Numerical Methods in Civil Engineering
https://nmce.kntu.ac.ir/
Numerical Methods in Civil Engineeringendaily1Thu, 01 Jun 2023 00:00:00 +0430Thu, 01 Jun 2023 00:00:00 +0430Optimization of time and temperature of dam construction for thermal analysis of roller compacted concrete dam
https://nmce.kntu.ac.ir/article_169194.html
The growing number of roller compacted concrete dams built around the world demand good methods to reduce the risk of thermal cracks. In roller compacted concrete dams, usually, large amounts of concrete are poured in a short time and the heat generated by the hydration of the cement, leads to an increase in temperature in the body of the dam, which results in a significant heat slope. In this research, Abaqus software, a finite element software, was used for thermal analysis of the dam during construction and concreting. The method of applying thermal changes is as follows. For the structure, hypothetical 50 cm layers are considered, each layer takes up 72 hours of analysis time. In general, the problem under analysis is analyzed 12 times. Each analysis is based on the start of the project from different months of the year to achieve the optimal constructing time based on the maximum temperature in the concrete of the dam and the stresses created by it by collecting the information and using the perceptron network algorithm. Perceptron algorithm and machine learning were performed on the 12 mentioned analyzes and then the process output was generated for 365 days of the year as the start of the project. Finally the optimal time to start construction was achieved.Experimental modeling of Electric kinetic barrier (EKB) in Porous Medium, Explain its numerical solution methods and analysis of the relations in the Hydraulic-Electric coupled flow
https://nmce.kntu.ac.ir/article_167671.html
This research project is aimed at developing the theoretical knowledge of hydraulic-electric coupled flows and its results can be used to zero the flow in a porous medium such as seepage in engineering barriers made with clay and And also the definition of a new concept called electrokinetic engineering barrier. Also, the simulation of the electrokinetic barrier process was carried out using the finite difference method, and the methods of solving the numerical model of this process were investigated. Finally, the Forward Difference Approximation method was proposed due to more accuracy for coding in the MATLAB software. Laboratory studies was provided by an innovative physical model. To achieve this, several experiments were performed on kaolinite soil with a specific gravity of 1.3 gr/cm3, 1.315 gr/cm3, and 1.33 gr/cm3 under different electric potentials and the results of the experiments. They were compared with each other. The results showed that &nbsp;ability of the electrical gradient to generate electro-osmotic flow to overcome the hydraulic flow and create an electrokinetic barrier is affected by the input voltage as well as the dry specific gravity of the samples in the cell and with increasing them, this ability increases so that in the denser sample the electrical gradients applied to the cell were able to stop the hydraulic flow in the higher hydraulic heads while in the less compacted samples the hydraulic heads were stopped at lower values.Prediction of strength parameters of concrete containing different additives using optimized neural network algorithm.
