The classification of hydraulic concretes into zones corresponding to the working conditions for individual parts of the structures and the use of different types of cement makes possible a discriminatory approach to concretequality requirement and the avoidance of their being set unjustifiably high and, in consequence, leading to cost increases for structures. However, the use of several types of cement in construction has its own undesirable aspects. This will be illustrated by specific examples.The design for the construction of the foundation structures of the Dneprodzerzhinsk hydroelectric station specified 18 concrete standards. Because the mixes used during construction have various workabittties and different aggregate sizes,and the cements delivered to the construction site may be of different standards and types, the total number of working concrete mixes increases 2 to 2.5 times; i.e., it becomes impracticable to provide the guaranteed standard in one and the same item. An unjustifiably increased number of concrete standards can lead to an inadmissible combination of differen:t mixes. Therefore, the number was reduced by grouping,and four concrete standards were finally adopted for the project.For the submerged parts of the structures, one concrete standard was adopted, namely R 200~0, W4,~ 0, Frs 50z8 , with a cement content of 235 kg/m s and W/C (water-cement ratio) = 0.55; for concrete in the zone of fluctuating water levels (spiral chamber without a slab facing or liners, spillway surfaces and the upper levels of dam apron slabs to a depth of 1.5 m) the adopted concrete standard was R200~0, W41s 0' Frs 100 ~, with a cement content of 265 kg/m 3 and W/C = 0.53; the interior massive structures of the lower portions of the apron stab, and of the upstream and downstream lock pier down to the zone of varying water levels, were constructed with concrete of standard R 150,g 0' W 4~0, with a cement content of 210 kg/m 3 and W/C = 0.57; the slopes of earth structures were protected with concrete of standard R 200~Q, W 4,~ 0, Frs 100~. with a c e m e n t content of 280 kg/m 3 and W/C = 0.53.Notwithstanding this radical reduction in the number of standards, the concrete plant in some instances had to deliver six or seven concrete mixes, depending on the type of cement, sizes of aggregates, and the requirements for workability of the concrete mix, art of which created certain difficulties.For the construction of the Kanevsk hydroelectric station, some 16 concrete standards were specified in the design, with aggregate sizes ranging up to 70 ram. Later, the Scientific-Research Station (NIS) of the Art-Union Scientific-Research and Design and Planning Institute of Hydrotechnicat Construction (Gidroproekt) reduced the n u mber of standards to eight; nevertheless, even this number is fairly high.The experience on previous structures had convincingly demonstrated that the number of concrete standards should not exceed three for the whole hydroelectric-station scheme. Experience has shown that a reduction in the numb...

At the stage of design research of armored bodies of lightly armored vehicles it is extremely important to determine the range of their natural frequencies and natural forms of oscillation. For this purpose, the finite element method is usually used. It is necessary to substantiate the parameters of the finite element model, which provide an acceptable level of accuracy of numerical modeling of dynamic properties of this type of structures. For this purpose, data from parallel numerical and experimental studies of the mock-up of the armored hull of the armored personnel carrier are used. The mock-up of the upper projection of the armored hull is made in the appropriate scale. The material is sheet steel. This mock-up is subjected to dynamic excitation on a vibrating table. Resonant excitation frequencies are recorded, as well as the natural vibration forms. Shock-pulse excitation of the armored hull’s mock-up was also performed. The response to this excitation is recorded using accelerometers. Then, the spectrum of natural vibration frequencies is determined from these oscillograms. In parallel, numerical modeling of natural frequencies and natural vibration forms of the armored hull’s mock-up is carried out. After that, the results of numerical and experimental studies are compared. By varying the parameters of the finite element model, a satisfactory correspondence between the results of numerical calculations and experimental measurements is achieved. In particular, the following are determined: the acceptable type of used finite elements; the number of finite elements required to satisfy the accuracy of numerical modeling of the dynamic properties of similar structures; zones of the recommended thickening-rarefaction of a grid of finite elements, etc. According to the research results, the parameters of finite-element models have been established, which can be used to study the dynamic processes and properties of full-scale armored hulls of lightly armored vehicles. Keywords: lightly armored vehicle, mock-up, natural frequency, spectrum of natural vibration frequencies

