جستجوی مقالات مرتبط با کلیدواژه "high" در نشریات گروه "عمران"
تکرار جستجوی کلیدواژه «high» در نشریات گروه «فنی و مهندسی»-
کاربرد بیس استئارامید اتیلن در قیر موجب کاهش دمای اختلاط و دمای تراکم آن و بالتبع کاهش مصرف انرژی در تولید مخلوط آسفالتی می شود. در این پژوهش، پلی فسفریک اسید (PPA) به منظور جبران اثرات مخرب EBS بر رفتار دمای پایین قیر مورد استفاده قرار گرفته و تاثیر آن بر رفتار دمای بالای قیر با استفاده از پروتکل سوپرپیو و همچنین آزمایش MSCR ارزیابی شده است. به این منظور PPA در سه درصد مختلف 5/0، 1 و 5/1 درصد وزنی به قیر حاوی 3 درصد وزنی بیس استئارامید اتیلن اضافه شده و با استفاده از رئومتر برشی دینامیکی (DSR) آزمایش متداول پروتکل سوپرپیو و نیز آزمایش خزش بازگشت در سطوح تنش چندگانه (MSCR) روی آن انجام شده است. نتایج آزمایشگاهی نشان داده است اضافه کردن 5/0 درصد وزنی پلی فسفریک اسید در حالی که دمای اختلاط و تراکم قیر حاوی بیس استئارامید اتیلن را به طرز محسوسی افزایش نداده منجر به حفظ نسبی و مطلوب دمای بالای عملکردی قیر در مقایسه با صرفا استفاده از PPA شده است. با این حال نتایج آزمایش MSCR نشان داده است که می بایست در این خصوص محافظه-کارانه تر برخورد نمود زیرا در سطوح ترافیکی موردنظر استاندارد قیر حاوی 3 درصد وزنی EBS و 5/0 درصد PPA نتایج مناسبی نظیر آنچه در معیار رده بندی عملکردی پیشین گزارش میشود ارائه نکرده است.کلید واژگان: بیس استئارامید اتیلن, پلی فسفریک اسید, خزش بازگشت, دمای عملکردی بالا و پایین, MSCRUsing Ethylene Bis(Stearamide) (EBS) decreases mixing and compaction temperature of bitumen and consequently decreases energy consumption of asphalt mixture production. In this study, polyphosphoric acid (PPA) is added to EBS-modified bitumen to mitigate low-temperature deteriora-tion of EBS. Also, the effect of adding PPA and EBS on high-temperature behavior of bitumen is investigated using supepave protocol and multiple stress creep and recovery (MSCR) test. For this purpose, PPA is added to EBS-modified bitumen (having 3% of EBS) in three different dosages of 0.5, 1, and 1.5% (based on the original bitumen weight). Then, using a dynamic shear rheometer, both superpave protocol test and the MSCR test are performed on all samples at high temperatures. Also, using a bending beam rheometer, the low-temperature behavior of all samples are evaluated. The results showed that while adding 0.5% of PPA did not change mixing and compaction tempera-ture of EBS-modified bitumen significantly, it can improve high-temperature behavior of bitumen. However, MSCR results showed that it is required to consider the high-temperature behavior of modified bitumen conservatively as the bitumen modified with 0.5% PPA and 3% EBS cannot meet standard requirement for three traffic categories.Keywords: Polyphosphoric Acid, Ethylene Bis(Stearamide), Creep-Recovery, High, Low Performance Temperature, MSCR
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نشریه مهندسی عمران و محیط زیست دانشگاه تبریز، سال چهل و هشتم شماره 1 (پیاپی 90، بهار 1397)، صص 89 -100هدف این مقاله تعیین تاثیر احداث ساختمان های بلندمرتبه، خارج از مقررات طرح جامع شهری، بر عملکرد هیدرولیکی شبکه توزیع آب اهر است. برای این منظور، ابتدا مدل EPANET و الگوریتم جامعه مورچگان در محیط Matlab با هم تلفیق شدند. سپس با کمینه کردن اختلاف فشار مشاهداتی و محاسباتی در گره های شبکه، ضرایب هیزن ویلیامز لوله های مدل شبکه تنظیم شد و بهترین مدل، برای ارزیابی عملکرد هیدرولیکی شبکه مورد استفاده قرار گرفت. برای مقایسه عملکرد هیدرولیکی شبکه از سه شاخص قابلیت اطمینان فازی، شاخص اطمینان پذیری فشار و شاخص اطمینان پذیری نیاز آبی استفاده شده است. مقایسه نتایج مدل ها نشان می دهد که شبکه توزیع آب اهر بعد از ساخت و سازهای موجود از عملکرد مطلوبی برخودار است هر چند چون شبکه توزیع آب اهر قبل از ساخت و سازها با مشکل کمبود فشار در برخی مناطق مواجه بوده است، ساخت و سازهای انجام شده، این مشکل را تقویت نموده است. اما هنوز خللی در عملکرد هیدرولیکی، اکثر مناطق شهری ایجاد نکرده است. در صورتی که برنامه ساخت و سازها به شکل گذشته خود و خارج از طرح های جامع شهری ادامه پیدا کنند به دلیل این که در کوچه و پس کوچه های شهر و در نقاط خاصی از شهر تمرکز یافته است، عملکرد هیدرولیکی شبکه را دچار مشکل خواهد نمود، به طوری که فشار در گره 42 از 6/31 متر به 7/21 متر و مقدار منطقه ای شاخص قابلیت اطمینان فازی از 44/0 به 19/0 کاهش پیدا می کند.کلید واژگان: ساختمان های بلندمرتبه, شبکه توزیع آب اهر, الگوریتم جامعه مورچگان, عملکرد هیدرولیکی, شاخص قابلیت اطمینانJournal of Civil and Environmental Engineering University of Tabriz, Volume:48 Issue: 1, 2018, PP 89 -100Gradually, with urban population growth and development of Ahar city, old houses in the lanes and alleys are changing into high-rise buildings. In most of these buildings the regulations are violated. This issue has created a lot of problems for the inhabitants. The goal of the paper is to answer this question: "what is the consequence of high rise building constructions without observing urban rules and regulations on hydraulic performance of the Ahar water distribution network?" To answer this question, Ahar water distribution network was selected as a case study and its hydraulic performances were investigated in different situations.Keywords: High, rise building construction, Ahar water distribution network, Ant colony optimization, Hydraulic performance, reliability index
