Abstract
Abstract: The randomness of transient events, and the variability in factors which influence the
magnitudes of resultant pressure fluctuations, ensures that waterhammer and surges in a pressurized
pipe system are inherently stochastic. To bolster and improve reliability-based structural design, a
stochastic model of transient pressures is developed for water conveyance systems in hydropower
plants. The statistical characteristics and probability distributions of key factors in boundary
conditions, initial states and hydraulic system parameters are analyzed based on a large record of
observed data from hydro plants in China; and then the statistical characteristics and probability
distributions of annual maximum waterhammer pressures are simulated using Monte Carlo method
and verified by the analytical probabilistic model for a simplified pipe system.
In addition, the characteristics (annual occurrence, sustaining period and probability distribution) of
hydraulic loads for both steady and transient states are discussed. Illustrating with an example of
penstock structural design, it is shown that the total waterhammer pressure should be split into two
individual random variable loads: the steady/static pressure and the waterhammer pressure rise
during transients; and that different partial load factors should be applied to each individual load to
reflect its unique physical and stochastic features. Particularly, the normative load (usually the
unfavorable value at 95-percentage point) for steady/static hydraulic pressure should be taken from
the probability distribution of its maximum values during the pipe's design life, while for
waterhammer pressure rise, as the second variable load, the probability distribution of its annual
maximum values is used to determine its normative load.