Numerical Methods in Civil Engineering
https://nmce.kntu.ac.ir/
Numerical Methods in Civil Engineeringendaily1Fri, 01 Dec 2023 00:00:00 +0330Fri, 01 Dec 2023 00:00:00 +0330Numerical study of the effect of the width-to-thickness ratio of incline strips on the behavior of slotted steel plate shear wall under cyclic loading
https://nmce.kntu.ac.ir/article_178446.html
This paper numerically studies the effect of the width-to-thickness ratio of inclined strips on the behavior of a novel slotted steel plate shear wall (SPSW). The slotted SPSW consists of horizontal and vertical boundary elements (BEs) and two inclined-slotted plates (ISPs) connected by high-strength steel bolts. The directions of the slots in each infill plate are opposite. Steel bolts are used to connect the two infill plates through the created holes at the intersection of each inclined slot. This paper numerically examined four slotted steel shear walls with different width-to-thickness ratios of strips. The research showed that when the slotted steel shear walls were put under cycling loading, the inclined steel strips on one side of the wall were placed in tension; however, the strips on the other side undoubtedly were in compression. Additionally, the study showed that when the width-to-thickness ratio of strips was properly used, the strength, stiffness, and energy absorption capabilities of slotted SPSWs were significantly increased, whereas the out-of-plane displacement was minimized by 40.00 %.The impact of environmental conditions of Persian Gulf on the probability of chloride corrosion initiation in reinforced concrete structures
https://nmce.kntu.ac.ir/article_186100.html
According to the technical literature, the amount of chloride that is transported by air from the sea surface depends on the amount of salt in the seawater in that area, the speed and direction of the wind, and the distance from the sea. Accordingly, data on the highest annual wind speed and direction of the wind are collected in several reinforced concrete structures (RC structures) in southern cities near the Persian Gulf at different distances from the sea. In this paper, by applying probabilistic modeling and utilizing the Hasofer&ndash;Lind and Rackwitz&ndash;Fiessler (HL-RF) method of reliability by aligning the enhanced Colliding Bodies Optimization method (ECBO) algorithm, and utilizing the data from the National Meteorological Organization, for concrete structures located in different distances with different speeds and directions of the wind from the Persian Gulf, the time of chloride corrosion initiation in reinforced concrete structures and the durability of these structures has been surveyed.Development of a System Dynamics Model for Prediction of Karaj Reservoir Share in Tehran Water Supply
https://nmce.kntu.ac.ir/article_188044.html
Tehran's water consumption (TWC) is rising as a result of rapid population growth, climate change, and precipitation decline. As water resources of Tehran are also affected by a variety of factors, the water supply scheme becomes so complicated and it is necessary to consider the complexity and dynamics interactions in water supply system before any decision making. In this study, Karaj reservoir as an important surface water resource of Tehran&rsquo;s water supply system was modeled through system dynamics (SD) approach for prediction of Karaj Dam share in Tehran water supply. The SD model was implemented in AnyLogic software using the historical data from April 2006 to March 2022, and the stock and flows and dynamics variables were predicted for April 2023 to March 2023. The novelty of this research is the development of SD model of Karaj Dam to simulate its relationships and interactions for prediction of Karaj Dam share in Tehran water supply in 2023. In this regard, the TWC and Karaj Dam inflow were predicted by using SARIMA(1,0,0)(0,1,1)12 model for April 2023 to March 2023. Finally, to assess the precision of the results obtained from the SARIMA and SD models, the criteria of coefficient of determination (R2), Error percentage (E%), and Nash&ndash;Sutcliffe model efficiency coefficient (NS%) was calculated. The results showed that the Karaj Dam inflow will be decreased during April 2023 to March 2023 due to the precipitation decline, consequently the Karaj Dam reservoir volume will be reduced and for this reason less water can be harvested from Karaj Dam reservoir for different applications. Therefore, it is clear that in the future we will have faced the challenge of water supply in Tehran.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;Projected changes in precipitation and air temperature over the Volga River Basin from bias-corrected CMIP6 outputs
https://nmce.kntu.ac.ir/article_188045.html
This paper investigates future changes in annual mean precipitation and air temperature across the Volga River basin, which serve as significant drivers of climate-induced changes in the Volga River's discharge, the primary input to the Caspian Sea. The thirteen Global Climate Models (GCMs) outputs under four Shared Socioeconomic Pathways (SSPs) scenarios (SSP1&ndash;2.6, SSP2&ndash;4.5, SSP3&ndash;7.0, and SSP5&ndash;8.5) from the sixth phase of Coupled Model Intercomparison Project (CMIP6) are used for this study. In the historical period (1950-2014), using comprehensive rating metrics and Taylor diagram, the GCMs are ranked according to their ability to capture the temporal and spatial variability of precipitation and air temperature. The Multi-Model Ensemble (MME) is generated, and bias-correction techniques are utilized to reduce the uncertainties and correct the biases in CMIP6 outputs. Bias-correction techniques are assessed in the historical period and the average of proper methods utilized for future projections (2015-2100). In the 21st century, future projections show that the Volga River basin could mainly experience a temperature increase of 0.4&deg;C to 7.5&deg;C, alongside a precipitation rise of 0.7% to 37%, depending on the scenarios considered. Comparison of future projections with an observational dataset from 2015 to 2017 indicates that the SSP2&ndash;4.5 is more likely scenario to represent the future climate of the Volga River basin.A MODEL FOR EVALUATING DRIVERS' MEAN SPEED : USING PSYCHOLOGICAL AND DRIVING SIMULATOR DATA
