From the Editorial Office. General questions concerning the method employed to compute the steel-reinforced-concrete conduits at the Sayano-Shushenskoe hydroelectric plant were raised in a paper by D. P. Levenikh et al., together with a description of design solutions for the plant's turbine conduits. In this connection, the editorial office considers it necessary to point up the following:i. The authors are correct in stating that the computational case of complete failure of a steel lining over a 4-m span contradicts the universally accepted approach to the planning of structural designs. 2. Assuming that steel-reinforced-concrete designs come into increasingly widespread use in hydraulic construction, the editorial office considers expedient the development of a single branch methodology for the computation of these designs, proceeding from the basic positions taken in Construction Norms and Regulations (SNIP) 11-50-74 and 11-56-77. The experience of the Lengidroproekt in the design of steel-reinforced-concrete conduits installed in hydroelectric plants, particularly for the high-pressure penstocks at the SayanoShushenskoe plant, is brought to light in a paper by Levenikh et al. [I]. In our opinion, however, the paper takes a debatable position, which may lead to an overconsumption of metal. The authors state that: "... in the upper sections of a pipeline, where, according to computations, an insignificant amount of circular reinforcement is required for a known thickness of 16 mm, its minimum section was determined by two conditions: an allowable crack opening of 0.3 mm and the inadmissibility of catastrophic failure of the reinforced-concrete collar with possible failure of the steel lining formed from two steel sheets over a distance of 4 m owing to a possible weld or sheet-metal defect."If the first condition can be satisfied, the second places us in a quandry. Defects of this size ahould be recognized as impossible with modern inspection methods and the 16 m thickness of metal specified. If the presence of this defect is even suggested, it will be detected when the pipeline is filled. It is difficult to present the approach to the design of any structures, and in particular, steel hydraulic structures (spiral chambers, gates, etc.), where the possibility of these large-scale defects is considered.Problems associated with improvement of the method employed to compute steel-reinforcedconcrete designs are set forth in the paper in a distorted manner. As early as 1960 the AllUnion Lenin Order S. Ya. Zhuk Scientlfic-Research Institute for Design and Exploration and the B. E. Vedeneev All-Union Scientific-Research Institute of Hydraulic Engineering were the first in domestic and world practice to propose the design of steel-reinforced-concrete structures as a single entity with an overall safety factor K ~2. Extensive investigations conducted at the B. E. Vedeneev All-Union Scientific-Research Institute of Hydraulic Engineering and the Scientific-Research Institute of Concrete and Reinforced Concrete from 1960 ...

The development of hydropower in our country is aimed at the construction of economical and hlgh-head hydroelectric stations on rivers of Siberia and Central Asia with the use of large-capacity turbines. For such turbines with a large-diameter conduit the usual decision to use metal runs into difficulties when the values of the product of the internal pressure (P) and inside diameter (D) PD~II MPa-m, since machining of sheet metal with a thickness of more than 40 mm, especially high-strength, is difficult and its welding is associated with considerable compllcations.The problem of creating the designs of waterways of large-capacity units was formulated and solved in the 1960s. The scroll casings of high-head powerful hydraulic turbines operate most severely in the conduit, since considerable bending stressesoccur in them. Therefore it is natural that the search for a solution began precisely with this most stressed part. Already during designing of the Bratsk hydrostation it was established that the usual construction does not meet the strength requirements.The lower part of the scroll casing was usually supported on a concrete mass and the upper part was left exposed or separated from the concrete in which is was situated by a yielding pad, which should have provided independence of its deformation.To solve the problem of the most rational construction of scroll casings, various constructions were examined and tested on brittle large-scale models with reference to the turbines of the Nurek, Krasnoyarsk, and Ingurl hydrostations.Steel welded with ribs, cast, and banded constructions, reinforced-concrete (prestressed in an annular meridional direction) and pretest monolithic (reinforced by prestressed elements) and also various combined steel and relnforced-concrete constructions were tested.Metal did not provide reliability, and even without consideration of the metal shortage factor the cost of the construction was high.The reinforced-concrete scroll prestressed in a meridional direction by means of bundles on high-strength reinforcement showed good crack resistance with a quite low consumption of reinforcement. However, such a construction did not gain recognition in view of doubts about its service life owing to possible corrosion of the high-strength reinforcement in the event of poor-quality grouting, possibility of stress loss with the course of time, and in view of its technological inefficiency.The construction reinforced with prestressed bars showed a low crack resistance and also could not be recommended.The combined steel and relnforced-concrete construction showed high rellability, lower cost compared to the metal construction, did not require mastering new processes, and, what is the main thing, it could be realized at practically any values of the parameter PD.The steel and reinforced-concrete construction (Fig. 1) consists of a steel shell located in a reinforced-concrete block. The shell, made in the form of a scroll, absorbs a part of the forces. It should be made of mild steel with a thickness t...

