Nonlinear Cable and Frame Interaction

Methods of modifying a program written for the standard stiffness method to account for the nonlinearity introduced by cable action and axial compression, or both, are shown. For the case of axial compression, a member is divided into a number of divisions. Standard stiffness method is used but secondary effects due to axial compression on deflected geometry are taken into account. Two examples are shown. The method can be applied to members of variable cross section and with axial forces distributed along the member. For the case of cables, a modified modulus of elasticity method is used. The method differs from that introduced by Tung in that cable tension is solved directly from the nonlinear cable equation and unbalanced forces due to differences between the curved cable and the substituted straight member are taken into account. Comparison of the results by the proposed method with those by a more exact iteration method are given for two examples involving interaction of cable and compression members. Finally, solution of a transmission tower with cable members is illustrated.