جستجوی مقالات مرتبط با کلیدواژه « non » در نشریات گروه « عمران »
تکرار جستجوی کلیدواژه «non» در نشریات گروه «فنی و مهندسی»-
یکی از روش های متداول بهسازی خاک، استفاده از افزودنی ها به منظور بهبود خصوصیات مقاومتی و نفوذپذیری خاک است. اغلب از سیمان یا مواد شیمیایی به عنوان عامل چسبنده ذرات خاک استفاده می شود که باعث افزایش مقاومت برشی خاک و کاهش هدایت هیدرولیکی آن می شود. در این پژوهش با استفاده از آخرین فناوری زیستی میکروبی، نوع جدیدی از مصالح ساختمانی، یعنی سیمان زیستی، به عنوان جایگزینی برای سیمان و یا مواد شیمیایی ایجاد شده است. سمنتاسیون زیستی یا فرآیند رسوب میکروبی کربنات کلسیم (MICP)، بهبود مقاومت و سختی خاک و سنگ با استفاده از فعالیت های میکروبی و فرآورده های آن هاست. در این پژوهش از خاک ماسه ای با درصد متفاوت سیلت %0، %5،%10، %15 و %20 و در دو حالت سست (Dr=40%) و متراکم (Dr=100%) و از باکتری Sporosarcina Pasteurii به دلیل فعالیت اوره آزی بالا و غیر بیماری زا بودن در فرآیند MICP استفاده شد. به منظور در نظر گرفتن شرایط خاک بر عملکرد این نوع روش بهسازی، پارامترهای آزمایش تک محوری و میزان رسوب کربنات کلسیم موردبررسی قرار گرفت. با توجه به نتایج، افزایش درصد ریزدانه از 0 تا 20 درصد منجر به کاهش %40 و %46 در میزان رسوب کربنات کلسیم، افزایش %57 و %41 در مقاومت تک محوری و افزایش %79 و %71 در مدول الاستیسیته نمونه ها به ترتیب در دو حالت سست و متراکم گردید. بنظر می رسد این تغییرات ناشی از کم شدن فضای خالی و افزایش سطح تماس بین ذرات خاک بوده است.کلید واژگان: بهسازی زیستی, رسوب میکروبی کربنات کلسیم, مقاومت تک محوری, خاک ماسه ای, سیلت غیرخمیری}One of the most common methods of soil improvement is to use additives in order to improve strength properties and permeability of the soil. Cements or chemicals are usually used as binders for soil particles, which lead to increase the soil shear strength and reduce its hydraulic conductivity (i.e. permeability). Nevertheless, these materials are not suitable for soil improvement in the long term because they require significant natural resources. The use of cement and chemicals for soil improvement is expensive and time-consuming. Management of renewable natural resources (microorganisms and their products) could lead to solve geotechnical and environmental problems and achieve great economic benefits in the building industry. In addition, the application of microbial biotechnology in the building industry make easier some of the existing methods of construction. Using the latest microbial biotechnology, a new type of building materials, namely biocement, has been produced as an alternative to cement or chemicals. Biocementation is the improvement of strength and stiffness of rock and soil by using microbial activity and their products. The process of the formation of precipitates or biocement in the presence of microorganisms is called microbialy induced calcium precipitation (MICP). Biocement can be used in solid and liquid states. In the liquid state, biogrout can flow like water with very low viscosity. Therefore, compared to cement and chemicals, it will be transmitted into the soil, more easily. Naturally, biocement is formed in the presence of microorganisms in ambient temperature and thus, it requires less energy. Because of the abundance of microorganisms in the nature and easy to reproduce with low cost, this type of cement is sustainable. The Microorganisms that are suitable for the production of biocement are usually non-pathogenic and environment friendly. In addition, unlike cement, soil can be improved without disturbance of ground and the environment; since microorganisms can penetrate into the soil and grow in it. This dissertation aims to realize the effect of ground condition on the MICP process in non-cohesive soils. Since this method is still in the laboratory stage, for being used in practical projects, it is required to carry out laboratory experiments, including relative density and particle size distribution, to evaluate the performance of this method in different ground conditions. For this purpose, it was used from Sandy soil with different silt contents of 0%, 5%, 10%, 15% and 20% in two states of Loose (Dr = 40%) and dense (Dr = 100%) conditions in this research. The high urease activity and non-pathogenic bacteria S. Pasteurii was also used in the MICP process. In order to consider the soil conditions on the efficiency of this type of improvement method, uniaxial compressive test parameters and precipitated calcium carbonate content were investigated. According to the results, increasing of silt content from 0% to 20%, leads to reductions of 40% and 46% in precipitated calcium carbonate content, increases of 57% and 41% in the uniaxial strength and increases of 79% and 71% in the elasticity modulus of the samples in two loose and dense conditions, respectively. It seems that these changes were resulted from shrinking of the empty space and increasing of the contact area between the soil particles.Keywords: Biological Improvement, Microbial Induced calcium carbonate Precipitation (MICP), Unconfined compressive strength, Sandy soil, Non, plastic Silt}
