NONLINEARITY IDENTIFICATION FOR A FRAME MODEL STRUCTURE WITH MR DAMPERS UNDER LIMITED EXCITATIONS

摘要

Nonlinearity exists widely in engineering structures and may arise in damaged engineering structures, but the dynamical system theory for nonlinear system is far less established than its linear counterparts. Strictly speaking, the identification methodologies based on eigenvalues and eigenvectors extracted from structural dynamic response are only suitable for linear systems. It is critical to develop general vibration-based identification and damage detection methodologies suitable for nonlinear systems. For civil engineering structures, the restoring force provides a direct indicator of nonlinear extent and damage severity. In this paper, a 4-story frame structure equipped with magneto-rheological (MR)dampers was employed to mimic a nonlinear structure and its nonlinear restoring force was identified in a polynomial form. Firstly, each coefficient of the polynomials was identified by a least-squares technique, only using limited excitations applied on a certain floor and the corresponding acceleration responses. Subsequently, in order to validate the accuracy of the identified restoring force, the hysteretic performance of the MR dampers was extracted from the identified nonlinear nonconservative restoring force and compared with the test measurements. Results show that the proposed data-based approach is efficient for nonlinear restoring force identification of engineering structures.