Novel Wirelessly Synchronised Modal Testing of Operational Buildings Using Distributed OCXO High-Precision Data Loggers

This chapter describes a novel and oven-controlled crystal oscillator (OCXO) high-precision synchronised wireless data acquisition system for modal testing of large structures. The system was used for the first time for a rare FRF-based modal testing of a full-scale multi-storey building in operation. National Instruments’ CompactRIO and LabVIEW were utilised to develop wireless multi-channel data loggers to resolve typical, and sometimes insurmountable, problems related to the logistics of long cables connecting sensors with data acquisition in ambient vibration testing (AVT) exercises on operational structures. Several OCXO-based data loggers were used to distribute sensors wirelessly across the structure, using a sub-microsecond sensor synchronisation procedure to measure simultaneously not only the structural vibration response but also the forcing function needed in FRF measurements. As part of the setup, a spectrum analyser (SA) was used to provide the shakers’ excitation signal and perform a point accelerance FRF measurement at a location close to the data acquisition centre and with minimum wired infrastructure. Two different data acquisition systems (OCXO- and SA-based) used independent time clocks. To validate the OCXO-based FRF measurement in buildings, modal testing was carried out on a 15-tonne laboratory-based test floor and a full-scale seven-storey condominium building made of cross-laminated timber. The combination of distributed OXCO-based wireless and synchronised data loggers coupled with an SA-based force generation and FRF point mobility quality assurance measurement was successfully used to identify the sway modes’ dynamic properties of the structure.