VIBRATION STUDIES OF FRAMED BUILDINGS

Abstract

Vibration tests on full-scale structures provide a unique opportunity to verify the validity of analytical models used for design and research. Free vibration and forced vibra-tion tests were carried out on two double-storeyed R.C. framed buildings. Free vibration tests were performed by pulling the buildings and thus giving an initial displacement to the struc-tures. The forced vibration tests were carried out by exciting the buildings with an eccentric mass mechanical oscillator. Tests were carried out along longitudinal and transverse direc-tions of the buildings, placing the oscillator at roof, first floor and ground floor. The responses were picked up by accelerometers, amplified through universal amplifier and recorded by ink-writing oscillographs. . Natural frequencies and damping factors of the build-ings have been determined from the analysis of free and forced vibration records. Four analytical models have been developed. One con-siders the bare frame, neglecting the effect of infill walls. The effect of infill walls have been taken into consideration in the other three models. It is observed that the analytical model which considers the infill walls to act as a system of parallel springs with the frames, with cantilever behaviour of infill walls, yields frequency values which are close to experi-mental values.