A NUMERICAL INVESTIGATION CONCERNING THE INFLUENCE OF INFILLED CONCRETE AND BEDROCK MATERIAL PROPERTIES TO EXTERNAL PRESSURE BUCKING OF EMBEDDED PENSTOCKS

Abstract

 Prevention of external pressure buckling is important for the design of embedded penstocks. Different behavior from exposed pipe is shown due to the constraint effect of infilled concrete and bedrock, and the Amstutz’s formula assuming infilled concrete and bedrock as rigid body has been used since the 1960’s. In order to respond to the demand for large pumped storage power plant and high head in the 1970s and thereafter, the strength of steel pipes has been increased, but the discussion of the necessary rigidity for infilled concrete and bedrock has not been made. Since degradation of hydraulic structure and situational change of external pressure due to aging are points to keep in mind, in this paper, nonlinear FEM parametric analyses are executed considering the material properties of surrounding materials and contact condition between the penstock outer surface and concrete. After verifying the FEM analysis model by comparing with the test results by Borot, the influence on the external buckling pressure is examined according to actual conditions.