Analysis of the Joint Bearing Capacity of Composite Cushion-Spiral Case Structures for Hydropower Stations Considering the Damage Mechanisms of Surrounding Concrete

The spiral case structure is an essential part of a hydropower station. To accurately explore the joint load-bearing effect of the cushion-spiral case structure, a cushion-spiral case structure with a high HD value was selected, modeled, and analyzed in this study. The reliability of the model was verified through measured data. Given the contact relation between the spiral case and the cushion, the cushion laying range was used as the control parameter to investigate its impact on the joint bearing capacity of the structure. In addition, the concrete damage theory was introduced to probe the damage mechanism of the structure under assumed extreme working conditions. The steel spiral case bears most of the internal water pressure in the joint bearing system, and the bearing ratio of the surrounding concrete and reinforcement decreases with the increase in the cushion wrap angle. A 1.1-1.2 overload head is the main section that forms penetrating cracks. For the spiral case structure with a high HD value, a reasonable cushion can significantly reduce the damage level of the surrounding concrete and regulate the uneven lifting of the turbine pier and the shear strength of the stay ring. This study can provide reference points for the spiral case arrangement and range and the structural failure response under extreme working conditions.