https://nmce.kntu.ac.ir/article_188276.html
Driving speed has always played an important role in safety. Many variables influence the driver's behavior to choose the speed, one of which is the individual's psychological variables. In this study, the direct and indirect relationship of a series of psychological variables (latent variables) on the mean speed and the relationship of the latent variables with each other have been investigated. For this purpose, two questionnaires of aggressive drivers and DBQ were used. Also, a driving simulator was used to record the mean speed of the driver . The number of participants is 71 (38% women and 62% men). one proposed model that includes 8 hypotheses was modeled using the structural equation model (partial least square method) that hypotheses were significant at the 99% level. And the results showed that there is a direct relationship between attitude with hostile behavior (H1), hostile behavior with risky violation (H3) , hostile behavior with Self-willed violation (H4), risky violation with Self-willed violation (H5) and Self-willed violation with Inexperience violation/error (H6). subjective norm have inverse relationship with risky violation (H2). Also, people who have a high Self-willed violation usually drive at a high speed (H7).Mechanical behavior of new lightweight concrete with fiber and ingredients
https://nmce.kntu.ac.ir/article_177893.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;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) has 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 were first used about 200 years ago. Helical Apiles 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&nbsp; environmental compatibility make them popular for working in urban areas. In this research, using the finite element method, the optimal dimensions of FCV apparatus were selected, and the FCV apparatus with optimal dimensions were 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 relative density of soil 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.Vibration-based damage detection of buildings using a decision-tree-based algorithm
https://nmce.kntu.ac.ir/article_189442.html
Previous studies revealed that traditional methods of damage detection (e.g., visual inspection) are time-consuming and require large monetary resources. In the last three decades, machine learning algorithms, sensor technologies, and computer science have progressively advanced, which paved the way for implementing machine learning-based damage detection frameworks. This paper presents a damage detection framework for civil structures using machine learning algorithms. The decision-tree classifier is used to classify the state of damage in the building based on the damage indicators obtained from the output acceleration signals of the building. The braced-frame structure known as the IASC-ASCE structural health monitoring benchmark building was used to verify the presented approach. The total number of 6000 Gaussian white noise signals with 10s length was applied to the case study model as ambient vibrations using the Matlab platform. Five different damage indicators, including the vibration intensity, mean period, mean, variance, and the fundamental frequency of the structure, were used to train the classifier. A Bayesian Optimization algorithm was implemented to tune the hyperparameters of the decision-tree classification learner. The results indicate that the proposed approach could estimate the state of damage in the building with promising accuracy.Application of the material point method in the modeling of arching effects behind retaining walls with active movements
https://nmce.kntu.ac.ir/article_188275.html
Numerical modeling of problems with large deformations is one of the main challenges in computational mechanics. Conventional numerical approaches cannot accurately model large deformations. Recently, the material point method (MPM), which comprises advantages of Eulerian and Lagrangian descriptions of movement, has been developed to solve complicated numerical problems such as large deformations. In this paper, the MPM method is employed to model the behavior of a soil mass behind a rigid retaining wall during active movement. It is the first time that the accuracy of the MPM method has been evaluated in the modeling of retaining walls with active movements. The accuracy and efficiency of the MPM are measured using two small-scale physical modeling tests and an analytical approach (for translational motion). In addition, a comparison between the results of the MPM and conventional FEM is provided. It is shown that the MPM can model the arching effect in the soil media better than the FEM; however, the material point method leads to smaller stresses on the wall compared to experimental results. It is demonstrated that the employed MPM can accurately model arching effects on the soil media behind the retaining walls with active movement. For transitional movement, arching effects lead to the upward movement of the resultant horizontal force on the wall, which occurs higher than 1/3H (H is the height of the wall). The achieved results indicate that the traditional methods can lead to overestimated designs without considering arching effects.Comparison of numerical methods for the solution of Richards' equation in layered porous media
https://nmce.kntu.ac.ir/article_178230.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.Experimental and Numerical Investigation of Bottom Intake Structure for Desalination Plants
https://nmce.kntu.ac.ir/article_182556.html
