h. heidarzadeh
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Scientia Iranica, Volume:29 Issue: 6, Nov-Dec 2022, PP 2773 -2788In this paper, for the first time, the combination of these two concepts is used for the earthquake acceleration wave. For this purpose, eight earthquakes from four different locations in the world have been selected. Initially, each earthquake is filtered up to 5 stages using a discrete wavelet transform. Due to the close approximation of the frequency content of the wave to the original earthquake, the approximate wave is used for subsequent calculations. In the next stage, the spectrum of Fourier and the diagram of five of the frequency of dominant of the earthquake are plotted. Also, using the continuous wavelet transform, the time-frequency curves of the main earthquakes and the time-frequency curves of the wave obtained from the discrete wavelet transform are investigated. The goal is to find the best stage of a discrete wavelet filter based on frequency content to reduce computations to over 80%. In the next step, the study examines the time of the strong ground motion, the structure response of single degree of freedom, and the dynamical response of the timing of the structure of a degree of freedom. By examining the above parameters, the best-performing wavelet transformation step is inferred.Keywords: wavelet transform, Frequency content, Fourier spectrum, earthquake
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در مطالعه ی حاضر، به منظور بررسی تغییرات به وجود آمده در حدود اتربرگ و تنش برشی خاک های ماسه یی رس دار از آزمایش های حدود اتربرگ و برش مستقیم در درصدهای مختلف نانورس بر روی ماسه های رس دار با ترکیب گوناگون درصدهای ماسه و رس انجام شده است. همچنین، جهت بررسی میکروسکوپی بافت نمونه ها از میکروسکوپ الکترونی روبشی برای پیمایش سطح نمونه ها استفاده شده است. بررسی تصاویر نشان می دهد ذرات نانورس در صورت نبود رس در نمونه ی خاک (یعنی خاک ماسه یی خالص) یا عدم پراکندگی یکنواخت، اثر معکوس در رفتار خاک خواهند داشت. در صورت وجود رس در خاک ماسه یی و همچنین پراکنده شدن یکنواخت نانورس در خاک، پارامترهای ژیوتکنیکی خاک بهبود می یابند. برای خاک مورد مطالعه در پژوهش حاضر، بهترین ترکیب از نظر مقاومت برشی، مربوط به خاکی است که از ترکیب 80٪ ماسه و 20٪ تشکیل شده و با افزودن 4٪ نانورس به آن، بهترین نتیجه از نظر مقاومت برشی به دست آمده است.
کلید واژگان: بهسازی خاک، نانورس، حدود اتربرگ، مقاومت برشی، برش مستقیمThe improvement of soil treatment by additives is one of the most critical issues in geotechnical engineering. Typical additives such as cement, lime, fly ash, and bitumen have been investigated in the past. Nanomaterials have unique features. The application of this type of material has led to a significant development in other branches of engineering. However, in geotechnical engineering, the investigation of the effects of this type of material is a new subject. Hence, in the present research, the effects of nano clay on geotechnical parameters of clayey sand are investigated. The principal purpose of investigation in this scale is the creation of new compounds with changes in ingredients and the detection of a new class of materials with new functions. These types of researches can make an appropriate base for future researches in this context. The Atterberg limits test and direct shear tests were carried out on different types of clayey sand. Various percentages of nano clay were used in the study. Ball mill was applied for uniform dispersion of nanoparticles. Also, in order to obtain optimum water content and maximum specific weight for prototyping, a standard compaction test was carried out on samples without nano clay particles. Based on the results, in general trends of tests, liquid limit and plastic limit are increased by increasing nano clay. The plasticity index has decreased when the percentage of the nano clay is increased by up to 1%. The plasticity index has increased again in a higher percentage of nano clays (more than 1%). Also, the shear strength of clayey sand in direct shear tests is improved in a specific percentage of nano clay. The optimum percentage of the nano clay for the friction angle φ is 1% in the direct shear test, and its best percentage for the cohesion C is 4%. Also, nano clay has a negative effect on the shear strength of pure sand. Therefore, according to the results of experiments, nanoparticles can be an acceptable choice for improving the geotechnical properties of clayey sand soils.
