FULL-SCALE DYNAMIC TESTING AND ANALYSIS OF A RESERVOIR INTAKE TOWER

Dynamic tests were conducted on a 50m high intake tower at Wimbleball dam in the U.K. The results were compared against predictions from a c orresponding numerical model. The aim of this work was to validate the assumption that the compressibility of the reservoir water is not a s ignificant factor in the seismic analysis of intake towers. Three sets of tests were conducted on different occasions with different water l evels in the reservoir. In the first two tests, modal characteristics of the tower were determined from the measured responses under ambient , hammer and human excitation. These results were used in planning the final set of tests where rotating eccentric mass exciters were used t o vibrate the tower. Structural accelerations and hydrodynamic pressur es were measured over the height of the tower for three important bend ing modes of vibration. The finite element method was used to develop a numerical model for Wimbleball tower. The tower was discretized with traditional solid elements and the reservoir with incompressible flui d elements. This model was analysed to predict the modal characteristi cs acid harmonic responses of the tower and reservoir under the variou s conditions imposed during the dynamic tests. Theoretical predictions of the tower's accelerations and hydrodynamic pressures in the reserv oir were compared against the test results. Excellent agreement was fo und for the natural frequencies and mode shapes while predictions of t he harmonic responses were only fair. The observed responses of the to wer and reservoir support the assumption that reservoir compressibilit y is not a significant factor in the seismic analysis of towers of thi s size.