كاربرد زوج پانل برشي براي بهبود رفتار لرزه‌اي قاب‌هاي مهاربندي شده برون‌محور

Study of Using Double Shear Panel to Upgrade the Seismic Behavior of Eccentrically Braced Frames

چكيده- استفاده از ميراگرهاي جاري شونده به علت قابليت بالا در اتلاف انرژي زلزله با استقبال قابل توجهي در دهه اخير روبرو شده-است. با توجه به پيشرفت‌هاي فاحش روش‌هاي كنترل غيرفعال براي استهلاك انرژي زلزله و نيز جلوگيري از خسارات لرزه اي در اعضاي اصلي سازه، اين مقاله يك سيستم جديد اصلاحي مناسب به خصوص براي بهسازي لرزه اي سازه هاي فولادي داراي مهاربندي برون محور پيشنهاد نموده است. در اين مقاله عملكرد لرزه اي قاب‌هاي مهاربندي برون محور با افزودن زوج پانل برشي به عنوان ميراگر هيسترزيس مورد بررسي قرار گرفت. نمونه هاي عددي به روش تحليل اجزا محدود غيرخطي تحت بارگذاري چرخه‌اي (رفت و برگشتي) و بارافزون (پوش اور) ارزيابي شدند. نتايج حاصله، منحني هاي هيسترزيس پايدار و بدون افت چشمگير و خروج نواحي خرابي از قسمتهاي اصلي سازه و انحصار آن در پانلهاي برشي را نشان دادند. در نمونه ها ظرفيت تغييرشكل‌هاي زاويه اي پانل‌هاي برشي بين 08/0 تا 15/0 راديان بدست آمد. با افزودن زوج پانل برشي، حداكثر تغييرمكان قايم دو طرف پيوند افقي بين 5/0 تا 25/1 سانتيمتر بدست آمد كه حاكي از كاهش تغييرمكان تحميل شده به تير پيوند افقي است. همچنين با توجه به منحني‌هاي هيسترزيس نمونه ها، استفاده از زوج پانل برشي باعث بهبود رفتار قابهاي مهاربندي برون محور داراي پيوند افقي با طول بلند مي شود. ضريب رفتار اين سيستم بطور محافظه كارانه بيش از 8 بدست آمد كه مي‌توان اين روش را براي بهبود رفتار اين نوع قاب‌ها مناسب و عملي دانست.

Recent damaging earthquakes in Iran and around the world have induced great death and damage providing serious reminders of seismic vulnerability of existing structures. It is more crucial in Iran, where many structures have been built when seismic codes were not effective enough, especially considering the fact that construction has not been perfectly consistent with design specifications and drawings. Many of existing building, therefore, have inadequate strength when subjected to earthquake. To prevent such damage and tragic event, efficient ways are necessary for seismic upgrading of these buildings. One of useful extensively used methods is passive control. By reducing seismic demand and increasing ductility, these control ways can reduce rate of seismic damage. One of the most effective mechanisms available for dissipating seismic energy through inelastic deformations of metallic substances is use of shear panels. Use of such yielding dampers has been increased recently for their high capability in energy dissipation. Despite eccentrically braced frames, EBFs, these pieces are not embedded in floor and can be exchanged easily with little cost after earthquakes. The basic role of shear panel system is to absorb a major portion of input seismic energy, thus reducing energy dissipation demand on structural members and minimizing probable structural damage. Due to recent advances in these passive control methods specifically significant improvements in earthquake energy dissipation and prevention of damage in the main parts of the structures, this paper provides a new hysteretic damping system, especially beneficial to retrofitting steel structures having Eccentrically Braced Frames, EBFs. This research studies the seismic performance of EBFs with double shear panels. Five specimens have been evaluated using nonlinear finite element analysis under cyclic and monotonic loading. The findings present the proper performance of proposed revision for EBFs, the rise in energy dissipation and the elimination of damage to the main parts of structure (column, bracing, main beam) and its concentration in shear panels reducing displacement of horizontal link (main beam) of EBFs. The analytical results showed the shear panel shear distortion capacity of 0.08 - 0.15rad (displacement of horizontal link of 0.5 - 1.25cm). The response modification factor of this system was also obtained in the range of 8.7-9.8. Based on the results obtained in this paper, using double SPS in addition to dissipating more than 70% of imposed energy and increasing the structural ductility, can reduce lateral displacements due to decreasing seismic demand. Finally, using shear panel is highly recommended as an effective and efficient way for seismic design of new steel building structure and also for seismic retrofit of existing steel buildings.