Abstract: Based on the Newmark-β numerical simulation method， a modified Newton-Raphson iteration method is used to minimize the substitution error of tangent stiffness for variable stiffness for a single-degree-of-freedom nonlinear system. Then， the iterative solution process of dynamic response of the nonlinear system under the known external excitation and system characteristics is deduced， and the inverse iterative solution process of dynamic load under the known dynamic response and system characteristics is deduced. A numerical example shows that the modified iteration method is feasible for load identification of nonlinear systems and overcomes the shortcoming of error accumulation without the iteration method.

Key words: Newmark-β, Newton-Raphson iteration, nonlinearity, load identification, error accumulation