جستجوی مقالات مرتبط با کلیدواژه "مقاومت" در نشریات گروه "عمران"

A large amount of waste from sugar factories is accumulated as waste. The purpose of this research is to recycle the waste of these factories, called carbonate cake (calcium carbonate mud, lime carbonate and lime sludge), which production is a serious problem for these factories and the environment, as a substitute for part of cement used in concrete. Due to the heterogeneous size of particles and for the greater similarity of the size of its grains with cement particles, carbonated cake with three methods dissolved in water of mixing plan, sieved and ground, was used in different designs. Laboratory concrete samples were made with a water-cement ratio of 0.35 and with different percentages of replacing carbonate cake instead of cement equal to 5, 10, 20, 30 and 40, and finally, the compressive strength of 28- and 56-day samples and the tensile strength of 28-day samples was measured. It is possible to replace it up to at least 20% by weight of cement, without significantly reducing the compressive and tensile strengths in concrete; Quantitatively, the results indicate that the compressive strength of 28- and 56-day samples and tensile strength of 28-day samples with 20% waste powder instead of cement have decreased by 6.5, 10, and 5.4%, respectively, compared to the control samples without powder. It is worth noting that carbonate cake recycling causes reduction in industrial waste, waste transportation cost, waste disposal cost and removing inappropriate smell and organic materials. The use of this green concrete in construction industry is recommended.

In addition to the mechanical properties and durability of concrete, its production cost can also affect the choice of materials. Changing the amount of materials in the concrete mix design is effective on the strength, as well as the materials cost, and these two factors are very important in deciding the amount of materials used based on the purchase price of manufacturers in the concrete industry. High-strength concrete having high-strength, and have a low water-to-cement ratio and a greater variety of materials, therefore, choosing the exact amount of materials to achieve a specific strength category, and at the lowest cost, is difficult. In this research, using the meta-heuristic genetic algorithm, the data of a reference research in terms of strength and the price of construction materials were optimized so that in addition to achieving the highest-strength and the lowest cost, in order to achieve the target strength, the minimum cost can be achieved. The results showed that the optimal answer of the genetic algorithm, compared to the optimal point of the reference research, and had strength of 10.2% more and the price 8.2% lower. Considering that the genetic algorithm has the ability to choose the mixture design for different strength categories, the examination of the mixture design showed that the algorithm works on changing the amount of intelligent materials and has applied the changes in a way that in the process of obtaining required strengths, changes in the amount of consumables should be suggested by applying the lowest possible price.

To directly measure the strength and permeability of concrete, a core should be separated from the concrete and then tested in the laboratory with destructive methods. For example, to measure the permeability of concrete by existing standards, concrete must be broken and divided into half. Also, acute conditions such as temperature cycles that concrete faces in summer can have negative effects on concrete characteristics. Therefore, in this research, by using innovative tests, in addition to investigating the effect of temperature cycles (40, 80, 120, and 160 cycles) on the permeability and surface resistance of concrete at different ages, measuring the depth of water penetration and resistance Concrete is compressed without breaking it. According to the results, by using the calibration charts and the equations obtained from the methods of the cylindrical chamber and friction transfer, it is possible to obtain the depth of water penetration and the compressive strength of concrete without the need to break the concrete and with a correlation coefficient of over 96%. It was also observed that the cycles of temperature changes have negative effects on the durability and surface resistance of concrete in such a way that the number of 40, 80, 120, and 160 cycles of temperature changes increases the permeability of concrete by 4.1, 8.7, and 7 12.5 and 16.5 have been equaled. Also, the acute conditions of temperature changes have negative effects on the surface resistance of concrete in such a way that the surface layer resistance of concrete has decreased by more than 44% under 160 cycles of temperature changes. Considering that the surface layer of concrete has a direct relationship with the penetration of harmful substances into the concrete, it was observed that with the increase in the strength of the surface layer of concrete, the volume of water penetration into concrete has decreased. By increasing the resistance of the surface layer by 15%, the volume of water infiltration into the concrete has decreased by about 140%.

