s. abrishami
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در پژوهش حاضر، به منظور کنترل لرزه یی پل بزرگراه محک، از کنترل کننده ی انطباق پذیر فازی خودتنظیم (STFC) و میراگرهای نیمه فعال MR استفاده شده است. کنترل کننده ی STFC، با استفاده از یک ساختار دو قسمتی، مزایای سیستم های استنتاج فازی را با الگوریتم انطباق پذیر ترکیب می کند. ساختار خودتنظیم توانایی تنظیم برخط کنترل کننده را با توجه به مشخصات تحریکات لرزه یی و شرایط سازه یی به دست می دهد. به منظور افزایش کارآمدی، برخی پارامترهای کنترل کننده ی پیشنهادی توسط الگوریتم ژنتیک تنظیم می شود. نهایتا کنترل کننده ی پیشنهادی تحت تحریک های تعیین شده برای پل محک قرار گرفته و معیارهای سنجش رفتار پل محاسبه شده است. بررسی رفتار سازه ی کنترل شده و مقادیر معیارهای سنجش از یک سو نشان می دهد که سیستم پیشنهادی، توانمندی بالایی در کاهش پاسخ های لرزه یی، به ویژه معیارهای مرتبط با خسارت، نظیر: جابه جایی میانه ی پل، تغییرشکل جداسازها و انرژی اتلافی در اعضاء سازه یی و از سوی دیگر، توان انطباق با شرایط مختلف لرزه یی را دارد.
کلید واژگان: کنترل لرزه یی، کنترل نیمه فعال، میراگر MR، کنترل کننده ی فازی خودتنظیم، کنترل کننده ی انطباق پذیر، پل بزرگراه محک، خسارتDuring the past few decades, extensive damage to structures due to severe earthquakes has encouraged structural engineers to use seismic control systems. Bridges are critical nodes in transportation networks and must remain utilizable after an earthquake. Therefore, a higher level of performance with less structural damage is required for bridges. In the present research, a self-tuning fuzzy controller (STFC) with semi-active MR dampers is proposed to reduce the seismic response of the benchmark highway bridge. This controller combines the advantages of fuzzy inference systems and adaptive control in a two-part control architecture consisting of primary and secondary controllers. More specifically, the self-tuning mechanism considers different characteristics of seismic excitations and structural conditions to increase the controller efficiency in different situations. The role of the primary controller is to determine the input damper voltage, while the secondary controller adjusts them online according to seismic excitations and structural conditions. In order to increase the effectiveness of the proposed controller, the output parameters of the Sugeno fuzzy inference systems in the primary controller were set by a genetic algorithm. Finally, the proposed STFC was employed under several patterns from actual benchmark earthquakes and the evaluation criteria of a seismically excited highway bridge benchmark were determined. The obtained results exhibited a higher ability of the proposed self-tuning fuzzy controller to improve the highway bridge benchmark criteria, especially those related to damage such as displacement at bridge midspan, deformation of bearings, curvature of bent columns, and dissipated energy at the structural members. On the other hand, the evaluation criteria suggest that the proposed self-tuning fuzzy controller could reduce seismic responses under different earthquakes and adapt to different seismic excitations. Moreover, comparing the proposed controller with another adaptive fuzzy controller indicates the higher efficiency of the proposed STFC approach, especially in improving damage-related performance measures.