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Load-Path Influence in the Response of RC Buildings Subjected to Biaxial Horizontal Loadings: Numerical StudyThe study of the reinforced concrete (RC) columns response to horizontal loads is of full importance to understand how earthquakes affect the integrity of structures, essentially those already built and especially vulnerable to this type of action, as is the case with many existing buildings on significant seismic activity zones which are not adequately prepared for that eventuality. Consequently, there is also the need to perform a significant number of experimental and numerical studies to understand how much the columns resistance is affected by the horizontal loading path combined with axial load. The present study focus on the comparison between the RC columns response when subjected to uniaxial and biaxial loading through a literature review of the experimental test data results. Additionally, a parametric study was performed to analyze the load-path influence in the columns response. Non-linear static pushover analysis were performed in more than 36 columns with different cross-sections, reinforcement ratios and axial load ratio, performing a total of 1300 analysis. The numerical results will be presented in terms of capacity curves, maximum strength comparison between the uniaxial and the biaxial response and several ratios were also determined to a do a better comparison.Keywords: RC columns, Biaxial loading, Axial load, Experimental tests, Numerical modelling, Non, linear static pushover analysis, Maximum strength}
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در این مطالعه آزمایش های نیمه مخرب break-off و Pull-off برای ارزیابی مقاومت بتن حاوی الیاف فولادی در محل مورد بررسی قرار گرفته است. امروزه استفاده از الیاف فولادی، بعنوان یکی از راه حلهای مناسب مقابله با شکست ناگهانی بتن بسیار رواج یافته است، لذا بعنوان بتن مورد بررسی در این مقاله مورد استفاده قرار گرفته است. به منظور فراهم کردن یک پایگاه آماری کامل، 24 طرح اختلاط انتخاب گردید. سپس، عوامل تاثیرگذار بر خصوصیات بتن حاوی الیاف فولادی و نتایج آزمایش Break-off و Pull-off مورد ارزیابی قرار گرفت. بررسی ها نشان می دهد علاوه بر مشخصات آزمایش، درصد و مشخصات الیاف فولادی تاثیر بسزایی بر خواص بتن و نتایج هر دو آزمایش دارد. نتایج نشان می دهد که ارزیابی مقاومت با روش های فوق دارای قابلیت اعتماد مناسب می باشند، هر چند تخمین مقاومت بتن براساس یک منحنی کالیبراسیون کلی ممکن نیست. لذا منحنی های کالیبراسیون مستقل برای هر بتن به منظور تفسیر واقع گرایانه نتایج ارائه گردیده است.کلید واژگان: آزمایش break, off, آزمایش Pull, مقاومت بتن, الیاف فولادی, آزمایش نیمه مخرب}Here, the efficiency of the non-destructive Break-Off (BO) and Pull-off tests was investigated for assessing the in-place compressive strength of steel fiber reinforced concrete (SFRC). SFRC was studied due to its advantages in increasing tensile and flexural strength in particular. To provide a through and comprehensive database, 24 mix designs were selected with cement contents of 400, 450 and 500 kg/m3 with constant water/cement ratio of 0.4 for all mixes, two maximum aggregate sizes of 12.5 and 25 mm along with steel fiber volume fractions of 0%, 0.33%, 0.67% and 1% for ages of 14, 28 and 90 days. A total of 360 Break-Off and Pull-off tests and 216 standard cube tests were carried out in this investigation.Then, effective parameters of SFRC and non-destructive tests results were evaluated. The studies showed that volumetric percentage and features of steel fibers had a significant influence on concrete properties as well as Break-Off and Pull-off tests results. According to the experimental results it could be generally concluded that the influencing factors, namely, SFRC properties due to presence of steel fibers and non-destructive tests significantly affect the results as follows:Generally, for a constant W/C ratio, it can be concluded that raising the cement content increase the mean values of Break-Off and Pull-off strengths.
