areas of the guy cables, are demonstrated.