جستجوی مقالات مرتبط با کلیدواژه "المان محدود" در نشریات گروه "عمران"

Retaining structure or retaining wall is a wall that acts as supporting structure and the stability of another structure. This wall is used for preventing collapse of soil and generally wherever lateral support is needed. The retaining wall can be designed as gravity, cantilever and supported. Considering that the retaining walls are essential in protecting the related structures to them, therefore, studying the dynamic behavior of these structures is very important due to the financial and human damages. Such structures should be stable against the forces acting on the wall. In addition to static loads, which are always an inseparable part of the calculations of such walls, forces such as cyclic forces caused by the movement of machinery and also dynamic forces caused by earthquake occur on the wall during the period of operation. These forces can be effected on retaining walls and should be investigated and evaluated. Trying to investigate and analyze the dynamic behavior of different retaining walls is one of the most challenging for different researchers. The wavelet theory in the dynamic analysis of the issues related to civil engineering is going to be widespread. This research aims to investigate the effect of using wavelet theory in the dynamic analyses of concrete retaining walls. For this purpose, a soil medium along with concrete retaining walls with different dimensions (heights) are considered. Dynamic analyses are performed based on the finite element method. In the first stage of modeling, the Sarpol-e Zahab earthquake record is filtered during four steps using the discrete wavelet theory. The numerical models are prepared and subjected to the available records. The percentage of the difference in the results of the analyses done with the records obtained from the different steps of filtering record with wavelet compared to the analyses done with the main record, along with the reduction of the time consumption, is evaluated. As expected, the best match of the post-filtering results to the main earthquake results is for the first-step filter. It can be seen that even the first step filter reduces the analysis time by about 60%. Based on the obtained results, the difference between the results obtained with the filtered records becomes less compared to the main earthquake with the increase in the height of the wall. It has also been observed that acceptable results are still obtained, and the analysis time is reduced by almost 80% until the third step filter. It should be noted that the Mohr-Coulomb behavioral model is used in the conducted analyzes in this research. This behavioral model is not inherently able to model hysteresis damping behavior at low strains. Therefore, this issue can affect the results of deformations and stresses obtained from dynamic analysis. However, the purpose of this research is to evaluate the performance of the wavelet in the dynamic analysis of the retaining wall. Considering that in all the analyses (both the performed analysis with the main earthquake and the performed analyzes with the wavelet filtered records) the same structure and trend are used, it can be concluded that the effect of using the wavelet compared to the main earthquake gives an acceptable overview and quality

With the development of new engineering materials, such as shape memory alloys, their use in civil engineering applications has increased greatly. Thus, in the present study, the mechanical behavior of yielding metal dampers made from shape memory alloys in steel frames is investigated numerically. For the purposes of evaluating the seismic performance of the proposed new system, a nonlinear static analysis has been conducted using the ABAQUS software. Using Brinson's behavioral model with considering the phase transformations, as well as the Drucker-Prager failure criteria, we were able to simulate the superelastic behavior of shaped memory alloy materials, both of which were implemented in ABAQUS with the UMAT subroutine. We have continued this investigation by studying the effect of geometric variables on the performance of the system as well as the stiffness, ductility, and energy absorption capacity of the different specimens. The damper that we propose is capable of providing high energy absorption and can be easily replaced by other flowing metal dampers such as TADAS and ADAS. The proposed system shows a significant improvement in terms of ductility and energy absorption as compared to the braced frame with a corresponding steel damper, which can be used in various engineering applications.

Blast load is a load with a dynamic nature similar to an earthquake, with the difference that its effects take much less time than an earthquake, are more intense, and directly affect the structure itself. Therefore, in this case, in addition to carrying out the usual retrofitting, it is necessary to reduce this explosive effect by changing the architecture of the structure. One of the solutions for this problem is the dual-purpose use of seismic elements such as shear walls, which can not only resist earthquakes but also resist explosive loads. Meanwhile, concrete structures have shown good resistance to explosion compared to steel structures, and one of the design methods in these types of structures is the use of concrete shear walls. One of the solutions to reduce the dimensions of the columns is to use a concrete shear wall. One of the capabilities of this method is the possibility of creating an opening in it, and it reduces the limitations created in the architectural discussion. In this research, the performance of arched concrete shear wall with opening against explosive load has been investigated, and the considered samples with and without opening have been compared. Also, the effect of compressive strength of concrete has been investigated. Finally, it was determined that when creating the opening, full care and inspection should be done and the area around the opening should be reinforced. Arched concrete shear wall with 10 cm thick opening has performed best against explosive load.

