بررسي تأثير ميراگر اصطكاكي سيلندري بر پاسخ لرزه اي سازه هاي فلزي

Effect of Cylindrical Frictional Dampers on Seismic Response of Steel Structures

در اين مقاله ، پاسخ لرزه اي سازه هاي فولادي با استفاده از ميراگر اصطكاكي سيلندري (CFD) مطالعه شده است. ميراگر اصطكاكي سيلندري شامل دو عنصر اصلي، شفت(استوانه توپر) و سيلندر(استوانه توخالي) است. اين دو عنصر به طور كامل درون هم قرار مي گيرند. اگر نيروي محوري ميراگر بيش از نيروي اصطكاك بين شفت و سيلندر شود ، شفت داخل سيلندر حركت مي كند كه منجر به جذب قابل توجه انرژي خواهدشد . براي ارزيابي اثر بخشي ميراگر اصطكاكي سيلندري، قاب هاي فولادي مختلف مورد تجزيه و تحليل قرار گرفته است. قاب ها تحت تحليل غير خطي تاريخچه زماني و تحليل غير افزايشي ديناميكي (IDA)قرار گرفته اند كه پاسخ هاي قاب فلزي داراي ميراگر اصطكاكي سيلندري و بدون آن ، تاكيد بر اثربخشي ميراگر اصطكاكي سيلندري در بهبود پاسخ لرزه اي دارد.نتايج نشان مي دهد ميراگر اصطكاكي سيلندري به شكل قابل توجهي پاسخ هاي لرزه اي را كاهش مي دهد.

In this investigation, seismic response of steel structures utilizing Cylindrical Frictional Ders (CFD) is studied. CFD is an innovative frictional der which comprises two principal elements, the shaft and the hollow cylinder. These two elements are assembled such that one is shrinkfitted inside the other. If the der’s axial force overcomes the static friction load, the shaft inside the cylinder will move and results in considerable mechanical energy absorption. To assess the efficacy of CFD, various steel frames are constructed and analyzed . Nonlinear time history analyses and Incremental Dynamic Analysis (IDA) are applied to the frames and clear distinction has been drawn between the frames comprising CFD and the counterparts without CFD to emphasize the effectiveness of CFD in altering seismic responses. The results show that CFD extremely improves the seismic response of the structure.Frictional devices dissipate energy through friction caused by two solid bodies sliding relative to each other. The idea of using frictional ders was first proposed by Pall (1979). Pall and Marsh (1982) proposed frictional ders installed at the crossing joint of the Xbrace. Tension in one of the braces forces the joint to slip thus activating four links, which in turn force the joint in the other brace to slip. This device is usually called the Pall frictional der (PFD). B. Wu et al. (2005) introduced improved Pall frictional der (IPFD) which replicates the mechanical properties of the PFD, but offers some advantages in terms of ease of manufacture and assembly. Sumitomo friction der (1990) utilizes a more complicated design. The precompressed internal spring exert a force that is converted through the action of inner and outer wedges into a normal force on the friction pads. Fluor Daniel Inc., has developed and tested other type of friction device which is called Energy Dissipating Restraint (EDR) (1994). The design of this friction der is similar to Sumitomo friction der since this device also includes an internal spring and wedges encased in a steel cylinder. The EDR utilizes steel and bronze friction wedges to convert the axial spring force into normal pressure on the cylinder. Constantine et al. (1990) proposed frictional ders composed of a sliding steel shaft and two frictional pads cled by high strength bolts. Grigorian et al. (1998) studied the energy dissipation effect of a joint with slotted holes both analytically and experimentally. Mualla and Belev (2002) proposed a friction ding device and carried out tests for assessing the friction pad material. Cho and Kwon (2004) proposed a walltype friction der in order to improve the seismic performance of the reinforced concrete structures. Recently Mirtaheri et.al. (2011) proposed an innovative type of frictional der called cylindrical friction der (CFD). In contrast with other frictional ders the CFDs do not use highstrength bolts to induce friction between contact surfaces. This reduces construction costs, simplifies design computations and increase reliability in comparison with other types of frictional ders.