Embedment of Steel Spiral Cases in Concrete: Lessons from a Structural Deformation Accident in China

Abstract

A spiral case structure (SCS) plays a significant role in the safe and reliable operation of a hydroelectric power plant (HPP). In an HPP with 700 MW class turbine in China, a structural deformation accident happened in the construction period causing severe loss. Based on in-situ measured data, this study focuses on two major differences of this SCS that might cause the accident: (a) the construction condition, and (b) the shape of steel spiral case (SSC). The accident is reproduced in numerical study, and the simulation results agree reasonably well with in-situ measured data. The results show that the construction condition is a main factor causing the accident, but it is not the only cause of the raising deformation. The findings reveal that the post-accident stresses of steel structures are still at a relatively low level, and it would not be a major concern. The study also shows that the SSC with non-circle sections tends to have larger deformation under internal water pressure, and the deformation of the stay ring needs more attention in the construction period. The major limitation of this study is that this study merely focuses on the construction period. If such SCSs were to be used in a wider range, a follow-up study focusing on the operation period should be considered.

Assessment of the Embedment of Francis Turbine for Pumped Hydraulic Energy Storage

“…The scientific investigations directed to the influence of the different factors over the design scheme and structure is of significant importance since they could reveal the factors that influence of the structure damages. Figure 3 shows the structural deformations after the accident of the concrete in the Xiluodu hydro power plant located on the Jinsha River, Southwest China [25]. In [28] Three-Gorge Dam on the Yangtze River near Sandouping, China was taken as an example to evaluate hydraulic forces including water pressure pulsation, the effect of the cracks on natural frequencies and the vibration responses of the powerhouse under hydraulic and earthquake forces.…”

“…In the paper [25] a Chinese hydroelectric power plant with 700 MW class turbine is discussed for which a structural deformation accident happened in the construction period causing severe loss. The study focused on two major differences of the spiral case structures that might cause the accidents, i.e., the construction condition, and the shape of steel spiral case.…”

“…Further down the methods will be shortly discussed using the abbreviations most often used in the practice. In [25] detailed explanation with profound pictures and schemes are presented. Here we will shortly explain the essence of each of them.…”

“…The principle consists in filling the spiral case with water. For this purpose, to ensure the tightness of the case, test head and test barrel are placed as it is explained in [25]. Then a pressure is applied inside the case with a value depending on the chosen engineering solution, for example half of the working pressure.…”

“…In many articles [25,[28][29][30][31] the structures of the spiral case and the concrete using the methods M and N -types are analyzed applying different numerical methods and software systems. The investigations of the friction process between steel structures and concrete are also largely studied [26,27].…”