This report deals with the modeling and analysis of the earthquake
behavior of concrete gravity dams. This task becomes very challenging
when the interaction with the reservoir and foundation has to be
considered. In addition, a concrete gravity dam may get severely damaged
by dynami- cally propagating cracks when subjected to a severe
earthquake ground motion. This strongly nonlinear behavior of dams
impedes the application of state-of-the-art frequency-domain meth- ods
for the analysis because the Superposition principle is no longer valid.
As a consequence, the model has to be formulated in the time domain
complicating the analysis even more. In this report, which is based on a
doctoral thesis, a new method is presented that permits to develop
absorbing boundary conditions for the nonlinear time-domain analysis of
concrete grav- ity dams. These conditions are based on a approximation
of dynamic stiffness matrices using series of orthogonal functions and
advanced model reduction techniques of linear systems theory. The new
absorbing boundary conditions are very accurate so that they are
virtually equivalent to dynarnic stiffness matrices obtained by a
rigorous solution of a far field. This allows to reduce the size of near
fields dramatically and permits an accurate and numerically efficient
nonlinear time- domain analysis.