توجه: محتویات این صفحه به صورت خودکار پردازش شده و مقاله‌های نویسندگانی با تشابه اسمی، همگی در بخش یکسان نمایش داده می‌شوند.
۱3D FINITE ELEMENT MODELLING OF BOND–SLIP BETWEEN REBAR AND CONCRETE IN PULL–OUT TEST
نویسنده(ها): ، ،
اطلاعات انتشار: سومین کنفرانس بین المللی بتن و توسعه، سال
تعداد صفحات: ۱۱
A reinforced concrete material is a composite material made up of two components with unequal mechanical behaviour and physical features. In general, the external load is already applied to concrete and the reinforcing bars receive its part of the load only from the surrounding concrete by bond. In composite structures, the bond between different components of reinforced concrete member has a primordial role and its negligence conducted to poor structural response. Therefore, for modeling of reinforced concrete structures one needs a simple and realistic bond–slip model. There are various finite element models for bond–slip relationship between reinforcement and concrete. In this paper, modeling of the transition region between steel and concrete as a cohesion layer in the finite element program (Ansys) is discussed. A 3D finite element model to represent this layer has been introduced. The layer involves modeling the ribs and effects of slip and bond stress of the bar. The accuracy of the models is assessed by comparison of the finite element numerical response with experimental data from pullout test.<\div>

۲AN EXPERIMENTAL STUDY ON STRUCTURAL BEHAVIOR OF RECTANGULAR RC COLUMNS DAMAGED BY REBARS CORROSION AND STRENGTHENING THEM WITH FRP
نویسنده(ها): ،
اطلاعات انتشار: سومین کنفرانس بین المللی بتن و توسعه، سال
تعداد صفحات: ۸
This paper presents the results of an experimental study on the structural behavior (strength and ductility) of rectangular RC columns which have been damaged by rebar corrosion. 22 small–scale reinforced concrete columns with dimensions of 160×160 mm in section and 340 mm in height were tested. Ten specimens were conditioned to three levels of accelerated corrosion and six were conditioned to
natural corrosion. The specimens were subjected to concentric compression load in order to assess the change of their mechanical properties due to the corrosion effects. Twelve specimens were strengthened with carbon and glass fiber reinforced polymer (CFRP and GFRP) to see the efficiency of different strengthening schemes. Based on this research it was concluded that the damaged columns show less strength and ductility in comparison with two undamaged columns and, FRP wraps could greatly enhance the strength and ductility of
damaged specimens.<\div>

۳EFFECTS OF FRP WRAPPING ON THE BOND–SLIP BEHAVIOR OF REINFORCING BAR
نویسنده(ها): ، ،
اطلاعات انتشار: سومین کنفرانس بین المللی بتن و توسعه، سال
تعداد صفحات: ۱۰
Fiber reinforced polymer (FRP) composites are being successfully used for strengthening of existing reinforced concrete (RC) structures because of their superior properties. Effects of wrapping with FRP on the strength and ductility of concrete members have been extensively investigated but information about effects of external confinement on the bond–slip behavior is very limited. In this paper the effect of external confinement with CFRP strips and internal confinement with transverse stirrup at beam splice test is evaluated and the results of two confinements are compared with one another. The main examined parameters include concrete cover, development\splice length, diameter of the reinforcing bar, concrete compressive strength and the amount of ordinary transverse reinforcement in the splice\development region. Test results indicated that external confinement with CFRP is more effective than internal confinement on bond strength and bond failure ductility.<\div>

