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In this paper, crack detection possibility in an arch dam structure is investigated by wavelet transform analysis. An arch dam is a solid concrete dam, curved upstream in plan. In addition to resisting part of the pressure of the reservoir by its own weight, it obtains a large measure of stability by transmitting the remainder of the water pressure and other loads by arch action into the canyon walls. The complete necessity of high safety, economical design, complex of designing and its application increase the importance of concrete arch dams. Successful arch action is dependent on a unified monolithic structure, and special care must be taken in the construction of an arch dam to ensure that no structural discontinuities such as open joints or cracks exist at the time the structure assumes its water load. According to the principles of theory of structures, there is a relationship between the dynamic and static responses and, consequently, the stiffness. Any sudden change in stiffness leads to dynamic and static response variation. This condition will help to estimate the damage and to investigate the structural response before and after the failure. Wavelet analysis has recently been considered for damage detection and structural health monitoring (SHM). It provides a powerful tool to characterize local features of a signal. The basis function in wavelet analysis is defined by two parameters: scale and translation. This property leads to a multi-resolution representation for stationary signals. It has high ability in analysis of static and dynamic response signals. Staionary wavelet transform (SWT) can show the location of frequency changes. That these locations are the points that they have been damaged. The case study is the concrete curvature arch of KAROON-1 (Shahid Abbaspour) dam with the height of 200 m. This dam is considered as one of the most complex dams because of different external and internal radia and angles, as well as asymmetrical center of the external and internal archs in different levels. Using the geometrical dimensions of the above-mentioned dam- from respective design sheetsand its mechanical and physical properties, the dam with and without crack was modeled by the ABAQUS FE software package. After frequency analysis of the dam by ABAQUS for both safe and cracked models in the same frequency mode, displacement responses at the cracked level (crest) were extracted along the reservoir’s longitudinal axis. Afterwards, the responses were used for the wavelet analysis by the wavelet toolbar of the MATLAB software and the detection of crack in the dam structure was investigated with SWT. The results of wavelet analysis showed that the graphs have considerable rise at or around the crack location. But there was no noise or any harmony in the graphs of the safe dam. Hence, detecting the location of crack in dam structures is possible with wavelet transform.

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The most prominent feature of sheet material forming process is an elastic recovery phenomenon during unloading which leads to springback and side wall curl. Therefore evaluation of springback and side wall curl is mandatory for production of precise products. In this paper, the effects of some parameters such as friction coefficient, sheet thickness, yield strength of sheet and blank-holder force on the springback and side wall curl radius in U-bending of dual phase steel sheets were investigated by performing experimental tests and finite element method. ABAQUS software was used for finite element simulation. Comparison of experimental and finite element results shows good agreement. The results of this research shows that increasing of sheet thickness, reduces springback and side wall curl and increasing of yield strength increases springback and side wall curl. Springback and side wall curl initially increase with raising the friction coefficient and blank-holder force but they decrease again when they go beyond certain values.

