Object of the study is a structural adhesive sealant. The aim of the study is to investigate the influence of the hinged facade system (HFS) substructure with metal cassette cladding on the stress–strain state of the adhesive joint by means of numerical analysis (finite element method) and analytical calculations in accordance with international regulatory documents. Method. The bonded connection was investigated using numerical analysis. Four finite element models of the adhesive joint within a HFS were developed, differing in the degree of substructure modeling detail. Static analyses were performed for each modeling approach to determine the resulting shear and tensile stresses in the adhesive joint. The obtained stress values were compared with those calculated according to the provisions of the ETAG 002 guideline. Results. The numerical analysis under isolated modeling conditions demonstrated that when the fastenings of the metal cassette to the HFS substructure are not taken into account, stresses induced by the self-weight of the cladding are uniformly distributed among the adhesive joints, whereas wind-induced stresses exhibit a non-uniform distribution. The distribution of shear stresses within the adhesive joint is significantly affected by the stiffness characteristics of the fastening nodes connecting the cassette to the HFS substructure, with deviations ranging from 28 % to 31 %. Wind-induced stress distribution is influenced by both the fastening system and the adopted structural scheme, resulting in differences of up to 8 % when the load-width participation factor is considered. Neglecting this factor leads to discrepancies of up to 29 % compared with calculations performed in accordance with ETAG 002.
This article proposes a constructive solution for a protective combined geotechnical barrier to minimize the impact on existing buildings and structures from the construction of a subway tunnel. The barrier is utilized during the construction of a metro tunnel in weak soils on a developed area. The object of research is existing buildings and structures in the area affected by underground construction. The research subject is the additional deformations of the foundations and structures of existing buildings and structures. The aim of the study is to reduce the impact on neighboring buildings during the construction of the metro tunnel. Method. The research was conducted using numerical modeling. Three-dimensional and planar finite element models were developed in the Plaxis software package for analysis. Results. The values of additional foundation settlements and stresses in the building structures were determined. The effectiveness of the installation of a geotechnical barrier along the escalator tunnel is confirmed. The barrier reduces the maximum absolute foundation settlements of the surrounding buildings by an average of 40 % and the relative differential settlement by 66 %.
The article explores the comprehensive stress-strain state, reliability assessment, and monitoring of the caisson frame of the S-1 Ship Passage Structure, part of the St. Petersburg Flood Protection Complex. The relevance of this study lies in the uniqueness of the structure, which is unique in the country in terms of its length, as well as the complex and dynamic operating conditions in the Neva Bay. The structure is subject to a variety of factors, including variable hydrostatic pressure, ice loads, and temperature deformations, which shape the stress and strain patterns in the load-bearing elements. Particular attention is paid to the presence of initial residual deformations in the frame, recorded during in-kind inspection, which impact the performance of the structure. The study methodology is based on the finite element method. A detailed finite element model was developed that takes into account the actual geometry of the structure, the physical and mechanical properties of the materials, and the actual initial deformations. A series of calculations was conducted for a set of key operational scenarios: the caisson gate in wet and dry dock, initial moment of movement, and various temperature conditions. For each case, stresses, displacements, and reactions in the support hinge were analyzed. The calculation results showed that local and overall stresses in the frame do not exceed permissible values. Similarly, forces in the support hinge remain below the ultimate load-bearing capacity. However, deformation analysis revealed large deflections, which may be due to installation errors. Large deflections are observed in areas 45-95 meters from the support hinge. Based on the analysis of stress and deformation fields, critical areas of the structure most susceptible to loads and deformations were identified. Recommendations for the placement of vibration, deformation, and strain gauge sensors within the monitoring system were developed for these areas.