The concrete surface is the most significant part as it is in direct contact with the outside world. Therefore, increasing the surface strength of concrete could reduce the absorption of harmful substances into the concrete. Permeability and surface strength can be regarded as factors that affect the durability and service life of a concrete structure. As a result, a concrete structure with the desired surface strength and low permeability is of paramount importance. Hence, this study attempted to measure the surface strength and permeability of concrete through “twist-off” and “Cylindrical Chamber” tests under temperature cycling. Relations between the surface strength and permeability of concrete samples were obtained. In addition, a linear function was used to estimate the relation between penetration depth and volume with high precision. According to the twist-off test results, extending the curing age of plain concrete would increase the surface strength; the surface strength at the age of 120 days exceeds that of 7 days by approximately 42%. However, when temperature cycling was performed on the samples, the surface strength of the concrete caused by the twist-off Test decreased. Further, results from the permeability tests using a cylindrical chamber indicate that temperature changes have a negative influence on the permeability and penetration depth in concrete samples. The permeability and penetration depth of concrete under temperature cycling caused an 8-fold and 3-fold increase after 120 days, respectively. According to the results of the study, moderate temperature cycles significantly affect permeability and penetration depth.

One of the important reasons that causes cracking and deformation in concrete elements, especially in the surface area of concrete, is different climatic conditions and temperature changes. In the previous researches, not many researches have been done regarding the relationship between the penetration rate value and the surface strength. The reason for the lack of research in this regard is the lack of simple methods or the high price of equipment to evaluate surface strength. In this article, infiltration- reducing materials with the brand names of Supergel and Mesocrete are used, which are widely used in Iran today. A simple "twist-off" test has been used to evaluate the surface strength. Also, "cylindrical chamber" test was used to measure the permeability. To apply the cycles of temperature changes, the samples were subjected to cycles of 50, 100, and 150 cycles. The obtained results show in the 150th cycle, the surface resistance of ordinary concrete has decreased by about 30%, but the reduction of the surface strength of concrete with penetration-reducing materials is less than 20%. Also, the increase in the permeability of ordinary concrete in the 150th cycle is equal to 486%, but this value is half of this value in concretes containing permeation-reducing substances. In the following, by using MATLAB software, it was determined that the relationship between permeability and concrete strength is close to each other, and this issue is established in terms of formulation with a first-order plane equation with a correlation coefficient of about 91%.

In this study, we attempt to have numerical and software analysis of behavior, deformation and strain caused by local dental loads (dent) in GFRP tanks. The load-displacement and the load- Strain diagrams in experimental and software conditions have also been analyzed, compared and evaluated. The research can be used in oil company projects, water organization and different types of tanks which are exposed to local loads. the experimental and theoretical researches on GFRP tubes and tanks under dental loads and concluded that all samples have linear behavior from beginning to end and proceed with the same slope which is due to the behavior of the GFRP materials (Zarrin, 2018). To test the behavior of experimental specimen under the influence of Dent’s load, wedge is used. In another studies different types of dental loads are applied to the tanks like Dome-shaped dental load, Circular dental load and Rectangular dental load (Jajo, 2014). To understand the importance and necessity of research, we must first study the dental load, how it is applied to the tanks, the dangers of applying it to the tanks and the ways of resistance against these loads.

The mechanical and chemical characteristics of concrete undergo changes in extreme environmental conditions, which often reduce the strength and durability. Therefore, the use of additives that increase the reliability of concrete in acute conditions is required. It is also important to use tests that are able to measure the permeability and resistance of concrete both in situ and in the laboratory without damaging the concrete. Therefore, it was decided to investigate the effect of some additives on the durability of concrete, which are recently widely used in Iran. There is not much research on the effect of these materials on the durability and reliability of concrete in extreme environmental conditions. In this research, by using in-situ cylindrical chamber and twist-off tests, the effect of different cycles of freezing and thawing on the permeability and surface resistance of ordinary concretes and concretes was evaluated. Contains additives. Contrary to DIN 1048 and BS EN 12390-8 standards, which require breaking concrete to measure permeability, the volume and depth of water penetration can be measured in the cylindrical chamber test without damaging the concrete. The obtained results show that by using the cylindrical chamber . Also, about 78% decrease in the strength of the surface layer of concrete occurred in the first 50 cycles and the remaining 22% occurred in the next 100 cycles. The permeability of concrete containing microsilica gel and supergel was calculated to be about 50% and 30% lower than the permeability of normal concrete, respectively.

