Field investigations on the stresses in a penstock at the Krasnoyarsk hydroelectric station

Abstract

1. Before application of the hydrostatic pressure, temperature and shrinkage cracks had appeared in the reinforced-concrete shell. During the period of their maximum widening the stresses in the ring reinforcement, through which the cracks passed, reached 1300 kg/cm2 when no hydrostatic pressure was applied inside the penstock. In sections where cracking did not occur the stresses in the reinforcement were in the range of 100–350 kg/cm2. In the steel shell the circumferential stresses due to temperature variation were primarily compressive while the tangential stresses were tensile. The maximum value of the tangential stresses, generated by temperature variations, was about 1000 kg/cm2. 2. In the steel shell and the ring reinforcement located in the areas where the shell did not exhibit temperature cracks, the observed stresses due to hydrostatic pressure were lower than those determined by the multilayered-ring analysis assuming combined action for the steel and concrete shells. In locations where the concrete shell shows temperature cracks, the stresses in the ring reinforcement are higher than the calculated values. 3. The maximum observed stresses, caused by the combined action of hydrostatic pressure and the temperature variations, were found to be in the neighborhood of 475 kg/cm2 (circumferential stresses) for the steel shell, and 575 kg/cm2 (1st row) and 1200 kg/cm2 (2nd row) for the ring reinforcement. On comparing these values with the data of Table 1, it is obvious that with respect to the design values the maximum observed stresses were 3.8 times lower in the steel shell and 2.7 times lower in the ring reinforcement. The ratio of observed stresses in the steel and concrete shells might have been different if the concreting specifications, envisaged in the initial design, had been adhered to.