In mechanics of rock fracture and comminution, researchers have always been looking for a relationship between the consumed energy and the particle size distribution of the disintegrated rock specimen. This relationship has important industrial applications considering the fact that comminution of rock is a very energy demanding process and its efficiency is very low. Furthermore, investigating the damage evolution of rock under different loading rates, helps to better understand and more accurately design rock structures such as tunnels, rock slopes and foundations subjected to dynamic loading. In this work, a hybrid finite-discrete element numerical model was used to simulate rock disintegration under different loading rates in the Split Hopkinson Pressure Bar (SHPB) system. The rock and the steel bars in the SHPB apparatus were simulated by the Bonded Particle Model (BPM) and finite element model, respectively. BPM is a simplified version of the discrete element method in which the discrete particles are spherical in shape. Spherical particles or balls in the BPM are very useful in reducing the computational time; the contact detection of the spherical particles is computationally very fast. The computer program CA3, which is a 3D code for static, dynamic and nonlinear simulation of geomaterials was used for the numerical analysis. To capture the rate dependent behavior of rock, a micromechanical model was utilized in which the bond strength at a contact point increases as a function of relative velocity of involved particles. The numerical model was calibrated to mimic the mechanical behavior of Masjed Soleyman sandstone. To facilitate and expedite the calibration process of the BPM system, the curves and dimensionless parameters introduced in the literature were used. Input pulses with different intensities were applied to the specimen in the numerical modeling of the SHPB system. The input energy and the energy consumed to disintegrate the numerical rock specimen were evaluated by the numerical integration. Different particle sizes in the BPM system were used to investigate the impact of combined particle size and input energy on the rock disintegration. The results suggest that the energy consumption density for rock crushing changes linearly with the stress rate. Furthermore, it is shown that the dynamic strength of the rock increases with the increase in the consumed energy density. The disintegrated numerical specimen was carefully inspected and its particle size distribution was obtained. This was achieved by using a searching algorithm to identify the clusters in the damaged specimen; each cluster was made of one or several spherical particles. The volume of each cluster was calculated by finding the volume of its constituent particles and the porosity of the specimen. This volume was used to obtain the equivalent radius of the cluster; the cluster shape was imagined as a sphere to identify the equivalent particle or cluster size. The mean particle size (D50) of the damaged numerical specimen shows a linear relationship with the stress rate in a logarithmic coordinate system, which is consistent with the physical test results reported in the literature.

Large number of road crashes and their consequences has made road safety a worldwide challenge. Behind any traffic conflict indicators are assumptions which takes them away from statistical analysis of real road crashes. We conducted road crash simulation using finite element methods and analysis them to asses safety. To high accurate scrutiny crashes, finite element is used. By running crash finite element models in Ls-Dyna simulation is ran based on angles and relative velocities in different states (area stucked in crash). In other words multy body elasto-plastic dynamic finite element model is simulated. By analyzing vehicle sets before and after crash and by means of kinetic energy law, dissipated energy is calculated. Dissipated energy reveals as transformation in area stucked in crash. Therefore for each crash scenario dissipated crash energy is calculated and graph for each one is derived. Different mode of material is assessed and reflected in crash analysis. So by energy absorbtion crash severity is predicted.

Calculating the ultimate bearing capacity of a foundation by limit analysis allows determining the exact upper bound of bearing capacity of the foundation. In the present study, the cohesion coefficient (Nc) of a strip foundation on a single layer of soil overlaying bedrock was calculated. For this purpose, the upper bound of limit analysis combined with finite element method (FEM) was used. The soil behavior was assumed to be plastic and the Mohr-Coulomb failure criterion was used which allows description of soil mass by two parameters of cohesion and internal friction angle. It was assumed that the soil cohesion is not constant with depth and rather increases linearly. Finally, the bearing capacity was obtained using an optimized procedure (i.e., linear programming). In this regard, the Mohr-Coulomb criterion should be linearized in a stress condition. The cohesion depends on different parameters such as friction angle (φ), the ratio of soil depth to foundation width (b/h), and the cohesion variation with depth (ρ). To validate the results, obtained constant cohesion values were compared with those obtained by other researchers. The effect of the parameters on N_c was separately plotted and the calculated design charts were discussed.

