Shetty & Allen - A General Iwan Element Derived from Quasi-Static Force-Displacement Data - IMAC2021
Built-up structures are known to show non-linear, hysteretic behavior due to the slipping of interfaces that are bolted together. The Iwan model, which is a category of Masing models, is commonly used to simulate this non-linear behavior. There have been many adaptations of the Iwan model, with the key distinction between them being the definition of the distribution function which determines 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 and in several cases, this has led to frustration when the model does not fit experimental measurements as well as is expected. This paper presents
an alternative, non-parametrized approach in which the distribution function itself is derived from the 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-parametrized Iwan element, which can then be
integrated to simulate the system’s dynamic response at a greatly reduced computational cost as compared to integrating the full model. The accuracy of the proposed method has been investigated in this paper. While it currently provides a quick way to get a dynamic model from quasi-static simulations, the proposed method could eventually be used to define a model from an experimentally obtained load-displacement curve.