It is difficult to determine the real strength of concrete in an existing structure because it depends on curing type record, concrete compaction quality, and pouring of concrete method. A core test is the most effective and reliable way to measure the concrete characteristics of the structure. The cores provide reliable and useful results because they are mechanically tested up to the destruction stage. The use of rebar in the concrete core samples tested in the parts of the reinforced concrete that have bar compaction is unavoidable. In most codes, using rebar is ignored, and the other factors are considered adequate on core test results; it has just been discussed and suggested to ignore the cores, including rebar. Therefore, this research aims to survey about the effect of using bars on the strength of concrete cores. In this regard, variables such as length to diameter (L/D) ratio of core, core diameter, the diameter of steel bar, number of steel bars, steel bars’ order, the configuration method of rebar, the distance of bar axis from the nearer end of the core, the moisture condition and water to cement ratio (concrete strength level) are considered. In the first step, concrete samples, including rebar, were tested with a concrete core. The examined samples were validated using numerical studies and ANSYS software; then about 200 cylindrical core samples using this software were studied in order to determine the pressure drag and also the effective parameters on the behavior of cylindrical concrete core containing rebar, and the results including the pressure drag and collapse mechanism were investigated and compared. Using rebar in the cores plays an important role in the stress and strain variation of the concrete core and the bars inside

Despite the fact that in most operating conditions, concrete components, compaction and curing affect the performance of concrete, but premature failure of concrete structures due to problems with the durability of concrete structures also occurs a lot. Due to the lack of information on the effect of type and strength of aggregates on the durability of self-compacting concrete, in this article, using the tests of "friction transfer" and "drilled core" to investigate the effect of strength of different aggregates on the reliability of concrete Self-compacting has been exposed to sodium sulfate. 9 types of stones with the names of travertine, granite, basalt, andesite, marble, green stone tuff, crystal green tuff, rhyolite and limestone have been used to make self-compacting concretes. Compressive strength tests of self-compacting concretes cured with water and sodium sulfate solution were performed at ages 7, 14 and 28. The results showed that the volume change of rocks with higher water absorption percentage was less and there is a direct relationship between the compressive strength of self-compacting concretes treated in water and sodium sulfate solution with the strength of the parent rock. We also see an increase in compressive strength of self-compacting concrete placed in sodium sulfate solution at a young age compared to samples placed in water. There is also a linear relationship with a high correlation coefficient between the results of the friction transfer test and the core correction test. Compressive strength of crystalline green tuff, green tuff, andesite, rhyolite, travertine, lime, marble, granite and basalt are 31.76, 33.12, 39.92, 43.43, 48.41, 51/97, 59.66, 62.17 and 75.41 Mpa, respectively. With increasing compressive strength, the results of friction transfer test also increased so that for the mentioned rocks are equal to 132.4, 146.9, 155.9, 168, 176.3, 185.3, 189.8, 5 / 198 and 9/207 Nm.

The concrete structures exposed to the earthquake have the potential of cracking and reduction in stiffness and strength. Because of their low deformability, there would be some cracking and plastic hinging in the moment-resisting frame. The utilization of dampers is a solution to improve the behavior of the constructed structures. Dampers play a crucial role in improving structural performance level and bearing capacity. In the present study, 9 concrete frames were tested, and steel yield dampers have been used for the seismic rehabilitation of the concrete moment-resisting frames. The yield dampers elements are ADAS dampers (Added Damping and Stiffness) connected to the concrete frame using steel braces. The concentric-type steel braces connect the dampers and concrete beams. Furthermore, to investigate the influence of the braces on the structure’s strength and behavior three concentrated braces have been installed in the structure. The structure in which ADAS dampers was employed demonstrated more strength and less recorded damages than the simple moment-resisting frame. In the present study, the effect of braces and dampers have been investigated in the behavior of the structure, cracking, and strength. The strength of the frames was increased by 48% and 21% by employing steel braces and yield dampers in the concrete frames, respectively, comparing the control frame.

