Output Only Structural Identification with Minimal Instrumentation

Abstract

It is of interest to the modal testing and structural health monitoring community to be able to identify the mass and stiffness parameters of a system from its vibration response measurements. However, incomplete instrumentation of the monitored system, and the more general ambient vibration situations, result in measured mode shapes which are incomplete and not normalized. In this paper, we consider the problem of mode shape expansion, normalization, and subsequent physical parameter identification, for shear-type structural systems with output-only (ambient vibration) measurements. It is shown that only two sensors, located at the first and last degrees of freedom of the system, are sufficient for parametric identification of the system. A mode shape expansion – physical parameter identification algorithm, starting from the incomplete modal parameters identified using a stochastic subspace based method, is discussed. The algorithm incorporates the information available from the structural topology of the physical system in terms of its modal parameters. The advantage of the algorithm lies in its ability to obtain a reliably accurate identification using the minimal necessary instrumentation, and the minimal necessary a-priori information about the system. The efficiency of the proposed algorithm is finally validated through numerical simulations of ambient vibration experiments on a 7 story shear-type structure, including the effect of white/colored measurement noise.