75504
2712-8172
Magazine of Civil Engineering
4
88
2019
1-79
RAR
RUS
3-13
Le
Tu Quang Trung
Peter the Great St. Petersburg Polytechnic University
quangtrung1690@gmail.com
29 Politechnicheskaya St., St. Petersburg, 195251, Russia
56091980300
0000-0003-3850-424X
Lalin
Vladimir
Peter the Great St. Petersburg Polytechnic University
vllalin@yandex.ru
29 Politechnicheskaya St., St. Petersburg, 195251, Russia
Bratashov
Alexey
Peter the Great St. Petersburg Polytechnic University
aleks.kuskus@mail.ru
29 Politechnicheskaya St., St. Petersburg, 195251, Russia
Static accounting of highest modes in problems of structural dynamics
The calculation of building structures for dynamic effects is usually performed according to the method of decomposition by its own forms of vibrations. However, the problem is that such a method gives an exact solution of the dynamic problem with full consideration of the entire spectrum of modes. Moreover, when solving practical problems with the use of software systems, dynamic calculations are performed approximately taking into account a limited number of the first natural modes of oscillation. The contribution to the dynamic response of the structure of unaccounted higher forms of oscillations, as a rule, is not evaluated at all. The results show that the error of such a solution to a dynamic problem can be significant. Consequently, this paper is devoted to the method of static registration of higher forms of oscillations in problems of the dynamics of building structures. The description of the main provisions of the method is given, examples of its implementation in the calculation of spatial structures under the action of an external harmonic load are given. With the help of a computational program complex, the displacements of nodes and internal forces in the elements of the structures under consideration are determined. Various parameters of the dynamic effect and the number of vibration modes taken into account were set. The adopted method of static accounting for higher forms of oscillations requires solving one dynamic problem and two auxiliary static problems. An important circumstance of the approach is that one of the static problems should be solved by the method of decomposition in its own forms of vibrations. The approach proposed in the article allows to significantly reduce the computational costs of dynamic calculation in comparison with the classical approach. This result can be of great importance when solving problems for complex dynamic effects and for structures that are not uniform in hardness.
10.18720/MCE.88.1
structural dynamics
spectral method
vibration modes
highest modes
static accounting
spatial structures
https://engstroy.spbstu.ru/article/2019.88.1/
01.pdf
RAR
RUS
14-24
23493671500
Shakhov
Sergey
Siberian Transport University
sashakhov@mail.ru
57194617402
Rogova
Elena
Siberian Transport University
elena.rogova4@yandex.ru
Factors affecting the ultrasonic disaggregation of powders
Using finely dispersed mineral particles of various origins and morphologies offers a promising strategy in controlling the structure formation in cement composites. However, the use of such additives is hampered because those additives proved to be prone to consolidation into rather dense aggregates. Fine dispersion and disaggregation of powders is possible with the aid of cavitation ultrasonic treatment. However, the optimal conditions for such processing can not be established without conducting simulation studies. The purpose of the present study was the identification of ultrasonic-action factors and conditions ensuring an efficient disaggregation of finely dispersed powders of various origins and particle morphologies. In our study, we used diopside, granulated blastfurnace slag (GBS), wollastonite, ash, and calcium carbonate powders. It is found that the process of ultrasonic treatment of aqueous suspensions is accompanied not only by the dispersion of initial particles and aggregates but, also, by simultaneous formation of new aggregates. That is why the observed variations of the specific surface area and the optical density of powders can be attributed to the variation of the fractional composition of dispersed phase. The activating capability of a mineral additive is due to the fraction of the particles less than 1 μm in size exerting a key influence on the variation of the specific surface area of the powder. Our estimate of the energy efficiency of the cavitation disaggregation of powders during an ultrasonic treatment shows that the most energy-favorable one is the ultrasonic treatment lasting for 1–5 minutes, i.e. during the period of the first half-wave of the variation of the particle fraction less than 1 μm in size.
