33407 2304-6295 10 73 2018 1-37

RAR RUS 7-15 Sinyakov Leonid Peter the Great Saint Petersburg Polytechnic University Ivanova Elena

Polytechnicheskay, 29

Strakhov Dmitry Aleksandrovich sdaleks2008@rambler.ru Joint work of steel floor beams and vaults In the buildings of the pre-revolutionary construction period, overlaps are laid, representing a roll of concrete or brickwork in the form of cylindrical vaults on steel beams. In such historic buildings, the replacement of structural elements is undesirable, so it is necessary to know the exact nature of the structure in order to avoid unnecessary replacement of the elements. Usually in such designs, when carrying out verification calculations, the joint work of the steel beams and the vault is not taken into account - only the steel beams are calculated, and the vault is taken into account only as an additional load of its own weight. According to the results of these calculations, steel beams do not meet regulatory requirements, whereas in reality they can withstand high loads. The article explores the discrepancy between the results of traditional calculations and the actual nature of the work of the collaboration of steel floor beams and vaults. The article considers the calculation of the approximate model of the structure realized with the use of the software complex "SCAD". The actual stress-strain state of the structure is determined. The influence of various factors on the distribution of moments is investigated. 10.18720/CUBS.73.1 69 overlapping; steel beams; beams of basements; bearing capacity; collaboration (joint work); strength and rigidity; vaults https://unistroy.spbstu.ru/article/2018.73.1/ 73_1.pdf

RAR RUS 16-27 6506150284 0000-0003-1139-3164 Moscow State University of Civil Engineering Sainov Mikhail Petrovich mp_sainov@mail.ru

Moscow, Russian Federation

Peter the Great Saint Petersburg Polytechnic University Zatonskikh Matvei

Polytechnicheskay, 29

Structural cracks initiation in reinforced concrete faces of rockfill dams The article deals with the facts of damage of some reinforced concrete faces integrity in rockfill dams; a review of opinions was made regarding the causes of crack formation in reinforced concrete faces. Analysis shows that the zones and the mechanism of crack formation in the considered cases are different. This permits speaking about the fact that various reasons may exist for crack formation. The data of field observations is not sufficient for obtaining unique understanding about the stress-strain state of the reinforced concrete face. At present there is no general opinion on the causes of crack formation in reinforced concrete faces. Consequently, the proposed measures on prevention of crack formation are based on empirical approach and require theoretical validation. 10.18720/CUBS.73.2 69 Concrete faced rockfiil dams; cracks; crash; stress strain state; data of field observations https://unistroy.spbstu.ru/article/2018.73.2/ 73_2.pdf

RAR RUS 28-37 Kazan State University of Architecture and Engineering Mukhametrakhimov Rustem muhametrahimov@mail.ru

1, Zelenaya st., Kazan, 420043 Russia

Fiber-cement compositions modified by flocculating additives Chemical additives in the production of cement-fiber products are used to improve the properties of cementfiber suspension and freshly formed sheets, as well as to accelerate the process of filtration and sedimentation of the solid phase in recuperators. To improve the filtration properties, flocculating additives are added to the composition of cement-fiber suspensions. The purpose of research is to establish the influence of the degree of ionic charge and the molecular weight of polyacrylamide (PAA) on the kinetics of cement hydration, the rate of precipitation of cement-fiber suspension and the strength of cement-fiber plates. According to the results of the first stage of the performed experimental studies, it was established that the deposition efficiency increases with an increase in the degree of ionic charge of PAA. At the second stage, it is determined that the amount of PAA from 0.05-0.15% by weight of cement slightly increases the normal density (NG) of the cement paste and, depending on the content, has approximately the same effect on its setting time. The beginning of the setting occurs at 54-64 minutes later, and the end of the setting at 16-31 minutes before the composition without additives. At the third stage, the kinetics of cement hydration with the studied additives of PAA was studied. The process of cement hydration was studied by systematically determining a quantitative indicator of the kinetics of heat release and contraction of the Portland cement system and subsequent analysis and change it over time. The achievement of the temperature maximum on the curves of hydration of Portland cement with the content of PAA up to 0.1% indicates the intensification of the hydration process in the initial period of hardening. The increase in the amount of PAA in the composition of more than 0.1% leads to a slower process of cement hydration and a decrease in the temperature maximum. Also, the specific heat of Portland cement in all periods of hydration increases with increasing content of PAA to 0.1% and decreases with a further increase in its dosage. In this regard, the optimal content is 0.5-0.1% for all brands of PAA. The growth of activity and the value of specific contraction of Portland cement contraction curves increases with the content of PAA to 0.1%. The increase in the number of PAA in the composition of more than 0.1% leads to a decrease in activity in the value of specific contraction. Introduction to the composition of more than 0.10% of PAA hinders the filtration ability of the cement-fibrous mass during pressing due to the high water-holding capacity of the composition. At the next stage, it is noted that the greatest increase in strength is achieved when using anionic PAA Besfloc K4046, which has a high degree of ionic charge. The introduction of this additive in the cement-fiber mixture in the amount of 0.05-0.1% increases the bending strength by 10-15%. 69 10.18720/CUBS.73.3 construction materials; concrete modification; cement; fiber cement; cellulose fibers; dispersed reinforcement; flocculation; modifying additives; chemical additives; polyacrylamide https://unistroy.spbstu.ru/article/2018.73.3/ 73_3.pdf