Narrow Results

The mutation of mass and stiffness between the superstructure and substructure of a hydropower station can lead to the whiplash effect on the hydropower house during an earthquake. This paper explains the mechanism of the whiplash effect based on the theory of structural dynamics. A Chinese hydropower house was taken as a test case to discuss the whiplash effect on this type of structures. An integral finite element model and partial models of the hydropower house were established according to its structural features, arrangement forms and loading features. The dynamic response and the whiplash effect of the hydropower house were investigated by direct time integration using the Newmark method.

In order to thoroughly study the seismic resistance of gravity dams with longitudinal joints, a contact model based on constraint function method is used to simulate the shear keys within the joints and a concrete smeared crack model is selected to present the cracking characteristics of concrete materials. Because of the great size difference between the shear keys and the dam body, a glue mesh is proposed to implement multi-scale modeling. A dam-foundation-reservoir interaction system with longitudinal joints considering the various shear keys is developed and analyzed by nonlinear time-history method. On the basis of actual construction, arrangement and loading features of shear keys, a gravity dam is taken as a test case and a finite element model of the dam is established with triangular or trapezoidal shear keys. The working behaviors and failure patterns of various shear keys under earthquakes are explored. Moreover, the effects of various shear keys on the seismic resistance of the gravity dam are discussed. The results show that the seismic responses of shear keys are resulted in designed forms. The occlusion and dislocation of the shear keys within the longitudinal joints have an impact on seismic resistance of the gravity dams.

Central columns have long been demonstrated to play a vital role in withstanding not only static gravity loads but also seismic loads like earthquakes. A series of modeling tests are implemented on shaking table instrument to reflect the mechanism of soil — structure interaction and examine the validity of method of uplifting underground structural seismic resistance through strengthening central columns. An innovative method of enhancing central columns by adhering carbon fiber cloth onto column’s peripheral surface is introduced into a series of shaking table modeling tests, in which two two-layer underground model structures are constructed for comparison, one without any column remedy acts as a benchmark for reference and the other is amended with carbon fiber cloth adhered on column surface. Test results show that soft round model box adopted in tests serves well in simulating earthquake actions with negligible boundary effects on wave transfer; soil dynamic characteristics and the relative stiffness of structure to surrounding soil will interactively limit mutual motion and deformation. Racking deformation assumption may be not applicable for overall two-layer underground structure deformation analysis, but may be suitable for inter-layer displacement calculation for single layer in multi-layer rectangular underground structures. The adopted column enhancement measure could not only greatly increase the stiffness ratio of model structure to soil, reducing structure deformation, but also improve the integrity of underground structure by narrowing down the deformation difference between two structural layers, certifying that such a measure could be validly used in improving the seismic resistance capacity for already built underground structures without enough aseismic consideration when designed.