https://nmce.kntu.ac.ir/article_169386.html
In this research, a multilayer feed-forward backpropagation error neural network has been used to predict the strength parameters of a concrete sample containing different additives. To achieve the most optimal neural network structure, the strength parameters of the concrete have been evaluated for different neural network arrangements. Control criteria are the use ofnumerical values of performance, the correlation between training functions, validation and,testing in the neural network, gradient and results of regression diagram to determine the most optimal neural network structure. It was found that the function of the neural network largely depends on its geometric structure. Revealed by the research findings, the most optimal prediction of the neural network has occurred in the case of using three layers with 30 neurons in each layer in the neural network. In this case, the numerical value of the neural network performance and the regression were obtained as 58.5 &times; (10-9) and 0.9846 , respectively. By determining the optimal neural network, different percentages of concrete raw materials based on the pre-performed experimental study are introduced to the selected neural network and the considered resistance parameters are predicted through residual analysis. According to the results, the differences between the predicted values of the neural network and the numerical values of the experimental study concerning the parameters of compressive, flexural, and tensile strength were also found to be equal to 1.68%, 1.92%, and 0.21%, respectively. Such a slight difference reflects the optimal accuracy of the chosen neural network in predicting the strength parameters.Diamond cable bracing with rings for steel Structures
https://nmce.kntu.ac.ir/article_167674.html
Cable bracing has many advantages, such as high tensile strength and lack of buckling in evaluation with traditional braces, the use of a cable as a brace is necessary. The aim of the present research is the use of cable bracing with a new configuration so that all cables remain in tension. For this purpose, a diamond cable bracing system for steel Structures was proposed. Sap2000 software was used to model the cables and rings. It was found that the proposed system eliminated the main weakness of the x-shaped cable bracing system. Ability to install for existing structures, easy installation, and repair, lightweight and delicate dimensions are the capabilities of this type of bracing, which makes its use in the field of reinforcement significant. Increasing or reducing the diameter of the cables can control the amount of displacement.&nbsp; Among the studied models, MRF has the least amount of axial force applied to the beams. By adding steel cable braces to the frame, a large amount of axial force is added to the floor beams. In this case, by increasing the diameter of the cables, the amount of this force can be reduced.&nbsp; &nbsp;Meshless Analysis of a box culvert resting on Modified Vlasov Foundation
https://nmce.kntu.ac.ir/article_160554.html
In this paper, we compare computational design of box culverts using Kleinlogel&rsquo;s formulas and three-dimensional models based on Winkler and Modified Vlasov Foundation (MVF) by Radial Point Interpolation method (RPIM) . In order to extend the RPIM to the study of box culverts, a method of decomposition by subdomain and a creation of a fictitious rotation is made. Similar results are observed between the RPIM_Winkler and STAAD PRO (FEM software) with fewer nodes in the case study. The Kleinlogel&rsquo;s formulas or the Winkler model gives a maximal increase in stresses at the middle of the raft of 5%, and a 12 times increased displacement. Finally, it emerges that for the same type of soil and a single structure, the reaction and shear modulus of the soil are highly dependent on the distribution of loads on the structure.Investigation of Climate change effect on Optimization of Dam reservoir operation using Dolphin echolocation and Gravitational search Algorithms
https://nmce.kntu.ac.ir/article_167673.html
Considering the recent human activities and the resulting climate change in optimizing the operation of the dam reservoir, the effects of climate change should also be examined. In this research, for extracting command curves by dolphin echolocation and gravitational search algorithms, the monthly inflow of the reservoir, the reservoir storage volume and the downstream demand of the reservoir in case of climate change were calculated and the optimal output values of the reservoir of Lar Dam were determined by the approach of minimizing the total square of the monthly relative deficiencies in supply demand and climate change conditions based on the river flow.According to the research, using HADCM3 and scenarios RCP2.6, RCP4.5 and RCP 8.5, climate change has increased the maximum temperature by 5%, 5.2% and 6.2%, respectively, and has increased the minimum temperature by 3.5% and 5.6% and 5.17% and increased precipitation by 8.5%, 9.5% and 13%, respectively, and the runoff from the intermediate scenarios indicates an increase of 3.3% compared to the base period. Also, to examine the water allocation policies required downstream, two future and basic conditions are considered. In this study, reservoir efficiency indices in the conditions of (future) climate change and its corresponding values in the base period were compared. The results showed that in the context of climate change, the reliability index in dolphin echolocation and gravitational search algorithms increased by 9.73 and 12.46 percent, respectively, and vulnerability decreased by 21.4 and 26.51 percent, and reversibility increased by 18.27 and 17.64 percent, respectively.Mechanical behavior of new lightweight concrete with fiber and ingredients