Research on the possibility of using Reclaimed Asphalt Pavement (RAP) as a part of pavement materials is increasingly carried out. Economic and environmental considerations are the most reasons in this regard.  In this process, the reclaimed asphalt pavement replaces some of the aggregates in the concrete or asphalt mixtures. Since the previous studies mainly showed the negative effect of reclaimed asphalt pavement on fracture and compressive strength of concrete and on the other hand some studies indicated the positive effect of fibers on the strength of cement concrete, in the present research study the effect of Polypropylene, Polyolefin and steel fibers on mechanical properties (compressive strength, tensile strength and fracture resistance) of concrete containing reclaimed asphalt pavement was evaluated. For this, three different percentages (2, 5 and 8% by weight of cement) of each type of fiber were added to the concrete containing 15, 30 and 45% reclaimed asphalt pavement, and compressive strength, tensile strength and fracture resistance tests were carried out. The specimens used in the fracture resistance test were semi-circular and had three notch depths of 25, 32 and 38 mm. investigation of the tests results indicated that the addition of the fibers to concrete containing RAP may lead to slight increase in compressive strength (up to 7%), small increase in tensile strength (up to 19%) and considerable effect on fracture resistance (up to 30%).

One of the most important components in steel structures is their joints. It is a matter of correct design of steel members, especially fittings. Since the beam flange is not connected to the column flange in the side plate connection system, all the vulnerabilities and uncertainties of the brittle behavior of conventional joints that in the full penetration welding behavior of the beam flange to the column wing are eliminated. Today, the use of composite sections filled with concrete has been widely considered in many structures. One of the steel joints that has been proposed in the past years is the use of side plates, which to some extent guarantees the linear behavior of the connection spring. In this research, the behavior of side joints with side panels in composite steel and concrete frames has been investigated. Thus, after ensuring the modeling process by validating a steel connection in Abacus software, a U-shaped steel beam composed of a CFT column with a side plate is modeled and parameters has been investigated.The effects of compressive strength of concrete were also investigated. The results showed that except for the diameter of the screws, other factors affect the strength, hardness and ductility . Increasing the width of the plate has increased the strength, stiffness, ductility and energy absorption. By decreasing the d / t ratio of the column, the strength, stiffness and energy absorption are increased and the ductility is reduced. As the compressive strength of concrete increases, the amount of strength, stiffness, ductility and energy absorption increases. The arrangement of the screws, the diameter of the screws, the d / t ratio of the beam and the addition of the thickness of the side plate do not have much effect on the strength, stiffness and ductility and energy absorption of the joint.

RCC remains a widely used construction material over the last decade. RCC is placed in a manner similar to paving; the material is delivered by dump trucks or conveyors, spread by small bulldozers or specially modified asphalt pavers, and then compacted by vibratory rollers. By definition, Roller Compacted Concrete (RCC) is the concrete compacted by a roller in a hardened state. RCC is a special type of concrete that has essentially the same ingredients as concrete. However, at different ratios, partial substitution of fly ash is increased for Portland cement. This type of concrete has facilitated constructing many new dam and pavement projects and reducing costs by shortening the time duration of implementation. Rolled concrete materials are generally applied instead of the soil-cement mixtures in projects. Soil-cement and rolled concrete are both completely compacted mixtures of cement, aggregate, and water, while their main differences are the type and size of aggregates. Using this kind of concrete has provided a chance for the construction of many dams and new pavements with economic advantages, leading to the quick construction management. Since these structures are exposed to climatic factors, their durability, especially against alternate thawing-freezing cycles, is of paramount importance. In the current research, silica nanoparticles were added to the RCC mix of three different diameters (10, 15, and 30 nm) and three different ratios (1, 3, and 5% by cement weight) in 50, 100, and 300 cycles to investigate their effects on compressive strength, dimensions, and weights of RCC samples. The experimental results illustrated that mixtures containing nano-silica had a better durability and strength than non-additive mixtures.

