جستجوی مقالات مرتبط با کلیدواژه « مقاومت برشی » در نشریات گروه « عمران »

The present study has investigated the effect of vinyl acrylic polymer emulsion (VA) on the shear strength of aeolian sands in the Khuzestan plain. For this purpose, after sampling the aeolian sands of the mentioned area, a standard compaction test was performed and the optimum water content and maximum dry density of the aeolian sand were determined. Then, solutions with percentages of 10, 20 and 30% of polymer material were made and added to the aeolian sand in such a way that it reached the optimum water content. The prepared soil with maximum dry density was placed in square metal molds kept in the laboratory for 1, 7, 14 and 21 days and then subjected to direct shear test. The results of the direct shear test on the stabilized samples showed that by increasing the curing time and the concentration of the polymer solution, cohesion and the shear strength increase and the angle of internal friction decreases. So the polymer solution with a concentration of 30% has caused a 146% increase in shear strength aeolian sand. Electron microscope images (SEM) show the creation of bridges between sand grains in the stabilized samples, which is the reason for the increased cohesion and shear strength of the samples.

Shear force is one of the most important influencing forces of structural beams and especially unreinforced deep concrete beams that cause sudden failure and sudden collapse of the structure and for this reason, it is of interest to designers and implementers of structures. The study of the conducted research shows that the proposed methods including the use of artificial neural network cannot predict Provide an accurate description of the behavior of deep reinforced concrete beams against shear force. This research, while specifying the cause of the error of the artificial neural network in estimating the shear strength of deep reinforced concrete beams, presents a solution to achieve accurate results by optimizing the artificial neural network by the meta-heuristic algorithm of particle swarm. For this purpose, 309 laboratory samples of deep concrete beams were collected from the research literature and the particle swarm algorithm was used to optimize the weights in the artificial neural network using MATLAB software. The comparison of the results of this method with the results of these letters and other existing methods that were examined in this research showed that the use of the combination of particle swarm algorithm and optimized artificial neural network to estimate the shear strength of unreinforced deep reinforced concrete beams provides more accurate answers.

In recent years, the mixture of sand and rubber particles has been used in various fields of civil engineering, such as the stability of roofs, retaining walls, and drainage materials in landfills due to its durability, cost-effectiveness, and solving environmental problems. The purpose of this study is to investigate the effect of tire crumb on the shear strength and dilation in a static state and the liquefaction resistance in a dynamic state. In this regard, in this research, a static and dynamic undrained triaxial test was performed on a mixture of Babolsar sand and tire crumb (size between 1 and 8 mm) under constant confining pressure. The effect of parameters such as the amount of different tires’ crumbs (0, 5, 10, 20, and 30% by weight) and different relative densities on the static and dynamic behavior of the mixture of sand and rubber crumb and the created pore water pressure was investigated. In the static (consolidated-undrained) triaxial test, the relative densities of the sand–tire mixtures were 45, 60, and 80 percent. The tests were carried out on the specimens at 100 kPa cell pressure. Also, the specimen was loaded at a strain rate of 0.30% per minute for all the tests until the axial strain reached 20%. In cyclic triaxial tests, the relative density of the sand–tire mixtures was 45 percent, and the confining pressure of 100 kPa was used in the experiments. The sinusoidal waveform was applied to the specimen with a frequency of 0.5 Hz. For accuracy evaluation, the behavior of the sand-tire mixture, as well as corrections such as membrane penetration corrections, membrane force, and cross-sectional area, were applied. The results showed that adding tire crumb to sand reduces the shear strength and dilation of sand. Also, the ratio of the mean diameter of tire particles to the mean diameter of sand particles affects the behavior of shear resistance and dilation of the sand-tire mixture. As the ratio of the mean diameter of tire particles to the mean diameter of sand particles increases, the shear strength and dilation of the sand-tire mixture increases. Also, increasing the amount of tire crumb in sand reduces the excess pore water pressure and, as a result, reduces liquefaction potential in cyclic loading. This behavior can be attributed to the compressible nature due to the low elastic modulus of the tire crumb.