Keywords: seismic control, Semi-active control, MR damper, self-tuning fuzzy controller, Adaptive controller, benchmark highway bridge, Damage -
ی از پارامترهای موثر بر رفتار خاک و عملکرد شالوده ها «سرعت بارگذاری» است و تخمین رفتار پی ها نیازمند شناخت اثرات کمی و کیفی این پارامتر است. در این نوشتار، نتایج مطالعات آزمایشگاهی صورت گرفته روی مدل پی نواری واقع بر سطح خاک ماسه یی غیرمسلح و نیز مسلح به ژئوگرید تحت بارهای استاتیکی، به صورت کنترل نیرو و با سرعت های مختلف ارائه شده است. سپس اثر نرخ بارگذاری بر ظرفیت باربری و نشست نهایی مدل پی بررسی شده است. آزمایش ها با استفاده از سیستم آزمایشگاهی جدیدی که برای مدل سازی فیزیکی رفتار شالوده ها توسعه یافته، انجام شده است. نتایج حاصله ضمن اثبات دقت و تکرارپذیری مدل فیزیکی، به ویژه در حالت غیرمسلح، نشان می دهد که اثر نرخ بارگذاری بر رفتار شالوده های مسلح و غیرمسلحمتفاوت است. افزایش سرعت بارگذاری منجر به کاهش اندک ولی قابل مشاهده ی ظرفیت باربری و افزایش نسبی نشست های نهایی خاک مسلح می شود.
کلید واژگان: خاک مسلح، ژئوگرید، ماسه، نرخ بارگذاری، مدل سازی فیزیکی، ظرفیت باربری، نشستThe loading rate is an effective factor influencing the interaction between soil and foundation. Increasing the loading rate on different footings, particularly those resting on saturated or partially saturated soils may resultin a rapid build-up of pore pressure and foundation failure due to a sudden decrease in effective stresses. The problem would be of greater importance in many special foundations, such as those designed to resist explosions, or missile launching platforms, which are under shock and impact loadings.Numerical modeling of this case for dry soils is not possible without developing an appropriate behavioral model, since, in most numerical modeling, the soil is assumed to be a continuum medium. The existing routine modelsusually evaluate the influence of the loading rate on the liquid phase, and, then, assess the counter effect of the liquid phase on the whole medium. Because development of a suitable model needs a physical modeling, similar to real conditions, to be undertaken, the present study may play an effective role, in this respect, for backing by a new physical model.In the current research, first, some tests are carried out on soil and the geogrid to determine the physical and mechanical characteristics of the materials, and, then, the initial tests for modeling are implemented using a new physical model developed in the soil laboratory of Amirkabir University of Technology (Mir Hosseini & Abrishami). The capability of the model was checked and evaluated during these tests, as well as the design and planning of the main test programs, to investigate the different effects of soil-foundation interaction, such as loading rate, on reinforced soils.The main tests in this study consist of two groups, namely: reinforced and unreinforced. The major objective of the unreinforced tests was to get some experimental data as a base reference for evaluation and comparison of the behavior of the footing on reinforced soil. In the group of reinforced tests, a different series of experiments were carried out for different purposes, one of which was planned to study the effect of loading rate on ultimate bearing capacity, and, also, the behavior of footings on sands reinforced by geogrids. Sand density and the method of testing were quite the same as those used in unreinforced tests. The only difference in this series was the presence of a geogrid layer located at optimum depth, which was revealed to be half of the footing width, according to the results of the initial experiments. Based on the results of the performed tests in this series, the ultimate bearing capacity of reinforced sand, in the opposite direction to unreinforced sand, decreases as the loading rate increases. The amount of bearing capacity reduction is about 12 percent compared to that of unreinforced soils. However, the final settlement of the footing on reinforced sand increases about 10 percent, and the total stiffness of the system is reduced. The main reason for these findings may be attributed to the lack of sufficient time which is needed for the interaction between soils and geogrids to happen entirely. Increasingthe loading rate, together with soil inertia, may cause the stress distribution in the mass to attain the state close to punching failure. As a result, a higher stress magnitude is applied to a small area of geogrid, leading to an increase in strain and settlement, and a reduction in bearing capacity, accordingly.Some other important findings associated with the loading rate on footingsresting on reinforced sand have been resulted, a detailed description andtechnical discussion of which are presented in the full paper.
Keywords: Reinforced Soil, Geogrid, Sand, Rate Of Loading, Physical Modeling, Bearing Capacity, Settlement
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