In adition to, conventional numerical regression model was developed in this study. Statistical indices were used to compare the efficiency and accuracy of model. The result of this study has confirmed the accuracy of linear regression model for non-destructive tests.Keywords: Break, off test, Pull, Steel Fiber, Non, destructive, Regression model} -
A Baseline-Free Modal Strain Energy Method for Damage LocalisationThis study describes the work carried out with the intention of accomplishing the ultimate objective of effective damage detection in structures, using their vibration parameters. As compared to the other vibration parameters, i.e., mode shape curvatures, damage indices, and flexibility curvatures, modal strain energy method (MSEM) showed high stability of damage detection. However, MSEM requires the information of a baseline model or healthy structure, which is then compared with that of a tested structure, to locate any stiffness reduction. In this paper, a baseline-free approach is presented to improve the accuracy of damage detection using the MSEM. Results from numerical simulations with experimental testing on a beam are presented by considering various damage scenarios, i.e., single and multiple damage with damage severity as small as 25% and as large as 50% thickness reduction. For all cases, the proposed approach is found to generate results with comparatively fewer noisy peaks in the damage index without requiring any reference or baseline data.Keywords: Damage detection, Modal strain energy method, Non, destructive inspection, Beams}
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در این تحقیق در بررسی پدیده برکنش ابتدا، مزایا و معایب این پدیده و نتایج بدست آمده در تحقیقات گذشته در مورد اثرات آن بر سازه ها بیان شده و سپس روش های مدلسازی و تحلیل پدیده برکنش بررسی گردیده اند. آنگاه چند قاب فولادی با تعداد طبقات و دهانه های مختلف در دو حالت با و بدون برکنش توسط دو روش استاتیکی و دینامیکی غیرخطی تحلیل ومقایسه شده اند. بر اساس این تحقیق، پدیده برکنش در حالت کلی نقش مهمی در تغییر رفتارلرزهای سازه و کاهش پاسخ آن دارد، ولی همزمان خود می تواند باعث بعضی آسیب های موضعی و در حالت نادر آسیبهای کلی شود. نتایج تحقیق نشان دادند که برکنش باعث افزایش زمان تناوب موثرسازه، افزایش انرژی جذب شده توسط سازه با درصد میرایی متعارف و کاهش تغییرمکان های نسبی بیشتر اعضای سازهای ودرنتیجه کاهش نیروهای داخلی این اعضا می شود.افزایش زمان تناوب برای سازه های مهاربندی شده این تحقیق بیشتر بوده و به بیش از 25درصد نیز می رسد.در مورد تغییرمکان، نسبت افزایش از حالت بدون برکنش به با برکنش برای سازه های با زمان تناوب کوچکتر از 1/5 ثانیه برابر 1/8 و پس از آن 1/5 می باشد. همچنین نسبت شتاب حداکثر در حالت بدون برکنش به با برکنش برای همه زمان تناوبها در حدود 1/3استکلید واژگان: برکنش, سازه های فولادی, تحلیل استاتیکی غیرخطی, تحلیل دینامیکی غیرخطی, واکنش لرزه ای}In design of structures for applied loads, the common assumption is that the structure is tightly attached to its base, i.e. no vertical rigid-body motion can happen at the same place. During a major earthquake, the couple of axial forces associated with the overturning moment can overcome that of the gravity loads in lateral load bearing columns and result in an uplifted column. With a building losing some of its contact points to the ground, a reduced lateral stiffness can be expected. This in turn can result in a reduced seismic base shear. At the same time, the structural members around the uplifted part can undergo large local deformations and perhaps a more extensive seismic damage. Illuminating the above predictions is the incentive of this research. In this paper, in the numerical part, a number of steel frames having various numbers of stories and bays are studied in two cases of without uplift (fxed base) and with uplift. The methods of analysis are the non-linear static and dynamic analysis procedures.According to the fndings, the uplift phenomenon generally has an important role in changing the behavior of structure and reduction of its response. At the same time, it can result in locally increased damages that sometimes can add up to total failures. The results showed that uplift increases the structural period and the absorbed energy, and decreases the displacements of most parts of the structures and their internal forces.Keywords: Uplift, Steel Structures, Non, linear Static Analysis, Non, linear Dynamic Analysis, Seismic Response}
