خطاهاي محتمل در پيكره بندي ميراگر TADAS

Some probable mistakes in the design of geometric configuration of TADAS damper

ميراگرهاي الحاقي TADAS نوعي سيستم كنترل غيرفعال مي باشند كه امروزه مي توان در طراحي لرزه اي يا مقاوم سازي سازه ها از آن ها استفاده نمود. در اين مطالعه، رفتار ميراگر TADAS در تغييرمكان هاي بزرگ مورد بررسي قرار مي گيرد و بعضي از خطاهاي محتمل در طراحي آن كه در صورت عدم توجه مي تواند خساراتي را براي سازه در پي داشته و توانايي اتلاف انرژي ميراگر را كاهش دهد، بيان مي شود. براي تحقيق درباره اين موضوع، مدل اجزاء محدود ميراگر TADAS با تمام جزئيات در نرم افزار آباكوس شبيه سازي شد و تحت بارگذاري مونوتونيك منتهي به تغييرمكان هاي بزرگ قرار گرفت. مشخص گرديد كه سختي ميراگر در تغييرمكان هاي بزرگ به صورت ناگهاني افزايش مي يابد كه اين افزايش ناگهاني مي تواند منجر به پاسخ هاي نامطلوب و حتي كمك به تخريب سازه گردد. در اين مقاله پيشنهاداتي براي جلوگيري از اين وضعيت، ارائه شده است. در ادامه يك قاب مجهز به ميراگر TADAS در آزمايشگاه تحت بارگذاري چرخه اي تا تغييرمكان هاي بزرگ قرار گرفته است. اين قاب همچنين در نرم افزار آباكوس نيز شبيه سازي گشته و رفتار آن با نمونه آزمايشگاهي مقايسه شده است. از مطالعه مدل هاي آزمايشگاهي و نرم افزاري مشخص شد كه هرچند رفتار چرخه اي ميراگر در تغييرشكل هاي بزرگ هم پايدار و مناسب است ولي دو نقص مهم در اجراي اين ميراگر مشاهده مي شود. يكي از اين نقص ها، كمانش بادبندها به دليل چرخش تكيه گاه هاي قاب و ديگري لقي پين ها و پيچ هاي اتصال ميراگر، درون شكاف هايشان مي باشد. نشان داده مي شود كه چگونه اين لقي سبب تاخير در عملكرد ميراگر شده و موجب آن مي شود كه ميراگر در زلزله ها نقش كمتري ايفا كند.

Additional dampers TADAS are a kind of passive control systems which can be used in seismic design or retrofit of structures. In this study, behavior of TADAS dampers in large deformation has been examined and some of the possible errors in its design are expressed. It is shown that how the lack of attention can result in damage to the structure and reduce the ability of energy dissipation in the damper. To investigate this issue, TADAS damper with all its details was simulated in ABAQUS finite element software. TADAS damper made up of several components, these components include the upper plate, the lower plate, triangular plates, rods rollers (pins) and connection plates. Damper modeling in ABAQUS determined that in a large deformation, the damper stiffness strongly and suddenly increases. It is examined that this sudden changes in damper characteristics is mainly due to the collision of the damper pin and the upper wall of its slot. This sharp increase could lead to adverse responses and even help to the destruction of the structures. In this paper, two suggestions are presented to prevent this situation. These suggestions include increasing the slot height and putting pins in the lowest point than slot bottom during damper installation. Assuming uniform curvature over the damper plates, a relationship has been proposed to predict the amount of the large displacement corresponding to the high stiffness of the damper. Using this relationship can get awareness of the occurrence or non-occurrence of increasing stiffness of the damper in the various stories of structures. It can also be used as a design tool for selecting the proper height of the damper slots. Also, a frame equipped with TADAS damper is constructed and get under cyclic loading to large deformation. This frame was simulated in ABAQUS and its behavior was compared with laboratory sample. This comparison indicates that there is a good agreement between laboratory and software results. From laboratory and software models, it became clear that the frame equipped with TADAS damper even in large deformation has stable and acceptable behavior, but two very important defects are observed in the frame. One of these defects is buckling of braces despite their design based on the toleration of the maximum capacity of damper. This buckling has occurred due to the rotation of beam-to-column connections. To prevent damper from degradation, it must be considered in the design process as far as the large deformations is concerned. As per the design codes, damper’s retainer system TADAS (Chevron braces) should not be damaged or buckled. The second defect is related to the looseness of damper’s pins and the looseness of damper’s connection bolts inside their slots. It will be shown that how this looseness causes a delay in the performance of damper and will increase the possibility that the damper plays a lesser role during earthquake. Therefore, the looseness in pins and bolts must be properly prevented. In this study, 10 bolts with 24 mm diameter were used to the connecting damper to floor-beams and Chevron braces.