  The French Accelerometric Network (RAP) launched in November 2004 a marked
operation for the seismic behaviour assessment of a typical French building.
The main goal of this project is to collect accelerometric data in the building
and use them to calibrate models or alternative tools used for the seismic
behaviour assessment. The final goal of this project is to help the
vulnerability assessment of cities in moderate seismic hazard countries. The
French Accelerometric Network (RAP) chose to install a permanent network of 6
accelerometers recording continuously the vibrations of the Grenoble City Hall
at the basement and at the top. The 13-story building is a RC shear walls
building, typical of the RC structures designed at the end of the 60's in
France. All the data collected in the building are available on the online
access database of the RAP. In addition to the permanent network, an ambient
vibration experiment has been performed in 36 points of the whole building.
Using the Frequency Domain Decomposition method, these data allowed estimating
precisely the different modes of vibration of the structure for low amplitudes.
Only the first bending modes in each direction (1.15 and 1.22 Hz) and the first
torsion mode (1.44 Hz) are excited. We compared the frequencies obtained using
ambient vibration to those for a moderate earthquake recorded by the permanent
network. Thanks to the continuous recording, a statistical approach of the
torsion mode pointed out the position of the centre of rotation of the
building. A modal model extracted from ambient vibrations is proposed and
validated thanks to the earthquake recordings collected in the building during
the ML=4.6, September 8th 2005 Vallorcine (Haute-Savoie, France) earthquake.
