مقایسه رفتار لرزه‌ای قا‌ب‌های خمشی فولادی مجهز به میراگرهای ویسکوز خطی و غیرخطی تحت زلزله‌های نزدیک به گسل

در دهه‌های اخیر مطالعات گسترده ای درباره میراگرهای ویسکوز به عنوان یکی از انواع سیستم های کنترل غیرفعال سازه جهت استهلاک و جذب انرژی زلزله انجام شده است. در این تحقیق به بررسی اثر میراگرهای ویسکوز خطی و غیرخطی بر پاسخ لرزه‌ای قاب های خمشی فولادی 3، 9 و 20 طبقه پرداخته شده و پس از انجام تحلیل دینامیکی تاریخچه زمانی غیرخطی، پاسخ های سازه ای یکدیگر مقایسه شده است. بررسی نتایج نشان داد که جابجایی مطلق قاب‌ها در حالت وجود میراگر غیرخطی نسبت به حالت خطی با افزایش تعداد طبقات به ترتیب 67، 79 و 84 درصد کاهش یافته ولی برای حداکثر تغییر مکان نسبی برای سازه 20 طبقه اثر کمتری داشته و بترتیب 86، 83 و 40 درصد بوده است. همچنین میزان جذب انرژی میراگر غیرخطی در قاب های کوتاه و میان مرتبه با توجه به منحنی هیسترزیس استخراج شده با 7/5 و 157 درصد افزایش، دارای عملکرد بهتری بوده درحالی که در قاب بلند مرتبه به مقدار 74 درصد کاهش یافته است. همچنین توزیع مفاصل پلاستیک نیز برای این نوع میراگرها مبین کاهش خرابی در سطح عملکرد ایمنی جانی می باشد و موجب کاهش قابل ملاحظه ای در تعداد مفاصل پلاستیک تشکیل شده در سطح عملکرد قابلیت استفاده بی وقفه شده است. همچنین برش پایه قاب های 3 و 9 طبقه با میراگر غیرخطی نسبت به میراگر خطی حدود 21 و 10 درصد کاهش داشته و در عین حال اثر میراگرهای غیرخطی در قاب های بلند مرتبه چندان محسوس نبوده است. 

comparison of seismic behavior of steel moment frames equipped with linear and nonlinear viscosity dampers under near-fault earthquakes

the displacement-based design method in structural design codes, in which displacement is considered a criterion for evaluating the structure, has been accepted due to the dependence of failure on displacement more than forces, overcoming the inherent shortcomings of force-based design methods. on the other hand, different levels and states can be defined concerning structures’ performance. in the functional state of immediate occupancy, the relative lateral displacement due to cracking or plastic behavior does not remain in the structure. the structural members’ stiffness and strength do not change fundamentally, and microscopic cracks are created in the structural members and façade. in the second case, i.e., life safety, some stiffness, and strength will be lost in all classes, relative deformation due to plastic behavior in the structure will be observed, and the risk of loss of life will be slightly higher. at the performance level, the collapse threshold remains in the members of structures of low stiffness and strength to withstand lateral loads, but the columns and load-bearing walls maintain their function, the relative deformations are high, and the structure is likely to collapse due to aftershocks. due to decreased energy caused by earthquakes, dampers with passive control systems are installed in certain parts of the structure and absorb a relatively large part of the energy entering the structure under different mechanisms, and as a result, the structure does not suffer severe damage. after the northridge and kobe earthquakes, extensive laboratory studies were conducted to strengthen and increase the joints’ ductility, and many modified joints were proposed. extensive applied structural studies have been conducted on dampers’ seismic behavior as one of the advanced tools of passive structural control systems due to earthquake energy dissipation. this work compares the effects of linear and nonlinear viscous dampers on the seismic behavior of 3, 9, and 20-stories steel moment frames, and the structural seismic responses are discussed. in linear dampers, the axial force is obtained by multiplying the damping coefficient ratio at the relative speed of the damper’s two ends, and in the nonlinear state, the relative speed of the damper is between 0.2 and 1, in which 0.25 is used in the current study. the results showed that viscous dampers’ implementation generally reduced the responses and decreased the structural damage during the earthquake. absolute displacement of structural models in nonlinear dampers compared to linear ones has decreased with an increasing number of stories, but for maximum relative displacement with the increasing number of stories, nonlinear dampers had a more negligible effect. due to the hysteresis extracted, nonlinear dampers in short and intermediate structures have more energy loss, which is significantly reduced in high damping structures. the plastic hinge distribution for these dampers has eliminated the failure ls at the life safety performance level. the base shear of 3, 9, and 20 story frames with a nonlinear damper is significantly reduced compared to a linear damper and shows the nonlinear damper’s positive effect, especially on high-rise structural frame models.