Applying stone columns (SCs) is an economical method to improve loose soil. This laboratory study is conducted on the effects of simultaneous use of crumb tire (CT) and fly ash (FA) on the shear behavior of SCs encased with geotextile and fiber-reinforced polymer (FRP) in soft clay. A large-scale direct shear device was utilized to do the desired tests. The samples were exposed to normal stress values of 20, 40, and 70 kPa. First, optimal percentages of CT and FA were determined to be used with granular materials in the SCs. The impact of installing ordinary reinforced and unreinforced SCs on the shear behavior of the assembly was examined. Installing the SCs in soft clay bed and adding the CT-FA composite to the SC materials increased the shear strength. Supplementing the CT-FA composite to the SC materials increased shear strength of the assembly to 4.6%-10%. The shear strength rose more than twice when the normal stress increased from 20 kPa to 70 kPa and it was mobilized more since CT-FA composite is present. It increased due to a rise in the replacement ratio of the SCs in the assembly. By installing the ordinary composite SCs in clay bed under the normal stresses of 20 kPa and 70 kPa, the shear strength increased to 34% and 41.7% and it would rise in the encased mode more than in the ordinary mode. Furthermore, the FRP-based reinforcement enhanced the shear strength more than the geotextile reinforcement did.

The existences of loose soils such as soft sands have always created concerns for bearing the load. Their inability to withstand pressure and weak shear resistance have forced engineers to move the project site or accept expensive methods such as pile driving as solutions to overcome them. Today, many additives such as polymers, lime, cement, etc. have been introduced to improve soil properties and land improvement; however, each of them, having their strengths and weaknesses, has created problems for their use. Cement factory furnace ash, which is one of the by-products in the cement production process; at the outlet, the gases released from the furnace are collected by fabric filters or electrostatic precipitators. Due to its similarity with the compounds found in cement, the compounds of this material have some of the positive properties and characteristics of cement and can be used to stabilize weak soils due to its cheapness. In this research, the effect of cement furnace ash on the engineering properties of unsuitable and weak sand-blasted soil has been investigated, in such a way that cement furnace ash with proportions of 5, 10, 15 and 20% with sand-blasted soil in the periods of 7, 14 and 28 days processing of the combination and direct cutting test have been done on them. Also, in order to create ideal conditions, the standard Proctor compaction test was used to obtain the maximum dry weight of the soil and the optimum humidity for each sample. The results of this research show that the samples with 10% cement furnace ash compared to other samples create a more ideal composition and the shear strength is more than 7 times compared to samples without cement furnace ash.

The steel plate shear wall (SPSW) as a lateral bearing system in high-rise buildings has been focused in recent decades. Today, these lateral bearing members with high ductility, high energy absorption, and high initial stiffness are used in new buildings as well as rehabilitation of existing buildings, especially in earthquake-prone countries. The use of stiffeners in the SPSW reduces the thickness of the infill plate, and increases the strength and stiffness of the SPSW. The aim of this study is to present a new arrangement for stiffeners with high performance in order to achieve higher shear strength and lateral stiffness. For this purpose, after validating the numerical modeling, several SPSWs with common (horizontal-vertical and diagonal arrangement) and proposed arrangement (diagonally along with horizontal-vertical) of stiffeners were modeled in Abaqus finite element software and were subjected under monotonic and cyclic loads. The results showed that the suggested arrangement provided more confinement for the infill plate and enhanced the final shear strength of the SPSW by 47.5%.

