Determination of Building Modal Parameters Using Low-Level Excitation

Over the past few years, the authors have performed forced vibration testing on a variety of low-rise building structures. In this paper, the procedure to experimentally determine the modal parameters (natural frequency, mode shape, and damping) of building structures through forced vibration testing is described. In addition, a comparison of the experimental results to computational predictions of the building response is made to highlight the accuracy of the computational modeling. The experimental setup consists of a small linear shaking device that gently (below human perception) vibrates the building structure and highly sensitive (but inexpensive) hardware and software to collect and process the results. Great care must be taken to properly position the equipment, filter out the extraneous data, and process and interpret the data. Interpretation of the data is complicated by the excitation of all modes when the building is subject to forced vibrations. A procedure for determining the mode shapes directly from the forced vibration testing is presented and compared to the experimental results.