Experimental Evaluation of Dynamic Properties for Building Systems

Abstract

Advances in analytical techniques, availability of newer and more efficient materials have led to the construction of lighter and more flexible structures now a days. Due to flexibility, these structures have become more sensitive to dynamic loadings and have become dynamically responsive. Therefore, it is important to accurately assess the dynamic properties of structures, such as natural frequencies, displacement mode shapes, damping, transmissibility etc. Among all, damping is recognized as an important property, which is a measure of energy dissipation in a vibrating structures. Unfortunately, damping remains the most di cult dynamic property to predict, as it cannot be derived from the other physical properties of the structure, unlike the mass and sti ness properties. Thus assessment of damping demands experimentations either on real buildings or prototypes of buildings. Assessment of damping is largely carried out by experimentations conducted on real buildings or their prototypes in laboratory. Excessive dynamic response of structures set up high level stresses. In order to control such dynamic responses, structures are sometimes provided with bracings at various levels. The project includes experimental investigation of the dynamic properties of building models imparting free vibration and forced vibration. Experiments were performed on building models of single degree of freedom (SDOF), two degree of freedom(TDOF) and multi degree of freedom (MDOF) systems fabricated from aluminum material. Building models were placed on horizontal shake table (uni-directional) to impart both free and harmonic forced vibrations. For the uncontrolled building i.e. building without bracings, responses were captured using accelerometers and Data Acquisition System (DAQ) - LABVIEW 8.0. The recorded data were analysed both in time-domain and frequency-domain. Controlled responses of the SDOF building models were obtained using bracings in di ferent con figurations such as concentric and eccentric types. Dynamic responses obtained from both uncontrolled and controlled building models are compared to assess e effectiveness of the later.