Operational Modal Analysis of Frame Building Module during Road Transport

Abstract

A real structure performance does not necessarily match the way the structure’s numerical model reacts to a load applied – even though it was constructed by specialists in the field and with the use of a state-of-the-art generation of software based on the finite element method (FEM). Inconsistencies are even greater, when the construction material is not as uniform and isotropic as steel, but wood, whose mechanical properties depend on a greater number of variables, like whether the loads apply longitudinally or across the grain. In such cases, it is necessary to customise a previously developed numerical model (model calibration) to fit real conditions of the performance. More and more frequently, to carry out experimental modal analyses (EMA), some measuring equipment and software is used to this end, which allows for estimation of credible structure modal parameters, i.e. particular normal mode shapes and their equivalents of natural frequency and modal damping values, which are necessary for credible calibration of a numerical model developed in FEM. It is not in every case, however, that one can excite vibration in a structure by means of classical modal exciters or modal hammers. Being a relatively new approach in the structure modal analysis, vibrations present in immediate surroundings of a tested object are used for this purpose. An analysis of such type is called the operational modal analysis (OMA). This study seeks to estimate credible modal parameters for one of the wooden modules of a multi-storey, multi-unit residential building, constructed by UNIHOUSE in Bielsk Podlaski in Poland, during its test road transport to its project site. The operational modal analysis of the frame building module was conducted with the use of a dedicated software LMS Test.Lab Spectral Testing. Measurements of vibration accelerations were carried out in 12 measurement points of the tested frame building module using a 32-channel and 24-bit data acquisition hardware type SCADAS Recorder from SIEMENS with 130 dB dynamic range and signal to noise ratio – minimum 106 dB, as well as a set of 10 high sensitivity triaxial piezoelectric accelerometers type TLD356B18, manufactured by PCB Piezotronics and two uniaxial, high sensitivity accelerometers type 333B50 – also manufactured by PCB Piezotronics. As a result of the tests and analyses executed on the proposed structure modal model, it was possible to estimate modal parameters of a single module of a frame multistorey building, which may be used for calibration of the structure numerical calibration in the FEM software.