In general, shear reinforcement in reinforced concrete beams typically involves the use of stirrups. However, substituting stirrups with continuous rectangular spiral reinforcement can enhance construction efficiency and lower costs. Meanwhile, the adoption of fiber-reinforced concrete in concrete structures is on the rise due to its distinctive properties. To address the tensile and shear vulnerabilities of concrete, reinforcing it with fibers is a viable solution. This study explores the experimental replacement of stirrups with continuous rectangular spiral reinforcements in both traditional concrete and steel fiber-reinforced concrete (SFRC) beams. Three beams were subjected to static loading tests: the first beam, referred to as ST-NC, featured stirrups and normal concrete as a reference; the other two beams incorporated continuous rectangular spiral reinforcements with normal concrete (SP-NC) and steel fiber-reinforced concrete at a 0.75% volume fraction (SP-F0.75). The experimental findings indicate that the beam reinforced with continuous rectangular spiral reinforcements and fiber concrete exhibits improved shear resistance, energy absorption, and ductility compared to the normal concrete beam and the reference beam. The beams with continuous rectangular spiral reinforcements, using normal concrete and steel fiber-reinforced concrete, demonstrated a 23.8 and 46.5% increase in shear capacity, respectively, compared to the reference beam. Additionally, energy absorption in SP-NC and SP-F0.75 beams increased by 69 and 158%, respectively, compared to the reference beam. The ductility of the continuous rectangular spiral reinforcement beam with normal concrete and steel fiber-reinforced concrete is 0.87 and 1.17 times that of the reference beam, respectively. Notably, the results reveal a reduction in the ductility of the SP-NC beam compared to the reference beam, and the addition of 0.75% by volume of fibers to the concrete resolves this ductility weakness in the SP-NC beam. These findings underscore the advantages of employing continuous rectangular spiral reinforcements in beams constructed with steel fiber-reinforced concrete, as proposed in this study

Reinforcement of ballast with the help of Geogrids is one of the methods that have been studied by various researchers in the technical literature to increase the load capacity as well as reduce the deterioration of the ballast through the reduction of crushing and settlement. In this article, by introducing a new type of geogrids made with the help of waste rubber belts called Geo-scrape, their effect on the shear behavior of ballast in a large-scale shear test has been investigated. In this direction and in order to investigate the effect of the dimensions of the geo-scrap on the ballast shear behavior and by placing the geo-scrap with the dimensions of 5x5, 10x10 and 25x25 cm square in the upper layer, various tests were carried out under vertical loads of 50, 100 and 150 Kilopascal has been done and the results are presented in the form of shear stress-horizontal displacement curve, maximum shear strength, internal friction angle and dilatancy angle. The summary of the results shows that the mesh of 5x5 cm2 has provided the most favorable conditions for the ballast in terms of increasing the shear strength, increasing the internal friction angle and decreasing the dilatancy angle. So that by placing the geo-scrape with the dimensions the mesh of 5x5 cm2, the shear strength, internal friction angle and dilatancy angle are increased by 20%, 7% and 30% respectively compared to the unreinforced state.

In this study, the critical state shear strength of a type of sand with different silt percentages in saturated and unsaturated states has been investigated. For this purpose, a number of undrained consolidated (CU) and drained consolidated (CD) triaxial tests were performed on saturated and unsaturated samples, respectively. The samples were sheared under confining pressures of 50, 100 and 150 kPa and suction levels of 50, 100, 150 and 250 kPa for unsaturated samples. In the saturated state, the results showed that if samples are remolded with the same eeq, for the different percentages of fines the critical state lines are converged. In the unsaturated state and net stress state, the critical state line is not only dependent on suction, but also changes with changes in the percentage of fines. However, in the effective stress state, by applying the appropriate effective stress relations and the concept of equivalent intergranular skeleton void ratio, these lines can be converged independently of suction and fine content and reach a single critical state line in the stresses space.

In recent years soil reinforcement and improvement techniques have gained widespread applications in different aspects of geotechnical engineering. It is apparent that reinforcing/stabilizing a weak/problematic soil is more economical than replacing it with select fills. A contemporary method of soil reinforcement/ improvement is the application of fibers-natural or synthetic (polymeric) with random distribution within the soil (Hejazi et al. 2012). More recently, there has been a trend in utilization of recycled fibers for soil reinforcement/improvement purposes (Valipour et al. 2021). This treatment dwells on the application of Recycled Tire Polymer Fibers (RTPFs) for enhancing the shear strength of Babolsar sand.