10.18720/MCE.88.2
ultrasonic
cavitation
ultrafine additive
disaggregation
grinding
cement
construction
https://engstroy.spbstu.ru/article/2019.88.2/
02.pdf
RAR
RUS
25-41
6602801860
0000-0001-7532-0074
Loganina
Valentina
Penza State University of Architecture and Construction
loganin@mail.ru
Petukhova
Nadezhda
Penza State University of Architecture and Construction
npetukhova58@mail.ru
28 Herman Titov St., Penza, 440028 Russia
57199850188
0000-0002-2279-1240
Fediuk
Roman
Far Eastern Federal University
roman44@yandex.ru
8. Suhanova St. Vladivostok, st. Octyabrskaya. 690950. Russia
57194347544
Timokhin
Roman
Far Eastern Federal University
gera210307@yandex.ru
8. Suhanova St. Vladivostok, st. Octyabrskaya. 690950. Russia
Polystyrene paint with reduced contents of volatile compounds
The proposed organomineral additives are novel, eco- friendly components for polystyrene paints. A light brown-red loam was used as a filler for polystyrene paints. Rheological, technological and physico-mechanical properties of paints and coatings based on them were studied by a series of standard tests. Characteristics of frost and water resistance, hiding power and holding capacity of polystyrene paint confirmed the creation of durable paints with high performance properties. Comprehensive studies have shown that the addition of organic additives in the composition of polystyrene paint increases the critical volume concentration of pigment 1.2 times, increases the degree of grinding paint, reduces dispersion time (2 times) and reduces the speed of shelter from 160 to 112 g / m2. Analysis of the results of experiments showed that the addition of organic additives contributes to increased resistance to external influences, as well as the strength of adhesion to the substrate by 22 %. Using the obtained results will allow you to create polystyrene paints with a low content of volatile compounds and increased crack resistance.
10.18720/MCE.88.3
buildings
construction
facades
organomineral additive
polystyrene paint
clay
volatile organic compounds
https://engstroy.spbstu.ru/article/2019.88.3/
03.pdf
RAR
RUS
42-51
57202972366
Solovev
Sergei
Krylov State Research Centre
aerodynamics.spb@gmail.com
44, Moskovskoye shosse, St. Petersburg
57202054286
0000-0002-4050-6298
Khrapunov
Evgenii
Peter the Great St. Petersburg Polytechnic University
hrapunov.evgenii@yandex.ru
29 Politechnicheskaya St., St. Petersburg, 195251, Russia
Modeling of the mean wind loads on structures
Correct determination and consideration of wind loads are primary importance in the design of unique architectural objects such as high-rise buildings, sport arenas, airports, large-span bridges. One of the most accurate ways to determine wind loads is to carry out model tests in specialized wind tunnels. Nowadays, during wind tests much attention is paid to the correct modeling of natural wind properties. In present work comparison of the most popular approaches for turbulence length scale determination is presented. One of the purposes of this study is to compare the main aerodynamic characteristics of the simple cube model obtained in uniform flow and during ABL modeling. This paper provides a brief overview of the method for ABL modelling in test section of the Landscape wind tunnel and contains experimental data on mean flow velocity distribution, turbulence intensity, dimensionless spectral density and integral scale of turbulence. The comparison of experimental data obtained for cube model in various wind tunnels revealed the influence of ABL on geometry and intensity of separation zones at the cube sides, and, as consequence, the influence of the same on integral and local aerodynamic characteristics of the object. On the basis of the obtained experimental data, it was concluded that the intensity of the separation zones has significant influence on the total aerodynamic loads, which is usually not taken into account in the framework of applied calculations. The difference in numerical values of aerodynamic characteristics was up to 30 %.
10.18720/MCE.88.4
aerodynamic force on buildings
atmospheric boundary layer
wind loads
physical modeling
Silsoe cube
wind tunnel
pressure coefficient
facades
https://engstroy.spbstu.ru/article/2019.88.4/
04.pdf
RAR
RUS
52-59
55516020800
Zhao
Qianqian
Northeast Forestry University
492954791@qq.com
Harbin Heilongjiang, China
55434335600
Cheng
Peifeng
Northeast Forestry University
chengpeifeng@126.com
57204285919
Wei
Yuwei
Yellow River Survey Planning and Design Co., Ltd.
weiyuwei1991@qq.com
Wang
Jianwu
Harbin Dongan Automobile Engine Manufacturing Co,Ltd.