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Many flat slab -column frame structures have been built in many parts of the world, since the beginning of the century. The absence of beams makes the form work simple, increase the clear story height, and decreases total building height. However brittle punching failure is a problem that unnecessarily limits the widespread use of flat plates in active earthquake zones. Many slab -column connections in flat plate structures were damaged and failed in punching shear after the 1985 Mexico City earthquake, the 1989 Loma Prieta earthquake, and the 1994 Northridge earthquake. These shows that slab–column connections are prone to punching shear failure when lateral forces, due to earthquake loading, cause substantial unbalanced moments to be transferred from the slab to the column. Slabs with low or medium reinforcement ratios tend to fail in flexure rather than in punching shear. For slabs with reinforcement ratios of 1% and more, the mode of failure tends to be the punching shear type of failure. Fiber-Reinforced Polymers (FRPs) have gained increasing popularity in retrofit of reinforced concrete members in the last two decades. Using FRP materials to enhance slabs in flexure is very desirable from the application point of view due to the ease of handling and installing. FRP material, unlike steel, are not subject to either corrosion or rust in the long term. There is limited amount of research available on srengthening of slab connections. These studies include investigations where the slabs were strengthened using FRP laminates around a central stub column or bonded over the entire width of the slab. with regard to flexural strengthening, externally bonded FRP strips have been used for the strengthening of one way slabs as well as two way slabs. The determination of the structural behavior of FRP–strengthened concrete slabs requires extensive experimental and/or advanced numerical methods. as far as theoretical methods are concerned, Reitman and Yankelevsky have developed a nonlinear finite element grid analysis based on the yield line theory. Other researchers have employed finite element packages to investigate the structural behavior of strengthened slabs with FRP that a full bond between the concrete and the adjacent strengthening FRP materials was assumed. Recently, Binici and Bayrak reported the test results of a strengthening method using carbon fiber reinforced polymers (CFRPs) as shear reinforcement. Previous studies concentrated on enhancing shear capacity of slab-column connections for new construction. Stirrups, bent up bars and shear studs were used as shear reinforcement in previous studies. This study investigates the application of different methods of strengtheing of flat slabs. At first, slabs were model in ABAQUS in order to study the parameters that influences punching shear capacity. Analytical result indicate that increasing concrete compressive strength improves punching shear capacity. Based on this result, steel reinforcement ratios determines the mode of failure. Then, FEM models of slab were strengthend, and type of strengthening, type of FRP materials, number of strip and layer were investigated. The results show that using FRP strip increases punching shear capacity and reduces energy absorption.

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In this study, the use of Ultrasonic Peening Technology (UPT) on the of mill rollers graphite steel (GSH48) for enhancement of some of the surface mechanical properties was surveyed. One of the new technologies for severe plastic deformation is ultrasonic peening technology in which vibratory tool strikes the workpiece surface with continual reciprocating motions, resulting in severe plastic deformation on surface. This method improves mechanical properties like hardness, surface roughness, fatigue life and tension strength. With simulation and manufacturing of peening vibratory tool, preparation of process was accomplished including setting up the ultrasonic vibratory tool on lathe machine. The investigation of hardness tests, surface roughness, fatigue and tension strength on the pieces was performed in different conditions, before and after the process of ultrasonic peening with one, two and three passes. The results showed increase of hardness up to %36 in depth of 0.2 mm. Also, the surface roughness was reduced from Ra=1.376 µm to Ra= 0.545 µm. The most improvement in surface roughness and fatigue life was observed at the pieces with three passes of ultrasonic peening.

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In this study, a non-distractive method of x-ray diffraction (XRD) was used to determine residual stress of rolling mill rolls made of graphite steel (GSH48). This method utilizes the variations of distance between crystal planes as strain. The determination of residual stress was performed samples in different depths before and after conducting ultrasonic peening technology. In UPT process, impacts were exerted on the workpiece ball tool, resulting in the improvement of some mechanical properties such as residual stress by creating work hardening and compression. After the simulation and manufacturing of ultrasonic vibratory tool and then the installation of that on lathe machine, UPT operations were conducted on the prepared samples. Measuring residual stress from surface to 0.5 mm depth was performed before and after the UPT process. After the numerical simulation of the UPT, the distribution of experimental residual stress and numerical simulation was compared that the results suggested the increase of compressive residual stress about 0.4 mm from the surface after the UPT process. The rise of compressive residual stress in the rolling mill rolls leads to the increase of their strength and fatigue life and as a result, their working efficiency is boosted. After the UPT process, the grain size of the surface was calculated from the model of the x-ray diffraction using Viliamson-Hall relation that grain size was obtained 60.2 nm. The refinement of surface structure arises because of displacement arrangement again due to vibration with high frequency and severe plastic deformation after the UPT process.