Keywords: Soil improvement, Nanoclay, Atterberg limits, shear strength, Direct shear -
Scientia Iranica, Volume:28 Issue: 3, May-Jun 2021, PP 1096 -1108One of the most imperfections of the steel shear wall is out of plane displacements that cause severe damage in both structural and non-structural elements. In this paper, the effects of shape-memory alloys on steel shear walls are investigated. First, a numerical analysis using the finite element method in ABAQUS software has been carried out according to an experimental test. The results of the numerical analysis have been verified with experimental results. Next, shape-memory alloy fibers have been added vertically and horizontally to various parts of the steel shear wall. The results show that retrofitting with the shape-memory alloy reduces the out-of-plane displacement of the steel shear wall under both cyclic and seismic loadings. Besides, the buckling load in the steel shear wall increases when it is retrofitted with the shape-memory alloy. Also, the total out-of-plane movement (accumulated absolute displacements) of the steel shear wall and non-structural damage are controlled by the characteristic of a shape-memory alloy material called “super-elastic”.Keywords: Steel shear wall, Shape memory alloy, Retrofitting, Dynamic analysis, Cyclic behavior, Buckling analysis
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در این پژوهش، دو مدل رفتاری M C H و D P H معرفی شده اند، که ساختاری کاملا مشابه دارند و تفاوت آنها فقط در معیار تسلیمی است که برای آنها در نظر گرفته شده است. این دو مدل رفتاری در حقیقت از تلفیق مدل هذلولی، به ترتیب با سطوح تسلیم موهر کولمب و دراکر پراگر پدید آمده اند. پس از کالیبره کردن این مدل های رفتاری با داده های آزمایشگاهی در یک مسیر تنش خاص، نحوه ی عملکرد آنها در مسیرهای دیگر تنش با توجه به داده های آزمایشگاهی مورد ارزیابی قرار گرفته است. سپس به کمک زبان برنامه نویسی F i s h، این دو مدل رفتاری به نرم افزار F L A C معرفی شده اند، تا زمینه ی مناسب برای انواع تحلیل های عددی فراهم آید. به این ترتیب نحوه ی عملکرد این مدل های رفتاری و در نتیجه تاثیر سطوح تسلیم در تحلیل های عددی استاتیکی و دینامیکی مربوط به مسائل مختلف ژئوتکنیک)مثل ظرفیت باربری پی، تونل، و گودبرداری(مورد ارزیابی قرار گرفته است. در یک نگاه کلی، پیش بینی مدل های رفتاری به کاررفته در این پژوهش، با توجه به مسیر تنش کالیبراسیون)یعنی آزمایش سه محوری متداول(، در بارگذاری پی کمترین انطباق و در مسئله ی گود بیشترین انطباق را نشان داده اند.
کلید واژگان: سطح تسلیم، مدل های رفتاری، مسیرهای مختلف بارگذاری، تحلیل های عددی استاتیکی و دینامیکیIn geotechnical engineering, yield surface (criterion) is a subject that has attracted the attention of a large number of researchers in both elds of experimental and constitutive modeling. Various yield surfaces have been introduced by di erent investigators, of which, Mohr- Coulomb and Drager-Prager criteria are the most famous. Generally, yield criteria are used in constitutive model structures. On the other hand, the nal aim is to apply these constitutive models in numerical analyses of geotechnical engineering problems. Therefore, the question which arises here is; how high is the degree of e ect of these yielding surfaces on numerical analyses of geotechnical problems, and also, is a more accurate yielding criterion needed or not? In this paper, two constitutive models of MCH and DPH have been introduced in such a way that they have quite similar structures and the only distinction between them is their supposed yield surfaces. In fact, these models have been originated by a combination of the hyperbola model with Mohr-Coulomb and Drager-Prager criteria, respectively. After calibration of the two constitutive models by experimental data on a speci c stress path, their performance on other stress paths were also evaluated using laboratory data. Then, using Fish programming language, the two constitutive models were introduced into the FLAC program to enable investigation of various numerical analyses. In this way, performances of these constitutive models and, consequently, the e ect of the yield surfaces on the static and dynamic analyses of geotechnical structures (such as foundation bearing capacity, tunnel and excavation), were evaluated. Therefore, a better insight into the degree of e ect of various yield surface shapes on numerical analyses of di erent geotechnical problems could be obtained for engineers who use di erent constitutive models for design and numerical investigation, and also for researchers who study constitutive models.