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Property Assessment of Hybrid Fiber-Reinforced Ultra-High-Performance ConcreteThe purpose of this study was to determine the effect of steel/polypropylene hybrid fibers on the mechanical properties and microstructure of ultra-high-performance concrete (UHPC). Tests were carried out on UHPC without and with fibers (steel and/or polypropylene in amounts of 0.251%). In this study, granite or granodiorite coarse aggregate with a grain size of about 2/8 mm was employed. The three-point bending tests displayed prolonged post-peak softening behavior. In addition, increasing the content of polypropylene fibers reduced the fracture energy. Moreover, the SEM results illustrated that adding a certain amount of fibers to concrete considerably changes the microstructure. It was observed that the smallest micro-cracks in the interfacial transition zone between the paste and aggregate occurred in the concrete containing steel fibers.Keywords: Ultra, high, performance concrete, Hybrid steel, polypropylene fiber, Fracture energy, Microstructure
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Experimental and Analytical Study on Ultimate Load Capacity of RC Columns in the Subway Stations Under High-Temperature Gas Fume EffectsIn fires, reinforced concrete (RC) columns in the subway stations were seriously threatened by high-temperature gas fumes. In this paper, an axial compressive simulation test that involved eight RC columns was undertaken to investigate the effect of high-temperature gas fume on RC columns. Two of them were control specimens with different cross sections. The others were exposed to high-temperature gas fumes. The specimens were heated to 300, 400, and 500 °C. The effects of high-temperature degree on ultimate load capacity and failure mode were investigated. As the applied load was increased, the crack gradually spread to the unheated area. Meanwhile, the initial stiffness and energy dissipation capacity were also summarized. The test results show that the ultimate load capacity and initial stiffness of RC columns decreased sharply with the increase in temperature. Compared to unexposed RC columns with circle cross section, the ultimate load capacity of specimens exposed to high temperature decreased by 47.9, 56.0 and 67.9%. The initial stiffness of RC columns with circle cross section exposed to 500 °C was 13 times lower than those of unexposed RC columns. The energy ductility of RC columns increased with the flue gas temperature. Furthermore, an analytical model was established to predict the residual axial load-carrying capacity of RC columns. It was demonstrated that the analytical model is correct and the predicted results are consistent with experimental results.Keywords: High, temperature gas fume, Metro station, Reinforced concrete column, Ultimate load, carrying capacity
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The objective of this study was to investigate the effect of P-Delta analysis on the static and dynamic stability analysis of high rise steel buildings subjected to earthquake excitation. Different building models including ten, twenty, thirty, forty and fifty story composite steel buildings with symmetrical and asymmetrical layouts were analyzed. Finite element approach by using ETABS software was used to conduct this study. Different parameters were investigated including number of stories, structural elements stiffness, and bracing system. The "second-order" analysis, which includes geometric nonlinearity and P-Delta effect, used to check the adequacy of the "amplified first-order" analysis proposed by AISC specification for stability and strength design. Second-order analysis with linear and nonlinear time-history, including P-Delta effects was accounted for. The numerical analysis results presented reveal that the stability coefficient approach introduced in the ASCE 7-10 standard to consider P-∆ effects in the design and analysis of structures appears to be overly conservative. A maximum stability coefficient (θmax) greater than 0.25 would be necessary to account for P-Delta effects. This depends on the type of loading, number of stories, type of analysis as static or dynamic and shape of the buildings as symmetrical or asymmetrical.Keywords: Dynamic Analysis, High, Rise Building, Finite Element, P, Delta Effect, Stability
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جداسازی لرزه ای یکی از مناسب ترین ابزارهای مهندسی زلزله در زمینه کنترل غیرفعال می باشد. اگرچه این روش در ابتدا برای سازه های کوتاه مرتبه با رفتار روسازه نسبتا صلب توسعه یافت، با این حال، کاربرد آن در سازه های متوسط و بلند رو به افزایش است. کمترین نتیجه ای که جداسازی لرزه ای در سازه های بلند به همراه دارد، کاهش تغییرمکان نسبی جانبی (دریفت) طبقات به علت تغییرشکل مود نخست، به علاوه تامین یک مکانیزم استهلاک انرژی مناسب در کف ساختمان می باشد. برای حفظ کارآیی جداسازی، زمان تناوب سیستم جداساز باید به اندازه کافی بزرگ درنظر گرفته شود. چنین سازه ای ممکن است در برابر زلزله های پریودبلند آسیب پذیر باشد. در این مقاله، عملکرد لرزه ای سه مدل ساختمان برشی 8، 14 و 20 طبقه جداسازی شده، توسط دو نوع جداساز سربی-لاستیکی و آونگ اصطکاکی، تحت اثر زلزله های پریود بلند، مورد مطالعه قرار می گیرد. نتایج نشان می دهد که با افزایش ارتفاع، میزان اثرپذیری سازه از زلزله های پریود بلند بیشتر می شود و این حرکات قادرند نیاز جابجایی بالایی را به جداساز تحمیل کنند.