A non-parametric Iwan model for friction-induced nonlinear dynamics

Built-up structures are known to show nonlinear, hysteretic behavior due to the slipping of interfaces that are bolted together. The Iwan model is commonly used to simulate the observed nonlinear dynamics. There have been many adaptations of the Iwan model, with the key distinction between them being the definition of the distribution function which determines the force-displacement relationship of the joint. These existing models, however, are parametric in nature; the flexibility offered by them is limited to the finite number of parameters that can be tuned. In several cases, the model does not fit experimental measurements or finite element simulations as well as is expected. This paper presents a novel, non-parametric Iwan model in which the distribution function itself is derived from the nonlinear force-displacement backbone curve of the hysteretic system, thus allowing for greater flexibility. Quasi-static analysis is used to obtain the backbone curve of a system, and a model inversion method is implemented to characterize it using a non-parametric Iwan element. Numerical integration of the resulting model simulates the system’s nonlinear dynamic response at a greatly reduced computational cost as compared to integrating the full model. Two numerical case studies are considered to verify the proposed approach. The results show that the proposed model is orders-of-magnitude faster that integrating the whole finite element model and provides greater accuracy than existing alternatives such as the four-parameter Iwan model.