Identification of clearance-type nonlinearities

In this paper, the identification problem is discussed for clearance-type nonlinearity, a common situation in many practical applications, and this clearance may lead to difficulties in predicting the system response. The proposed approach is applied to an experimental problem, by using a recently developed method, termed nonlinear subspace identification (NSI). The experimental application described hereafter is a multi-storey building and the nonlinearity of the structure is represented by a buffer mounted on a lower deck with a certain gap, introducing a nonlinear asymmetric behaviour when the amplitude of the motion exceeds the fixed limit. Since NSI is able to treat many nonlinearities at the same time, several ad hoc functions are defined and adopted in order to identify the clearance-type characteristic, showing advantages with respect to the traditional polynomial approach. The asymmetric characteristic of the buffer contact, its intrinsic nonlinearity and the multi-degree-of-freedom (MDOF) system create an interesting miscellanea of the typical elements, which are often difficult to identify in nonlinear dynamics.