کلید واژگان: ساختمان برشی, جداسازی لرزه ای, ساختمان های بلند, زلزله های پریودبلندBase isolation systems may be considered as one of the most powerful tools of earthquake engineering pertaining to the passive structural vibration control technologies. It may enable a building or non-building structure to survive a potentially devastating seismic impact. Generally, it is thought that application of seismic isolation is limited to low- and medium-rise structures, and the use of isolation for high-rise buildings considered as impractical or unfeasible. However, existing examples of isolated high-rise buildings in Japan, also in Iran, suggest that these viewpoints clearly disagrees with the real state-of-practice that exists there. Since the 1995 Kobe earthquake, just fewer than 200 isolated high-rise buildings, ranging from 60 to 180 meters height, have been constructed in Japan. However, this strategy is still uncommon in most countries of the world. Implementation of base isolation can greatly decrease inter-story drifts and floor accelerations, which results in protection of buildings contents. As a result, high-rise buildings can be kept fully operational during the earthquake and also immediately occupiable just after the event. In other words, isolation can be adopted for the improved performance of high-rise buildings. To maintain the efficiency, the period of isolation system has to be considered between 4 and 7 seconds. Clearly, structures like this will be vulnerable to long period ground motions. Therefore, it is necessary to study the behavior of these structures under such earthquakes. Long-period ground motions can be divided into far-source and near-fault classes. Most far-source long-period ground motions were generated by large earthquakes and effective propagation paths. Therefore, far-source long-period ground motions are generally associated with offshore earthquakes in subduction zones. Near-fault long-period ground motions are generated mainly by rupture directivity effects in the vicinity of earthquake source faults,. They consist primarily of rupture directivity pulses, which can be damaging, especially when combined with site effects and basin edge effects. In this paper, three base isolated models of 8-, 14-, and 20-story shear buildings using isolator type of lead-rubber bearing (LRB) and friction pendulum system (FPS), under long-period ground motions are studied. A set of 14 long-period ground motions 5 far-source long-period motions and 9 near-fault long-period motions as well as 14 short-period ground motions were selected. Total earthquake input energy per unit mas was used as a measure to distinguish long-period motions so that those which had a significant input energy over the periods of 2 seconds were considered as long-period motions. For each model two isolators LRB and FPS were designed so that the design displacement and the period of systems were exactly the same. The isolators were designed carefully and all dimensions and parameters were checked to insure practicality of the design. Then nonlinear dynamic analysis was implemented to evaluate the response of the structures. Results show that in the cases that input motions are short-period, increasing the height of the structure doesnt significantly affect the structure response and the isolation displacement are nearly the same. On the other hand, as the height of the structure is increased, its response due to the long-period ground motions becomes more significant, and these motions impose a great displacement demand in the isolation system.Keywords: Shear Buildings, Seismic Isolation, High, Rise Buildings, Long, Period Ground Motions
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International Journal of Advances in Railway Engineering, Volume:2 Issue: 2, Summer - Autumn 2014, PP 93 -106With speed increasing in high-speed trains, due to limitations of other types of brakes, aerodynamic brake has become an important braking method. In this task to make better use of brakes panel different configurations are examined and the best panel shape which provides the reasonable drag coefficient is introduced. The results of simulations are carried out with the computational fluid dynamic (CFD) software for a high speed train moving at speed of 360Km/hr. To provide the best arrangement of braking panel rows on the train roof, four cases are studied: a train without aerodynamic brakes, with one, two, and three rows of aerodynamic brakes panel over the roof of the train. The braking force per unit area of aerodynamic brakes is determined and compared with the results found in literature. With regard to the drag coefficient and necessary space for the placement of panels, the best shape and arrangement is introduced. Finally, to examine the material and thickness effects on operation of braking panels; stress and modal analysis have been performed and variation in: weight, maximum stress, displacement and first natural frequency are discussed.Keywords: braking panels, drag coefficient, high, speed train, natural frequency, CFD
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در این مطالعه به منظور انتخاب مناسب ترین بتن برای ساخت ساختمان های بلند مرتبه، روش فرایند تحلیل سلسله مراتبی (AHP) که مبتنی بر دانش کارشناسی بوده، مورد استفاده قرار گرفته است.
