Intern	Institution	Mentor	Project Title
Lisa Sarma	Columbia University	Thomas Heaton, Caltech	Investigation of the coupling between structures and ground vibrations and the implications on damping in buildings

Abstract:

Seismic waves were generated through forced vibration of the nine-story Millikan Library building located on the campus of the California Institute of Technology in Pasadena, California, in February of 1998, at the building's east-west natural frequency of 1.135 Hz.. The wave velocities produced by these vibrations were recorded at distances of 1 to 6 kilometers away from the building. The accelerations of each floor of the building in both the north-south and the east-west directions were also recorded. A mathematical model was developed, which predicts the radiation pattern from the rocking and shearing of a rigid disk on the surface of a homogenous half-space. The inputs to the model were the shearing force and the rocking moment that the structure transfers to the ground as a result of its motion.

The acceleration data was used to calculate the forces and the moments from the building. The experimental data was plotted as a function of its distance to the building and shows that the particle velocity decreases with distance according to a power law that varies for each component and with distance.

Further work needs to be done, ultimately comparing the experimental data to the model data and assessing the accuracy of the model. The forces and moments will be input into the model and a plot of the radiation pattern produced. Since February of 1998, seismometers have been placed in 68 different locations throughout the San Gabriel Valley between 1 and 7 kilometers away from Millikan Library. Data from the Southern California permanent broadband instrument network was also collected, and the signal from the building can be seen as far away as Barrett (~230 km South East of the building). At each point where data was collected, the energy predicted by the model will be compared to the energy received at that point. The ratio between the radiated kinetic energy and the input kinetic energy is instrumental in calculating the damping of the building due to energy radiation.

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