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گچ با توجه به خصوصیات منحصر به فرد آن یکی از مصالح ساختمانی پر کاربرد در ساختمان سازی است. اما در برابر نیروی خمشی و کششی وارد شده به آن ضعیف می باشد. از این رو در این نوع مصالح ساختمانی برای غلبه بر نیروی وزن سازه و همچنین بهبود خواص مکانیکی، میتوان از منسوجات که دارای قدرت کششی مناسب و وزن کم هستند به عنوان عضو تقویت کننده استفاده نمود. در این تحقیق تاثیر پارچه بی بافت سوراخ دار و ضایعات آن در مقاومت خمشی کامپوزیت گچ مورد بررسی قرار گرفته است. از روش سطح پاسخ برای تجزیه و تحلیل مقاومت خمشی کامپوزیت گچ به عنوان متغیرهای وابسته استفاده شده است. وزن پارچه های بی بافت، تعداد سوراخ و ضایعات این پارچه ها به عنوان متغیرهای مستقل انتخاب شدند. به عنوان یک نتیجه از مطالعه، مدل پیش بینی کننده مقاومت خمشی کامپوزیت گچ ارائه شده است و این مدل دارای ضریب تعیین بالا می باشد. همچنین با توجه به نتایج حاصل از این مطالعه مشخص گردید که استفاده از مواد نساجی به شکل ضایعات پارچه، تاثیر مثبت قابل ملاحظه تری نسبت به پارچه سوراخ دار بر روی بهبود خاصیت خمشی کامپوزیت گچ را درپی خواهد داشت .کلید واژگان: گچ, مقاومت خمشی, مسلح سازی, پارچه بی بافت سوراخدار, ضایعات پارچه}Gypsum is one of the most useful building materials in building industry due to its unique properties. But it is weak against bending and tensional forces acting on it. Therefore in this kind of building material to overcome the structure weight and also improving mechanical properties, textiles can be used as reinforcing member due to their tensional property and low weight. In this research, perforated non-woven fabric and its waste affection on bending resistance of gypsum composite has been evaluated. Response surface method has been used to analyze bending property of gypsum composite as dependent variable. Non-woven fabric weight, the number of holes and this kind of fabric waste has been selected as independent variables. As a result of this study bending resistance predictive model of gypsum composite is provided and this model has a high coeffcient of determination. Also according to the results of this study, it was determined that using textile materials in the form of fabric waste will follow more considerably effect on improving bending property of gypsum composite than the perforated fabric.Keywords: Gypsum, Bending Resistance, Reinforcing, Non, Woven Perforated Fabric, Fabric Waste}
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لوله های جدار نازک به عنوان معمولترین شکل و احتمالا قدیمی ترین شکل مورد استفاده در سیستم های جذب انرژی هستند. هدف از این تحقیق ارزیابی رفتار قاب های فولادی مجهز به میراگرهای فلزی جدار نازک آکاردئونی و تاثیرات جانمایی آنها در بهبود رفتار اینگونه قابها در برابر بار انفجاری می باشد. به منظور بررسی اثر میراگر، یک بار قاب بدون میراگر و باردیگر قاب مجهز به میراگر تحت اثر بار انفجار مورد ارزیابی قرار گرفت. سازه های فولادی مورد مطالعه، سازه تک دهانه ای با ارتفاع های مختلف یک و چهار طبقه بوده و تحت اثر دو نوع بار انفجاری با مقادیر مختلف قرار گرفتند. همچنین جهت استفاده میراگر در این سازه ها از دو روش برای جانمایی میراگر استفاده شده است. حالت اول استفاده از میراگر به همراه بادبند در تراز طبقه و دیگری تعبیه میراگر در میانه ستون برای کاهش اثرات ناشی از انفجار می باشد. برای تحلیل های دینامیکی غیرخطی مدل ها از نرم افزار ABAQUS استفاده شده است. نتایج این پژوهش حاکی از آن است که استفاده ازمیراگرهای جدار نازک آکاردئونی، بهویژه در انفجارهای بزرگ تا حد زیادی جابجایی کلی سازه را بهبود می بخشد (تا 98درصد برای سازه یک طبقه و 64درصد برای سازه چهار طبقه.) در عین حال با جایگذاری آن در نقاطی که تغییر شکلهای زیادی روی می دهد میتوان تغییرشکل های پلاستیک موضعی نقاط را کاهش داد.کلید واژگان: بارگذاری انفجار, تاثیر جانمایی میراگرها, میراگر آکاردئونی, مقاوم سازی, تحلیل دینامیکی غیرخطی}Thin-walled tubes might be considered as the simplest and, probably the oldest, type of dampers used in energy-absorbing systems. This paper investigates the effect of thin-walled accordion metal dampers and their arrangement in the frame on the behavior of steel frames against blast loading. For this purpose, one-bay frames with either one or four stories, and in both cases of with and without dampers, have been analyzed in ABAQUS software under two different blast intensity conditions. Results demonstrate that using such dampers would improve frame displacement to a large extend (up to 98% for one-story frame and 64% for four story frame), especially during an intensive blast. Furthermore, local Plastic deformations of the frame would be reduced by locating the dampers in points with large deformations.Keywords: Blast Loading, Damper Location, Accordion Damper, Retrofiting, Non, Linear Dynamics Analyses}