A review of the damages caused by previous earthquakes shows that a significant number of the structures constructed in the country are neither earthquake-resistant nor have enough strength. Consequently, reliable, fast, and easy retrofitting methods are needed to improve these structures to withstand lateral forces. In the present study, 9 concrete frames were tested, and yielding steel dampers have been used for the seismic rehabilitation of the concrete moment-resisting frames. TADAS (Triangular-plate Added Damping and Stiffness) dampers are attached to the concrete frame using steel braces. The dampers and concrete beams are connected with concentric steel braces. Moreover, three concentric braces have been installed to investigate the influence of the braces on the strength and behavior of the structure. Compared to the moment-resisting frame, the structure that used TADAS dampers exhibited greater strength and recorded fewer damages. Cyclic displacement loading was applied to these frames, and their characteristics, including strength and crack, were investigated. In comparison with the control frame, the steel braces and yield dampers increased the structural strength of the concrete frames by 48% and 28%, respectively.

In this work, the effect of MgO on the treatment of a natural and contaminated clay soil with phenanthrene was studied through conducting various experimental tests including Atterberg limits, standard compaction, uniaxial compressive strength (UCS), and SEM tests. The contaminated soil was prepared artificially in the lab. Natural and contaminated soil were mixed with 5, 10, 20, and 30% of MgO as an agent. The results showed that phenanthrene changes the structure of the soil and causes a reduction in Atterberg limits, wopt, UCS, and E50 of the soil. The results also indicated that the UCS and E50 of mixture natural and contaminated soil with different percentages of MgO are increased and the amount of increasing of them is dependent on the percentage of MgO and curing time. SEM results also showed that the formation of carbonation products due to hydration of MgO is effective in increasing the strength of treated soil samples.

By development of science and technology, new structural systems have been developed and researched. In the last four decades, extensive studies have been done on the application of the steel plate shear wall systems. Steel plate shear walls are made and executed in various shapes. Trapezoidally corrugated steel plate shear wall is a relatively new structural system. In this paper, the effects of position, geometric shape, percentage, distance from the boundary elements and the use of the stiffener around the opening were investigated in the seismic parameters of the trapezoidally corrugated steel plate shear wall system including stiffness, strength, ductility and dissipation energy by using 46 models. The openings were geometrically square, vertical and horizontal rectangular, equal to 10, 14, and 18 percent area of the steel panel. This research was performed analytically using ABAQUS finite element software. The results of the study show that the square-shaped opening has better performance than the rectangular opening in all positions. Also, models with central opening have lower strength, initial stiffness and energy absorption rather than other models. Overall, the best position to create the opening in the corrugated plate is in the middle top of the plate and at the distance of 160 mm from the beam and also in the upper corner of the plate but without distance from the boundary elements. Another result of this research is that by using stiffener around the opening, initial stiffness and strength and energy absorption of the corrugated steel shear wall can increase until 41% and 25% and 24%, respectively. In addition among the different stiffeners, the plate with 60 mm width and 3 mm thickness has the best dimension for the stiffener around the opening.

Earthquakes are one of the major phenomena affecting structures and engineers use design criteria to deal with their effects. In terms of the specific degree of safety for dams ‌, it is necessary that the design of large dams include the largest believable earthquake in hazard analysis and probability consideration regardless of the amount of time it returns in the design. Pebble dams have mainly concrete or asphalt coating, which in addition to impermeability to water, increases the stability of the dam. Since a number of gravel dams have been constructed in Iran and several other gravel dams are under construction, the study and analysis of this type of dam is very important for current and future studies of dam engineering. In this research, pebble dam modeling will be done in Abacus software as well as model validation. First, the model presented in the reference article is modeled and validated. The model used in validation and this research is Musouchura Dam. After ensuring the accuracy of modeling and analysis, the effect of concrete strength of dam cover under the effect of selected accelerometers and by changing the strength of concrete and also the effect of considering the damping of concrete were measured and finally the results were compared. The accelerometers used in this study are Northridge, Bam, San Fernando and Tabas. Changes in concrete strength in three types C20, C25 and C30 with nominal strength of cylindrical compression specimens of 20, 25 and 30 MPa were made and this increase in strength is about 8 to 10% in reducing lateral displacement under selected accelerometers in the dam crown has it. Considering the damping effect in concrete with a value of 0.0325, under selected accelerometers, there is a change of about 3% in the lateral displacement of the dam crown, while it has little effect on the tensile degradation of the concrete surface.

