Fundamental periods of soil obtained from measurements in buildings

To know the dynamic behavior of buildings in high seismic areas, structures are instrumented to record their response to the seismic action. With the same purpose, forced or environmental vibration may be used. This last type of vibration, called cultural noise, is generated by human activity as industrial machinery, traffic, etc. or by natural sources as wind, atmospheric pressure changes, etc. The measurement in these conditions permit to analyze the dynamic behavior of structures in low or moderate seismic areas; in addition this methodology is a quick and low cost procedure. In Barcelona City, a study about natural periods of buildings is being carried out. The acceleration, produced by the cultural noise, in the upper part of the structures is recorded. For seismic microzonation purposes, noise measurements on the soils have been also performed and have been analyzed by the Nakamura method. So we have been able to compare the records obtained on the buildings with the soil ones. It is interesting that, in some cases, in the Fourier spectrum of the signals recorded at the building roof, the soil fundamental frequency may be also identified. In this work, we present the results of that relationship between the fundamental periods of the soil and their measurement in buildings.