Keywords: Yield Surface, Constitutive Model, Di Erentstress Paths, Static, Dynamic Numerical Analyses -
با پیشرفت تکنولوژی در عرصه های مختلف، تجهیزات آزمایشگاهی نیز روز به روز پیشرفته تر می شوند. همگام با پیشرفت هایی که از مطالعات آزمایشگاهی حاصل می شود، نیاز به ارائه ی مدل های مناسب برای پیش بینی دقیق تر رفتار خاک، بیش از هر زمان دیگر احساس می شود. با مطرح شدن مفهوم حالت بحرانی و دائمی در مسائل مکانیک خاک، تحول عظیمی در مهندسی ژئوتکنیک پدید آمد. این تحول با ارائه ی مدل هایی در چهارچوب حالت بحرانی همراه شد. مدل های ارائه شده در این غالب، علی رغم موفقیت مناسب در پیش بینی رفتار خاک های رسی، در رفتار خاک های غیرچسبنده موفق نبودند. با مطرح شدن مفهوم پارامتر حالت و تایید آن در یافته های آزمایشگاهی، ایده ی استفاده از این پارامتر در مدل های رفتاری مطرح و این نقطه ی ضعف به طور قابل توجهی جبران شد. در این نوشتار، با اصلاح یک مدل کشسانی خمیری از خانواده ی مدل های با سطح حدی اثر پارامترهای حالت مختلف در بهبود پیش بینی مدل نشان داده شده است. سه پارامتر حالت $p s i$، $I_s$ و $R S R$ به طور مجزا به سه شیوه در فرمولاسیون مدل وارد شده است و توانایی پارامترهای حالت مختلف در اصلاح مدل اصلی با استفاده از نتایج آزمایشگاهی بر روی ماسه ی T o y o u r a ارزیابی شد.
کلید واژگان: پارامتر حالت، مدل رفتاری، سطح حدیLaboratory equipment is progressing, alongside advancements in technology, day by day. Along with these advancements in laboratory studies, the requirement to provide an appropriate model which can accurately predict soil behavior is felt more than at any other time. A great advancement was evolved in soil engineering by introducing the critical and steady state concept to geotechnical problems. This evolution was accompanied by an introduction to constitutive models in a critical state framework. In spite of successful predictions for clayey soil behavior, presented models failed to represent the behavior of granular soils. This weakness was significantly compensated for by introducing the concept of a state parameter in laboratory findings, and also by proposing the use of this parameter in constitutive models. In this paper, the effect of different state parameters on the improvement of model predictions has been shown by modifying an elasto-plastic model from the family of bounding surface models.For this purpose, the model of Manzari (1994) has been chosen. This model, which was developed in a bounding surface framework, is one of the elastoplastic constitutive models developed to predict sand behavior. The critical state concept was ignored by this model. In other words, the model of Manzari (1994) does not involve the concept of critical state and state parameters. Accordingly, this model predicts soil behavior without considering the current conditions of the sand, such as void ratio and mean effective stress. As a result, the model must be recalibrated when the state of the soil changes. In this paper, it has been attempted to modify the original model by adding different state parameters to it, in order to assess the effects of these parameters on the constitutive model predictions. Several state parameters have been introduced by some investigators, but there are three common ones used widely in a large number of papers. These state parameters ($psi$, $I_s$, RSR), in three different ways, were added to the main model formulation, and the capabilities of the modified model were evaluated by the results of laboratory data on Toyoura sand.
Keywords: State Parameter, Constitutive Model, Bounding Surface
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