معیار های مورد بررسی در این پژوهش شامل طراحی سازه ای، هزینه، کیفیت، زمان و سهولت اجرا می باشد. به منظور بررسی دقیق تر و به دست آوردن نتایج مستندتر، شش نوع بتن (با و بدون نیاز به ویبره) برای سازه 21 طبقه که در شهرستان بابلسر با بتن معمولی در حال اجرا می باشد مورد بررسی قرار گرفته است. سازه با نرم افزار ETABS مدل سازی و بررسی گردید. این سازه ها، براساس معیار های ذکر شده، با روش تحلیل سلسله مراتبی و استفاده از نرم افزار Expert Choiceمورد بررسی و ارزیابی قرار گرفتند. نتایج به دست آمده حاکی از آن است که استفاده از بتن سبک و سبک خودتراکم موجب کاهش وزن سازه به میزان 5/ 12درصد نسبت به بتن معمولی و خودتراکم و 9 /4 درصد نسبت به بتن مقاومت بالا و مقاومت بالای خودتراکم خواهد شد. بتن مقاومت بالا و بتن مقاومت بالای خود متراکم، مصرف میلگرد را به میزان 9/ 18 درصد نسبت به بتن معمولی و بتن خودتراکم و همچنین 8 /7 درصد نسبت به بتن سبک و بتن سبک خودتراکم کاهش خواهد دهد. با توجه به تمامی معیار های مورد بررسی در این پژوهش بتن خودتراکم مقاومت بالا در درجه اول اهمیت برای ساخت سازه های بلند مرتبه قرار گرفته است و همچنین با توجه به هر معیار، بتن ها اولویت بندی شده و نتایج گزارش شده است.
کلید واژگان: سازه های بلند مرتبه, بتن با و بدون نیاز به ویبره, تصمیم گیری چند معیاره, تحلیل سلسله مراتبیIn order to select the most suitable concrete for the construction of high-rise buildings, method of analytic hierarchy process (AHP) based on expert knowledge has been used. Investigating alternative contain designing structure, costs, quality, time and easy to do. In order to closer examination and get documented results, six types of concrete (with or without vibration) for a 21-storey building in the city of Babolsar is running with normal concrete is studied. Structures with the software ETABS modeling was investigated. These structures, based on listed criteria, the Analytical Hierarchy Process and Expert Choice software was evaluated. The results suggest that By using low weight concrete, and self compact low weight concrete, weight of the building reduced to %12.5 in comparison to normal, and self compact concrete and to 4.9% in comparison to high strength, and self compact high strength concrete. By using high strength, and self compact high strength concrete, the cost of consumed bar is reduced to 18.9% in comparison to normal, and self compact concrete and to 7.8% in comparison to low weight concrete. According to all criteria evaluated in this study, High strength self compacting concrete is primarily importance to construction high-rise is located.Keywords: high, rise buildings high, rise buildings, concrete with, without vibration, Multi, Criteria, Decision, Making, ahp -
High speed intercity passenger rail is an inherently strong railway application. It operates over 250 km/hour. For perspective, high-speed represents the ultimate development of preexisting standard gauge infrastructure. Network of high-speed passenger rail lines aimed at reducing accident, reducing traffic congestion, air pollution cutting national dependence on foreign oil and improving rural and urban environments. In implementing such a program, it is essential to identify the factors that might influence decision making and the eventual success of the high-speed rail (HSR) project, as well as foreseeing the obstacles that will have to be overcome. In this paper we review, summarize the most important HSR projects carried out to date around the globe, namely those of France, Germany, Spain, Japan and China. We focus our attention on the main issues involved in the undertaking of HSR projects: their impact on mobility, the environment, the economy and on urban centers. By so doing, we identify lessons for policy makers and managers working on the implementation of HSR projects in Egypt. The conclusion is that there is likely to be a good case for the lessons to benefits in Egypt and developing countries.Keywords: High, speed rail, transportation between cities, government investment, transport planning, rail costs
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لبه یکی از ویژگی های برجسته تصویر است، لبه ها حامل اطلاعات مهمی از تصویر می باشند و به خوبی بیانگر ویژگی شکل اجسام هستند. اهمیت لبه ها در تصویر تا به آنجا است که سیستم بینایی انسان نیز از یک مرحله پیش پردازش برای آشکارسازی لبه استفاده می کند. بسیاری از روش های ریاضی کلاسیک برای تشخیص لبه بر اساس مشتق پیکسل های تصویر اصلی می باشند، مانند اپراتورهای گرادیان، لاپلاسین و لاپلاسین از اپراتور گاوسی. در تصاویر سنجش از دور به علت بالا بودن میزان تغییرات اپراتورهای کشف لبه نام برده شده دچار ضعف در تشخیص صحیح محدوده ی عوارض و حفظ پیوستگی و انسجام محدوده ی آن ها می باشند، به منظور حل این مشکلات این تحقیق یک روش نوین به منظور کشف لبه بر اساس خصوصیات تصاویر سنجش از دور را ارائه می دهد. در این روش ابتدا به صورت منطقه ای به شناسایی حدود آستانه ی مناطق مختلف تصویر پرداخته می شود و سپس با استفاده از الگوریتم شانون آنتروپی لبه های عوارض مختلف تصویری استخراج می شود. با توجه به بررسی های به عمل آمده، در این روش نحوه انتخاب حدود آستانه منتخب تاثیر بسزایی بر نتیجه نهایی دارد، به این منظور از روش بهینه سازی الگوریتم رقابت استعماری (ICA) استفاده شده است. در نهایت به منظور ارزیابی روش، نتایج حاصل شده با الگوریتم های استاندارد کنی، سوبل، رابرتز، LoG، الگوریتم تشخیص لبه بهینه سازی مورچگان و الگوریتم تشخیص لبه با روش بهینه سازی حدود آستانه توسط آنتروپی تسالیس مقایسه شدند و مشاهده شد که این روش به شکل کارآمدی قادر به شناسایی لبه های تصاویر مختلف می باشد.
