16. Robustness of Modal Parameter Estimation Methods Applied to Lightweight Structures

On-going research is concerned with the losses that occur at junctions in lightweight building structures. Recently the authors have investigated the underlying uncertainties related to both measurement, material and craftsmanship of timber junctions by means of repeated modal testing on a number of nominally identical test subjects. However, the literature on modal testing of timber structures is rather limited and the applicability and robustness of different curve fitting methods for modal analysis of such structures is not described in detail. The aim of this paper is to investigate the robustness of two parameter estimation methods built into the commercial modal testing software B&K Pulse Reflex Advanced Modal Analysis. The investigations are done by means of frequency response functions generated from a finite-element model and subjected to artificial noise before being analyzed with Pulse Reflex. The ability to handle closely spaced modes and broad frequency ranges is investigated for a numerical model of a lightweight junction under different signal-to-noise ratios. The selection of both excitation points and response points are discussed. It is found that both the Rational Fraction Polynomial-Z method and the Polyreference Time method are fairly robust and well suited for the structure being analyzed.