Solving the problem with the meshless method is based on selecting a series of points from inside the computational area and boundaries without meshing. In the present study, the phenomenon of seepage below the dam under steady and unsteady flow conditions has been investigated by combining the Meshless method and the Finite Difference Method. Problem solving and calibrating operations were done by coding in MATLAB software. The Meshless method was used for spatial sentences and the Finite Difference Method was used for the discretization of temporal sentences. The results showed that the shape factor (α) for low points is 0.85 and for high points is 0.52, which indicates the proximity of the initial approximations to the main answer. Considering that, the shape factor depends on the geometry and the governing equation, so the same shape factor was obtained for the steady and unsteady conditions equal to 0.52. In the unsteady condition, with the water level behind the dam remaining constant, the water head below the dam also reaches a constant value over time. Also, examination of the results showed that in numerical problem solving, a low error is not a criterion and among the various basic functions, only the MQ function has the better hydraulic performance to draw equipotential lines, so that for 133 points, the shape factor and root mean square error index are 0.52 and 0.0108, respectively.

Due to the great importance of traditional structures and masonry materials and their high application, the effective parameters in the load-bearing capacity of these structural forms should be examined. In order to study the behaviour of building materials in traditional buildings and structures, due to the high cost and time-consuming laboratory studies, it is necessary to use software methods with accurate failure criteria. To achieve more acceptable and realistic results in the analysis of brick masonry structures, the Willam-Warnke fracture criterion, which is specific to brittle materials, is generally used. In this paper, the aim is to obtain the Willam-Warnke fracture criterion parameters for the combination of brick and mortar materials in macro modelling. For this purpose, with the help of laboratory studies on the combined materials of brick and mortar, the mechanical properties of these materials have been obtained. Finally, in order to validate the obtained parameters, these parameters were included in the numerical modelling of a semi-circular arch of building materials and compared with laboratory results. The results show that the developed parameters of Willam-Warnke fracture criterion predict the behaviour of building materials with a maximum error of about ten percent and a suitable and acceptable agreement is observed between the results of the analytical and laboratory model.

There are many different methods to modify the mechanical properties of saturated clayey soils. It may be chosen depending of location and function of the structure. among those methods, preloading in presence of vertical drains and installation of stone columns are similar together and it is the cause of comparison. In this thesis, each mechanism of modification of soil was studied lonely and then the results of every method were compared with all together. Subsequently the mentioned approaches were graded technicaly. For this reason, a two dimentional finite element software was used to make the models. It should be necessary to forcast the results of choosing one approach, because there is no proper procedure available for engineers to choose one of these method as the first index, and also the long time that must be spent for in situ consolidation.the results show that the finite element program has the ability of simulating the consolidation phenomena in saturated clayey soils and declare that installation of stone columns is better than preloading by installation of vertical drains. Of course, there are many parameters influences the selection of superiority.

Piled raft foundations are an effective and economical system in case of high-rise buildings and are a suitable alternative to conventional deep foundations. In this type of foundation, raft is in direct contact with the soil and hence it carries a significant portion of load. Regarding to the design of piled raft foundation, one of the uncertain issues is to determine the proportion of load sharing of the raft and piles. In this paper, Finite element analyses were carried out by developing three-dimensional models in ABAQUSE and with considering interaction effects for a piled raft foundation, the effective factors and their impact on load percentage carried by raft are investigated. In addition, a new equation for determining the load percentage carried by cap in granular soil is proposed for a group of piles for an alignment of less than 9×9 piles. The developed model is validated with available experimental results. The results of numerical analysis show that the distance of the piles from each other, the diameter of the piles, the internal friction angle of the soil and the number of piles in the pile group are among the most important and effective parameters in determining the load percentage carried by cap. In the current study, from the numerical analysis, it has been concluded that, the load percentage carried by cap, is 15% to 42%.

Graphic Statics is a visual analysis and calculation method to find the type and amount of internal forces in structures, which achieves this importance away from computational difficulties and only with a geometric approach focused on two reciprocal diagrams of form and force. In this paper, arched trusses based on Warren type are analyzed using graphic statics. For this purpose, the parametric model of form and force diagrams were programmed in the Grasshopper parametric plugin. Parametrization has also provided the ability to find and analyze any different types of free-form trusses based on the type of warren truss. To measure the validity of the method and the accuracy of the algorithm written in the Grasshopper add-on, the numerical results obtained from several samples of arched trusses under different loads have been compared with the finite element computational method. The results of the validation simulations indicate the high accuracy and speed of the proposed algorithm.

