Reinforcement Design of a Complex Hydropower Stay-Ring Support Structure: A Comparative Assessment of Simplified Calculations and Three-Dimensional Finite Element Analysis

The concrete support structure beneath a bottom-dismantled turbine stay ring is a geometrically complex load-bearing region in hydropower powerhouses. Large maintenance openings, variable section thickness, and interaction among the stay ring, spiral case, and surrounding concrete produce three-dimensional load transfer that conventional member-based calculations struggle to represent. This study compares simplified structural calculations and three-dimensional finite element analysis (FEA) for reinforcement design. In the simplified approach, the spatial concrete structure is idealized as planar frames, cantilever corbels, and fixed-end beams, and reinforcement is determined from sectional internal forces according to hydraulic concrete design provisions. A three-dimensional solid model is established in ANSYS, and reinforcement demand is evaluated using an elastic tensile-stress-region approach. For the stay-ring corbel, the simplified calculation gives a required reinforcement of 4926 mm2/m, whereas the FEA-based tensile-stress-region assessment gives 3079 mm2/m, corresponding to a reduction of about 37% relative to the simplified result. For the maintenance-gallery roof slab, the simplified calculation gives 4908 mm2/m, whereas the FEA-based assessment gives 3273 mm2/m, corresponding to a reduction of about 33% relative to the simplified result. These differences are mainly attributed to spatial restraint and load redistribution in the three-dimensional model. In practical design, the simplified calculation provides a transparent, code-based baseline for load-path definition and sectional reinforcement design, whereas the 3D FEA provides spatially resolved tensile-demand information for checking and refining reinforcement in geometrically disturbed regions; the two methods are therefore complementary.