Today, construction of large structures is growing quickly. For this reason, it is necessary to find the material with a rather low weight and high strength. For this purpose, Steel-Concrete-Steel (SCS) sandwich structures were proposed. SCS structures are composed of two steel layers and one concrete layer. Due to their low weight and high strength and flexibility, they have become popular among engineers. In the present research, first, three specimens of push-out test of strip shear connector were modeled and validated using ABAQUS finite elements software. Then, since the present equations to predict the shear strength of the shear connectors are complicated and are not so precise, the authors proposed an equation taking the effects of different geometrical parameters and the concrete's compressive strength in to account. For this purpose, using the experimental design, 17 specimens were designed and modeled. Then, an equation was proposed using the Genetic Expression Programming Algorithm (GEP) to predict the system's shear strength. Finally, the performance of the proposed equation was evaluated using the error parameters.

The filling material of the columns is generally sand, gravel or crushed stone which are sometimes called stone columns or gravel columns. The implementation of this system is widely used in geotechnical engineering to increase bearing capacity, reduce settlement and accelerate integration. The use of industrial wastes such as steel slag in soil stabilization can be an environmentally friendly, sustainable and cost-effective technique for solid waste disposal. There are many studies which have been conducted on the bearing capacity and settlement of improved soils with stone columns with or without geosynthetic. However, a very limited number of studies on conventional stone columns and steel slag columns with or without confinement and geosynthetic under lateral loading have been investigated. In this paper, the lateral load capacity of steel slag granular column-sand environments has been investigated using a large-scale direct shear test device. The effects of column material type (steel slag and sand), column diameter and the type of geosynthetic on the shear strength parameters of column-sand composites have been investigated. The experimental results show the effectiveness of using steel slag columns to improve the lateral load performance of sand. The results indicate that the maximum stress increases by 20 to 70% and the internal friction angle increases by 200 to 800% compared to the sand without slag column with increasing the diameter of the column from 5 to 25 cm, respectively.

Improving the physical properties of soil using industrial waste has always been of interest to researchers And it becomes more important when Accumulation of huge volume of borrowed Soil resulting from the development of Civil projects Due to improper engineering characteristics For reuse in Civil projects Cause a lot of problems. On the other hand Given that Iran is one of the hubs of steel production and Huge volumes of steel furnace slag are produced and accumulated annually in this country, It is necessary for the optimal recycling of this waste Conduct comprehensive research in various fields of science and technology. One of the goals for the optimal use of this waste, Their use is in soil improvement for use in road construction. The present study is based on the improvement of accumulated fine-grained soil in Mobarakeh Steel area Using processed steel slag in the size of 0 to 25 mm , Has been studied For use in road construction. Engineering properties of loan soil in Mobarakeh Steel Plant (Saba area), Includes Liquid Limit and Plasticity Index , classification and seive size, After sampling from different parts, Preparation and testing in the laboratory Was initially examined According to the specifications of road building materials, Soil unsuitable for use in road construction was identified. Eventually, by performing step by step experiments, Soil engineering properties were modified using different percentages of steel slag And achieve a suitable mixture for use in road construction. Also compare the geotechnical properties of soil samples to the samples of soil and slag mixture obtained Showed that these properties improved significantly by increasing the percentage of slag.