Inevitably, vibrations induced by vehicles passing over bumps and surface irregularities affect adjacent buildings. High-amplitude vibrations can be damaging to monumental and historic buildings. The passage of heavy vehicles on irregular road pavement surfaces generates dynamic loads that are transmitted to the buildings through the surrounding soils and cause them to vibrate. To address the aforementioned challenge, herein, a 2.5-dimensional numerical model was developed to investigate the effect of open-trenches with different depths on the amplitude of vibrations. For this purpose, initially, the axial load caused by a truck hurtling over a speed bump was simulated in MATLAB program. Then, a finite element model of the road and its surroundings was developed to evaluate the vibrations. The model was then validated by the results from Lambert field measurements. To evaluate the effect of trench depth, the particle velocity and the frequency content of vibrations at different points were investigated. Numerical analysis indicates that greater trench depth leads to more reduction in the vibrations’ amplitude and a decline in the amplitude of the dominant vibration frequency.

Recently, most underground structures are mechanized using excavation shields. Moreover, one of the major challenges in underground structures is the ground deformation. So, the analysis of this mechanism is necessary for safety purposes and project design. One of the effective parameters in the ground displacement is the geometry of the excavation shield. Since the pipes are connected to the excavation shield, the initial stress relaxation and displacement are not allowed. In this regard, having a cone excavation shield can solve this problem. In this research the effect of excavation shield conicality on the ground is investigated. The Plaxis finite element software is utilized for numerical modeling. Moreover, in order to validation, the results are verified with the field data and analytical analysis. Furthermore, the effect of stress on the pipeline is also investigated in this research. Finally, it is found that the relationship between conical excavation shield and ground surface displacement is linear. The load on the pipeline almost doubles with increasing the percentage of conicality of the shield from 0.3% to 0.9%. One of the most important applications of this research is the possibility of controlling the ground movement with respect to the effective parameters.

In design of hydraulic structures cutoff walls are needed for reduction of uplift force and exit hydraulic gradient. Upstream cutoff wall is used for reduction of the uplift force and downstream cutoff wall is used for reduction of the exit hydraulic gradient. This study tends to numerically investigate the double-cutoff beneath the hydraulic structures with variation in their location, distance and depth. Governing equations with boundary conditions are solved using the finite element method (FEM). Results showed that if the downstream cutoff wall is deeper than upstream cutoff wall, the resultant of uplift force would be more than the uplift force without cutoff walls. With a constant value for hydraulic structures width (B), decreasing in distance between two cutoffs (L), results the reduction in uplift force. Increasing in impermeable depth (D) and reduction in B, yields lower uplift force. Increasing in downstream cutoff depth (d2) and L, results reduction in exit hydraulic gradient (GR). When the two cutoffs are located in the end of the hydraulic structure, GR is lower than that when the downstream cutoff is located in L/B=0.33 and L/B=0.66 from upstream cutoff. Comparison between the available analytical solutions for two equal ending cutoffs with FEM, showed that FEM can predict PC and GR with maximum 5% error.

The present study investigates the effects of material mechanical properties and plate slenderness ratios on the nonlinear and cyclic behavior characteristics of metal shear panels (including carbon steel (CS), low yield point steel (LYP160) and aluminium (AL)), using the finite element method. The plates are first qualitatively and quantitatively classified into the five groups of very slender, slender, moderate, stocky and very stocky, regarding their slenderness ratios. Very slender plates have negligible buckling capacity and thus, they buckle at the initial stages of loading. Slender plates buckle in the elastic range of behavior. Moderate plates buckle in the inelastic range of stresses before material yielding occurs in the plates. Stocky plates buckle in the plastic (post-yield) range of stresses. The behavior of very stocky plates is only dominated by yielding phenomenon and they do not buckle during loading. Based on the statistical analysis of results, new relationships for estimation of inelastic and plastic buckling loads are also proposed. The cyclic analysis results show that the energy dissipation capability of very stocky/stocky/moderate plates is solely dependent on the material yield stress and elastic modulus of elasticity, whereas for the slender plates, the effectiveness of material yield stress in the energy dissipation of plates is decreased and the role of the material elastic modulus of elasticity becomes more important. In the case of very slender shear plates, the energy dissipation capability seems to be dependent on the initial and secondary modulus of material only.

Structural applications of composite materials in various structures such as oil and gas industries, water supply systems, marine industries, aerospace and military industries are included. Especially in structures where a high ratio of strength to weight is important, these applications are increasing, a common example of which is cylindrical composite tanks. External loads may enter the tanks by means of compression tools such as falling objects or colliding with machines, etc. These loads may cause serious and sudden damage to the tanks. For this reason, it is very important to study the effect of such forces. This paper is the result of a laboratory study in which four samples of GFRP tanks with an inner diameter of 800 and 400 mm and a thickness of 4 mm were tested and examined under a dental load. Also, for numerical simulation of the tests performed, Abacus software was used and the load-displacement diagrams obtained from the experiment with finite element results were examined and analyzed, which shows the appropriate estimate of finite element analysis. The experimental results showed that reducing the sample length has a significant effect on increasing the bearing capacity and also the results obtained in vitro are in good agreement with the numerical simulation results.