Construction of the Dnestr hydrofacility requires the solution of complex problems associated with power generation, regulation of river flow, and the creation of water reserves for irrigation. According to the original design for the hydrofacility, a concrete gravity-type dam plus a powerhouse built into the dam, with an overall concrete volume of 1.5 million m a, were to be constructed. In this scheme, the use of fly ash as an additive to the concrete to replace part of the cement (chiefly for the intramassive zones) is extremely expedient and could have a significant economic effect.The most recent design was reviewed, however, and according to final approved plans, a spillway-type powerhouse with right-and left-bank earth-rock dams was adopted. A n assembly platform abuts the powerhouse on the right bank. Comprising the hydrofacility are the 53.5-m left-bank dam, the 165=m powerhouse, the 197=m rightbank dam, and the 48-m assembly platform. Because of a nonuniform daily load on the units, a buffer reservoir was designed to control the downstream flow of the Dnestr. The head at the power station is computed to be 40.5 mand the installed capacity to be ~702,000 kW. Structurally, the powerhouse consists of three sections, each .53 m long and 55 m wide with a maximum height of 80 m. Six diagonal hydroturbine units rated at 117,000 kW are installed in the powerhouse.An additional expansion joint, which runs along the axis of the central forebay, divides the upper half of each section to reduce temperature stresses. The powerhouse is a complex spatial structure consisting of an upper slab that follows the curved outline of the spillway, a series of vertical wails and horizontal floors that form the service compartments, and a lower foundation slab, as well as a space where the units, penstocks, and draft tubes are located. The blocks are divided by the vertical wails of the forebays. The thickness of the vertical wails and horizontal slabs ranges from 2 to 4 m. Concrete blocks up to 9 m thick are built into the foundation slab on the upstream side. Thus, the reinforced=concrete structures of the powerhouse will consist of elements that arecomparalively thin-walled for hydraulic construction; in this case, there is virtually no massive concrete. The overall volume of concrete in the hydrofacitity amounts to 92~,000 m 3. Table 1 shows the distribution of the volumes of monolithic concrete (thousands of m 3) placed according to grade and structure.

The work describes a general approach to dynamic processes modeling under action of pulsed reactive forces of recoil during firing shots from combat modules weapons. The combat module can be presented as a discrete system; this approach also applies to elements of drive, engine, transmission, etc. They are characterized by a local compact concentration of mass and high rigidity of the structure itself compared to the same armored hull or special elastic elements of suspension system. Then the reaction of this complex mechanical system to the action of dynamic forces is of interest. On the basis of the developed approach to analysis of the dynamic response of the combat module of a lightly armored vehicle equipped with a small-caliber automatic gun to the action of reactive recoil forces, it is proposed to carry out a qualitative analysis on simplified models at the first stage. The influence of a single shot and burst firing on the deviation of the axis of the barrel from the direction to the target is analyzed. For this, a simplified test model was built. Further, on the obtained simplified models, the results are compared with the results of the analysis on more complex models. The introduced piecewise linear approximation dependence of the time distribution of the reactive recoil force makes it possible to parametrize such force distribution with one parameter. As evidenced by the research results, the nature of the response of the studied dynamic system is strongly influenced by the damping level. If the damping level is high, and the frequency of the pulses is not a multiple of the natural oscillations frequency then the influence of individual pulses can be considered in isolation from each other. The characteristic features of the transient and stable modes of movement of lightly armored vehicles combat modules are determined. These qualitative features determine the nature of the response of the dynamic system to the action of a single pulse and to the action of a series of such pulses. The same features are also characteristic of systems with a large number of degrees of freedom, as well as systems with distributed parameters. Keywords: dynamic system, combat module, lightly armored vehicle, transition process, steady process, integration of differential equations system, reactive recoil forces during firing shots

The physicotechnicaL properties of synthetic structural materials depend largely on the homogeneity of the starting mixtures and the finished articles [1,2]. A decrease in homogeneity usually leads to deterioration of the properties, particularly in the case of concretes for hydraulic structures. Such concretes are characterized by a relatively low cement consumption, so that uniform cement distribution in the concrete presents difficulties. Owing to fluctuations in the moisture content of the aggregates, the plastic-viscous properties of the mixtures may vary widely, which has a deleterious effect on the homogeneity of the hardened concrete. Concrete mixers have large mixing compartments and the period of mixing is very brief, which reduces the possibility of obtaining uniform masses. Transport of the concrete mix over long distances leads to layer separation (which is also observed during compaction by vibrators).From data in the literature and practical experience, we know that the addition of surfactants to cement Or concrete improves the homogeneity of the latter and its principal physicomechanical properties, owing to the specific character of the effect of such additives on cement systems [3, 4]; e.g., additives which render concrete hydrophobic have a plasticizing effect, or reduce the viscosity of concrete mixes under mechanical influences (mixing and vibration). However, the flocculating effect of such additives prevents layer separation of concrete mixes during discharge, transport, and placing. This paper deals with the homogeneity of hydraulic concretes in relation to their principal physicomechanical properties and with the effect of various surfactants on these characteristics.The criteria presently used in factories and research laboratories for assessing the homogeneity of mixtures enable us to make only an indirect and somewhat subjective judgment (after much time has been expended) of the homogeneity and subsequent layer separation of the principal components during transport and placing.The homogeneity of a mixture, obtained during its preparation, is usually assessed from the results of tests on the most characteristic properties of the materials after all operations have been performed. For concretes and mortars, the relevant properties may be the unit weight or strength indices of specially fabricated specimens. However, these indices depend on a number of technological factors, which naturally distort the true picture; furthermore, determination of the strength, for example, is performed on specimens of 3-, 7-, and 28-day age. Therefore, intense research has been performed in order to develop practical, rapid methods of assessing the homogeneity of mixes, the most promising of these being the radioactivity method and the method of luminophors. The first method, based on the use of radioactive specimens, requires the construction ofa specialisotope laboratory, and also complex safety procedures.The Luminophor Method. The rapid method of determining the optimal operational indices of mixing ...