In this paper the nonlinear response of zero-force members is investigated in linear elastic pin-jointed trusses and it is shown that in such members the normal force is typically a quadratic function of the load parameter, and so the sign of the normal force does not depend on the sign of the load. A simple, intuitive method is provided to determine the sign of the normal force. A ‘degenerate’ example is also demonstrated, containing zero-force members in which the dependence of the internal force on the load parameter is of arbitrary order.
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