Inconsistent gap-closing behavior of spiral case structures in hydropower stations: Mechanism and structural role

To withstand the internal water pressure (IWP) in hydroelectric power plants (HPPs), this study designs a spiral case structure (SCS). It can be considered a composite structure made of steel and concrete. The steel component is typically called a steel spiral case (SSC). An SSC embedded in a pressurized condition is featured by the gap between the steel liner the concrete. Seeing that the conventional knowledge concerning gap-closure behavior is challenged by some in-situ data, the present study conducts a complete simulation procedure with the ABAQUS program. The numerical simulations are reasonably consistent with the experimental results. The novelty of this paper is the investigation of the mechanism of the inconsistent gap-closing behavior in SCSs of HPPs and its structural role. It has two significant findings: (a) a strong link has been found between the inconsistent gap-closing phenomenon and the hydraulic thrust on the SSC along the axis of its inlet; and (b) the structural role of the gap closure in affecting the IWP-transferring behavior in SCSs is underlined. The present findings highlight that the gap-closure behavior should be carefully considered in the structural design of SCSs as it has significant effects on the structural and operational safety of HPPs.