One of the most important hydraulic structures which are used to divert flow is lateral intake. It can be performed by different methods, such as channels, pipes, orifices and etc. This study investigates the effects of various geometric and hydraulic parameters on bottom intake which is widely used as seawater intake for desalination plants. Observation shows that the flow velocity is higher in the square shape than in the circular shape in the front of velocity cap, while it is more at the both sides of the velocity cap in circle type. The correlation of various factors on the discharge coefficient was analyzed based on 180 physical tests by using Python code. Results show that the discharge capacity of the circle shape intake velocity cap is about 2% to 4% higher than that of the square shape intake cap. In addition, discharge coefficient of intake is affected by the approach flow Froude number and area of intake, while the height of the velocity cap has less effect on discharge trough intake. Furthermore, numerical investigation invests on flow pattern around velocity caps. Observation show that separation zone located at the back side is bigger in the square shape than in the circular shape.Investigating Concrete Arch Dam Behavior Under underwater explosion (Case Study:Karun4 Dam)
https://nmce.kntu.ac.ir/article_186103.html
Studying the responses of dams to explosion-induced loads and evaluating their overall safety under such loads is highly significant regarding the strategic importance of dams. The present study investigates TNT-induced wave effects on the Karun-4 Dam in Iran. For this purpose, dynamic analyses were carried out on the dam reservoir and foundation system via the finite element method (FEM) in ABAQUS. The CONWEP theory allows the imposition of pressure loading caused by an explosion in the air. The reservoir was considered empty, and then three different heights of 225, 115, and 5 m were analyzed. The failure explosive weights of the three heights were calculated by trial and error. Analyses were performed with 1000, 1200, and 1300 kg of TNT for the height of 225 m, 1900, 1950, and 2000 kg of TNT for the height of 115, and 1800, 1900, and 2000 kg of TNT for the height of 5 m. It was observed that the dam failed at loads of 1300, 2000, and 2000 kg of TNT when the explosion occurred at 225, 115, and 5 m, respectively. The analyses were performed based on these loads. The results indicated that the reservoir water level had a negligible effect on the arch dam's failure blast load. Moreover, analysis results of the dam-reservoir-foundation system in filled-up and empty reservoir cases suggest that the failure explosive loads of filled-up and empty reservoir dams do not significantly differ, and the failure explosive load of the filled-up case is slightly lower than that of the empty case. For example, at an explosion height of 225 m, the failure load of the filled-up reservoir case was derived to be 1500 kg of TNT, while that of the empty reservoir case was obtained to be 1300 kg of TNT.&nbsp;Evaluation of ground motion amplification across empty valleys subjected to inclined SV waves using boundary element method
https://nmce.kntu.ac.ir/article_188046.html
Many recorded earthquakes in last recent decades have shown that the damage distribution and seismic response of an area depends on Source characteristics, pathway of seismic waves and also on local conditions of the site; these conditions can change the amplitude of displacement and frequency properties of ground movement. Local site effects include geotechnical and topographical effects. Unfortunately, most modern seismic codes consider geotechnical effects, and those who consider topographical effects, focus on simple geometries but other parameters such as wave characteristics are not taken into account; the main reason is lack of quantitative amplification predicting methods and practical information in topography constructions.2D seismic site effects in empty valleys are evaluated in present study. Numerical analysis is carried out by HYBRID software. HYBRID is a nonlinear, two phase, code for solving 2D problems of propagation of the waves; this software combines F.E.M in near field and B.E.M in far field. Empty valleys are modeled, with different shapes including rectangle, triangle and trapezoid and with depth ratios equal to 1, 0.8, 0.6, 0.4 and 0.2. Oblique SV waves of Ricker type are considered as seismic solicitation and its angle of incidence varies from -90&ordm; to 90&ordm; every 10&ordm;. It is shown that the incidence angle is able to change the maximum amplification and critical incidence angle of a half-space is changed by topography.Reliability based assessment of reinforced concrete columns under eccenric loads using refined first-order reliability method
https://nmce.kntu.ac.ir/article_190558.html
This paper presents an efficient approach for the failure probability assessment of reinforced concrete (RC) columns under the combination of the gravity and seismic loads considering uncertainty in the load eccentricity. In the proposed approach, Limit State Function (LSF) are conditionally formulated for the load eccentricity in column and the conditional reliability index is assessed using Refined First-Order Reliability Method (R-FORM) based on cross-entropy optimization method. The conditional reliability index along with the probability density function of the load eccentricity have been used to estimate the failure probability of the column. The important feature of the proposed approach is precise find of the most probable failure point, which provide a precise estimation of the failure probability of the RC columns under different load eccentricities. The results indicate that the failure probability of the RC columns is sensitive to uncertainty in the load eccentricity as well as of structural system, particularly when the load eccentricity is in the tension failure region. The effect of longitudinal reinforcement varies depending on the probability density function of the load eccentricity and the region of the interaction diagram where the column is loaded.