: combined system, weir, gate, hydraulic analysis Abstract. This study explores the hydraulic analysis of a combined system of rectangular sharp-crested weirs and rectangular gates, essential to control water flow in various applications. The weirs and gates are used for flow measurement in water distribution systems, reservoirs, sewage systems, and irrigation networks. The study aims to optimize design and operational strategies for the combined system, contributing to the field of hydraulic engineering. Five models of compound rectangular weirs with rectangular gates were tested using a downstream support. The first three models had a gate width of 10 cm, while the remaining two had a lower opening width of 10 cm and gate widths of 8 cm and 6 cm. The discharge coefficient increases with water head ratio as shown in experimental runs with gate width = 10 cm and lower weir width = 10. The discharge coefficient rises by 10.81 % due to a decrease in the lower opening weir with a constant gate width. It increases by 29.14 % as the gate width decreases with a continuous lower opening.
This paper presents the effect of compaction pressure level and wheat straw addition on the durability, mechanical behavior, and thermal conductivity of geopolymer stabilized rammed earth. Rammed earth specimens were prepared by static compaction to 5, 10, and 25 MPa of mixtures containing predefined amounts of sand, silt, clay, and wheat straw, stabilized with fly ash geopolymer. A number of unstabilized specimens made of the raw materials were also prepared for comparison. These specimens were cured inside plastic bags at 35 °C so that the least energy consumption is achieved. The durability was investigated by performing a dip test and spray test. The results of the geopolymer stabilized specimens demonstrated an excellent resistance to erosion by water, unlike the unstabilized specimens, which almost failed completely. The mechanical behavior was evaluated by performing unconfined compression test. The results indicated that material’s stiffness and strength increased considerably with increasing compaction pressure and curing age, with the majority of the increase occurring during the first month of curing. Compressive strength values of 4.2 and 10 MPa were recorded from tests on stabilized specimens compacted to 5 and 25 MPa, respectively, then cured for 60 days. These figures are promising, keeping that, a threshold unconfined compressive strength of 1–2 MPa is typically acceptable by many building codes. A relatively low thermal conductivity of about 0.35–0.5 W/(K.m) was recorded from the hot wire method on specimens prepared from various mixtures, suggesting that the stabilized rammed earth outperforms most of the traditional building materials such as concrete. The inclusion of wheat straw improved material’s ductility by increasing strains, at which shear failure occurs. However, this inclusion led to undesirable reduction in strength and stiffness over the first two months of curing and almost no change in thermal conductivity, with respect to those obtained on the stabilized specimens. This response was attributed to material wise incompatibilities.
The main disadvantage of gypsum and gypsum concrete products molded by casting, vibrating, rolling, and pressing methods is low water resistance, which manifests itself in a significant decrease of strength at humidification. The authors have shown the possibility of increasing the strength and water resistance of pressed gypsum products by modifying their structure with an additional crystallization framework of sparingly soluble calcium hydrogen phosphate dihydrate. The purpose of the research is to obtain an adjustment equation that makes it possible to determine the rational dosages of modifying additives depending on the values of the specified strength and water resistance of pressed gypsum composites, as well as to assign the optimal duration of mixing the semi-dry molding mixture until the sealing pressure is applied to it. Using mathematical experimental planning methods, there was investigated the effect of the mixing time of the molding mixture and the dosages of the modifying additives on the basic physical and mechanical properties of pressed gypsum composites compacted at a pressure of 40 MPa. Ammonium dihydrogen phosphate and carbonate-containing sludge from the chemical water treatment of thermal power plant were used as modifiers. It has been revealed that in the proposed technology, along with the dosages of modifying additives, the physical and mechanical properties of the material are significantly affected by the duration of mixing the molding mixture, during which chemical interaction occurs between its components, which increases the strength and water resistance of gypsum modified pressed composites. Experimental and statistical models of the most important technical characteristics of the proposed material have been developed, depending on the main prescription and technological factors, which make it possible to determine the conditions for obtaining pressed gypsum products with specified properties. An adjustment equation has been obtained that makes it possible to establish rational dosages of modifying additives and the optimal mixing time of the molding mixture at a given value of the softening coefficient.