Regarding Iran's need to increase its current oilfields production, especially in the South Pars field and decommissioning new fields, it is a necessity to fully understand and comprehend the Floatover installation method as a cost-effective and reliable method and as an alternative for traditional lifting method. This method is complex and demands the study of all environmental parameters and elements involved. All of these parameters contain uncertainty. This study examines the environmental uncertainties and uncertainty in steel by comparing leg mating units and using Taguchi design and response surface methods. A model including a jacket, topside, and a barge with 6 degrees of freedom was developed to assess hydrodynamic analysis in the Persian Gulf. Then, using the Taguchi design and the Box-Behnken method, and by monitoring the maximum Von Mises stress, the explicit limit state function was generated. This stress was calculated using a finite element model that represents impacts and interactions. By creating two limit state functions, a reliability analysis was performed. In these functions, the effect of environmental parameters on the failure of the leg mating units was investigated.  Finally, the effect of environmental uncertainties and the yielding stress of steel in the Floatover method were evaluated using FORM and SORM methods and Monte Carlo simulation. It was concluded that uncertainties in steel and some of the environmental parameters have a significant impact on failure.

Developing transportation system in populated cities needs to construct subsurface infrastructures, such as tunnels. With a close attention to densely surface structured urban environments, it is most likely that tunnels would inevitably cross near of adjacent structures. It should be considered, whether the settlement induced by tunneling are in allowable range or not. Several factors may affect the magnitude of ground movement due to tunneling and consequently the tunnel- structure interaction, such as ground geotechnical properties, adjacent structure stiffness and relative position of structures and tunnels, and tunnel construction parameters.When pile foundations are exposed to intense dynamic transverse loads during earthquakes, soil- structure interaction (SSI) plays an important role in allocating the response of pile foundations to lateral excitation. The numerical investigation with analysis subway tunnels and deep foundation interaction behavior under seismic loads by the finite element method was carried out.

These types of structures are very disposed to instability, which can limit the amount of load that can be tolerated and deformed structures, and play a fundamental role in designing structures whose loads borne by their members are mainly axial-compressive or axial-tensile. So it is important to study the stability of these structures to determine the maximum load-bearing capacity of the structure, to find the optimal geometric shape, the stiffness of the structure and collapse behavior under different loading conditions. Under different loading conditions, dome-shaped space structures exhibit various modes of instability, including member instability, nodal instability, member length instability, and general instability. Considering this type of instability, in this study, the dome-shaped space structure of the tomb of Sheikh Safi al-Din Ardabili with the special form of the dome, which has been obtained by parametric study, have been investigated. These are done by collapse analysis and the use of finite element methods. Factors such as early geometric imperfections, balanced snow load pattern in nodes, unbalanced snow load pattern in two orthogonal directions, taking into account three different height to span ratios, two lengths to width ratios of the dome and yield stress are considered In the stability behavior of the single-layer space structure of Canopy the tomb of Sheikh Safi al-Din Ardabili. The results show that the height to span ratio is an influential factor in this type of structure and with increasing this ratio, weight, the initial hardness and load capacity (for design with the same sections for all structures) increases; also the structural form of the single-layer dome-shaped space structure of the tomb of Sheikh Safi al-Din Ardabili, with its special form, is very uneconomical and inefficient, and is not recommended for structural designs and has only a beautiful aspect.

Accurate prediction of pore water pressure, settlement, soil stress and pore water pressure coefficient (Ru) in the body of earth dams during construction is one of the necessary measures in the management of earth dam stability. In the present study, which is a case study, a three-dimensional numerical simulation was performed using the Plaxis software for the Kabudval Dam located in Golestan province, Iran. The values obtained from the numerical simulation were compared with the corresponding measured values using the dam instruments. Calibration was carried out using back analysis method (BAM) and some dam geotechnical parameters were corrected based on BAM. The results showed that the hardening soil (HS) model with the statistical indicators of R2, RMSE and GMER is more accurate compared with the Mohr- Coulomb (MC) model. The results of the numerical model were calibrated at the end of construction for Kabudval Dam and showed that the maximum increase in pore water pressure, stress, settlement and horizontal displacement occurs in the central part and its value in the axis and middle part of the dam is more than its sides. The middle part and close to the dam axis have similar changes with the fill process of the dam body; while with moving away from the dam axis due to the transfer of stresses to the sides, they have less impact from the dam filling process. In addition, in the central part, the effects of filter and drainage is low.