Experimental determination of natural frequency of confined masonry building by ambient and forced vibration testing

Field testing of full scale structure always gives a better idea about its characteristics properties as compared to analysis of the structure in different softwares which includes lot of assumptions and idealization, leading to approximation of the results .This study aims at investigating the fundamental period of vibration of confined masonry buildings located at the campus of IITGN, by measurements of ambient and forced vibrations. This study is extensively carried out on Type-III housing buildings of IITGN and extended to Type-I and Type-II housing buildings. Ambient vibrations were measured for various time durations and on different positions at roof level of a selected three story building by a single seismic accelerometer. Auto spectral density plots for ambient vibrations gave a fair idea of natural frequency of a building .Further, forced vibration testing were also carried out repeatedly on various locations at roof level of a building using electrodynamic mass shaker. Natural frequency was confirmed by plotting auto spectral density functions for ambient and forced vibrations of the buildings, signal to noise ratio plots, and Acceleration Response factor obtained from harmonic input vibrations to the building. The results obtained from experiments are compared by natural frequency obtained from modelling the buildings in SAP 2000. On the basis of results, a new formula for calculation of natural time period for confined masonry buildings has been recommended.