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تهیه سنگدانه مصرفی در بتن که حدود سه- چهارم از حجم بتن را تشکیل می دهد، امروزه به موضوعی چالش برانگیز برای توسعه پایدار به دلیل مسائل زیست محیطی تبدیل شده است. یکی از مناسب ترین راه کارها به ویژه در مناطق ساحلی دریاها و اقیانوس ها استفاده از ماسه لایروبی دریا (DMS) برای ساخت بتن می باشد. در پژوهش حاضر، با توجه به اینکه در جزیره ها و برخی از نقاط حاشیه خلیج فارس منابع و معادن شن و ماسه طبیعی مناسبی برای ساخت بتن وجود ندارد، مطالعه ای آزمایشگاهی روی نمونه های بتنی غیرمسلح ساخته شده با ماسه لایروبی دریا انجام شد تا بدین وسیله هزینه های ساخت بتن به طور قابل توجهی کاهش یابد. در این تحقیق از سه نوع سیمان پرتلند (پوزولانی ویژه، تیپ II وتیپ (V، الیاف و سرباره استفاده شده است همچنین آزمایش های انجام شده عبارتند از: آزمایش مقاومت فشاری، جذب آب و عمق نفوذ آب، که نتایج حاصل از این پژوهش نشان می دهد استفاده از ماسه لایروبی خلیج فارس تا محدوده 25 درصد، بجای ماسه معدنی نتایج مناسبی را از لحاظ مکانیکی و پایایی به دنبال دارد.کلید واژگان: بتن غیرمسلح, ماسه لایروبی دریا, دوام, پایایی, مقاومت فشاری}Preparation of aggregate, as an essential ingredient that forms three-fourth of the concrete volume is an issue for the environment and the sustainable development. One of the most appropriate solutions, especially in the coastal areas of seas and oceans is to use the marine aggregates particularly the dredged aggregates, dredging the sand from the sea (DMS) for producing concrete.In this research, with due attention to the fact that there is no proper sand for concrete in some coastal areas of Persian Gulf and the Gulf islands, an experimental study has been carried out in order to develop a method to produce non-reinforced concrete, focusing on the application of the DMS. This method would also economize the expenses. In addition, for cementitious material's preferences and influences, three different types of cement, which are also known as the most appropriate ones for the applicable concrete in the mentioned areas, are studied; Portland Pozzolana cement, type II and type V. Conducted experiments on the concrete samples include uniaxial compressive strength tests, water absorption, determination of water penetration depth of cubic samples.Results show that from the mechanical and durability point of view, using the DMS as a substitution aggregate is best to be kept up to 25 percent of the total aggregate volume.Keywords: Non, reinforced concrete, Dredged marine sand, Durability, stability, Compressive Strength}
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هدف این مقاله، بررسی عددی یک سیستم نوین جذب کننده انرژی در قاب های خمشی فولادی است. قاب های خمشی به عنوان یکی از مطلوب ترین سیستم های باربر جانبی شناخته می شوند. بااین حال، شرایط حداقلی اندازه دهانه به عمق تیر که به منظور تشکیل مفاصل پلاستیک در دو انتهای آن در آیین نامه ها الزام شده، به عنوان یکی از محدودیت های این سیستم شناخته می شود. با قرارداد یک فیوز برشی در میانه تیر، مفاصل پلاستیک خمشی از دو انتهای تیر به مفصل پلاستیک برشی در میانه آن انتقال می یابد. بنابراین تسلیم فیوز دربرش، پیش از تسلیم خمشی در دو انتهای تیر اصلی اتفاق می افتد و درنتیجه، سیستم پیشنهادی محدودیت آئین نامه ای را مرتفع می نماید. فیوز بخشی از تیر است که با ورود به تغییر مکان های غیرخطی مانع ورود باقی اعضا به این محدوده می شود. به منظور ایجاد فیوز برشی، با ایجاد شیارهایی با الگوی مشخص در جان میانه تیر، تضعیف مقاومت برشی حاصل می گردد. مدل های عددی این قاب در نرم افزار اباکوس ساخته و با نتایج آزمایشگاهی صحت سنجی شده است.کلید واژگان: قاب خمشی فولادی, مفصل پلاستیک, فیوز برشی, بهسازی, تحلیل غیرخطی}The aim of this paper is to investigate a new energy dissipating system in steel moment resisting frames using finite element method, namely, slitted moment resisting frame system. Moment resisting frames are considered as one the most favorable novel lateral force resisting system. However, the minimum requirement of the beam span to depth ratio, to form the plastic hinges at the two ends of the beam to satisfy. By placing a sheer fuse in the middle of the beam, the flexural plastic hinges are transferred to the middle of the beam through nonlinear shear behavior. Therefore, shear fuse yielding precedes flexural yielding at the two ends of the beam and consequently the proposed system satisfies the code limitations. The fuse is a part of the beam, which, by entering into the nonlinear behavior, prevents other part of the beam from entering into the nonlinear behavior. Numerical models of the proposed system are developed in ABAQUS and are compared against the experimental results.Keywords: Steel moment resisting frame, Plastic hinge, Shear fuse, Non, linear analysis}