https://nmce.kntu.ac.ir/article_160560.html
Iran is among the earthquake-prone countries in the world. Since infill-wall materials have a brittle behavior, they result in considerable damage under large displacements. Therefore, it seems essential to modify the behavior of infill-wall&rsquo;s materials. The present article seeks to correct this drawback by using a kind of ductile lightweight concrete (DLC) with a soft behavior. To this end, lightweight concrete was produced from cement, polypropylene, filler, and fine fibers. In order to obtain the modeling and design parameters in buildings, the compressive strength, stress-strain curve, material ductility, Poisson&rsquo;s ratio, and shear strength of the mortar were evaluated. According to the results, on average, the compressive strength, Poisson&rsquo;s ratio, and elastic modulus equaled 6 Mpa, 0. 14, and 800 Mpa, respectively. By using machine learning method the stress-strain graph of DLC has been showed and maximum compressive strength and friction angle of the mortar obtained from the designed setup and regression were 0.633 Mpa and 23&deg;, respectively.&nbsp;Study of the Elastic and Inelastic Resistance to Lateral Torsional Buckling of Steel Semi-Compact I-Sections
https://nmce.kntu.ac.ir/article_160557.html
In this paper, a parametric numerical study is carried out to assess the performance to Lateral-torsional buckling (LTB) of several semi-compact beams: S1, S2 and S3. The carrying capacity of these beams predominantly loaded in bending is approached by elastic and inelastic buckling analyses. A series of parameters that are believed to influence the resistance to LTB of class 3 beams to (EC3) steel I-beams namely : bouandary conditions, flange thickness, load application level are investigataed. An eigenvalue analysis which predicts the theoretical buckling strength through 3D computational models of elastic beam is first conducted by means LTBEAM software and ABAQUS. A very good agreement in the prediction of Mcr was found. Then, a parmetric inelastuc buckling analysis is performed using Riks method implanted in ABAQUS. Results have shown the importance of the lateral restraint conditions and the transverse stiffeners to LTB resistance of compressive flange slendreness in accordance to EC3-1-1 for cross sections with a class 3 web and class 1 or 2 flange. In addition, an interaction of local buckling (LB) and LTB in the flanges was observed exclusively for restrained beams. The level of the applied load effects strongly the elastic and inelastic resistance of beams to LTB.&nbsp;Axial bearing capacity of helical piles in moist and saturated conditions using frustum confining vessel (FCV)
https://nmce.kntu.ac.ir/article_167675.html
Due to the increasing demand in construction and use of different types of piles on the one hand, and the high cost of conducting large-scale tests on different types of piles, on the other hand, new methods have been proposed to study the behavior of different types of piles. Physical modeling provides the researcher the capability of studying model piles in the scaled environment at low costs. Among the different methods of physical modeling, the use of frustum confining vessels (FCV) have gained attraction in recent years. FCV is a cone-shaped vessel that can produce a stress distribution similar to the idealized linear stress distribution in depth. Helical piles are common types of deep foundations which their first usage dates back to about 200 years ago. Helical piles are driven to the soil by applying a torque to the end of piles, in the presence of vertical loads. Their quick and noise-free installation method, the minimal disturbance during the installation, and their environmental compatibility make them popular for working in urban areas. In this research, FCV apparatus with optimal dimensions were designed and constructed. A total of 18 compression tests were performed on Anzali sand in different relative densities and moisture contents using single-helix and three-helices piles. Results indicate that increasing the number of helices and soil relative density increases the pile and sand contact and causes higher bearing capacity for helical piles. Soil saturation, on the other hand, significantly reduces the ultimate strength.Finding the design collapse capacity of a multi-story RC frame in near-fault based on the collapse risk by using the ratio method
https://nmce.kntu.ac.ir/article_167530.html