Using a simple shear test, it is possible to investigate the behavior and recognition of soil resistive parameters. Cementation is one of the subsets of soil remediation that falls into the category of physical and chemical remediation that binds soil particles together and prevents the breakdown of the soil skeleton and increases shear strength (Consoli, 2009; Finn, 2002). The behavior of soil resistance parameters is investigated using simple shear tests. Shear stresses in the soil can be divided into static and dynamic (Li et al, 2016). One of the best ways to reduce cement consumption and production is to use pozzolanic materials, especially natural pozzolans, and replace them with cement. Pozzolans are widely used in the cement and concrete industry (Rahgozar et al, 2018). Micro-silica, perlite, methakaolin and zeolite are the most well-known natural pozzolans. Since the cost of producing pozzolans other than zeolite is almost high, their use would not be economical on a large scale. Zeolite mainly contains silica, and aluminum oxide, which reacts with calcium oxide and thereby increases the strength of the resulting compound. The addition of zeolite improves the spatial structure properties of the zeolite, as well as reduces the porosity of the resulting mixture (El Mir and Nehme, 2017). This paper presents the results of laboratory investigations on the shear strength of cemented sand and the effect of zeolite replacement on cement. To achieve this purpose, mineral zeolite, Shahroud cement, and Babolsar sand were used.

Creating slits in steel plate shear walls is a new way to improve the seismic performance of these walls. The creation of slits turns the steel sheet into a number of links, each of which dissipate the seismic energy at both ends of the links. In this study, the effect of slit location and orientation on the cyclic behavior of steel shear panels is considered. For this purpose, in a laboratory study, the effect of slits location in the central area (conventional method), in the middle of the boundary elements or sheet corners on the stiffness, strength and capacity of energy dissipation and drift corresponding to the start of sheet rupture was investigated. Experimental results show that, contrary to the conventional method with slits located in the central area of the sheet, changing the location of the slits leads to a fundamental improvement in the seismic performance parameters of the wall. The best performance is observed for the specimen with slits in the middle of the boundary elements and with parallel set of slits. The increase in the strength and drift is 39 and 100%, respectively, for the specimen with parallel set of slits in the middle of the boundary elements compared to the conventional specimen with slits in the center of the sheet. Better performance could be expected with optimization of slits spacing and patterns.

Soil bio-remediation is one of the developing methods of soil improvement and the reduction of environmental problems due to the injection of chemicals in the soil is one of the superior features of this method compared to other common methods. It was created by linking the fields of civil engineering, geochemistry, and microbiology. The basis of soil improvement by biological cementation method is based on the microbial production of calcium carbonate precipitation, which is inspired by the formation of sandstone in nature and with the help of bacteria that have precipitation and hydrolysis of urea to enhance the technical specifications of soil. The steps of soil remediation in this method are that in the presence of Bacillus Pasteurii bacteria, crystals are formed which are the result of urea reaction and a source of calcium, which is usually calcium chloride. These crystals are placed in empty spaces of the soil and represent the reason why the adhesion of soil particles increases significantly and its strength increases. In order to manage the consumption of materials used, it is better to obtain optimal values during studies. For this purpose, in this study, the cemented samples were subjected to triaxial tests, permeability, and SEM testing. In consolidated undrained triaxial experiments, the trend of soil resistance over time was investigated by considering different retention times and different molarities. The optimal amount of molarity of the materials used and the concentration of bacteria and the optimal retention time were obtained according to the results of experiments performed in this method. Also, by examining the resistance of cemented samples, an increase in strength in the range of compared to clean sand was observed. Examination of the time parameter pointed to the formation of calcium carbonate precipitation and their final setting up to days. After days, the trend of increasing soil resistance exhibited a constant amount.

Soil-cement is a mixture of cement, water and soil that by compaction and hydration of cement , its components are joined together to form a compound with very low permeability , durable and abrasion resistant . Considering that the main applications of soil-cement as a base layer in road paving are sealing elements in earthen and concrete dams and foundation improvement, and since in recent years the addition of cement on mechanical parameters and The soil-cement physics has been investigated . In this study , the effect of adding different weight percentages of hemp fibers, polypropylene fibers and nanosilica to the soil-cement before and after successive melting and freezing cycles in shear and behavioral strength parameters . In this research, the sample soil of Nazarabad industrial town of Karaj was used . The measurement parameters in this research are different enclosing stresses, different processing times, different weight percentages of hemp fibers, propylene fibers and nanosilica and after successive melting and freezing cycles . This study is in Unreinforced non-drained triaxial test . The results indicate the improvement of behavioral and resistance parameters in all materials and increased durability after successive cycles of melting and freezing in samples containing nanosilica .