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Nowadays, the use of polymer-based composites has been growing. Composites due to mechanical, chemical and physical properties are widely used, but the inherent combustion of these materials and the lack of strength at high temperatures, especially when exposed to the fire is one of the challenges of using composites in industries. When composites are exposed to fire, matrix of composite decomposed with heat release, smoke, soot and toxic fumes. Due to the influence of fire on the composite structure, several thermal processes occur such as thermal conductivity in the structure, production and escape of the gases from the composite and resin decomposition. The aim of this study is the investigation of the effects of fire on the composite structures. Analysis of composite resistance to fire, determine the amount and duration of the fire-resistant composite as well as the effects of thermal stress in composite structure requires thermo-mechanical analysis of the composite. ABAQUS software is used for solving the problem in this study. Appropriate model for analyzing the thermal and mechanical parts of the problem according to the governing equations is developed and imported to the Abaqus software through Abaqus subroutines. Thermo-mechanical model validated with the results of valid studies. Finally, this model is used for thermo-mechanical analysis of a composite cylindrical structure exposed to the fire. The results showed that by estimating the failure time of the composite, it is possible to determine the amount of load that can be applied to the structure under different conditions of fire.

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Pipelines are considered as lifelines, because they are used for transportation of different fluids such as natural gas, oil and water, which the human life depends on their existence. The damages to the pipelines are usually associated with human fatalities, financial losses and also environmental pollution. Earthquake wave propagation and permanent ground displacement (PGD) caused by surface faulting are potentially devastating natural events which threaten buried pipelines. Although small regions within the pipeline network are affected by faulting hazards, the rate of the damage is very high since fault movement imposes large deformation on pipelines. On the contrary, the whole of pipeline network is influenced by the wave propagation hazards, but the damage rates is lower which leads to lower pipe breaks and leaks per unit length of the pipe. On the other hand, buried pipelines due to their long length, have to pass through active faults which their large movements may lead to failure and rupture of the buried pipes. It is, therefore, essential to investigate the behavior of buried pipelines against fault displacements in order to mitigate the losses caused by these natural events and to try to keep them in service under various situations. Over the years, many researchers have attempted to analyze pipeline behavior via numerical, analytical an experimental modeling, but most of these works were designed to assess pipe response to strike-slip faulting and some were implemented to recognize the behavior of pipelines under normal faulting with right deformation angles. In the present study, In order to understand the behavior of the pipelines under reverse fault movements, the effects of different geotechnical and geometric conditions on the response of the pipes is examined. Numerical simulations have been conducted using the software ABAQUS based on finite element method. In most of the previous studies, a simplified beam-spring model was used to simulate the behavior of the pipes, but in this study a 3-D continuum model is employed to simulate the behavior of the buried pipes against reverse fault movements. In order to increase the accuracy of the analysis, it is tried to use the elements that best match with reality of the nature of soil and pipe behavior and the interaction between them. The results of the numerical study confirmed that the compressive strains in pipe caused by reverse faulting are larger than the tensile strains, thus compressive strains are considered as the main cause of the failure of the buried pipes in the reverse fault motions. Investigating the pipes behavior in different soil types demonstrated that the buried pipelines in loose and soft soils experience less amount of strain in comparison with those which are bureid in other types of the soils. This is due to the fact that the displacement of the pipeline in loose and soft soils is easier and there are less soil resistance forces against pipe displacement. The assessment of effect of soil dilatation angle illustrated that in large fault displacements, the amounts of pipe strain decline with the reduction of the dilation angle, while changing the modulus of elasticity of the soil has no impact on the response of the pipes. The results also showed that by reducing the burial depth, the level of strain induced in the buried pipes decreases.