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بعد از زلزله نورثریج اتصال با مقطع کاهش یافته جهت بهبود عملکرد اتصالات پیشنهاد گردید. در ویرایش اخیر مبحث دهم مقررات ملی، تشکیل مفاصل پلاستیک انتهای تیرها در خارج از محدوده اتصال به ستون ملزم گردیده است. استفاده از تیر با مقطع کاهش یافته راهکار موثری برای این منظور می باشد. در این تحقیق جزئیات جدیدی برای این اتصال که شامل ترکیبی از حالت جان کاهش یافته و جان موجدار می باشد پیشنهاد و ضمن مقایسه با گزینه های دیگر مدلی برای توصیف رفتار این اتصال جدید تهیه میشود. برای این منظور از نتایج تحلیل مدل اتصال به روش اجزای محدود استفاده شده است. سپس ساختمان فولادی با سیستم قاب خمشی ویژه در حضور تیر با مقطع کاهش یافته طرح و با استفاده از نرم افزار تحلیل غیر خطی در محدوده غیرارتجاعی تحلیل و رفتار کلی سازه با جزئیات اتصال جدید و معمولی بررسی می شود که شامل بررسی شکل پذیری و تعیین ضریب رفتار می باشد. تحلیل موضعی اتصالات، افزایش 9 درصدی ظرفیت چرخش پلاستیک در صورت استفاده همزمان از جان موجدار و کاهش یافته را نشان می دهد هرچند افزایش در ضریب رفتار قابهای فولادی مدل شده با چنین اتصالی چندان قابل توجه نبوده است.کلید واژگان: تیر با مقطع کاهش یافته, تحلیل غیر ارتجاعی, شکل پذیری, ضریب رفتار}After Northridge earthquake reduced beam sections were suggested to improve connections performance. A new detail has been evaluated for reduced beam sections that includes a combination of two previously investigated models; reduced web section and accordion web section. According to comparison with other models through finite element analysis, it was found that the stresses and plastic strains have been more effectively reduced in the beam to column connection region of the combined detail and up to 9%. Increase in plastic rotation capacity may be achieved without a noticeable loss in strength. According to performed nonlinear static analyses results for well-designed 5, 10 and 15 story steel buildings with special moment resistant frame system, the amount of plastic drift capacity using the reduced beam sections slightly increases and this increase is more in connections with accordion web and accordion web together with reduced web sections respectively. Pushover curves indicate that the reduced beam sections has little effect on the linear part of the curves but increasing drifts, added strength is reduced. The rate of decrease for two connections with accordion web sections and accordion web with reduced web is more. Average rates of behavior factors 11.38 and 11.73 and 11.88 have respectively been obtained for moment resistant frames with reduced beam section and accordion web sections and accordion web with reduced web sections. It can be said that the average rates of behavior factor for frames that are designed based on the behavior factor of 8 has been considerably increased.Keywords: Reduced beam Section, Non, elastic analysis, Ductility, Behavior factor}
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در نوشتار حاضر، اثرات نامنظمی های جرم، سختی، مقاومت، و ترکیب سختی و مقاومت در ارتفاع، در عملکرد لرزه یی سازه های فولادی با سیستم باربر جانبی قاب خمشی فولادی ویژه، در قالب منحنی های سطوح اطمینان عدم تجاوز از اهداف عملکردی ارزیابی شده است. اثرات انعطاف پذیری پی با درنظر گرفتن رفتار غیرخطی خاک، در مدل های تحلیلی اعمال شده است. نتایج به دست آمده نشان می دهد که نامنظمی های غیرهندسی مذکور باعث می شوند تا با افزایش شدت ارتعاشات لرزه یی و تقاضای جابجایی متناظر با آن ها، نسبت به سازه ی منظم، از قابلیت اطمینان سازه کاسته شود. در بین تمام مدل های نامنظم مورد بحث مشاهده می شود که دسترسی به سطوح قابلیت اطمینان مطلوب در سازه های با نامنظمی ناشی از تغییرات مقاومت، عمدتا در شدت ارتعاشات لرزه یی پایین مقدور است که به موجب آن جابجایی و تقاضای متناظر با سطوح اطمینان کاهش می یابد؛ به نحوی که در مقایسه با سازه ی منظم، اختلافی تا مرز 85\٪ در نتایج مشاهده می شود.