کلید واژگان: لبه, الگوریتم رقابت استعماری, تصویر هوایی و ماهواره ایEdges are one of the salient properties of the image in which they have important information of the image and represent shape characteristics of the objects. Edges are important features due to the fact that the human visual system uses a preprocessing step for edge detection. The majority of the classical mathematical algorithms for the edge detection، such as Gradient، Laplacian and Laplacian of Gaussian operators are based on the derivative of the original image pixels. In the remote-sensing imagery، because of the high rate of changes، these edge detection operators perform weakly in correct detection of the feature boundaries and keeping their consistency. In order to solve these problems، this research presents a new technique using Shannon entropy based on Imperialist Competitive Algorithm (ICA). In this method، firstly a piecewise thresholding is used to identify the threshold of different parts of the image، and then the area boundaries are extracted using the Shannon entropy based on the selected threshold. According to obtained results، selection of thresholds have a high influence on the final results، Based on this، ICA optimized method is used in this research. In order to evaluate the performance of algorithm، the results from the proposed technique are also compared with the results obtained from Canny، LOG، Sobel، Roberts، Ant colony optimization edge detector and other Entropy edge detectors. The results show that the proposed method presents higher reliability in detecting the edges of different digital images.Keywords: Edge detection, Using Imperialist Competitive Algorithm, High, resolution satellite images -
High speed trains are an indispensable part of rapid transportation systems in many countries. As the fastest means of transport on the ground, these trains are extremely sensitive to the terrain and track conditions. Geometrical irregularities and mechanical characteristics of the track, together with inconsistencies in the lane (including bridges that support the track) are considered important parameters in defining performance and functionality for a train-track-bridge system. In this work a model for interaction study on such systems is proposed that introduces the skipping effect of load movement on track assembly. In this model the train system is consisted of rigid bodies and the bridge model is based on the modal approach. The prospect of using TMD devices for vibration control of bridge-train system is also provided in the model. For the track system a multi layered model using elastic foundation concept is adopted. Using this model, the roles of track characteristics in behaviour of train-bridge systems have been studied. Results of analyses show a clear distinction between different track technologies in providing performance and functionality for a typical train-bridge-track system. These results also indicate the effectiveness TMD devices in reducing bridge-track responses at resonance speeds.Keywords: vehicle, bridge interaction, high, speed trains, load skipping, track dynamics, vibration control
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طراحی لایه ی آرمور و تامین پایداری آنها مهم ترین مرحله در طراحی موج شکن های توده سنگی به شمار می رود. تاکنون، طراحی لایه ی آرمور متکی بر روابط تجربی و آزمایش های مدل فیزیکی بوده، که پارامترهای فیزیکی موج را به قطر آرمور مرتبط می کنند. در این روش ها، رابطه ی مستقیمی میان نیروی امواج و پایداری قطعات آرمور وجود ندارد. در این مطالعه با مدل سازی عددی، نیروهای وارد بر قطعات آرمور محاسبه و پایداری آنها در برابر امواج دریا مطالعه شده است. این مطالعه منحصر به بررسی پایداری آرمورهای مکعبی بدون درنظرگرفتن اثرات قفل و بست میان قطعات است. آنالیزها شامل محاسبه ی نیروها و لنگرهای اعمال شده به قطعات آرمور و ارزیابی سه مود ناپایداری برکنش، لغزش و چرخش قطعات به ازاء پارامترها و محل های مختلف قرارگیری آرمورهاست. نتایج حاصله نشان می دهد که نوع شکست موج تاثیر مهمی در میزان نیروهای وارده و پایداری قطعات آرمور دارد. تراز متوسط آب دریا و تراز بیشینه ی پایین روی موج، بحرانی ترین محل برای ناپایداری لایه ی آرمور تشخیص داده شده اند. در انتها، روابطی برای محاسبه ی میزان نیروها و لنگرهای وارده بر قطعات آرمور پیشنهاد شده است.
