Effect of concrete cracks on dynamic characteristics of powerhouse for giant-scale hydrostation

Abstract

With the increase of capacity and size of the hydro-generator unit, the spiral case becomes a more super-giant hydraulic structure with very high HD value, where H and D denote water head and maximum intake diameter of spiral case, respectively. Due to the induced lower stiffness by the more giant size and adverse operation conditions, dynamic performances of the powerhouse and the supporting structure for the giant units have become more important and attracted much attention. If the manner of steel spiral case embedded directly in concrete is adopted, on some locations of the concrete surrounding the spiral case, distributed and concentrated cracks will emerge due to high tensile stress. Although the concrete is reinforced well to control the maximum crack width, definitely these cracks will reduce the local and entire stiffness of the powerhouse. Under dynamic loads such as hydraulic forces including water pressure pulsation in flow passage acting on the structure, effect of the cracks on the dynamic characteristics of the local members and entire structure needs to be evaluated. However, research on this subject is few in hydroelectric engineering. In this paper, Three-Gorge Project was taken as an example to evaluate effect of such cracks on natural frequencies and the vibration responses of the powerhouse under hydraulic and earthquake forces in detail. Results show that cracks only reduce the local structural stiffness greatly but have little effect on the entire powerhouse especially the superstructure; vibrations of powerhouse with cracks in concrete surrounding the spiral case are still under the design limits. Results in this paper have been verified by practice of Three-Gorge Project.

Keywords

giant-scale hydrostation / powerhouse / concrete crack / dynamic characteristics / numerical simulation

References

[1] Chen J., Ma Z., Liu Z., et al. Vibration analysis of powerhouse due to the pressure pulsation of hydro-turbine[J]. Water Power, 2004, 30(5): 24-27.

[2] Chen J., Zhang Y., Ma Z., et al. Study of dynamic characteristics of a giant spiral case with different embedment manners[J]. Journal of Dalian University of Technology, 2007, 47(4): 593-597.

[3] Hu Z.. Investigation on the Structural Vibration in a Large-Scale Underground Powerhouse [D]. 2004, Tianjin: Tianjin University.

[4] Lu Z., Dong Y.. Study of dynamic elastic modulus of distributed cracks[J]. Journal of Dalian University of Technology, 1991, 31(3): 367-371.

[5] Wang Qizheng. A preliminary study on the effects of the joints and cracks to the dynamic properties of the rock mass and its structure [J]. Journal of Hydraulic Engineering, 1993(2): 22–29(in Chinese).

[6] Ma Z., Dong Y.. Vibration and Its Corrective Action of Water Turbine Generator Set and Power House[M]. 2004, Beijing: China Water Conservancy and Hydropower Press.

[7] Ma Z., Shen C., Wang Y., et al. Studies on the anti-vibration and reinforcement of powerhouse in Hongshi hydropower station[J]. Journal of Hydroelectric Engineering, 2002, 21(1): 28-36.

[8] Shen K., Zhang Z., Liang Z.. Hydraulic vibration calculation of Yantan hydropower house[J]. Hydroelectric Energy, 2003, 21(1): 72-75.

[9] Wang Y., Ma Z., Zhang Y., et al. Fatigue analysis of metal parts in giant hydropower station subject to pulsating water pressure[J]. Water Resources and Power, 2006, 24(5): 1-4.

[10] Zhang H., Zhou Y.. Study of fluid-solid interaction vibration characteristics of the large scale powerhouse structure[J]. Journal of Hydroelectric Engineering, 2007, 26(5): 134-137.