کلید واژگان: نامنظمی غیرهندسی در ارتفاع, مهندسی زلزله ی عملکردی, تحلیل دینامیکی افزایشی, سطح اطمینان تامین اهداف عملکردی}In this paper, the seismic performance of vertically irregular steel buildings is evaluated. A ten-story steel building with special moment resisting frames is considered as the superstructure. The sufficiency of structural elements was evaluated by the earlier Iranian Seismic Codes. The three-dimensional finite element model of soil with nonlinear material behavior was attended below the superstructure to incorporate the foundation flexibility effects into the analytical models. The irregularities of mass, stiffness, strength, and concurrently stiffness and strength were assigned to different stories. Irregularity position was limited to the 1st, the 5th, and through the bottom half floors (stories 1 to 5). Through a series of nonlinear incremental dynamic analyses, the flexible-base structural performance levels were evaluated in the framework of probabilistic performance-based earthquake engineering. The confidence level curves of both regular and irregular structures were developed at two performance objectives: collapse prevention and global instability.It is observed that the mentioned non-geometrical irregularities reduce the confidence levels of irregular structure as the intensity of the ground motion and related displacement demands increase. In comparison to the regular structure, depending on the position of irregular stories through the structure height, the seismic intensity and corresponding demands to a specific confidence level, change. As the structures pass through the collapse prevention performance level 40% to 60% variation is observed in the seismic capacity of no uniform distribution of strength along the structure height. Meanwhile, mass irregularity of the bottom floor has low variations in both demands and seismic intensity compared to the regular model. Generally, at rigorous nonlinear phase of structural behavior, the irregularity effects are highlighted. Among all the irregular structures, an appropriate confidence level of strength irregularity models is obtained at low seismic intensities. The displacement demands are also decreased so that in comparison to the regular structure, 85% differences are observed.
Keywords: Non, Geometric Vertical Irregularity, Performance, Based Earthquake Engineering, Incremental Dynamic Analysis, Confidence Level Of Performance Objectives} -
This paper investigates the reduction of stiffness, variation of flexural rigidity and nonlinear response of RC member to detect flexural cracks. The positive cyclic pseudo static load was applied stepwise to the specimen to induce damage. Flexural rigidity characteristics were studied by conducting free vibration test on RC beam at various stages. Vibration characteristics of each damage state were successfully identified to detect the relationship between damage levels and fundamental frequencies under various failure loads. Due to flexural cracks longitudinal bars may yield resulting in reduction in effective flexural rigidity and hence frequency. This yielding of reinforcement in longitudinal bars can be detected from change in natural frequency. The non-linearity was detected by checking the changes in the fundamental frequency during various stages of loading.Keywords: Stiffness degradation, natural frequency, non, linearity, reinforced concrete beam}
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This paper investigates the effective parameters on seismic efficiency of tuned mass dampers, TMD, in dual systems of moment resisting frame and cross bracing with 15, 20 and 25 stories. TMDs with different mass ratio were located at different heights. Non-linear time history analyses were conducted under three earthquake records. The results showed that the reduction of base shear is significant at all the cases, and by increasing the number of stories, reduction of the base shear is increased. However, in terms of displacement and acceleration of the roof, TMD could be very sensitive to its parameters.Keywords: Tuned mass damper, non, linear dynamic analysis, vibration control, passive control, energy dissipation}
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The present paper deals with the behavior of reinforced concrete beams in presence of plasticity and cyclic loadings. The model takes into account the nonlinear material behaviors of the constituents steel and concrete. A numerical model based on the finite element method is investigated for the study of the reinforced concrete beams under cyclic loads undergoing large deformation in the plastic range. In the study, nonlinear material behavior laws are introduced in presence of plasticity and cyclic behavior in the concrete in compression and in the reinforcement steel bars under tension stresses. The concrete steel interactions as well as the crack damage are also considered in the model. An incremental iterative method in adopted in the solution of the equilibrium equations. The model is validated and compared to some benchmark solutions available in literature. The agreement is good in the case of beams under monotonic loads or cyclic loads with high cycles.Keywords: Reinforced concrete, cyclic behavior, non, linear, flat structures, plasticity}
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Instead of the complicated non-linear response history analysis (NL-RHA), engineers are more likely to use simplified non-linear static procedures (NSPs). Because of various deficiencies of the conventional pushover procedures, different researchers presented advanced NSPs. Some of these advanced NSPs used first two modes of the structure and the others offered using more than first two modes. In this study, the higher mode contributions in the structural responses are investigated through NSPs including modal pushover analysis (MPA) and modal shear-based pushover (MSP) procedures for far-field and near-field ground motions. Finally, the optimized number of considered modes for different situations is suggested.Keywords: Response history analysis, non, linear static procedure, higher mode effects, modal contribution ratios, far, field ground motion, near, field ground motion}
