Tests of cores drilled from various depths in zones of concrete dam blocks and special investigations of the strength of large concrete cylindrical specimens performed at the B. E. Vedeneev All-Union Scientific-Research Institute of Hydraulic Engineering (VNIIG) and abroad [1, 2] showed that the strength of concrete varies over the height, increasing from the top toward the bottom of the layer. Figure 1 shows the function Rh/R o = f(h), where Rh/R o is the ratio of the strength of the layer at distance h from the top of the layer of concreting to the strength of the concrete of the upper zone of the layer of concreting.An analysis of the strength of cores with a diameter of 15 cm and height of 30 cm drilled from concrete blocks of the Sayano-Shushenskoe hydrostation showed that Rh/R o ffi 1.18 for a layer height of about 600 ram. Thus a multilayer concrete block represents an alternation of weak and strong zones of concreting.Investigations of models of a block being concreted on specimens with a transverse size of 100, 200, and 300 mm consisting of layers differing in strength showed that the average strength of concrete of multilayer specimens consisting of layers of various strength is higher than the strength of the weakest layer R w and lower than the strength of the strongest layer R', and the standard deviation of the strength of multilayer specimens is less than the standard deviation of the strength of single-layer specimens.An analysis of the stress--strain state of models of a block showed that weaker and more deformable layers and zones of layers of concreting (w) are confined by stronger and more rigid ones (s), and vice versa; the stronger and more rigid layers and regions of the layers of concreting acquire additional transverse strains 9 as a consequence of the effect of the more deformable layers of low strength (Fig. 2).An increase of the average strength and decrease of the standard deviation of the block selected in the form of a prism with a ratio of the height to the width H/B = 4 depends on the number of layers in the model. Thus, if the layer of concrete is characterized by two regions: an upper weaker region (R w) and lower stronger region (R s) with heights t w = t s = tlffi/2, where t]a is the thickness of the layer, then the ratio tw/B will determine the number of layers of concrete in the model and, consequently, the massiveness of the model of the block.The strength of a model of a block with three regions S, W, S is determined by the expression [3] R'b I =R~W-i-{[ ( R : -}-Rt-~S) /2]--R, w'}K:in ,where Ri s, Ri w, Ri_l s, R bl are respectively the strength of the strong and weak region of the i layer of concreting, strong region of the i layer of concreting, and model of the block; Kin is the coefficient of influence of the strength, determiner experimentally.The values of Kin as a function of tw/8 are given in Fig. 3 for a three-layer specimen for t, 9 t w with a middle less strong region. The average value of the strength of the block is obtained by substituting into expression (...
When evaluating the quality of concrete on the basis of core test data there is some difficulty in converting to the strength of standard cube and prism test specimens. This conversion should be made with consideration of the influence of such factors as the scale effect, aggregate size, effect of the boundary conditions of load application, geometry of the specimen, technology of preparing the specimen (boring out, sawing off), etc. Thus, the influence of the scale effect, according to the data of [i, 2], is different for specimens of different shape and different ratio of the height h of the specimen to its width D. On increasing the volume of a cylinder specimen with a diameter of 15 cm and height of 30 cm by 8-fold the strength, according to the data of [i], decreases by 1.05 times, and, according to the data of [2], on increasing the volume of a 15 • 15 • 15-cm specimen by 8-fold the compressive strength decreases by 1.22 times. Obviously, to the effect of an increase of scale is added the effect of confinement of the bearing surfaces by the press plate, which, confining the deformations of the concrete specimen, create in regions adjacent to the plates a state of nonuniform triaxial compression, which is indicated by the form of fracture of the specimens and deformation curve. Regions of specimens tight against the press plate usually separate from the remaining regions in the form of cones. A study of transverse deformations of 150-mm-diameter, 450-mm-high core specimens, carried out at the All-Union Scientific-Research Institute of Hydraulic Engineering (VNIIG) by means of laser techniques, and also on large specimens