Christian GASSER

Parameter identification and damage detection based on the ambient dynamic response with emphasis on the method of additional masses, illustrated on a small-scale shear frame

The objective of this master’s thesis is the identification of mass and stiffness of a structure by means of different dynamic methods, based on mathematical modelling in Matlab and on experiments on a small-scale vibratory frame with four dynamic degrees of freedom.

At the beginning the calculation of the vibration response of a multi-degree-of-freedom system is described analytically and subsequently implemented into Matlab. Then the modal parameters of the system, i.e. eigenfrequencies, mode shapes and damping coefficients, are identified using the Peak-Picking method and the Stochastic Subspace Identification technique. In all the experiments so-called Operational Modal Analysis is adopted, which means that just the vibration response is measured, but not the excitation. A large part of this work is dedicated to scaling of the mode shapes by application of additional masses. Additional masses are collocated differently in an effort to reveal its optimal distribution within the structure. Scaled mode shapes are needed to identify mass and stiffness matrix. The stiffness matrix and its inverse, the flexibility matrix, are used in the last part of the thesis to detect and to locate damage of a gradually damaged frame based on different approaches.