۴IMPROVEMENT IN AXIAL STRESS–STRAIN BEHAVIOR OF COLUMNS USING PRE–STRESSED NON–LAMINATED FRP
نویسنده(ها): ، ،
اطلاعات انتشار: سومین کنفرانس بین المللی بتن و توسعه، سال
تعداد صفحات: ۱۱
As a new approach to obtain high efficiency from FRP confinement, pre–stressing of FRP composites have been introduced. Pre–stressed FRP straps change confinement situation from passive to active confinement. At active confinement, without considerable axial stress, confining stresses due to pre–stressed FRP composites are present in perimeter of column. In this paper, an innovative method is presented to confine square reinforced concrete columns using non –laminated CFRP straps. Tests were carried out on three medium scale columns (2.0 m high with a cross section of 0.4 m x 0.4 m). Numerical analyses are performed to predict the effects of the pre–stressing at square column. In this paper, a new geometrical model to account for the effects of FRP pre–stressing and shape modifying of the section is proposed which describes better distribution of confinement stresses. Using FE modeling and proposed model, effectiveness of FRP confinement is revised and effectively confined area increased.<\div>

۵Analytical Model For Bond–Slip Behavior Under Monotonic Loading in Concrete
نویسنده(ها): ، ،
اطلاعات انتشار: اولین کنفرانس ملی مهندسی و مدیریت زیر ساختها، سال
تعداد صفحات: ۱۰
The stress transfer between reinforcing steel and surrounding concrete plays an important role in the response of reinforced concrete structures. As disregard the Slip between rebar and concrete and assume full bond between them, conducted to poor structural response with respect to actual structural response. In this paper the distributions of bond stress, slip and strain are analyzed. The local bond–slip law is idealized by a piecewise linear relationship, for each part of which closed–form solutions are obtained for bond stress, slip and strain distributions. The steel bar length is divided into four zones in the general case. Conditions of continuity between zones and boundary conditions are used to solve the length of zones, and strain and slip distributions. Simultaneous transcendental equations are obtained and solved using Newton's tangent method. The analytical predicted results compare well with test results in tension.<\div>

۶Application of Artificial Neural Network for Modeling of Acetylene Hydrogenation overPd–Ag\ –Al2O3 Nano Bimetallic Catalyst
اطلاعات انتشار: سومین کنفرانس نانوساختارها، سال
تعداد صفحات: ۴
The application of neural networks to model a full–scale industrial acetylene hydrogenation on the Pd–Ag\ γ–Al2O3 nano bimetallic catalyst in olefin plant has been studied. The operating variables studied are the, input temperature of reactor, output–temperature of reactor, hydrogen ratio of reactor, [C2H2]input and [C2H6]input. The studied operating variables were used as the input to the constructed neural network to predict the [C2H6]output at any time as the output or the target. The constructed neural network was found to be highly precise in predicting the quantity of [C2H6]Output for the new input data, which are kept unaware of the trained neural network showing its applicability to determine the [C2H6]Output for any operating conditions. The enhancement of [C2H6]Output as compared with [C2H6]Input was a consequence of an low selective acetylene hydrogenation to ethylene.<\div>

۷Application and performance of composite materials
نویسنده(ها): ،
اطلاعات انتشار: دومین کنفرانس بین المللی کامپوزیت، سال
تعداد صفحات: ۶
External strengthening with Fiber Reinforced Polymer (FRP) fabrics is an effective technique for improving the structural performance and life span of the existing reinforced concrete structures. FRP composite materials has been attracted by many researchers because their advantageous characteristics such as high strength to weight ratio, good corrosion resistance, light–weight, nonconductive, and resistance to chemicals. Moreover, there are several advantages such as ease of bonding to any irregular and curved surfaces, easy to install on site without any special equipments and less time consumption. In this paper FRP composite materials, history about their appearance, properties of their material and components has been studied. In addition, various forms of using of this materials in the building has been explained and unique features of them in strengthening and retrofitting has been investigated. Finally various modes of failure about arming with polymer composites and their mechanisms are discussed and ways to prevent this type of breakdown is proposed.<\div>