Rubber tires present a serious disposal problem as millions of tires are discarded every year producing serious smoke pollution when burnt. The objectives of this research are to examine how recycled rubber from used tires affects properties of mixes of bituminous concrete, and to find optimum rubber content that will provide rubber-asphalt concrete mixtures with best properties. In current study, recycled rubber from used tires is used to modify characteristics of asphalt mixture (AM). Marshall mix design procedure was used to obtain optimum binder content (OBC) and to study impact of rubber on AM properties. Mixtures' moisture susceptibility was determined using Marshall immersion test and indirect tensile strength test. Scrap rubber at 0, 1, 2, and 3 % of total weight of mixture was mixed with crushed limestone or basalt aggregate. By total weight of mixture, asphalt binder (AB) was added at five different percentages (4.0, 4.5, 5.0, 5.5, and 6.0 %). Findings indicate that adding 1 % of rubber to a mixture of limestone and basalt yielded bituminous mixtures with best qualities overall. Increased air voids and flow and reduced unit weight, void in mineral aggregate, and stability has occurred by adding scrap rubber to mixes. Compared to limestone bituminous mixtures, basalt bituminous mixtures exhibit greater stability, unit weight, air voids, voids in mineral aggregate, smaller flow, and slightly smaller voids filled with bitumen. Dry specimens exhibit higher stability compared to wet specimens. Nevertheless, for both limestone and basalt bituminous mixtures at OBC, the flow of wet specimens is higher than that of dry specimens. For both limestone and basalt aggregate-bituminous mixtures, indirect tensile strength reduces as rubber concentration increases at OBC. Also, retained stability ratio (RST) and retained indirect tensile strength ratio (RTSR) in basalt mixtures at OBC is larger than those for limestone aggregate-bituminous mixtures at OBC.
Introduction: The reliability of the assessment of the level of tensile stresses in order to predict the risk of early cracking during the construction of massive monolithic reinforced concrete structures increases when taking into account the deformations of autogenous shrinkage, which are often unreasonably ignored. Purpose of the study: to quantify the effect of autogenous shrinkage of concrete on the formation of a stress-strain state in the early period of the construction of massive monolithic reinforced concrete structures. Materials and methods: Modeling the formation of a stress field without taking into account relaxation in a massive block of 20×20×2 m with a layer overlap time ("layer birth time") of 4 hours. At the first stage of research, stress calculated as a result of the development of only temperature deformations. At the second stage of research, stress calculated as a result of the development of temperature deformations and autogenous shrinkage. When calculating the temperature field, the layered laying of the concrete mixture is taken into account by assigning an abnormally high coefficient of thermal conductivity to each layer before it is laid (1000 W/(m·°C)) and zero heat capacity. Results. The effect of a decrease in the heat transfer coefficient from 23 to 3 W/m2·°C on top of the plate is resulted in a decrease in the maximum stress level in the section by 28–32 % when taking into account only temperature deformations and by 14–27 % when taking into account temperature deformations and autogenous shrinkage. The influence of the kinetics of heat dissipation and hardening during the transition from the rapid group to the slow group is resulted in a decrease in the maximum stress level in the cross section to 6 % when taking into account only temperature deformations. Possible increase in the maximum stress level in the cross section up to 20–56 % take place if temperature deformations and autogenous shrinkage are taking into account.
In fact, constructing low-weight buildings over expansive soil is usually risky, directly influencing urban development. Therefore, this type of soil needs to improve before loading, and one of the new and sustainable methods is using geopolymer materials. This study uses fly ash-based geopolymer with different percentages (i.e., 0.5, 1, 2, 4, and 6 %). After that, the 2 % was selected and applied directly to the laboratory model to improve the surface layers of the soil. It can seem that, the soil transfers from high swelling potential to very low when using this percentage in both the free surface of soil and soil under load. The free swelling decreased from 13 to 0.3 %, at the 6 % geopolymer ratio, and the swelling pressure also reduced from 230 to 7 kPa at the same geopolymer ratio.