The collapse risk role has increasingly drawn engineers&rsquo; attention in the performance-based design field and engineers tend to design the structures in a way to be qualified enough to resist earthquakes, especially at near-fault sites. Due to specific characteristics of near-fault records, structures in near-fault required more collapse capacity in comparison with far-fault sites. Furthermore, it is necessary to determine the collapse capacity that structures should be designed to comply with standards and to meet the collapse risk limit in the given site. In this research, the ratio method is presented to determine the design collapse capacity of structures based on the risk value of 1% in 50 years as well as the site hazard stemming from the integration scenario for near-fault. In this method, the structure behavior and fundamental period are incorporated, and effect of pulse period is considered as well. This method utilizes the ratio of the collapse capacity of the structure in near-fault to that of far-fault named &gamma;. Consequently, efficient procedures based on nonlinear static pushover are used for obtaining the collapse capacity in far-fault and near-fault. Then, the ratio method is employed on a mid-rise RC frame and the design collapse capacities are acquired for two amounts of Tp/T. The result shows ratio method can be used for any Tp/T values especially those corresponding to the governing Tp at site. Moreover, the least value of &gamma; can be used conservatively since the design collapse capacity of the structure in near-fault is raised by reducing &gamma;.Comparison of numerical methods for the solution of Richards' equation in layered porous media
https://nmce.kntu.ac.ir/article_167524.html
In this research, the advanced finite volume scheme of the Dual Discrete method has been used for the numerical modeling of Richards' equation. Three forms of Richards' equation, including head form, water content form, and mixed form with a modified Picard linearization, are developed and assessed in the two-dimensional domain. Various examples using different soil properties, boundary conditions, and grid structures are solved. The results agree very well with the analytical and numerical solutions in both homogenous and layered porous media. The different forms have been compared in terms of accuracy, the number of iterations, and mass balance ratio. For the test cases considered in this study, the water content form has been determined as the superior method due to the low mass balance error, higher accuracy, and less number of iterations. Also, the modified Picard form improves the conservation of mass and efficiency in comparison to the head-based method. The results indicate that for the head form, a small time step is required to obtain an accurate mass balance, while the two other schemes yield superior mass balance results, even for large time steps. Moreover, the proposed finite volume method shows stable solutions without any numerical oscillations for all of the test cases.Numerical study of soil-structure interaction effects on the natural frequency of offshore wind turbines
https://nmce.kntu.ac.ir/article_167529.html
Offshore wind turbines (OWT) are considered as one the most promising ways of harvesting green energies in the world. OWTs are dynamically sensitive as their loading frequency is close to their natural frequency, allowing a narrow band of frequency to avoid resonance. Therefore, precise estimation of their natural frequency (fn) can be crucial. Soil-structure interactions (SSI) can be of great importance in estimation of dynamic characteristics of OWTs. In this study, a standard offshore wind turbine is modeled using FLAC-3D in two cases of fixed-base, i.e. with no SSI and another case with full system of soil and structural parts to estimate the effects of SSI on the natural frequency of the OWT systems. The result showed that modeling the OWT in the fixed base state results in overestimation of the system&rsquo;s natural frequency for 20 percent which can be misleading in the design process. Besides, the damping ratio was largely underestimated in the fixed base condition due to the main contribution of soil damping. Therefore, the importance of soil-structure interactions was emphasized in modeling and design of offshore wind turbines.&nbsp;Seismic Performance of Retrofitted Masonry Building Considering Soil-Foundation-Structure Interaction
https://nmce.kntu.ac.ir/article_167531.html
Open Access proceedings Journal of Physics: Conference series Around the world, there are many unreinforced masonry buildings have been constructed for different uses, such as schools. Studies have shown the seismic vulnerability of these building so nonlinear analysis and seismic assessment of these buildings and improve the &nbsp;retrofitting methods is necessary. One of the retrofitting methods in these buildings is use of shear wall. In most seismic rehabilitation projects of masonry buildings, piles are used in the foundations of shear walls and the major retrofit project costs are the foundations and piles. This study in improving the accuracy of seismic assessment of these buildings is evaluated the effect of soil and structure interaction in seismic behainior of these buildings and to reduce the cost of retrofitting was considered strip shallow foundation for new added shear walls including the effect of rocking, sliding and settlement responses. It was shown that the interaction of soil and structure in seismic behavior of masonry building retrofitted by squat concrete shear wall reduces the base shear and increases the maximum drift of building. If this increase in lateral drift of building can be tolerated, it will reduce considerably cost of retrofitting of unreinforced masonry buildings.