پديد آورندگان :
ميربد احمدرضا دانشگاه اصفهان - دانشكده عمران و حمل و نقل - گروه مهندسي عمران , داعي مريم دانشگاه اصفهان - دانشكده عمران و حمل و نقل - گروه مهندسي عمران , تاجمير رياحي حسين دانشگاه اصفهان - دانشكده عمران و حمل و نقل - گروه مهندسي عمران
كليدواژه :
سيستم جداساز لرزه اي , رفتار غيرخطي , روسازه , شكل پذيري تقاضا
چكيده فارسي :
در طراحي سازه هاي متكي بر سيستم جداساز لرزه اي، انتظار مي رود كه جداساز به تنهايي وارد ناحيه غيرخطي شده و روسازه رفتار الاستيك خطي از خود نشان دهد. اما با توجه به اين كه تحت شرايط خاص امكان ورود روسازه به حوزه ي رفتار غيرخطي وجود دارد، در اين مطالعه به بررسي دقيقتر رفتار غيرخطي اين گونه سازه ها پرداخته شده است. در بخش اول مقاله به منظور بررسي تاثير ميزان غيرخطي شدن روسازه و اثر تغيير ديگر پارامترهاي سيستم بر پاسخ سازه، از مدل دو درجه آزادي با جداساز خطي استفاده شده است. نتايج نشان مي دهد كه با وارد شدن رفتار روسازه به محدوده ي غيرخطي، ميزان شكل پذيري تقاضا به شدت با افزايش همراه خواهد بود. در بخش دوم براي لحاظ كردن اثر مودهاي بالاتر به كمك مدل چند درجه آزادي و سيستم جداساز با فرم رفتار دوخطي، اثرات تغيير پارامترهاي سيستم مورد كنكاش قرار گرفته است. نتايج بدست آمده در اين قسمت نيز مويد افزايش پاسخ سازه براي روسازه با مقاومت پايين است. در نهايت با توجه به افزايش شديد پاسخ سازه در صورت استفاده از ظرفيت روسازه، راهكاري با هدف طرح بهينه ي همزمان روسازه و سيستم جداساز ارايه شده است. اين راهكار از تلفيق تئوري شكل پذيري يكنواخت و الگوريتم فراابتكاري كلوني زنبور عسل مصنوعي استفاده مي كند. بدين ترتيب مي توان با استفاده از ظرفيت شكل پذيري روسازه و جداساز، علاوه بر دستيابي به روسازه سبكتر، به ميزان شكل پذيري مطلوب در جداساز نيز دست يافت.
چكيده لاتين :
In the design of seismically base-isolated structures, it is expected that the isolator will experience nonlinear behavior while the superstructure still behaves linearly. Therefore for modeling these systems, a linear behavior is assumed for superstructure and different nonlinear models are used for isolator. But there are special conditions such as strong ground motions in which superstructure behave nonlinearly. In this study, the nonlinear behavior of seismically base-isolated structures is more accurately investigated. This is done using nonlinear time history analysis of structures using ground motions. Two sets of ground motions are selected which represent earthquakes with 475 and 2475 years return period. OpenSees software is used for modeling these structures. The effective parameters on the response of seismically base isolated structure which are investigated are: response modification factor of the superstructure, stiffness of the isolator, damping ratio of the isolator, stiffness of the superstructure and damping ratio of the superstructure. Studies of this paper are divided into two parts. In the first part, two-degree freedom model with viscoelastic isolator has been used to investigate the effect of superstructure nonlinearity. Also a sensitivity analysis is done to find important parameters which have more effects on the systems response. Results of this part show that, nonlinear behavior of superstructure increases system ductility demand drastically. It is concluded that the period of isolator and superstructure have the most effect on the ductility demand. In the second part, the effect of different parameters and higher mode effects on the response of seismically base-isolated structures is investigated using muti-degree of freedom models sited on isolator with bilinear behavior. Results obtained in this part also confirm the increase in the response of the system when the superstructure has low strength. Likewise in this condition, the isolator deformation decreases. Distribution of ductility demand in the height of structure is also non-uniform in this condition and lower stories are more vulnerable. Isolators with a lower fundamental period and also isolators with a lower yield force lead to the least amount of isolator deformation and ductility demand of superstructure. By increasing damping in the isolator, ductility demand of superstructure will increase. A stiffer superstructure with nonlinear behavior has a much more ductility demand rather than similar structure which is more flexible. But when the superstructure behaves linearly, the fundamental period of superstructure and isolator deformation increase or decrease together. Finally, due to the intensive increase in the ductility demand of the superstructure when it behaves nonlinearly, a solution is proposed with the aim of simultaneous optimization of the superstructure and isolator systems. This strategy uses a combination of uniform ductility theory and a modified artificial bee colony algorithm. By applying this method and using ductilities of superstructure and isolator simultaneously, it is possible to obtain the desirable ductility in the isolator, in addition to achieve a more economical choice for the superstructure. If there is no constraint around the structure for movement, by increasing the target ductility of the superstructure, the weight of the superstructure can be reduced by reducing its yield force.