کلید واژگان: سازه های ساحلی, موج شکن های تاج بلند, پایداری لایه ی آرمور, نیروی امواج دریا, اندرکنش سازه و سیال, مدل سازی عددیRubble-mound breakwaters are common marine structures, which make a calm and safe area for ships to berth. To protect these structures from sea wave attack, armoured layers consisting of rocks or concrete blocks are put on their outer surface. Providing the stability of an armour layer is of great importance in the design of breakwaters. Until now, design of the armour layer has been based on empirical formulae and physical tests. In these conventional approaches, wave parameters are correlated to the armor weight. The current research aims to study the stability of the armour layer by a numerical method, employing the commercial code FLOW-3D. In the present research, the effects of geometrical parameters, such as breakwater slope and armour diameter and, also, physical parameters, such as wave height and period and still water depth, on the stability of the armour, are studied. For this purpose, four locations consisting of breakwater toe, still -water level and maximum of wave run-up and run-down levels are selected for placement of the armour. The breakwater is assumed to be high-crested and trapezoidal in shape. The armours are cubical and rigid. Also, monochromic waves are used in this study. Analyses are undertaken to determine forces and moments acting on the armour, which is assumed to have no interlocking between it for the sake of simplicity. The results show that wave breaking type has an important effect on the force and stability of the armour. Also, results indicate that the armour placed in the still water and maximum wave run-down levels are subjected to the most severe wave forces. Finally, some formulae are presented for computing wave forces, moments and stability numbers for armour blocks in different locations. Using these formulae allows the user to compare the stability modes of the armour for different wave characteristics.
Keywords: Coastal Structures, High, Crested Breakwaters, Armor Layer Stability, Sea Wave Load, Numerical Modeling -
This paper investigated the shear, impact and fracture strengths of high-strength concrete reinforced with two different industrial waste fibres. Locally available steel lathe waste and nylon waste were used at different volume fractions as fibre cocktails in concrete. Steel lathe wastes were used as-received lengths and nylon fibres were chopped into 40 mm lengths in this investigation. In total, 12 hybrid mixes were casted and tested at four different volume fractions (0.5%, 1.0%, 1.5% and 2.0%). The experimental programme was used the slump test and the air content test on the fresh concrete. The hardened concrete was tested for its shear and impact strength. A flexural test on notched beams under three-point bending was also carried out according to the RILEM 50-FMC committee recommendations. Load vs. mid-span deflection and load vs. crack mouth opening displacement were obtained and the fracture energy was evaluated.The best performance was obtained in hybrid which was enhanced due to the hybrid nature of the fibre cocktails of all the mixes, 2% volume fraction with a combination of steel ½ + nylon ½ fibres gives the best performance. The steel lathe waste fibres mainly contributed to limiting the crack initiation and lightweight non-metallic nylon fibres restricted the crack propagation. The combined advantages of these fibres provide high mechanical and fracture strength. Hence this hybrid fibre reinforced concrete with industrial waste fibres is doubly advantageous as it provides a superior performance without increasing the cost of the concrete.Keywords: Fibre reinforcement, high, strength concrete, mechanical properties, fracture energy, industrial waste
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در سال های اخیر توجه به دینامیک پل های راه آهن به عنوان یکی از مقدمات ضروری جهت احداث خطوط قطارهای سریع السیر افزایش یافته است. در این تحقیق، پاسخ دینامیکی پل راه آهن دوخطه یزدان از خط راه آهن قم ساقه با بیه های مختلف 0، 15، 30، 45 و 60 درجه تحت بار قطار عبوری و تاثیر بیه عرشه بر پاسخ دینامیکی سازه مورد بررسی قرار گرفته است. تحلیل دینامیکی بر پایه یک مدل سه بعدی از مجموعه پل و قطار و اندرکنش بین آن ها صورت گرفته است. با افزایش بیه پل مقدار فرکانس مربوط به مد اول پل افزایش یافته و در حالت کلی پاسخ دینامیکی پل با افزایش بیه کاهش می یابد. همچنین در سرعت های نزدیک به تشدید، با عبور هر گروه از محور چرخ ها از روی پل، مقادیر پاسخ ها به طور قابل ملاحظه یی افزایش می یابد.