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Estimating the pressure required to maintain the tunnel face is one of the most important factors regarding safe and optimal excavation using mechanized tunnel boring machines in urban areas. Applying a pressure more or less than the balance to the face would cause collapse and blow out in the tunnel face respectively. This pressure depends on several factors such as soil type and its engineering specifications, underground water conditions, excavation method, amount of surcharge and tunnel section area. In this paper, the influence of soil elasticity modulus, friction angle and underground water condition on the optimum amount of face pressure in granular soils were studied. For this purpose, a 3D finite element model was used employing the ABAQUS software (Ver. 6.14). The model takes into account relevant components of the construction process as separate components in the model (including: soil and ground water, tunnel lining and tail void grouting). Twenty-four steps have been performed according to the real construction sequences to achieve realistic model’s results. As regards, there are too many parameters involved in mechanized excavation, the geometry of tunnel, lining segments, injection grout and the surrounding soil properties are adapted from the under construction of Tabriz urban railway line 2 project. The tunnel surrounding soil above the ground water level were discretized by 8-node first order fully integrated continuum elements (C3D8). The tunnel lining and TBM shield were simulated by S8 shell elements. The soil under the ground water level and the grout material were modelled as saturated porous media using pore pressure elements (C3D8P). The soil behaviour was assumed to be governed by an elastic perfectly-plastic constitutive relation based on the Mohr–Coulomb criterion with a non-associative flow rule. Tunnel lining and TBM shield were simulated as an elastic behaviour. The ingress of ground water into the tunnel was not considered in this study. The paper gives a detailed description of the model components and the stepwise procedure to simulate the construction process. More than 70 3D models were analyzed and optimum pressure in the tunnel face was determined through measuring the amount of induced average displacement in the tunnel face. For various elasticity modulus, internal friction angle and underground water conditions different values of face pressure were applied in tunnel face and corresponding average tunnel face displacement were measured for each state. Results show that elasticity modulus of soil has a remarkable effect on the amount of the optimized face pressure and for minimize the tunnel face displacement, elasticity modulus should be considered in calculation of the applied face pressure. As the soil elasticity modulus increase the value of optimum face pressure decreases. Also the face pressure was calculated using analytical and experimental methods and the results were compared with the obtained optimum pressure. The results are in good agreement with those obtained from the COB method. In the cases with low elasticity modulus (less than 20 MPa in this study) the COB method obtained face pressures are less than optimal pressure resulted in this study. This difference increase with lowering of ground water level.

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Piles are a common type of foundation, and in the context of offshore energy supply, they are used widely as foundations for wind farms or as anchors for floating facilities for oil and gas production. In both these applications, the pile response under lateral loading is critical, although the latter application is more capacity sensitive whereas the former is deformation sensitive. All piles are under small or large lateral loads and the behavior of the piles under the lateral load must be controlled, but for most of the time. The lateral load can cause a spacing between the pile and the surrounding soil in the upper layers. If such a situation happens, it cannot be assured for the vertical load bearing capacity in the upper layers. Usually, the effect of lateral loads on the design and construction of the pile is ignored due to its small size versus vertical load, but in some cases, the analysis of the pile is necessary under lateral loads and should be considered using the appropriate methods. The piles used in the base of bridges, wind turbines, piers, etc. are subjected to relatively large lateral loads, and in the pile design of these structures, the lateral effect is dominated. One of the ways to increase the lateral load bearing capacity is to use the technique of fin piles, which is a relatively new method. Fin piles are one type of piles that have four or more metal sheets that are welded at different angles to the pile environment. The behavior of fin piles is difficult to explain using simple pile–soil theories or two dimensional numerical analyses because of the complicated geometry of the piles. Due to the progress of numerical methods and the use of three-dimensional software, numerical modeling of the pile and soil environment is possible more precisely. A fundamental study of soil response of piles subjected to static lateral loads in sand is conducted using the non-linear finite element approach. The effects of pile properties, i.e., length and diameter, and the effect of fins i.e., fin length and fin width on the pile response of a pile subjected to lateral loads are also investigated. In this research, the behavior of singular fin piles under lateral loading in sandy soil is modeled using 3D finite element software (ABAQUS) The ABAQUS program is a robust engineering simulation program that, based on finite element method. Abaqus is capable of solving various problems from simple to complex nonlinear problems. With a large library of materials and elements, the program is capable of modeling materials such as metals, rubber, polymer, composites, concrete, soil and rock. In addition to solving structural problems, the ABAQUS program is able to solve complex heat transfer problems, thermal-electrical analysis, and soil mechanics problems. In this research, the performance of finned piles with respect to ordinary piles has been compared. The results show that the use of fins causes an appreciable increase in the bearing capacity of the piles compared to ordinary piles without fins.

