Stiffness degradation of hydropower house substructures subjected to cyclic water pressure

This study investigates the structural implications for hydropower plants under evolving operational paradigms driven by renewable energy integration, focusing on substructure stiffness degradation caused by cyclic internal water pressure (IWP). A plane axisymmetric finite-element model of the intake section from an actual plant is developed in the Abaqus software program, employing the extended finite-element method to simulate concrete crack initiation and propagation. Numerical results demonstrate that the elastic modulus of the membrane material is the predominant factor influencing substructure stiffness degradation. While the inner reinforcement surrounding the steel spiral case contributes significantly to long-term stiffness retention, the frictional interaction at the steel–concrete interface exerts only a marginal influence when the weld slope-cutting details are considered. Furthermore, the fracture energy of concrete shows no substantial impact on stiffness degradation, provided its value remains within the conventional range for mass concrete (e.g. >150 N/m). Importantly, the numerical analysis indicates that the observed stiffness degradation does not translate into significant adverse effects on two key engineering concerns: generator pedestal uplift and the fatigue life of the steel spiral case. These findings provide critical insights for assessing the long-term performance of hydropower infrastructure under evolving operational demands.