۸SURVEY OF MAXIMUM DISPLACEMENT RATIO (C1) IN REHABILITATION CODES FOR SHORT PERIOD BUILDINGS ON SOFT SOIL UTILIZING ACCELEROGRAMS OF IRAN
نویسنده(ها): ،
اطلاعات انتشار: ششمین کنفرانس بین المللی زلزله شناسی و مهندسی زلزله، سال
تعداد صفحات: ۸
Survey of short period structures on soft soils and on modelings represents that the response of structures in nonlinear static analysis is in conflict with the real response. As a matter of fact, transition period of soil is obtainable with nonlinear static procedure in soft soils, but this studyrepresents that this estimation in valid Codes is underestimation of about two times and that difference will reach to maximum in near–field earthquakes. Studies show if the R ratio (Ratio of elastic strength demand to calculated yield strength coefficient) is big or the structure is nearthe fault, the elastic and in–elastic displacement will be considerably different, especially the target displacement in time history analysis exceeds the amount of nonlinear static analysis, and it means the underestimation. Moreover, the soil structure interactions can alter the demand on structures. It can alter the spectral acceleration and lateral forces and consequentially it alters lateral displacements and P–Delta effect. Considering the present challenges in valid authorities it is obvious the analytical methods for estimation of C1 is not complete. In this study we model a great number of structures on soft soils in a variety of districts in Iran, evaluating the maximum displacement ratio with a new approach utilizing different accelerograms of Iran, and eventually a new graph will be presented to evaluate the C1 for short period structure on soft soils.<\div>

۹The Advantages of Reducing the Length of Yielding Segment in Seismic Performance of Buckling Restrained Braced Frames
اطلاعات انتشار: ششمین کنفرانس بین المللی زلزله شناسی و مهندسی زلزله، سال
تعداد صفحات: ۸
Due to their better seismic performance, Buckling Restrained Braces (BRBs) have been widely replaced the conventional braces in Concentric Braced Frames (CBFs) in recent years. BRBs benefit from symmetric and stable hysteretic behavior in comparison with the normal braces and as a result have a higher energy absorption capacity. Nevertheless, the stiffness of a BRB frames degrades to a great extent when the core segments yield. Considering the high capacity of steel in the post–elastic region, the idea of reducing the length of the yielding segment of the BRBs is proposed and investigated. This leads in overstrength development in the structure and an increase in the post–yield stiffness of the braces and compensates the lack of high post–elastic stiffness of conventional BRBs. Reducing the length of core segment has other advantages such as simpler detailing for the restraining mechanism. Nevertheless, reducing the yielding length imposes large strain demands on this segment which pose some concerns about low–cycle fatigue failure. In this research a seven story building which is a benchmark example of BRBF is redesigned based on the proposed idea. The design procedure includes a special step for preventing the low–cycle fatigue failure. Nonlinear static analyses are conducted on the two buildings using the open source finite element platform, OpenSees (2007). The results show that the BRB with limited yielding length provides proper overstrength and facilitate the plasticity distribution in the structure. Moreover the pattern of story drifts does not change, but the deformation and residual displacements are reduced<\div>

۱۰Application of Dampers in High–rise Buildings to Enhance Seismic Performance
نویسنده(ها): ، ،
اطلاعات انتشار: چهارمین کنفرانس بین المللی مقاوم سازی، سال
تعداد صفحات: ۹
سازه های بلند به دلیل انعطاف پذیری ممکن است تحت اثربارهای جانبی ناشی اززلزله و باد درمعرض جابجایی های زیاد و ارتعاشات بسیارشدیدی واقع شوند این امرعلاوه برایجاد اختلال درتامین اسایش ساکنین منجر به بروز اسیب های شدید دراجزای سازه ای و ناسازه ای میگردد مروری برتاریخچه مهندسی زلزله حاکی ازآن است که رویکردهای کلاسیک مبتنی برکنترل پاسخ سازه های بلند ازطریق تنظیم سختی به تنهایی ازلحاظ اقتصادی و فنی جوابگوی نیازهای طرح نمی باشد از این رو استفاده ازسیستم های سازه ای اصلاح شده بهمراه تجهیزات کنترل و توزیع بهینه آن ها درسازه دردهه های اخیر بمنظور حصول به مقاصد طراحی با حداقل هزینه ممکن از اهمیت بسزایی برخوردار گردیده است کنترل ارتعاشات و بهبود پاسخ دینامیکی ساختمان های بلند نیازمند اتخاذ راه کار مناسب جهت افزایش سختی و میرایی سازه می باشد حصول سختی افزون تر دراینگونه ساختمان ه نه با افزایش مقاطع سازه ای به تنهایی بلکه با انتخاب درست نوع سیستم باربرجانبی مقدور میگردد. برای این منظور سیستم مهاربازویی و خرپای کمربندید رپژوهش حاضر مورد استفاده قرارگرفته است