The minimum thickness of the linings of free-flow tunnels in strong rocks (f -> 4) is usually limited by construction requirements, and in weak rocks (f < 4) their thickness often does not fit in the limits of minimum thickness. Linings of free-flow tunnels in weak rocks are calculated for the design vertical rock pressure (overload coefficient u = 1.5) in the presence or absence of free-flowing water in the tunnel. The horizontal rock pressure is not taken into account or is taken into account minimally, since it facilitates the operation of the structure.Since the resultant of the forces is located outside the limits of the concrete cross section of the lining (eccentric compression with large eccentricities), the strength of the extended zone of the most stressed section (usually the crown) is determining. In this case the structurally important coefficient msi = 0.75-0.95, the coefficient of working conditions m = 1, and the design tensile strengths from 6~ kg/cm z (for grade 200 concrete) to 8.4 kg/cm z (for grade 300 concrete) are introduced when estimating the strength of the section. Such a calculation is formally correct, but it does not take into account that a lining supported on rock is a statically indeterminate structure, and after the formation of even several cracks it does not lose its bearing capacity as a consequence of the effect of the rock's passive resistance (Fig. 1). Cracked linings of free-flow tunnels after grouting did not show any shortcomings in operation. The strength of such l~n~rtgs is provided reliably by their work in compression with elimination of the extended zone in the region of crack formation.The Instructions on the Design of Hydraulic EngineeringTunnels SN 238-73 permits calculating the lining structure with consideration of the formation of pliable hinges* A crack (Fig. 2b) forms in the most stressed section (Fig. 2a), as a result of which the extended zone of the concrete is eliminated and the lining is deformed such that the resultant compressive force is applied with the maximum possible eccentricity e 0. This eccentricity is limited as follows: a) by the condition of equilibrium of forces in the section when the normal force N is received by the compressed zone of the section xb/N = RcobX;, in this case e 0 = (hli --x)/2; b) by the instructions in the Standards that the supporting areabe not too small in this case e 0 -0.90(hli/2) = 0A5hli. The minimum of these values also determines the value of the bending moment in the pliable hinge m h = Ne 0. Here it is necessary to take into account that the greater value of the bending moment in the pliable hinge that is used, the more advantageous wiU be the operation of the structure in other sections (in quadrants of the span), since the presence of a positive bending moment in the span reduces the negative bending moments in the quadrants. Thus, the proposed method presumes the most advantageous operational scheme for the structure. In the further calculations the adopted moment in the pliable hinge is assumed constant in...

High-pressure penstocks are widely used to convey water to hydroelectric power stations. They usually involve special tunnels cut in the rock: this greatly adds to the cost of station construction.The most popular design for a penstock is a metal cylindrical casing of factory-rolled shells. The thickness of the metal casing depends linearly on the force per unit length ( Fig. 1),In present high-head stations, the diameters of the steel pressure pipes are usually limited by the thickness of the metal casing. For example, at the Krasnoyarsk hydroelectric station, each unit has two penstocks 7.55 m in diameter instead of one 10.9 m in diameter; at the Nurek station, 800-900 m of penstock passes through the rock to each unit, i.e., nine lines 6 m in diameter instead of three 10 m in diameter; at the Ingursk station, from the surge tanks to each unit special penstocks are also planned, five in all with a length of the order of 800 m. Joining the penstocks leads to such an increase in the parameters that it is practically impossible to make them of metal owing to the great thickness of the casing. Apart from bends and forks penstocks can also be made from steel wrapping. However, the technology of making steel pipes by wrapping sheets has not yet been developed in the USSP..

A changeover is presently in progress to the calculation of all the structures of hydraulic engineeringinstallalions for limiting states with separate safety factors. The main propositions of this method for all hydraulic engineering concrete and reinforced-concrete structures are set out in the section SNiP II-I.14-69. The essential working features of various types of hydraulic engineering installations and their design render necessary the formulation of separate standards for each of them. Such structure include tunnel linings, which have previously been designed by the method of permissible stresses. By way of discussion, it is advisable to set out the basic propositions for the calculation of tunnel linings for limiting states with separate safety factors proposed for inclusion in the "Instructions for the design of hydraulic engineering tunnels," revised 1971-1972.Separate Safety Factors. The use of separate safety factors provides more selective consideration of the part played by the different factors in the general working of the structure. Calculation of the majority of building structures has been changed over to this method so that long-range experience in its application is now available. The standards [1] consider the following separate safety factors, which it is necessary to lay down for all types of hydraulic engineering structures: homogeneity k, load distribution n, capital significance and combined load mkc, and work conditions m.