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Heeled concrete walls (T-Wall) are used for privacy, protection and some form of blockage. These walls can be built precast or cast in place and can be designed according to the possible loads such as blast loads, earthquakes, winds and so on. Also, the use of fiber concrete to absorb more energy and durability can be a good solution in the construction of such walls. Resistance, stability, and possibility of overturning of these walls due to the blast load and depth of buried walls are those that should be controlled by the designer. In addition to all the controls mentioned, one of the important issues is to optimize the cost of construction and consumables, so comparing reinforced concrete use with fiber reinforced concrete is of interest. In this study, six types of walls are considered: Type 1 and 2 walls with 3 m height and 2.5 m width, Type 3 and 4 walls with 4 m height and 2 m width and Type 5 and 6 walls with 5 m height and are 1.6 meters wide. Which, the walls of Type 5 and 6 are non-prismatic and are one meter buried in soil. In addition, type 1, 3 and 5 walls are made of fiber reinforced concrete and type 2, 4 and 6 walls are reinforced concrete. The purpose of this study is to investigate the resistance of concrete prefabricated walls against the impact and explosion. During an explosion, there is an explosive wave that spreads from the center of the explosion. Waves spreading at a later time are much faster than the speed of the initial waves. When a structure is exposed to the wave front, its surface pressure rises and reaches its maximum value in a very short time. This pressure affects the structure on all sides rapidly. This wave is a combination of high-pressure shock that emits outward from the center of the explosion and decreases as a function of the time and place of the explosion. The energy released by the explosion affects the structure in two ways. The first effect is the blast pressure, which is the key factor in determining the structural response, and the second effect is the dynamic pressure or the secondary pressure, which at high speed results in the debris being thrown around. Therefore, the most important parameter of an explosion is the forward blast pressure, the amount of which depends on the type of explosive and the weight of explosion. Hence, in order to find the above parameters, the 6 types of discussed wall modeled in Abacus software by CDP method. Also, the earthquake loading with different acceleration is applied to the walls and lateral displacements of them are calculated by using linear time history analysis with SAP2000 software. Finally, the performance level of walls under loads has been evaluated according to the national building earthquake loading criteria and 21th national building regulations. The results of the present study show that; the use of fibers has a positive effect on improving the performance level of prefabricated walls against dynamic loads such as explosion and earthquake.

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In this study, we aimed to design and make an electric forage chopper having a cylinder type cutterhead. In recent years, several models of forage chopper have been manufactured but each of these machines has had problems such as type of power supply system, type of cutting mechanism and feeding mechanism, lack of safety, etc. These problems were solved in this study. In the device that was manufactured in this research, feed rolls rotational speed, rotational speed of the cutting cylinder, blades’ helix angle and blades’ rake angle was adjustable. So, with these capabilities, these variables can be optimized for any kind of forage, and this information can be used to design and construct suitable machines for crushing any kind of forage. Alfalfa was used to test the machine, where its test matrix was determined using Response Surface Methodology (RSM) modeling method. The results showed that, on average, power requirements for chopping alfalfa was decreased from 12.6 to 9.7% by increasing the helix angle from 0° to 10° and from 10° to 20°, respectively. As rotational speed of the cutting cylinder increases from 500 to 800 rpm, the power used for chopping forage increases by about 56 W. In the conducted tests, maximum power requirements for chopping alfalfa was roughly equal to 200W, which was associated with 158.5 rpm feed rolls rotational speed, 800 rpm rotational speed of the cutting cylinder, and helix angle of zero. Contrarily, minimum power requirements for chopping alfalfa was 114W which was related to 158.5 rpm feed rolls rotational speed, 500 rpm rotational speed of the cutting cylinder, and 20º helix angle. Optimizing test results showed that the most suitable values for the feed rolls rotational speed, rotational speed of the cutting cylinder, and helix angle were 150 rpm, 677 rpm, and 9.22º, respectively, provided that power requirements and particle size are minimized and device capacity is maximized.
 

