پديد آورندگان :
بذرافشان، ارسلان نويسنده دانشگاه تربيت مدرس,ايران , , خاجي، ناصر نويسنده دانشگاه تربيت مدرس,ايران Khaji, Naser
كليدواژه :
زلزله‌هاي پريودبلند , جداسازي لرزه‌اي , ساختمان‌هاي بلند , ساختمان برشي
چكيده فارسي :
جداسازي لرزه‌اي يكي از مناسب‌ترين ابزارهاي مهندسي زلزله در زمينه كنترل غيرفعال مي‌باشد. اگرچه اين روش در ابتدا براي سازه‌هاي كوتاه‌مرتبه با رفتار روسازه نسبتاً صلب توسعه يافت، با اين حال، كاربرد آن در سازه‌هاي متوسط و بلند رو به افزايش است. كمترين نتيجه‌اي كه جداسازي لرزه‌اي در سازه‌هاي بلند به همراه دارد، كاهش تغييرمكان نسبي جانبي (دريفت) طبقات به علت تغييرشكل مود نخست، به‌علاوه تأمين يك مكانيزم استهلاك انرژي مناسب در كف ساختمان مي‌باشد. براي حفظ كارآيي جداسازي، زمان تناوب سيستم جداساز بايد به اندازه كافي بزرگ درنظر گرفته شود. چنين سازه‌اي ممكن است در برابر زلزله‌هاي پريودبلند آسيب‌پذير باشد. در اين مقاله، عملكرد لرزه‌اي سه مدل ساختمان برشي 8، 14 و 20 طبقه جداسازي‌شده، توسط دو نوع جداساز سربيلاستيكي و آونگ اصطكاكي، تحت اثر زلزله‌هاي پريود بلند، مورد مطالعه قرار مي‌گيرد. نتايج نشان مي‌دهد كه با افزايش ارتفاع، ميزان اثرپذيري سازه از زلزله‌هاي پريود بلند بيشتر مي‌شود و اين حركات قادرند نياز جابجايي بالايي را به جداساز تحميل كنند.
چكيده لاتين :
Base 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 nonbuilding structure to survive a potentially devastating seismic impact. Generally, it is thought that application of seismic isolation is limited to low and mediumrise structures, and the use of isolation for highrise buildings considered as impractical or unfeasible. However, existing exles of isolated highrise buildings in Japan, also in Iran, suggest that these viewpoints clearly disagrees with the real stateofpractice that exists there. Since the 1995 Kobe earthquake, just fewer than 200 isolated highrise 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 interstory drifts and floor accelerations, which results in protection of building’s contents. As a result, highrise 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 highrise 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. Longperiod ground motions can be divided into farsource and nearfault classes. Most farsource longperiod ground motions were generated by large earthquakes and effective propagation paths. Therefore, farsource longperiod ground motions are generally associated with offshore earthquakes in subduction zones. Nearfault longperiod 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 20story shear buildings using isolator type of leadrubber bearing (LRB) and friction pendulum system (FPS), under longperiod ground motions are studied. A set of 14 longperiod ground motions – 5 farsource longperiod motions and 9 nearfault longperiod motions – as well as 14 shortperiod ground motions were selected. Total earthquake input energy per unit mas was used as a measure to distinguish longperiod motions so that those which had a significant input energy over the periods of 2 seconds were considered as longperiod 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 shortperiod, increasing the height of the structure doesn’t 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 longperiod ground motions becomes more significant, and these motions impose a great displacement demand in the isolation system.
