| Penstocks of hydroelectric power station is one of the key structures in hydroelectric power system,and its safety and reliability are directly affect the safe production and normal operation of hydroelectric power station.With the service life increasing of steel lined reinforced concrete penstocks in the existing hydroelectric power stations,cracks of varying degrees have appeared in its external concrete structure,of which the maximum crack width value has far exceeded the crack width limit of the current code.The crack width calculation formulas used in the design of penstocks structure are all generated from experiments based on beam members.Due to the difference between the penstocks and the beam and slab concrete member structure,the crack control design of the existing steel-lined reinforced concrete penstocks is not completely reasonable.Thus,more in-depth basic research are required.Approximate formulas for calculating crack width of external concrete structures have been proposed by many scholars based on the stress characteristics of steel-lined reinforced concrete penstocks.However,the formulas proposed at present do not clearly reflect the calculation guarantee rate of crack width.In view of the above,the following studies were carried out:(1)The present crack width calculation theory and formula of steel-lined reinforced concrete penstocks are compared and analyzed by study the load bearing characteristics and cracking mechanism of steel-lined reinforced concrete penstocks.(2)Stress situation of external concrete structures before and after crack appearing under the influence of the internal water pressure is in-depth studied by statistical research on the distribution and width of axial cracks at external concrete of steel lined reinforced concrete penstocks with the method of combining experiment model test and numerical simulation analysis.Thereby,a model having a certain assurance for calculating axial cracks width of external concrete structure of steel lined reinforced concrete penstocks is established.(3)A reliability calculation method for crack control of steel-lined reinforced concrete penstocks based on durability is established with using Monte Carlo method and considering the relationship between concrete cracks and structure durability.The reliability of crack width formula existing in different pressure piping design specification is calibrated based on a large number of hydroelectric power station monitoring data and experimental model data.And the influence sensitivity of different factors on crack control reliability index are analyzed,which will provide significance references for pressure pipe crack control standard revision. |
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