نقش المان‌هاي با رفتار شكل‌پذير در عملكرد لرزه اي قاب هاي داراي مهاربند همگرا

The Role of Ductile Behavior of Connection Elements on Seismic performance of CBF

در اين پژوهش، سعي شده است تا نوع جديدي از مستهلك كننده‌هاي انرژي معرفي شود. اين مستهلك كننده متشكل از يك حلقه كه موجب افزايش شكل‌پذيري و جذب انرژي زلزله شده، در سازه‌هاي مهاربندي قابل نصب است. همچنين در هنگام وقوع زلزله، عضو مستهلك كننده قسمت قابل توجهي از انرژي ورودي به سازه را با ورود به مرحله غير خطي و تشكيل مفاصل خميري خمشي، مستهلك كرده و بدين صورت از ورود ديگر اعضاي سازه به مرحله غير خطي و همچنين كمانش اعضاي مهاربندي جلوگيري، يا آن را به تعويق مي‌اندازد. براي افزايش ظرفيت باربري اين عضو نيز، از يك قوطي كه به وسيله‌ي صفحات اتصال به حلقه شكل‌پذير متصل مي‌شود، استفاده شده است. با افزايش قطر ميزان شكل پذيري آن كاهش يافته و با افزايش ضخامت حلقه ميزان شكل‌پذيري آن افزايش مي‌يابد. تنش‌ها و تغيير شكل‌ها با استفاده از تحليل غير خطي به روش المان‌هاي محدود و تحت اثر بارهاي رفت و برگشت، مطالعه شده است. منحني‌هاي هيسترسيس به دست آمده حاكي از آن است كه المان معرفي شده مي‌تواند به عنوان يك عضو جاذب انرژي و همچنين يك فيوز براي كنترل كمانش يك بادبند عمل كند، ضمن آنكه شكل پذيري لازم را نيز تامين كند. همچنين عملكرد المان پيشنهادي در يك قاب دو بعدي با مهاربند همگرا تحت تحليل استاتيكي غير‌خطي بررسي شد كه نتايج به دست آمده حاكي از كاهش برش پايه و افزايش شكل‌پذيري در سازه است.

Nonlinear behavior of members and their connections during earthquake caused ductility in buildings. Also increasing the number of resisting elements of structure reduces cost of repair and reconstruction in bending structures. In contrast, the concentrically brace frames do not have sufficient ductility but their vulnerable members are limited, thus their reconstruction were much less expensive than bending frames. In order to overcome concentrically brace frames disadvantages and they providing good ductility for them, extensive research has been conducted in the past two decades by researchers. Several methods have been proposed by various researchers which were resulted in increasing the ductility of concentrically brace frames. In this research, a new type of energy dissipation elements was introduced. This dissipation consists of a ring which increased the ductility and earthquake energy absorption and can be used in braced frames. Also, during an earthquake, it has depreciates significant portion of input energy by entrance to non-linear phase and forming flexural plastic hinges, so it prevent entrance of other members to non-linear phase and buckling of brace members. In order to increase the capacity of this member, a box was used that connected to the ductile ring by two plates. By increasing the diameter, rate of ductility decreased. However increasing the thickness would enhance the ductility. Stresses and deformations have been studied by using the finite element under cyclic loads. Obtained hysteresis curves indicate that the introduced element can act as an energy absorbing member and also act as a fuse to control the buckling of brace, while providing to the required ductility. Pushover analyses for determining the seismic demand of structures and especially in earthquake engineering based on performance, it has been considered by many researchers. General basis of this method is a nonlinear mathematical model of the structure was under a lateral load pattern and this lateral load increases at a constant rate until the structure reaches a predetermined target displacement. This target displacement was measured at a control point. During the ascending increase in lateral load, resistance and stiffness of structural components were corrected at each step according to predefined nonlinear. Also performance of this ductile element was investigated in 2D concentrically brace frames under pushover analyses. Obtained results from pushover analysis indicated that ductile element can decrease base shear force and also increase ductility of structure. The obtained results indicate that installation or replacement of steel ring in proposed connection was easily possible with low cost and high speed. Furthermore, nonlinear static analysis obtained results reflects the lower base shear force for braced frame with proposed element compared to braced frames without proposed element which results in cutting down construction and foundation strengthening costs of building. At the end, results of pushover analysis of concentrically braced systems can be mentioned. High behavior coefficient of structural braced systems with proposed element represents suitable performance and ductility of proposed element in building. The obtained hysteresis curves suggest that introduced element can act as an energy absorbing member and a fuse to control the buckling of a brace and link beam in addition to providing the necessary ductility.