توسعه ميراگر شكافدار در محل اتصال تير به ستون با ايجاد شكاف‌هاي بيضي

Application of Elliptic Slits for Development of Slit Damper in Beam-to-Column Connection

ميراگر شكافدار فولادي يك ورق يا پروفيل استاندارد فولادي با تعدادي شكاف بريده شده در جان آن است. نوارهاي باقيمانده در جان ميراگر، با جذب تغيير شكل هاي غير الاستيك، انرژي لرزه اي را مستهلك كرده و مانع از انتقال آن به اعضاي سازه‌اي اصلي مي شوند. ميراگرهاي شكافدار فولادي با عرض نوار يكنواخت، به منظور جلوگيري از شكست ترد اتصالات و خرابي اعضاي سازه اي اصلي، در محل اتصال تير به ستون استفاده شده اند. طبق تحليل‌هاي صورت گرفته در نرم‌افزار المان محدود آباكوس، استفاده از ميراگرهاي شكافدار با عرض نوار يكنواخت در تحقيقات آزمايشگاهي قبلي، موجب تمركز تنش در قسمت هاي انتهايي نوارها، توزيع نامتوازن تنش هاي فون ميسز در طول نوارها و عدم مشاركت قسمت هاي مياني نوارهاي ميراگر شكافدار در استهلاك انرژي شده است. بنابراين، به منظور رفع اين مشكل و افزايش سطح جاذب انرژي در قسمت هاي انتهايي نوارها، ميراگر شكافدار با شكاف هاي بيضي پيشنهاد شده و با ميراگر شكافدار ارائه شده در مقالات قبلي، مورد مقايسه قرار گرفته است. نتايج تحليل اتصالات تحت بارگذاري تناوبي، نشان داده است كه استفاده از ميراگر شكافدار پيشنهادي با شكاف هاي بيضي، موجب توزيع بهتر تنش ها در طول نوارهاي ميراگر، عملكرد هيسترزيس بهتر و افزايش ميزان جذب انرژي در اتصال شده است. نتايج نشان داده است كه ميزان استهلاك انرژي و حداكثر دوران پلاستيك تجمعي تحمل شده توسط اتصال مجهز به ميراگر شكافدار پيشنهادي با شكاف هاي بيضي نسبت به ميراگر شكافدار با عرض شكاف ثابت، به ترتيب، 99/6 و 26/8 درصد افزايش يافته است.

The rigid steel connections were suffered severe damage because of low rotational capacity during earthquakes. Hence many investigations have been performed on the connections of steel structures. In order to prevent brittle failure of connections and damage of main structural members, steel slit ders with uniform strip width are used in the beamtocolumn connections. Slit der is a plate or a standard section with a number of slits in the web. The remaining strips in the web of der, dissipate the seismic energy with inelastic deformation absorption and also prevent seismic energy transmission to the main structural members. No special fabrication technique was involved in the slit ders, thus the device can be easily used in practice. To verify the accuracy of finite element modeling, the obtained results of ABAQUS finite element software were compared with an experimental study done by Oh et al (2009). The analytical results have a good agreement with experimental ones and the average error is about 2%. According to the analyses performed in the ABAQUS, using steel slit ders with uniform strip width is resulted in stress concentration at the ends of the der strips, unbalanced distribution of VonMises stresses along the strips length and low participation of middle parts of slit der strips in the energy dissipation. Therefore, to resolve these problems and energyabsorbing area rise in the end parts of strips, elliptic slit der is proposed and compared with the previous investigated slit der. Slits dimensions of elliptic slit der are calculated as such that both of present and previous slit ders have the same weight. The objective of this paper is to improve the seismic performance of steel slit ders. Nonlinear analyses are carried out in the beamtocolumn connections equipped with slit ders. Effects of geometrical and material nonlinearity are considered in the analyses. Nonlinear characteristics of steels are defined with stressstrain curves. Bilinear stressstrain curves are used for all steel parts except the slit der which is defined with completed stressstrain curve. Plasticity behavior of steel materials is based on the VonMises yielding criteria. Loading protocol recommended by FEMA350 is used for cyclic analyses. All parts of connection are modeled using shell elements except the splitT plates and the upper plate of slit ders which are modeled using solid elements. The results of connections analysis under cyclic loading show that the proposed elliptic slit der causes better distribution of stresses along the der strips, better hysteresis performance and increase the amount of energy dissipation in the beamtocolumn connection. Also elliptic slit der leads to strength and ductility increment in the connection. Additionally, it is concluded that in the proposed elliptic slit der compared to the slit der with uniform strip width, the energy dissipation and the maximum plastic rotation of connection increase about 99.6 and 26.8%, respectively.