One of the most important by-products of steelmaking and refining processes is steel slag. It is necessary to determine the geotechnical engineering properties of steel slag and assess their potential use in road and railways embankment constrictions. In this paper, the shear strength properties of steel slag were studied. Two types of steel slag, Blast Oxygen Furnace (BOF) and Electric Arc Furnace (EAF) slags that generated in Esfahan Steel Company and Mobarakeh Steel Company are used in this paper. The grain size distributions range of the test specimens have been selected under the characteristics of the road pavement and the existing laboratory facilities. In this study, two slags (BOF, EAF) with two grain size distribution and two difference compaction energy (standard and modified compaction) and the effect of saturation in California bearing ratio were evaluated. The results of the atterberg limits test showed that the material is none plasticity. The results of the compactions tests showed that dry unit weight varied between 1.94 to 2.74 gr/cm3 and optimum moisture content varied between 8% and 12.5%. Based on the California Bearing Capacity (CBR) tests, the CBR varied between 88 to 199 for BOF slags and 185 to 490 for EAF slags in socked and unsoaked conditions. In this study, direct shear experiments were performed on two types of granulation under four vertical stresses of 25, 50, 100 and 150 kPa in dry, submerged and dry-submerged. Based on the results, the above slags have an internal friction angle between 28 and 68 degrees and the adhesion of these materials was between 0 to 32 kPa. These results showed that steel slag has a much higher shear strength than natural soil and, according to the results of experiments, can be used as a material in engineering embankments.

It seems necessary to develop a simplified design approach in order to evaluate the shear strength of web panels under fire condition as the size of furnaces is limited, the cost of experiments aimed at testing the fire resistance of structures is quite high and access to simulation software packages such as ANSYS and ABAQUS is not always guaranteed. In this paper, web panel shear design relationships of AISC360-16 and AASHTO-14 specifications are exploited to be used in fire conditions. To this end, the stress-strain reduction factors provided in EN 1993- 1-2 are directly applied. Afterwards, the design curves are proposed for prediction of the ultimate shear strength and limiting temperature of steel plate girders under fire by taking into account the strength degradation caused by high temperatures and the effects due to sectional instability. According to the results, the proposed curves are more accurate in compact plates with plastic shear buckling at both ambient and high temperatures. However, by increasing the web slenderness, the difference is increased. At ambient temperatures, the maximum difference for compact, noncompact, and slender web plates is about 1.1%, 23%, and 28%, respectively. The difference at 400 C0 reaches to almost 3% and 7% for non-compact and slender web panels, respectively. In addition, at 600 C0, especially for slender plates, proposed curves yield values that are nonconservative for ultimate shear strength such that the difference is about 11%. Also, the maximum difference for existing experimental and numerical studies is about 20% and 4%, respectively.

According to the expansion of cities, the necessity of high-rise buildings construction and the need to retrofitting the old buildings is inevitable, particularly in metropolises such as Mashhad with expanded urban areas and neighbor areas of Imam Reza shrine built on the fine-grained deposits, the necessity of improvement and reinforcement of soil is evident. Nanotechnology can be significantly efficient as one of the most useful modern technologies in the recent century to meet the needs of the construction industry. The technology has a significant effect on the improvement of strength and mechanical parameters of soil because of a considerable increase in particle surface. In this regard, this study has investigated the effect of adding clay nanoparticles of type Montmorillonite and Silica of type "S" on the strength and mechanical parameters of silty-clay soils adjacent to Imam Reza's Shrine using laboratory studies. The results showed a significant increase in shear and compressive strength parameters and a decrease in settlement of soil in the Nanosilica-improved samples compared to nanoclay-improved ones. In this way, adding 1% nanosilica and 2.5% nanoclay could cause a 620 and 134% increase in bearing capacity of silty-clay soil, respectively.