کلید واژگان: اندرکنش پل و قطار, پاسخ دینامیکی, قطار سریع السیر, پل بیه دارIn recent years, interest in the dynamics of railway bridges, as necessary preliminaries for construction of high-speed railways, has increased rapidly. Increasing train speeds means that bridges are subjected to much higher dynamic effects. Therefore, the bearing capacity of structures must be increased in proportion to demand load, and dynamic effects must be considered in the structural design. In previous design methods, dynamic effects were often considered by introducing dynamic amplification factors, but, it can be seen that, in most cases, where train speed is more than 200 km/h, dynamic analysis of the bridge is required by increasing train speed. Correct understanding of the dynamics of railway bridges results in a realistic assessment of their structural responses under train loads. New bridge designs will be economical and also utilization of existing bridges will be proportional to their capacity. In this study, we have endeavored to specify the dynamic response of a double-track railway bridge to moving trains, and the influence of bridge skewness. Dynamic analysis is based on a three-dimensional model of bridge-train interaction. The Yazdan viaduct is an under construction bridge located on the Qom-Saghe double-track railway. It is also a simple span bridge with 22m span length that has been investigated under different skewness of 0, 15, 30, 45 and 60 degrees. To validate the accuracy of the model and the results of this study, a 30m span bridge from existing models in reputable international papers was used. The results of analysis demonstrated that the vertical displacement and acceleration of the bridge increase under high speed loads. At train speeds close to critical speed, due to moving axle groups, the bridge responses grew considerably as resonance occurred. Skewness was found to increase the fundamental frequency of the bridge, and with an increase in bridge skewness, the dynamic responses of the bridge decreased.
Keywords: Train, Bridge Interaction, Dynamic Response, High, Speed Train, Skewed Bridge -
در این مقاله برای تدوین استراتژی جهت بکارگیری قطارهای سریع السیر ریلی، ابتدا با بررسی و مطالعه گزارش های موجود و مصاحبه با خبرگان، فهرستی از نقاط قوت، ضعف، فرصت ها و تهدیدها احصاء، سپس تمامی عوامل با استفاده از تکنیک دلفی غربال و در نهایت 20 عامل خارجی شامل 10 فرصت و 10 تهدید در ارتباط با تدوین استراژی بکارگیری قطارهای سریع السیر ریلی جهت تشکیل ماتریس ارزیابی عوامل خارجی موسوم به EFE و 19 عامل داخلی شامل 9 قوت و 10 ضعف برای تشکیل ماتریس عوامل داخلی موسوم به IFE شناسایی و انتخاب شدند. نتایج حاکی از آن است که برای بکارگیری قطارهای سریع السیر ریلی در کشور بایستی با استفاده از استراتژی های محافظه کارانه(WO) از قبیل: ایجاد یک سازمان مستقل جهت اجرا و بهره برداری- توسعه نظام جامع اطلاعات مالی، مدیریت، برنامه ریزی و کنترل پروژه- بهره گیری از ظرفیت قانونی در جهت توسعه شبکه سریع السیر- گسترش تحقیق و توسعه(R&D) در جهت ارتقای دانش تخصصی، فناوری و همکاری های بین المللی- تدوین آیین نامه ها و مقررات لازم جهت تضمین ایمنی، کیفیت و قیمت گذاری خدمات - تربیت و آموزش نیروی انسانی کارآمد برای انتقال و جذب دانش و فناوری - جلوگیری از تاثیر تحریم و رکود اقتصادی بر ساخت و توسعه زیرساخت و تامین تجهیزات، به عنوان استراتژی های برتر مشخص شدند و در نهایت جهت کاربردی نمودن استراتژی های به دست آمده، برنامه عملیاتی پیشنهاد گردید.
کلید واژگان: استراتژی, برنامه ریزی استراتژیک, قطار سریع السیر, ماتریس SWOTWith regard to global economic growth and application of new technologies to expand public transportation، using of high-speed Rails in the country is an important issue and make the strategic planning a necessity. Meanwhile، analyzing and appropriate interaction with the internal and external environment is one of the factors for getting success in formulating an optimum strategy. In this paper، in order to formulate a strategy for using high-speed Rails in the country، first of all we will study and analyze the documents، the existing reports، and interviews with experts in the field of rail transportation and will obtain a list of strengths، weaknesses، opportunities and threats. At the end، by using the Delphi technique (consensus) all agents were screened and finalized. In the third phase، by using the SWOT model، we will formulate the appropriate strategies for deployment of high-speed Rails. Then، by using a matrix of quantitative strategies (QSPM)، we will prioritize the formulated strategies. At the end، an action plan was proposed. Research findings show that the Islamic Republic of Iran، by employing conservative WO strategies، in order to use high-speed Rails must use the opportunities ahead and overcome the internal weaknesses. Optimal strategies in this regard were developed and proposed.Keywords: Strategy, Strategic Planning, High, Speed Rails, SWOT Matrix -
Impact characteristics of high-performance steel fiber reinforced concrete under repeated dynamic loadingAn experimental study on the impact performance of silica fume concrete and steel fiber reinforced concrete at 28 days and 56 days under the action of repeated dynamic loading was carried out. In this experimental investigation, w/cm ratios of 0.4 and 0.3, silica fume replacement at 10% and 15% and crimped steel fibers with an aspect ratio of 80 were used. Results indicated that addition of fibers in high-performance concrete (HPC) can effectively restrain the initiation and propagation of cracks under stress, and enhance the impact strengths, toughness and ductility of HPC. Pulse velocity test was carried out for quality measurements of high-performance steel fiber reinforced concrete. Steel fibers were observed to have significant effect on flexural strength of concrete. The maximum first crack strength and ultimate failure strength at 28 days were 1.51 times and 1.78 times, respectively at 1.5% volume fraction to that of HPC. Based on the experimental data, failure resistance prediction model was developed with correlation coefficient (R) = 0.96 and absolute variation determined is 1.82%.Keywords: Silica fume, High, performance concrete, Steel fiber reinforcement, Mechanical properties, Pulse velocity, Impact resistance, Toughness
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Evaluation of Autogenous Shrinkage in High-Performance ConcreteRecent tendencies in concrete technology have been towards to high- performance concrete with a low water-cement ratio. However, high performance concretes have some problems. One of the problems is early-age cracking due to autogenous shrinkage.
