معرفي يك سيستم لرزه‌بر مهاربندي شده تركيبي به منظور عملكرد دو سطحي

Introduction and evaluation a combined system in order to a two-level performance

در اين مقاله، يك پيكربندي ابتكاري براي مهاربندي جانبي قاب‌هاي فولادي ارايه و مورد بحث قرار خواهد گرفت. قاب مهاربندي شده برون محور و زانويي كه در اين مقاله تحت عنوان (EKB) ناميده مي‌شود، از چهار قسمت سازه‌اي شامل، المان زانويي، مهاربند، تير پيوند و ستون تشكيل يافته است. المان‌هاي زانويي و تير پيوند به ترتيب نقش فيوزهاي سازه‌اي را براي سيستم پيشنهادي بازي مي‌كنند كه توسط مفاصل برشي و خمشي ايجاد شده در آنها، وقتي سازه تحت جنش متوسط و شديد زلزله قرار مي‌گيرد، انرژي ورودي را مستهلك مي‌كنند. مهاربند سختي قاب را تامين نموده و تا انتهاي بارگذاري ارتجاعي باقي مي‌ماند. براي بررسي رفتار سيستم، مطالعات عددي به وسيله‌ي برنامه معروف ANSYS انجام شده است. همچنين دو مدل تجربي با مقياس 2/1 با استفاده پروتكل بارگذاري SAC و يك پروتكل بارگذاري ابتكاري مورد آزمايش قرار گرفتند. نتايج تجربي و عددي نشان مي‌دهند كه ميزان شكل‌پذيري و انرژي تلف شده تجمعي به ميزان قابل ملاحظه‌اي افزايش يافته است.

In this paper a new and innovative configuration of lateral bracing for steel frame construction is presented and discussed. Eccentrically Knee Bracing (EKB) frame, as it is called in this paper, is made up of four structural elements, the knee element, the diagonal brace element, the link element and the columns. The knee and link elements are a fuse-like element that dissipates energy by the formation of plastic shear hinges or flexural hinges when the building is subjected to moderate and severe lateral loads, respectively. The diagonal brace element, on the other hand, provides the required level of lateral stiffness and remains in the elastic range at all time. In order to examine this system behavior, ANSYS, which is a well-known finite element software is used. Also two half-scale EKB were tested using the SAC loading protocol and an innovative loading protocol. The experimental and numerical results indicated that in this system, ductility and cumulative dissipated energy can be significantly increased. Past earthquakes have demonstrated that this idealized behavior may not be realized if the braced frame and its connections are not properly designed. Eccentrically braced frames (EBFs) are one of seismic load resisting systems in which the waste of energy (inelastic action) is performed through ductile links. In some of the common types of braced frames, one end of the link is attached to a column, and in these kinds of systems the correct behavior of this link is crucial to a safe performance of the EBF. The EBFs address the desire for a laterally stiff framing system with significant energy dissipation capability to accommodate large seismic forces. EBFs combine the high elastic stiffness of concentrically braced frames (CBFs) with the high ductility and energy dissipation capacity of moment resisting frames (MRFs). The excellent seismic behavior of EBFs reported in the first numerical studies on traditional eccentrically braced structures subjected to lateral static forces. To improve the seismic performance and behavior of the steel framed structures, further modification and innovation to enhance the structural performance is essential. For this purpose, a modified structural form that adopts eccentrically knee brace elements in the corner regions of the beams and columns, namely Eccentrically Knee Braced frame (EKB) is considered in this study. In an EKB, one end of the brace is connected to a short knee element instead of beam-column joint and other end of brace is connected to a short link element. The link element which is the short beam segment between the brace-beam and beam-column joint, is designed to dissipate energy through shear yielding during severe earthquakes. Thus, the link element acts as a ductile fuse to safeguard the brace against possible buckling. In this study, the knee element is designed in such a way that the knee yields in shear instead of flexure under moderate excitation and link element is designed to yield under severe excitation. The seismic performance and ductility of this proposed system is of great concern, which is covered in the current paper. All tests were of the cyclic quasi-static type for which similar displacement time histories were considered.