The fiat gate is the basic type employed to close the ports of water passages in domestic hydraulic structures. Owing to their technological nature, economic setting in the structure, and ease of installation, operation, and repair, flat gates of various design modifications are universally employed in deep and surface ports of considerable size over a broad range of working pressures. They have been the subject of considerable study and are quite reliable in operation. At some hydrofacilities, however, there have been instances of damaged flat gates. Analysis of the causes of these damages has yielded voluminous data, on the basis of which design standards have been rendered more precise, and rules governing the fabrication, installation, and operation of the equipment are upgraded. A few characteristic cases of damages incurred by fiat gates in the post-war period with a description of accompanying instances and an analysis of the causes are examined below.* During a temporary period of operation in March 1952 at one of the concrete spillway dams on the Svir' River, an emergency situation arose with a flat wheeled gate covering an opening of 27 m and designed for a head of 6.6 m. The gate was designed in accordance with technical specifications and norms issued in 1935, and was constructed by welding grade St. 3 steel with type E42 electrodes (TsM-7 coating). The mechanical properties and chemical composition of the steel met standard requirements. For three months prior to the emergency, the gate was set into the grooves of the repair gate and operated under a head of 6.0-6.5 m; at the time of the emergency the effective head was 5.72 m. For one weak prior to the emergency, a severe cold spell settled over the construction region, and nighttime temperature dropped to -30"C; at the time of the emergency the air temperature was-22"C.The emergency occurred on closing the spillway opening. Workers on the bulkhead heard a noise and grinding, experienced jolting, and saw that the facing of the gate had deflected severely in the downstream direction. First the left, and then the right end of the gate was torn away out of the grooves and the gate became pinned against the right-bank abutment (Fig. 1). On examination of the failed gate, the following were observed: rupture of the downstream flange of the cross beam at its splice point (at a distance of approximately 1/3 the opening from the left support), vertical and horizontal fracture and bulges in the lining, large deformations in the upper angle brackets on the gate, and fracture of the grate supports. The balance wheel was torn away. It was also established that the construction joint in the downstream flange of the cross beam at its splice point had been welded with gross disregard of techuical specifications.It was ascertained that a small opening in the ice was maintained in front of the gate during the winter. However, a layer of ice became encrusted on the cross beam, and particularly on the faces of the gate and on the lining, its thickness reaching 40 cm. ...
In connection with the use of high-head flat regulating gates the study of their vibrations in the stream becomes timely, Completed investigations [1-4] do not always permit an accurate analytical determination of the nature and magnitude of vibrational deformations of the gates, and the physical modeling of the process is quite difficult and involves distortion of the real phenomenon. Prototype investigations of the dynamics of the gate are therefore necessary.The main gate of the spillway of the XXII Congress CPSU, which is a welded triple 11 x 20 m structure [13], was selected as one of the objects of investigation. The gate operates under a static load with the partial openings from 0.5 to 4.0 m.For fiat, ribbed gates similar to those tested there is a theoretical method of determining the form and frequency of free fluctuations [5].With widely separated ribs and high rigidity of the gate in torsion the frequency of bending fluctuations is the smallest. This case is the most important because in actual gates small torsion deformations do not produce an appreciable effect on the frequency of free fluctuations.When the gate is immersed in the water the frequency of its free fluctuations decreases 1/q-n-fold, where n is the coefficient of increase of the mass of the fluctuating system due to the effect of the affected water mass.There are a number of papers on the determination of the affected water mass per unit length for fluctuation of fiat gates in a horizontal plane [8,11]. The recommended relationships are of the following form:The value of the coefficient K varies from 0.44 to 0.55 as was shown in ill].It is known that vibration of plane gates occurs in a submerged regime by the flow of water underneath the knife, i.e., as a rule, with gates located on a low spillway apron. Hydraulic conditions of flow around gates tocared on the crests of spillways of practical profiles are generally favorable, and pulsating loads on the gate are quite small (bending stresses caused by them on a given gate do not exceed 10 kg/cmZ). The purpose of this work was therefore to study the mechanism of the phenomenon, to check the theoretical method of determining the dynamic characteristics of a ribbed gate and of the magnitude of the affected water masses, and to investigate the reaction of the vibrating gate system to different dynamic disturbances: vibration of piers, aero-and hydrodynamic impulses, wave loads, etc. Accordingly, the experimental work consisted of two stages: 1) investigation of free vibrations of the gate in water and in air and determination of its dynamic characteristics; 2) investigation of the vibration of the gate under a head and with different gate openings.The following measuring methods were used in the course of the investigation: a) vibration sensors of various types (including mechanical and electromagnetic) for the registration of horizontal dynamic translocations of the gate and of the piers in the frequency range of 1.5-2.0 to 200 cycles. Electromagnetic vibration sensors of the *Deceased.
The first information about the specific properties of steel fiber-reinforced concrete -concrete randomly reinforced throughout the volume with segments of steel wire --appeared a very long time ago [i, 2], but so far'its industrial use in our country is quite limited and therefore there are no standards and guides concerning the characteristics of fiber-reinforced concrete and its use in various structural elements.
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