This study presents the results of an experimental investigation carried out to evaluate the autogenous shrinkage of high-strength concrete. According to this, effects of water/binder ratio, cement content, fine to coarse aggregate ratio and silica fume content were evaluated. From the results of this investigation, it can be concluded that the autogenous shrinkage strain of high strength concrete increases with reduction of w/b ratio. The results show also that the variation of cement content and fine to coarse aggregate ratio had only a limited effect on the autogenous shrinkage.Keywords: Autogenous Shrinkage, High, Performance Concrete, Silica Fume, High, Strength Concrete -
COMBINED EFFECT OF SILICA FUME AND STEEL FIBER ON THE SPLITTING TENSILE STRENGTH OF HIGH-STRENGTH CONCRETEThis paper presents the influence of adding steel fibers and incorporation of silica fume on the mechanical properties of high-strength concrete. The variables investigated were steel fiber volume fraction (0 to 1.5%), silica fume replacement (5, 10 and 15%) and water-to-binder ratio (0.25, 0.30, 0.35 and 0.40). The influence of fiber content in terms of fiber reinforcing index on the compressive and splitting tensile strengths of high-strength steel fiber reinforce concrete (HSFRC) is presented. The use of silica fume increased both the compressive and splitting tensile strengths of concrete at 28 days. On the other hand, the addition of crimped steel fiber into high-strength concrete improves splitting tensile strength significantly. Based on the test data, using regression analysis, empirical expression to predict 28-day tensile strength of HSFRC in terms of fiber reinforcing index was developed and the absolute variation and integral absolute error (IAE) obtained was 3.1% and 3.3, respectively. The relationship between splitting tensile and compressive strength of SFRC was reported with regression coefficient (r) = 0.9. The experimental values of previous researchers were compared with the values predicted by the model and found to predict the values quite accurately.Keywords: strength concrete, splitting tensile strength, silica fume, steel fiber reinforcing index, high, strength fiber reinforced concrete, modeling
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This paper presents on an experimental study of confined high-strength concrete columns tested under axial compression. The main objective of the research is to know the performance of spirals and hoops with medium strength (400 MPa < fy < 600 MPa) in their contribution on the behaviour of confined high-strength concrete columns. The parameters of the study were concrete strengths, confining steel characteristics i.e: type of confinement (spirals and hoops), yield strength, spacing and volumetric ratio. From the experimental results it was found that the strength enhancement and ductility of confined concrete will decrease with if both of concrete strength and spacing of spirals or hoops increase, and the strain in the test also showed that the release of a cover of concrete core occurs prematurely. Other results shows that satisfactory of circular hoops as confinement steel behaved as good as the spiral reinforcement. The spiral reinforcement provision adopted in the Indonesian Concrete Standard 2002 (SNI 03-2847-2002) is quite reliable when applied in the design of confining steel with medium strength of high-strength concrete columns, therefore it is proposed that the upper limit provision of yield strength of confining steel warrant to be modified.Keywords: High, strength concrete, confinement, strength, ductility, spiral, hoop
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Iranian Journal of Science and Technology Transactions of Civil Engineering, Volume:37 Issue: 2, 2013, PP 271 -283Hydrodynamics of open channel confluences is very complicated. Simulation of rightangled channel confluences using a recently-developed 2D high-resolution model is presented in this paper. Finite-volume discretization of governing equations is adopted and fourth-order Runge- Kutta time integration is used. The effects of three different and most influential parameters, including discharge ratio, width ratio and downstream Froude number on hydrodynamics of rightangled confluences are studied. Standard Cartesian grids are employed and a single-block strategy is used for modeling the confluence. Turbulence shear stresses are included within the numerical model based on an eddy-viscosity approach. The results are compared with experimental data and show satisfactory agreement, particularly in cases when 3D features of flow are negligible. Despite having 3D characteristics in most cases, the results of this study show that a much simpler and computationally effective 2D numerical model is also capable of detecting most important features of flow in confluences, including separation zone and zone of high-velocity.Keywords: Confluence, two, dimensional flow, finite volume method, high, resolution scheme
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