measuring 300 • 300 • 1200 mm showed transverse deformations reach maximum development at mid-height of the specimen, and their':change within the middle third of the specimen amounts to 3-4% of the maximum at a load of 0.B of the breaking load, if the deformations at the press plates are considered close to zero. This indicates a great effect of the press plates on the formation of the stress-strain state of the specimen. The effect of the boundary conditions and change in the ratio of height h to width D can be judged from graphs of the relative strength ~R as a function of h/D plotted from the data of testing the strength of specimens with a cross section of i0 • 10 cm (the maximum size of the aggregate was 20 nml) (Fig. i). The "hydrostatic pressure" on the bearing surfaces of the specimens was created by a device distributing the forces from the press uniformly on 36 bearing areas resting on a 2-mm-thick steel plate. To eliminate friction, "Naphthlen" fabric was placed between it and the specimen.The conditions of loading in layers of increased strength were created by making a "sandwich" specimen. The concrete of the layers adjacent to the press plates was 1.5 times stronger than the concrete of the middle part. The concrete caps were 15 • 15 • 15-cm cubes bonded by epoxy adhesive to the ends of prisms.Fine-grained, dune quartz sand was used in the sand tanks.The rigid steel plates wer...
The margin of strength of a massive hydraulic structure is determined by the strength condition according to the building code SNiP 2.06.06-85 "Concrete and Reinforced-Concrete Dams": V,W,~,;~
An evaluation of the actual quality of the concrete placed in the Sayano-Shushenskoe dam, its correspondence to the design requirements in connection with reaching heads close to the maximum are acquiring urgency. For evaluating concrete quality from cores with consideration of the requirements of the standards [1-6], the central construction laboratory of the Krasnoyarsk Hydroelectric Station Construction Administration (Krasnoyarskgesstroi) and the All-Union Scientific-Research Institute of Hydraulic Engineering (VNIIG) conducted tests of methods of determining the strength and deformation characteristics of cores in compression and conversion to the corresponding characteristics of standard specimens [7, 8].The result of the joint effort was the "Methods of Evaluating the Concrete Quality of Structures of the Sayano-Shushenskoe Hydroelectric Station from Core Tests," coordinated with the Leningrad Branch of the All-Union Planning, Surveying, and Scientific-Research Institute (Lengidroproekt) and approved by VNIIG and Krasnoyarskg6sstroi. The indicated methods enable testing cores for strength and deformation in conformity with the requirements of the appropriate State Standards GOSTs [4, 5] and checking the strength in conformity with GOSTs [ 1, 2]. A cube with an edge of 200 mm taken in the first years of construction in conformity with the existing Industry Standard OST [3] is the reference cube specimen, to the strength of which is referred the strength of the cores. The deformation characteristics of the cores, the modulus of elasticity E, and the Poisson ratio #, are referred to the corresponding characteristics of prisms 300 x 300 x 1200 ram, the size is dictated by the maximum size of the aggregate, 120 mm.For deformation tests of cores special devices were developed for fastening the dial-type indicators making it possible to measure longitudinal and transverse deformations on cylindrical and prismatic specimens. The place of fastening the devices on the core in the region of a homogeneous stress--strain state was determined by special investigations with the use of laser technology [8]. The size of the core was selected with consideration of a multitude of factors: convenience of drilling and testing, treatment of the ends, and presence of a drilling tool. One of the controversial questions is that of the effect of the size of aggregate on the strength. Special investigations [8] and a study of the literature showed that a decrease of the ratio of the transverse size of the specimen to the maximum size of the aggregate to 1.25 insignificantly changes the average strength and coefficient of variation of strength) which can be taken into account by appropriate conversion factors. The core diameter was 150 mm with mandatory diamond drilling.For determining the conversion factors taking into account jointly the effect of different factors, experimental lots of specimens and an experimental block were concreted, from which cores were drilled [7]. Since mandatory consideration of the characteristics of uni...
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