6. PERFORMING ORGANIZATION CODE 7. AUTHOR 8. PERFORMING ORGANIZATION REPORT NO.

Structural health monitoring of large multi-span flexible bridges is particularly important because of their important role in civil infrastructure and transportation systems. In this study, the response of the Yokohama Bay Bridge (YBB), a three-span cable-stayed bridge, to the 2011 Great East Japan earthquake is used to perform multi-input-multi-output (MIMO) system identification studies. The extensive multicomponent measurements are also used to develop and validate data driven nonlinear mathematical models that can predict the response of YBB to various earthquake records and can accurately estimate its damping characteristics when the system is driven into the nonlinear response range. A combination of least-square (parametric) and neural network (nonparametric) approaches are used to develop the mathematical models, along with time-marching techniques for dynamic response calculations. It is shown that the nonlinear mathematical models perform better than the equivalent linear models, both for response prediction and damping estimation. The importance of having a