Comprehensive researches to consider the behaviour of the metallic dampers have proven that the I-shaped link, designed to act as shear mechanism, serves as a ductile fuse. However, a key limitation is the reduced strength and stiffness of the system when these links are directly connected to the diagonal member of a concentrically braced frame. To improve the structural performance of I-shaped links, researchers have suggested increasing the web plate thickness, which, in turn, raises the load on the brace members. A novel solution to address this issue involves incorporating diagonal stiffeners into the dampers. This study numerically and parametrically investigates the effect of stiffening I-shaped links using finite element analysis. Numerical studies show that the stiffeners not only prevent the web plate from buckling (which improves its performance) but also share the imposed loading. By including stiffeners, a thinner web plate can be utilized instead of a thicker one to achieve greater ultimate strength and stiffness. The parametric analysis highlights that the thickness of the stiffeners plays a more critical role than the properties of the flange or web plate in determining damper performance. Based on these results, an optimal configuration for I-shaped dampers is proposed in this study.
This study aims to produce a new type of waste aggregate concrete by using fine and coarse waste ceramic as aggregate; the waste ceramic used in this study was in 2 types: red ceramic, which has a red colour and is produced from waste ceramic tiles, and white ceramic, which produced from the waste of tableware. Replacing ordinary fine and coarse aggregate with a ceramic waste aggregate improved the mechanical properties of concrete, compressive, tensile, flexural strength, and modulus of elasticity of normal concrete by using waste ceramic as aggregates. 20, 40,60, 80, and 100 % replacement by weight of aggregates are studied. Total replacement of normal aggregate with white ceramic aggregates led to an increase in compressive strength from 42.2 to 52.1 MPa; tensile strength also increased from 2.9 to 4.8 MPa, flexural strength increased from 4.3 to 8.7 MPa, and static modulus of elasticity has risen from 25.6 to 32.8 GPa. The mechanical properties of red ceramic increased until 60 % replacement; a slight decrement in mechanical properties was found after 60 % replacement. Studies show that waste white ceramic has better mechanical properties than red clay ceramic.
Large volumes of sediments are being drudged from the Euphrates River to maintain the stream of the river. These sediments are classified as loose sand with poor engineering properties such as poor grain size distribution, poor compaction, high permeability, and low shear strength. Therefore, these sediments need to be stabilized in order to be utilized as an available and cost-effective engineered fill. In this research, cement by 4, 6, and 8 % was used to improve the strength and durability properties of loose sand sediments dredged from the Euphrates River. Additionally, polypropylene fibers were added by 0.5 % to the cement-treated specimens. A series of laboratory tests were performed to evaluate the unconfined compressive strength and wetting-drying properties of the prepared specimens that were cured to 7 and 28 days. The results showed that adding cement led to improve the compaction process of the cement-treated soil. Furthermore, adding cement by 8 % produced an unconfined compressive strength value as high as 2000 kN/m2. Furthermore, when the polypropylene fibers were added, the strength was further increased by 52 %. The results also showed that treatment with cement caused a significant improvement in the resistance to wetting and drying cycles, as the treated specimens passed the test with loss in weight ranging from 16 to 39 % compared to the untreated specimens that collapsed in the first cycle of the test. As discussed herein, the improved sand may provide a valuable source of engineered fill that can be used for many projects such as dams, levees, and road ways.
River sand, despite being an available material, a low-cost, but loose sandy soil, cannot be used as a construction material in civil engineering works due to its poor grain size distribution and low bearing capacity. Geopolymer is recently considered a novel eco-friendly alternative to conventional soil enhancement and stabilization materials, such as ordinary Portland cement (OPC) and lime, which harm the environment in terms of high CO2 emissions and energy consumption. Hence, this study investigated the potential strengthening of loose sandy soil using geopolymer. Different alkaline activator (AA) solution ratios were used with varying curing temperatures for producing the river-sand geopolymer. The river sand-geopolymer specimens were matured in the oven at different temperatures for 48 hours. A series of unconfined compressive strength (UCS) tests were carried out on the 3, 7, 14, and 28 days of curing. The results show that the UCS of the river-sand geopolymer matrix significantly increased with increasing the main ingredient of its activator solution (sodium silicate) as well as the temperature. The UCS reached 13.42 MPa when the AA solution ratio was 0, whereas it decreased up to 1.15 MPa when the AA solution ratio became 1.5 at a temperature of 60 °C and 28 days of curing. Therefore, geopolymer is feasible and sustainable material to improve problematic soil for different applications.
