充水保压蜗壳与外围结构联合承载过程的力学仿真分析

Mechanical simulation analysis on joint load-bearing process of preload filling spiral case with its surrounding structure

水电站充水保压蜗壳兼备直埋式与垫层式蜗壳的优点,但受力分析复杂。为此,以一个HD值较高的蜗壳为例,应用三维有限元法研究了充水保压蜗壳与外围结构联合承载的过程,模型和计算过程精细,展示了联合承载过程中各结构的力学规律。结果表明:充水发电时,蜗壳与混凝土大部分区域闭合,脱开的面积约3%;外围混凝土大部分区域处在压应力状态,受拉部位少且拉应力较低,钢筋拉应力较小,此情况被现场观测所证实;采用常用公式或完全用有限法计算,蜗壳承载比的计算结果相差不超过3%;蜗壳充水保压值越低,充水运行期与混凝土的接触压力越大、蜗壳的承载比越小,因此蜗壳宜取较小的充水保压值,有利于减少振动;与常规打压顺序相比,非常规打压顺序不利于蜗壳与混凝土的贴合。此成果为该水电站的蜗壳设计提供了重要参考,电站已全面投产,蜗壳及外围结构工作表现良好。

Preload filling hydropower spiral case has the merits of both the types of directly embedded spiral case and spiral case with cushion layer,but the mechanical analysis of it is complicated.Therefore,the joint load-bearing process of the preload filling spiral case with its surrounding structure is studied herein with 3-D finite element method by taking a spiral case with higher HD value as the study case;for which the model and calculation process are refined and exhibit the mechanical laws of all the structures during the joint load-bearing process.The result shows that the most parts of the gap between the spiral case and the surrounding concrete are closed up with disjointed area of only 3%during water filling and power generation,while the most parts of the surrounding concrete are under compressive stress state with less tensile parts and lower tensile stress as well as less reinforcement tensile stress.This situation is demonstrated through the relevant in situ observation.The spiral case load-bearing ratio is calculated by common formula or totally by finite element method,for which the difference between them is not over 3%.The lower the water filling and pressure maintaining value of the spiral case is,the larger the contact pressure between the spiral case and the surrounding concrete is to be and the smaller the load-bearing ratio of spiral is to be,thus smaller water filling and pressure maintaining value is suitable to be adopted for the spiral case,which is favorable for decreasing structural vibration.Compare with the conventional preload water filling sequence,the unconventional sequence is unfavorable for the contact between spiral case and concrete.The study result provides an important reference for the design of spiral case of hydropower station and is already successfully applied to the construction of a hydropower project as well.