G.8.2.2 Nonlinear Cable and Truss Members
Cable members for the Basic Nonlinear Cable Analysis may be specified by using the MEMBER CABLE command.
While specifying cable members, the initial tension in the cable or the unstressed length of the cable must be provided. You should ensure that all cables will be in sufficient tension for all load cases to converge. Use selfweight in every load case and temperature if appropriate; i.e., don’t enter component cases (e.g., wind only).
The nonlinear cable may have large motions and the sag is checked on every load step and every equilibrium iteration.
In addition there is a nonlinear truss which is specified in the Member Truss command. The nonlinear truss is simply any truss with pretension specified. It is essentially the same as a cable without sag. This member takes compression. If all cables are taut for all load cases, then the nonlinear truss may be used to simulate cables. The reason for using this substitution is that the truss solution is more reliable.
Notes
Nonlinear cable elements differ from linearized cable members in the following ways:
Notes 1, 2, and 4 regarding linearized cable members will not apply to nonlinear cable analysis if sufficient pretension is applied, so joints may be entered along the shape of a cable (in some cases a stabilizing stiffness may be required and entered for the first loadstep). Regarding note 3 on linearized cable members: The Member Tension command is unnecessary and ignored for the nonlinear cable analysis. Point 5 above: The cable tensions are iterated to convergence in the nonlinear cable analysis.