The technique adopted in this study includes an innovative and unconventional method, which plays an important role in enhancing the bearing capacity of piles, called a recycling system. Full-scale models were conducted on two groups of piles: the first group was constructed without using this system, and the second group was constructed using it. All piles were tested by static load test. 3D finite element in the PLAXIS program was adopted to understand the load-carrying response of piled, several parameters were studied such as the thickness of the filter cake, type of soil, L/D ratio, and separation between the friction and end bearing. The results revealed that using the recycling system significantly increased the pile-bearing capacity, reaching 50 %. The effectiveness of the recycling system in cohesionless soils is more efficient than in cohesive soils. Pile's bearing capacity improvement ratio reaches 65 and 38 % for sandy and clayey soils, respectively. In addition, the thickness of the filter cake significantly reduces the pile-bearing capacity, which may exceed 40 % if this system is not used. Using the recycling system, the pile bearing capacity was improved by 60-64 % and 85-98 % for friction and end bearing, respectively.
The objective of this study is to examine the impact of elevated temperatures on the structural response of slender columns made of reactive powder concrete (RPC) subjected to eccentric axial loads. Nine RPC column specimens were exposed to a temperature at three different levels: 450 degrees C, 600 degrees C, and 750 degrees C, and to three eccentricities: 50 mm, 100 mm, and 150 mm. The columns underwent fire exposure while being subjected to axial loading equal to 60 % of their ultimate capacity. The outcomes of the experimental tests indicate a noticeable lateral displacement of the RPC columns at high temperatures. The results show that at a constant temperature 750 degrees C, the mid-height lateral buckling for various eccentricities is significantly higher comparing 50 mm with 100 mm and 150 mm by 59 % and 81 %, respectively. While this rate becomes 36 % and 35 % for 600 degrees C. At 750 degrees C, the lateral mid-height buckling is found to be significantly greater when compared to 450 degrees C and 600 degrees C by 106 % and 69 %, respectively (for 50 mm eccentricity). While the ratio becomes 48 % and 46 % (for 100 mm eccentricity), one of the main findings in the research is that a low eccentricity value 50 mm, which has a high load, gives higher buckling for each elevated temperature. The mode of failure regarding the column depended on the eccentricity value where the high eccentric loaded columns showed prolonged ductile behavior, while the least eccentric loaded columns showed a brittle type of failure.
This article presents a comprehensive computational study of the metal frame of the caisson gate of the C1 shipping opening, part of the St. Petersburg flood protection system. The relevance of this study stems from the need to ensure the strength, stability, and safe operation of this unique 120-meter-long structure, which supports the segmental caisson gate during its movement from the dry dock to the structure's span. The frame is distinguished by its cantilever structure of variable thickness and reinforced with stiffeners. The aim of the study was to develop an adequate spatial computational model of the frame and caisson gate and analyze their stress-strain state for a stationary position in a dry dock. The study was conducted using the finite element method, taking into account constant static loads, including the structures' own weight and hydrostatic pressure. The paper presents the developed spatial finite element model and describes the adopted boundary conditions and loads. Permissible stresses and deflections are determined. The calculations yielded stress and displacement fields. It was determined that the maximum equivalent stresses in the frame do not exceed permissible values. The maximum frame deflection is also within acceptable limits. An analysis of the dynamic characteristics of the structure was conducted. The natural frequencies of vibration were determined for the caisson gate. A stability analysis was performed, showing that the safety factor for the first positive buckling mode exceeds the minimum required. Based on the obtained results, a conclusion was reached that the calculated stresses and deformations comply with regulatory requirements and provide the necessary safety and stability margins. To monitor the condition of the structure during operation, it is recommended to install vibration sensors at critical points, as well as conduct further research.