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Thin-walled cylindrical steel silos are one of the major storage structures in most of industrial and agricultural sectors. There are different load cases that should be considered in design of silos, such as, filling and discharge loads, wind load, seismic load and thermal loads. Nevertheless, during the life cycle of a silo, filling and discharge of particulate solids exert the most frequent loads on the silo walls. Due to larger values of discharge pressures as compared with those of filling pressures, discharge loads are considered for structural design of silos. Considering small wall thickness of steel silos, they are susceptible to buckling failure. Under discharge pressures, high meridional (axial) compression and internal pressure form at the base of silos that can lead to elastic-plastic elephant’s foot buckling mode. Therefore, it is deemed as the main buckling failure mode under discharge loads of silos. 
The wall friction coefficient of silos mainly depends on the wall surface characteristic and type of the ensiled material. This coefficient is a key variable in determination of magnitude and distribution of discharge pressures. To assess the effect of this variable on buckling capacity of steel silos, three example silos with different aspect ratios were considered. Each silo was loaded by the concentric discharge pressures in accordance to Eurocode. Subsequently, 3D linear and non-linear buckling analyses (i.e., LBA and GMNA analyses, respectively) were performed for different amounts of wall friction coefficient that varied between 0.2 and 0.6.  
Considering the results obtained, LBA analyses predicted an elastic axial compression buckling mode in the upper edge of base strake, where there is a change in shell wall thickness. Also, an elastic-plastic elephant’s foot buckling mode at the base strake of each silo was predicted by the GMNA analyses. Moreover, the load-path curves of example silos extracted from the GMNA analyses showed a bifurcation buckling that was followed by a dramatic reduction in post-buckling resistance. This held true for all three silos and all different values of wall friction coefficient considered in this study. 
The discharge buckling resistances estimated by the LBA were up to three times larger than those predicted by the GMNA. Therefore, including non-linearity in discharge buckling assessment of silos is urgently required. The effect of wall friction coefficient on buckling capacities of steel silos was significant for the LBA analyses that governed by axial compression. However, the elephant’s foot buckling mode observed under discharge load is affected by the both axial and internal pressures. As a result, adopting more sophisticated analyzing procedure that includes geometrically and materially non-linearity in the calculations (i.e., GMNA analyses) showed quite marginal effects for this coefficient (with the maximum difference of 8% in buckling capacity). 
As an extra investigation, the Eurocode provisions on stress design of steel silos under meridional compression with coexistent of internal pressure have also been examined. Eurocode recommends a reduction in critical axial buckling stress due to accompanying internal pressure, in terms of the plastic pressurised imperfection reduction factor αpp. As compared with the finite element results, for all the cases considered in this paper, the critical axial membrane stress calculated with respect to the Eurocode provisions yielded satisfactory predictions. 

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Today, the use of metallic bipolar plates in the fuel cell industry has attracted the attention of many researchers due to its much lower cost than thick graphite plates produced by machining. The best method for the production of metallic bipolar plates is forming process. Among the different forming methods, the stamping process has a higher production rate, simpler process, and lower production cost. One of the major problems in the formation of the metallic bipolar plates is the springback of the sheet after forming, which causes distortion and non-uniformity in the formed channels. In this study, the effects of geometrical parameters such as draft angle, corner radius, depth of channel and process parameter such as lubricant on filling profile as well as springback of formed sheet made of stainless steel 304 with a thickness of 0.1 mm were investigated. For this purpose, the simulation was performed using ABAQUS finite element software and the results were verified by experimental analysis. Then the outputs were evaluated by changing the input parameters in the simulation. The results showed that the draft angle and channel width had the most influence on the springback value of the formed plates. The results related to the process parameter such as the lubricant effect showed that the springback value is almost independent of the lubricant parameter. However, in quite equal conditions, the stress distribution in the corners and channel walls is much more uniform when using the lubricant.
 

