Stress relaxation in concrete of massive hydraulic structures

Kogan, E. A.

doi:10.1007/bf02305447

Hydrotechnical Construction

1980

DOI: 10.1007/bf02305447

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Stress relaxation in concrete of massive hydraulic structures

E. A. Kogan¹

Abstract: In the general case the stress relaxation coefficient Kr(t, T) is a function of ~wo variables: age of the concrete T at the time of a change in stresses and the duration of the effect of a given stage of stresses (t--T) [1]. Heretofore the data on the relaxation coefficients obtained in investigations of the authors of [1-4] were used in calculating hydraulic structures. These data, although they are considered pertinent to concrete used in hydraulic structures, were obtained by tests of small specimens in whi… Show more

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“…In the construction period the modulus of elasticity of concrete changes according to the following relation [ 3]: In the construction period the modulus of elasticity of concrete changes according to the following relation [ 3]: …”

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Temperature regime and state of thermal stress of the Kurpsai dam

Dzyuba¹,

Fradkina²

1983

Hydrotechnical Construction

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The research department of the All-Unlon, Planning, Surveying, and Sclentific-Research Institute (Gidroproekt) has developed a method of investigating the temperature regime and state of thermal stress of massive concrete dams constructed by the lift-by-llft method with sectionallzation without pipe cooling.A vertlcal cross section of the dam during construction and operation is examined.The two-dimenslonal problem of thermal conductivity and thermoelasticity is solved [i]. In the construction period a region is discretely built up in time as blocks with variable physical properties of the concrete are poured one on another. The variability of heat liberation of concrete as a function of time and temperature and of the modulus of elasticity of concrete as a function of time is taken into account.Creep of concrete is taken into account approximately by means of relaxation coefficients.Various technological, construction, and climatic factors (construction of a tent, watering, effect of variations of the temperature of the outside air and reservoir water, breaks in the pouring of blocks, etc.) are taken into account when conducting investigations [2].The temperature regime and state of thermal stress of the dam of the Kurpsai hydroelectric station were investigated during 1975-1977 by means of the method developed with the use of a B~SM-6 computer.The possibility of constructing the dam by sectionalizing without pipe cooling [2] when certain measures were fulfilled was established:protection of the upper surface of concrete by a tent, watering in the warmlseason, placement of heat insulation on the outside faces, filling of the reservoir not in the cold season of theyear, etc.We still present the results of additional investigations of the state of thermal stress of the concrete masonry of the Kurpsai dam in the absence of insulation on the downstream face. The upstream face is covered w!thsoils , which is assumed equivalent to insulation with thermal resistance R = 1.3 m2.h-deg/kcal. This corresponds to insulation with a 20-cm-thick layer of dry sawdust.Four variants of constructing a dam for blocks with a height of 1 m are examined: two different breaks in concreting (6 and 10 days) and different time of starting the placement of concrete in the dam (summer and winter). Time of placing Break in placing No. of variant ht block tpl, day tbr , days 1 Ianuary I Iuly 1 Ianuary I Iuly 6 6 l0 10A tent is provided for above the upper concrete surface, where in the winter a constant positive temperature of +3~ is maintained and in the summer watering with river water is accomplished.For variants 1 and 3, where the concrete began to be placed in the dam in the winter, heating of the foundation was carried out for two weeks before the start of placement --a winter shelter with an average temperature of +3 ~ in it was erected.The amount of cement per 1 m 3 of concrete is assumed equal to 180 kg. In the construction period the modulus of elasticity of concrete changes according to the following relation [ 3]:

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Temperature regime and state of thermal stress of the Kurpsai dam

Dzyuba¹,

Fradkina²

1983

Hydrotechnical Construction

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Creep of roller-compacted concrete

Kogan¹

1991

Hydrotechnical Construction

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The technology of constructing concrete dams from roller-compacted concrete (rollcrete) with elimination of sectioning or with a considerable increase of the size of the sections has been being developed increasingly more in recent years. When solving problems of the thermal crack resistance of rollcrete masses, it is important to take into consideration creep of the concrete.To study this problem, the research department of the All-Union Planning, Surveying, and Scientific-Research Institute (Gidroproekt) in 1988-1989 conducted experiments on the design composition of rollcrete of the Katun hydroelectric station (Table i). Cylindrical specimens with a diameter of 30 cm and height of 90 cm were made for studying creep.Compaction of the stiff concrete mix (S = 25-35 sec) was carried out by a vibrating plate made by fastening a 29-cm-diameter steel plate on the end of the working part of an IV-90 suspended vibrator. The mix was compacted in layers 10-15 cm thick with a vibrating time of 40-60 sec. Such compaction technology was developed by conducting systematic tests with checking the density of the concrete, which reached values of about 0.96-0.98 of the theoretical in an absolutely compact body.The cylinders were loaded in devices with a pneumatic-~nydraulic power system providing constancy of the longitudinal force in time. The deformations of the concrete were measured in the middle part of the cylinder on a base of 400 mm from four sides by means of constant deformeters (scale division of the measuring head i ~m). Shrinkage deformations of the concrete were eliminated by means of "standard" specimens. Vapor insulation was realized by adhesive polyethylene film applied on the surface of the cylinder immediately after removing the molds (age of concrete 5-7 days).The age of the concrete during loading was 7, 28, 90, and 180 days and 1 year. Two cylindrical specimens were used for the 7-and 28-day ages and one specimen in the remaining cases. One of the 7-day-old specimens was finally discarded, since a high deformability of the concrete, which was related to incomplete compaction of the stiff concrete mix, was found during loading and initial stage of the tests.

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Thermal field in water pipe cooling concrete hydrostructures simulated with singular boundary method

Hong

Chen

Lin

et al. 2017

Water Science and Engineering

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Stress relaxation in concrete of massive hydraulic structures

Cited by 4 publications

References 4 publications

Temperature regime and state of thermal stress of the Kurpsai dam

Temperature regime and state of thermal stress of the Kurpsai dam

Creep of roller-compacted concrete

Thermal field in water pipe cooling concrete hydrostructures simulated with singular boundary method

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