Element-level system identification with unknown input

A finite element-based time domain system identification procedure is proposed to evaluate existing large structural systems at the element level. The procedure does not need any information on the input excitation forces. Since the input exciting forces are not required, there is no restriction on the type of exciting force, only a small number of observation time points are required and no information is required on the modal properties of the structure. The unknown exciting forces can be applied at the ground level representing the seismic excitation. The procedure is particularly applicable to identifying an existing structure. The method is verified using three examples. For verification purposes, both the noise-free and noise-included output responses are considered. In all cases, the proposed method identified the structural parameters very well. The errors in the estimation of the parameters are considerably smaller than those in the other methods currently available in the literature. The proposed method is very economical, simple, and robust.