FRF-based modal testing of horizontally swaying structures using ocxo synchronised wireless accelerameters for simultaneous force and vibration response measurements

This paper describes an experimental validation of a novel FRF-based modal testing system designed to measure experimentally sway modes of tall timber and other building structures. The test uses a set of synchronised electrodynamic shakers and oven-controlled crystal oscillator (OCXO) high-precision synchronised wireless accelerometers for simultaneous force and response measurements. This modal testing system makes no use of cables or radio-waves to connect all accelerometers simultaneously with the multi-channel data acquisition system but provides a perfect synchronised measurement of a practically unlimited number of force and response channels. The system will be used to to estimate experimentally sway modes of as-built tall timber buildings. Therefore, the aim of this paper is to demonstrate the feasibility of the OCXO-based system in high-rise building FRF measurements. Two nominally identical FRF-based modal testing exercises were carried out on a 15-tonne laboratory-based test floor structure supported by 4 columns in order to measure its horizontal'swaying' modes of vibration using: (1) a well-established and quality assured'wired' system based on a 20-channel spectrum analyser, and (2) OCXO-based wireless system. It was shown that the two methodologies produce almost identical modal testing results and that the OCXO-based method is robust and reliable for field utilisation on high-rise buildings.