White cement mortar suffers from the appearance of cracks when it is used in the facades of buildings, and these cracks affect its durability and shelf life. Therefore, three additives were suggested to be used with white cement mortar to reduce shrinkage, taking into consideration that they do not negatively affect other cement properties. A type of water-soluble polymer, Polyvinylpyrrolidone (PVP), as well as two types of steel fibers (hooked fibers and straight fibers) and they were all used in proportions 0 %, 1 %, 2 %, and 3 % of the weight of cement. A set of physical and mechanical tests were carried out in addition to dry shrinkage test such as setting time, compressive strength, flexural strength, and water absorption. It was found through these tests that all the additives reduced the dry shrinkage and the best results were obtained when using steel fibers with hooked ends by 3 % where the dry shrinkage was decreased by 75 %. The same type of fiber gave the highest flexural strength, with an increase of 16 % by using the same ratio. As for the use of 1 % straight steel fibers, it achieved the highest value in the compressive strength test, with an increase of 5 %. As for PVP, it reduced the water absorption by 6 % when it was used by 3 %.
This work is aimed at computational comparative studies of natural changes in soil temperature and under a building with a ventilated basement in Norilsk. In contrast to conventional projects, it was planned to locate a small part of the building directly on the ground, which could lead to additional thawing of the soil. Laboratory data on soil samples in the thawed and frozen state, taken from boreholes at the construction site, and the results of soil temperature measurements at a depth of about 14 m were used to perform calculations. When forming the boundary conditions of the calculation model on the outer surface of the soil, the radiation balance for the conditions of Norilsk was considered. It was found that the radiation balance from May to August is positive and leads to soil heating, and in the rest, most part of the year, it is negative and causes soil cooling. New results obtained demonstrate that a decrease in the moisture content of the surface soil layers reduces the influence of phase transitions on the thermal-inertial properties of the soil, which leads to an increase in the thickness of the active soil layer (where annual temperature fluctuations are observed), an increase in the depth of thawing in the summer-autumn period, and a decrease in the soil temperature under the active layer. The temperature distributions over the depth of soil under different sections of the building with a ventilated basement and in the immediate vicinity of the building in a long-term operation cycle after completion of its construction were calculated. According to calculation results, the maximum depth of soil thaw under a building with a ventilated basement decreased by 12 % compared to natural conditions, reaching 1.1 m. It is shown that for multi-story buildings with ventilated basements, individual structural elements with insulation can be located directly on the ground surface, and additional thawing of the soil will not occur under them. However, for this case, the absence of additional thawing of soil should be confirmed by a heat engineering calculation taking into account the ratio of surface areas of the ventilated basement and the structural elements located on the ground, as well as the features of their insulation.
This investigation is aimed at determining flow regimes in Y-junctions with flow division. Air velocity and velocity pulsations are measured using a hot-wire anemometer in a wide range of Reynolds numbers Re = 400-6000. A junction with diameter d = 6 mm is chosen as the object of study for the inlet and two outlet channels: a symmetrical arrangement of the outlet channels with an angle of 50 degrees between them. A long tube with diameter d = 6 mm and length l/d = 333 is connected to the junction inlet. Two techniques of the flow regime diagnostics have been developed. For the inlet channel of the junction, the critical Reynolds number is Re = 2000 (puff-type vortex structures appear for the first time). For two outlet channels, a significant increase in velocity pulsations occurs at lower Reynolds numbers Re = 1640-1660. By analogy with diagnostics of the flow movement in a round tube, the following classification of flow regimes in a junction is proposed: laminar flow at Re < 1640-1660, transitional flow at Re = 1660-2800, and turbulent flow at Re > 3000. The obtained data can be used to clarify the range of data for laminar, transitional, and turbulent flow regimes in round Y-junctions with flow division.
The evolution of the mechanical properties of concrete depends greatly on the hydration of the component binders such as cement and mineral additives. However, the prediction of the hydration degree of these binders is extremely difficult due to the complex physic-chemical mechanisms at the molecular level. In this article, the author proposes to use a multiphasic model that considers hydration development and chemical interaction between reactions while taking into account temperature and water content effects on reaction kinetics. The main goal of this study is a semi-adiabatic calorimetry test was applied to determine the input parameters by measuring the heat release during hydration. Based on the test results shown the application of three cases of blended cement paste samples is considered to show the efficiency of the model. Overall, thermogravimetric analyses and its derivative are applied to verify the delay effect of pozzolanic reactions on the hydration degree induced by portlandite content in the paste.
