EXPERIMENTAL DETERMINATION OF DYNAMIC CHARACTERISTICS OF STRUCTURES

For building design, the evaluation of dynamic characteristics of the structure, as natural vibration frequency or critical damping coefficient, is a necessary step to obtain the response to certain loads as, for example, the seismic or wind actions. The design characteristics can be different from the real structure characteristics, usually as result of the simplified design models and hypothesis. The experimental determination of the structural dynamic characteristics is important for new buildings and, also, for the existing ones. For new buildings, the experimental values are used to verify the design model and calculations or the build-up of the structures and for an existing structure those tests can be used to establish the present state of the building or to apply certain special retrofitting methods. This paper presents, by comparison, two experimental methods to estimate the structure dynamic characteristics. The first method is based on structure free vibrations and the second one is based on forced harmonic vibrations induced in the structure. Those methods are exemplified on a small scale model of a structure with two degrees of freedom. Also, the experimental response of the test structure, subjected to harmonic excitation, is compared with the response of the structure modeled with finite elements.