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RC coupled shear walls are known as one of the best and popular lateral load resisting structural systems. Most of the structural design codes have no seismic design considerations for base shear and fundamental vibration period. In current study finite element models were generated to provide a reliable data base to estimate the base shear and fundamental period. The differences between the behavior of in-plane and out-of-plane actions in these systems were investigated. In the final stage corrective coefficients will present according to analyses results. More accurate estimation of the demand makes more resistant structures against wind and earthquake loads.Keywords: RC coupled shear wall, base shear, fundamental vibrational period, non, linear finite element analysis}
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International Journal of Optimization in Civil Engineering, Volume:7 Issue: 2, Spring 2017, PP 257 -267Calculation of lateral earth pressure on retaining walls is one of the main issues in geotechnics. The upper and lower bound theorems of plasticity are used to analyze the stability of geotechnical structures include bearing capacity of foundations, lateral earth pressure on retaining walls and factor of safety of slopes. In this paper formulation of finite element limit analysis is introduced to determine plastic limit load in the perfect plastic materials. Elements with linear strain rates, which are used in the formulation, cause to eliminate the necessity of velocity discontinuities between the elements. Using non-linear programming based on second order cone programming (SOCP), which has good conformity with cone yield functions such as Mohr-Coulomb and Drucker-Prager, is another important advantage that remove the problem of using ordinary linear programming algorithms for yield functions such as divergent in the apexes. Finally, the optimization problem will be solved by mathematical method. The proposed method is used for calculating active earth pressure on retaining walls in cohesive-frictional soils. According to results of analysis, active earth force on retaining wall is decreased by increasing soil cohesion, wall inclination friction angle between backfill and wall and friction angle of soil wherein the force is increased by increasing surcharge on the backfill and the backfill slope. Mathematical method is used for obtaining accurate results in this research, however, heuristic methods are used when approximate solutions are sufficient.Keywords: upper bound, finite element method (F.E.M), optimization, non, linear programming, active earth pressure, cohesive, frictional soils}
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This paper presents a generalized numerical method to evaluate element stiffness matrices needed for the free vibration and stability analyses of non-prismatic columns resting on one- or two-parameter elastic foundations and subjected to variable axial load. For this purpose, power series approximation is used to solve the fourthorder differential equation of non-prismatic columns with variable geometric parameters. Then, the shape functions are obtained exactly by deriving the deformation shape of the column as power series form. Finally, the element stiffness matrices are determined by means of the principle of virtual work along the columns axis. In order to demonstrate the accuracy and the efficiency of presented method, several numerical examples including in the free-vibration and buckling analysis of non-prismatic columns, portal frame, and gable frame are presented and obtained results compared with the results of other available numerical and theoretical approaches. The method can be applied for the buckling load and natural frequencies computation of uniform members as well as non- prismatic members.Keywords: Stiffness matrix, Power series solution, Non, prismatic column, Buckling, vibration}
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Nowadays, as a result of increased terrorist and bomb attacks throughout the globe in the vicinity of strategic buildings, designing these structures against impact loads, particularly the blast-related ones, has been taken into more consideration. The current procedure for designing the structure against an explosion is a design against the local failure of the current elements in the first step and then, in the next step, against local damage as well as tactful thinking to prevent this damage from spreading to other parts of the structure. The present research investigates the impacts of explosives, derived from probable terrorstricken scenarios inside and outside a strategic four-story steel building with a special moment frame system. Then, the resistive capacity of the damaged building (due to blast) has been evaluated against the progressive collapse, and finally, the rate of the collapse risk and the reliability of the structure have been obtained by presenting a probable method. Thus, the vulnerable parts inside and outside the building are identified and safety measures have been determined, so that in case of no safety or excessive collapse risk- access to dangerous parts of the building could be reinforced or limited. Results show that progressive collapse probability and reliability of the building are 57% and 43% respectively.Keywords: Blast Load, Non, Linear Dynamic Analysis, Progressive Collapse, Risk Assessment, Strategic Building}
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In weaving section due to a strong need for lane changing, a type of turbulence is created in traffic flow; so, the speed and the capacity of the weaving section decreases. Therefore, investigation of the weaving section is very important. However, due to shortage of the manual for urban principal arterials (highways), calibration of these models is necessary. One of these models that are used to evaluate the level of service of the weaving sections is speed model which will be developed in this paper. Thus, data of the lane-changing rates and travel time (speed) have been collected in 9 principal arterials of Tehran. Then, two models for estimating of weaving and non weaving speed are developed. Validations also confirm the accuracy of the developed models. Exploration of these developed models reveals that speed decreases by increasing the weaving intensity. In addition, Comparison of the developed models and HCM 2010 for similar condition shows that the developed models estimate more than the HCM 2010 model.Keywords: Weaving speed, non, weaving speed, weaving section, urban principal arterials}
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