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Abstract: Although fossil fuel resources are declining, their use also pollutes the environment. Also, due to the increase in the average wind speed in the world, the use of wind turbines, which are classified in structures with new and renewable energy, will be very cost-effective. Wind turbine towers can be made of concrete, steel, conical, lattice, wood, or multi material. Given that the investment cost to build a wind farm and connect it to the transmission network is 75 to 85 percent, and the cost of building the structure is 15 to 25 percent of the total cost. Steel lattice towers can reduce the cost of building a wind turbine structure by 30 percent and therefore, a complete and correct model for analyzing these types of structures will be very important and economically noteworthy. Wind turbine lattice towers are usually made and executed with bolt connections. In this case, the number of bolts is very high, which increases the need for cyclical and reciprocal loads. Joint slip in these structures refers to the relative displacement of bolt connection under the influence of force. Therefore, creating a joint slip will be inevitable due to the ease and speed of execution in which the bolt hole is made of a larger bolt diameter. Joint slip increase the displacement of lattice towers So much so that the maximum displacement of the tower is twice as high as that of static methods. And not considering it will destroy the tower and assuming the reliability factor will make it uneconomical. In this type of structure, the tower is often made of angle and single angles are used in cross members and bracing and double angles are mostly used in the bases of lattice towers. With this explanation, in this study, the force curve of the displacement of the of three samples with single angle section in the laboratory and four samples with double angle section in Abaqus software was modeled and were affected by reciprocating loads and then the results of numerical modeling were validated with laboratory samples. In the models modeled in the software, after sensitivity analysis, the type and size of the mesh is precisely minimized the resulting error. In this investigation available data in joint slip develops bolt connections which include angles with equal leg. It offers force-displacement curve of different connections for double angles and their connections damping ratio are calculated likewise and the effectiveness of each variable on the slip of the node is expressed in double angles. The results show that joint slip occurs during service loads and this effect depends on the number of bolt, the diameter of the bolt, the bolt cross-sectional area, the thickness of the angle and the effective cross-sectional area among these, screw diameter is the most important variable for predicting joint behavior. Also, the viscosity damping ratio for single and double angle connections is almost equal and can be assumed to be 42.5. This ratio increases with increasing number and decreasing bolt diameter. This investigation is beneficial for designing wind turbine lattice towers and in it, provides structure behavior to the designer more accurately.

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Today, the use of different kinds of polymer, as the modifier of some repair mortars properties, is growing. Given the damages to concrete structures, it is necessary to use appropriate repair layers. In concrete structures, concrete and steel are connected, and in most cases, repair layers are applied in direct connections with steel. Therefore, in this research, the shear and tensile bond strength between steel and styrene-butadiene rubber polymer modified mortars was measured using semi-destructive friction-transfer and pull-off tests. In the "pull-off" test, to determine the bond between the mortar and the steel, a core with a 50mm diameter and is first mounted on the test surface using a diamond drill bit and a metal cylinder with a diameter of 50 mm and a thickness of 20 mm is attached to the partial core. Then, the tensile force is applied to the cylinder by means of a "pull-off" device to make the partial core fail. To measure adhesion with friction transfer method, first a small core was created from the mortar surface to the steel substrate surface using the coring machine. Thereafter, the friction transfer metal device was fixed onto the core and the torsional moment was applied using a typical torque wrench in order to cause failure in the core. Moreover, the effect of polymer on the shrinkage of mortar was evaluated. Shrinkage is one of the important problems that negatively affects the adhesion of repair mortar and steel. Due to the fact that hydrated cement paste has capillary pores that contain some water, shrinkage occurs after this moisture leaves the pores. The effect of polymer on mortars was investigated by taking images with a scanning electron microscope and using the “Image-J” and “Origin” software programs. Afterward, in order to evaluate the mechanical properties of mortars, the in-situ compressive and flexural strengths of the mortars were determined, and the calibration curves were plotted by comparing them with standard laboratory tests. Then, relationships were proposed to convert the results of in-situ tests to the compressive and flexural strength of the polymer modified mortars. Eventually, the cracks and stresses that appeared in the mortars were provided using ABAQUS software. The obtained results indicated the effect of polymer in reducing the shrinkage of mortars and increasing the shear and tensile bond strength between steel and mortar, along with a high correlation coefficient between the measurements in the in-situ and laboratory tests. Comparing the modified mortars with polymer and ordinary mortar, it is observed that at the age of 90 days, adding 10, 15 and 20% of SBR reduced the amount of shrinkage to 35.3%, 4.2% and 45.4%, respectively. Addition of styrene butadiene rubber to the repair mortar increased the shear bond strength obtained from the "friction transfer" test between the mortar and steel at the ages of 7, 42 and 90 days by 44.4, 178.2 and 303.1%, respectively. Adding SBR to the repair mortar increased the tensile strength of the "pull-off" test between the mortar and the steel at the ages of 7, 42 and 90 days by 58.7, 183.4 and 291.2%, respectively. A good agreement was also observed between the numerical and experimental results.

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