۱۱Artificial intelligence: a proper approach for prediction of water saturation in hydrocarbon reservoir
نویسنده(ها): ، ، ،
اطلاعات انتشار: سومین کنگره ملی مهندسی نفت، سال
تعداد صفحات: ۱۶
Water saturation (Sw) is a significant petrophysical parameter usually used for reservoir estimation and production. This parameter is one of the mostdifficult petrophysical properties to determine and predict. The conventional methods for water saturation determination are core analysis and well testdata. These methods are, however, very expensive and time–consuming. One of the comparatively inexpensive and readily available sources ofinferring Sw is from well logs. In recent decades, artificial Intelligent (AI) has many applications in the petroleum engineering as well as other areas ofresearch. The aim of this paper is to use two diverse machine learning technology named back–propagation neural network (BPNN) and generalregression neural network (GRNN) for predicting the water saturation of four wells in Burgan reservoir, south of Iran. Comparing the obtainedresults of these two methodologies has shown that BPNN is a faster and precious method than GRNN in prediction of water saturation.<\div>

۱۲GRAFTED NITROGEN DONOR BIDENTATE LIGAND INTO MESOPOROUS SILICA FOR OLEFIN TRIMERIZATION
نویسنده(ها): ، ، ،
اطلاعات انتشار: سومین کنفرانس بین المللی نفت، گاز و پتروشیمی، سال
تعداد صفحات: ۸
Mesoporous silica and organosilica materials are a class of nanostructured materials that have porous structures with tunable nanometer pores, large surface areas,high pore volumes, and, in some cases, well–ordered mesostructures. Mesoporous structures synthesized many applications in various fields including drug delivery, biosensors and as a support for catalyst. Various organic functional groups can be established on the surface of mesoporous silica and used in different reactions. This studyhighlights the different synthetic methods developed for mesoporous silica andorganosilica nanomaterials. The study discusses on the synthesis of regular SBA–15 silica and the functionalization surface of this mesoporous structures with donor nitrogen groups and chromium catalyst loading and finally using of this catalitic system for ethylene trimerization. The silica substrates regular mesoporous analysis using XRD, BET, FTIR has been studied and confirmed<\div>

۱۳Artificial Intelligence for prediction of porosity from Seismic Attributes: Case study in the Persian Gulf
اطلاعات انتشار: Iranian Journal of Earth Sciences، سوم،شماره۲، Oct ۲۰۱۱، سال
تعداد صفحات: ۷
Porosity is one of the key parameters associated with oil reservoirs. Determination of this petrophysical parameter is an essential step in reservoir characterization. Among different linear and nonlinear prediction tools such as multi–regression and polynomial curve fitting, artificial neural network has gained the attention of researchers over the past years. In the present study, two–dimensional (2D) seismic and well logs data of the Burgan oil field were used for prediction of the reservoir porosity. In this regard, broad–band acoustic impedance was first extracted from 2D seismic dataset, as the attribute most related to porosity. Next, other optimum seismic attributes were selected using stepwise regression and cross validation techniques. At the end, three types of neural network were used for inversion of seismic attributes and prediction of reservoir porosity. The results show that probabilistic neural network (PNN) is the best one for prediction of the reservoir porosity using seismic attributes.
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