nihaone@163.com
Factors effecting the recovery process of self-repairing concrete
In order to explore the influence of external environmental factors, the initial width of cracks and the placement of glass fiber tubes on the repairing effect of self-repairing concrete, glass fiber tubes are built in self-repairing concrete specimens, Self-repair test using repair adhesive. The repair rate α is characterized by the ratio of the initial crack width l to the time t used for repair completion, and the effects of the above three factors on the repair rate were analyzed. The results show that at –15~30 °C, the repair rate increases with the increase of temperature; at 0~30 °C, the growth rate of repair rate is obviously less than the growth rate of –15~0 °C. When the temperature is below 0 °C, the temperature plays a leading role in the improvement of the repair rate; The repair rate increases first and then decreases with the increase of the initial crack width. When the crack width is from 0.4to 0.6mm, the repair rate increases significantly faster than the crack width from 0.6to 1.0mm. The rate of repair of the crack width from 1.0 to 1.5 mm is significantly higher than that of the crack width from 1.5 mm to 2.0 mm. And when the initial crack width is about 1.0 mm, the repair rate reaches the highest level. When the initial crack width and the repair temperature are between –15 and 30 °C, the repair rate of the glass fiber tube is slightly better than that of the diamond when the inverted trapezoid is placed. The initial width of the crack has the greatest influence on the repair rate. Followed by temperature conditions and placement of fiberglass tubes. The corresponding factor levels at the maximum repair rate are 1.0mm, 30 °C and inverted trapezoids.
10.18720/MCE.88.5
self-repairing cement concrete
initial crack width
placement method
external environment
repair rate
https://engstroy.spbstu.ru/article/2019.88.5/
05.pdf
RAR
RUS
60-69
55534147800
0000-0001-5290-3429
Kolchunov
Vladimir
Southwest State University
sjs28@mail.ru
57202804437
Dem'yanov
Alexey
Southwest State University
speccompany@gmail.com
The modeling method of discrete cracks and rigidity in reinforced concrete
Cracks can be quite critical for the safety of architectural structures so their investigation is crucial. Excessive crack opening in reinforced concrete structures leads to corrosion of the reinforcement, which significantly reduces their serviceability. An extraordinary problem on the width of crack opening was considered for RC (reinforced concrete) elements under the affects of bending and torsion. Its solution was proposed on the basis of RC theory involving the hypotheses of fracture mechanics. The initial hypotheses about the formation and disclosure of spatial cracks for multilayer RC structures were formulated. These proposals allowed assessing the resistance of concrete in tension and the distance between the cracks, as well as the width of its disclosure. Hence, specific features of a double-cantilever element adjacent to spatial cracks were investigated with both mathematical calculations and experimental studies. The results demonstrated that developed new technique can be used for estimating the width of the spatial cracks for RC elements under the affects of bending and torsion.
10.18720/MCE.88.6
reinforced concrete
crack fault
bending-torsional coupling
computational models
splitting tensile strength
https://engstroy.spbstu.ru/article/2019.88.6/
06.pdf
RAR
RUS
70-79
57203962119
0000-0001-9723-5161
Nguyen
Trong-Chuc
National Research Moscow State Civil Engineering University
ntchuc.mta198@gmail.com
57208303308
Luu
Xuan Bach
Tri Dung Construction Transportation Joint Stock Company
xuanbachmta@gmail.com
Dong Nai, Vietnam
Reducing temperature difference in mass concrete by surface insulation
The heat which is produced in the cement hydration is rather high in mass concrete structures like dams, pavements, piers. In fact, it takes a longer time to cool the inner of the mass than its surface. The main reason for this result is that having the temperature difference between the hot inner mass and its cooled surface. Such a gap like that is the cause of appearing a large number of cracks in the surface of the mass concrete at several days age. In this study, the application of using a sand-layer insulation to control mass concrete block cracks at an early age. Specifically, these processes are performed by the program Midas Civil 2017 in cases: without sand-layer insulation, and with the application of using sand-layer insulation have thickness in range of 0–7 cm for heat preservation. In conclusion, the results in this study showed that when using an insulation thickness of 7 cm, it led to that the maximum temperature differences between the surface and the center of mass concrete block is lower than the limitation. The recommendations made as a result of this study is that sand-layer insulation should be used to prevent and limit cracks of the mass concrete block at an early age.
10.18720/MCE.88.7
heat of hydration
temperature gradient
crack
mass concrete
mathematical model
sand-layer insulation.
https://engstroy.spbstu.ru/article/2019.88.7/
07.pdf