Increasing the resistance of members or adding constraints to the structure does not jeopardize the overall safety of the structure. This can be proved under certain static loads by the safe theorem which is one of the fundamental theories of plastic analysis. Although this theorem has not proved in the condition of dynamic loads, its results are used in the everyday design under dynamic loads, so this paper attempts to numerically study these results under dynamic loads. Since the concept of mechanism and collapse cannot be investigated under transient loads, the level of ductility demand of structural components is considered to ensure the safety of the structure. For this purpose, the plastic rotation of the members was extracted after a minor variation in resistance and stiffness of the beams in a 2D-five-story steel moment frame by performing dynamic analysis. To compare ductility demand in dynamic analysis with criteria values, the evaluation was surveyed under nonlinear static analysis. The results analysis shows that with the increasing resistance, in most cases the ductility demand decreases, and in some cases the maximum increases by 7.3%. With increasing stiffness, the ductility demand has increased by a maximum of 16%.By comparing the results of dynamic and static analysis, it can be concluded that the required ductility in the dynamic analysis by increasing characteristics has been lower than the corresponding value in static analysis. Therefore, the increase in the partial stiffness and resistance of the beams under dynamic loads has not caused the structural collapse.

As yet, various systems have been proposed to withstand lateral loads caused by wind and earthquakes, which can be called bending frames, types of braces, concrete shear walls, types of energy consuming systems. The most important parameters that are considered in choosing a system resistant to lateral loads are: hardness, strength, ductility. Steel shear walls, which are used in both smooth and reinforced forms, are a relatively new system for lateral wind resistance, and studies by researchers over the past four decades have shown that thin shear walls are a suitable and economical bracing system. Due to their geometric shape, corrugated sheets have a higher hardness and ductility than flat sheets. In this laboratory study, the stiffness, strength and shear base of a smooth and corrugated shear wall of vertical trapezoids with a wave angle of 45 ° under cyclic loading have been investigated.

According to the basic theorems of plastic analysis of structures, increasing the strength or stiffness of a part of the structure does not weaken it under a specific static load. This result is widely used to simplify the modeling and design of structures, but these theorems have not been proven under dynamic loading like earthquake excitations. This study applies the results of the safe theorem numerically in a two-dimensional steel moment-frame structure with five stories under nonlinear dynamic analysis with 29 different earthquake ground motion records. Under transient dynamic loading conditions, because the mechanism or collapse does not occur in the structure, the safety of the structure is investigated by maximum rotational deformation of the members. By changing the characteristics such as local stiffness and strength of the members in the range of 0.8 to 1.5 times the initial value, the maximum deformation demand of the members has been compared. The results of the dynamic analysis show that upon increasing strength, in most cases, the demand for ductility decreases and with increasing stiffness, in almost all cases, the ductility demand increases. The results of nonlinear static analysis are compared with the nonlinear dynamic analysis in cases where increasing stiffness has increased the ductility demand. From this comparison, it can be concluded that upon increasing the stiffness of the members locally, the demand for ductility in the dynamic analysis is less than its corresponding value in static analysis. As a result, it can be said that by increasing the stiffness of the structure, observing the limitations of the codes for the ductility capacity of members and connections leads to the safety of the structure. Generally, it is concluded that the safety of the structure is not compromised by minor increase in the strength and minor increase in stiffness of some members of the structure under dynamic loading if regular limitations of the codes for the ductility capacity have been observed.