ارزیابی رفتار لرزه‌ای سازه‌های فولادی مجهز به میراگر Madas در مقایسه با سیستم قاب خمشی

هدف از این مقاله ارزیابی مشخصات میراگر adas اصلاح شده و عملکرد لرزه ای سازه های فولادی کوتاه و میان مرتبه مجهز به این نوع میراگر می باشد. ورق های x شکل مورد استفاده در میراگر adas اصلاح شده (madas) به گونه ای قرار گرفته‌اند که علی رغم مقید نمودن درجات آزادی چرخشی در دو انتها، تغییر مکان آنها در امتداد قائم کاملاً آزاد است و در نتیجه هیچ گونه نیروی محوری در میراگر ایجاد نمی شود. بدین‌ترتیب، رفتار ورق ها تحت نیروهای جانبی کاملاً خمشی بوده و از سوی دیگر بارهای ثقلی طبقات یا مولفه قائم در تیرها و بادبندها نیز کوچک‌ترین تاثیری در رفتار میراگر جدید ندارند. در این مقاله مدل عددی میراگر به منظور صحت سنجی نتایج مدل عددی با مدل آزمایشگاهی ایجاد شده است. در ادامه عملکرد لرزه ای سازه های مجهز به میراگر madas به وسیله مدل‌سازی عددی بررسی و پارامترهای لرزه ای از قبیل ضریب رفتار، میرایی معادل و جابجایی نسبی طبقات برآورد شده است. نتایج حاصل بیانگر رفتار برتر سازه های مجهز به میراگر madas در مقایسه با سازه های خمشی متوسط بوده است. همچنین مطالعات رفتار چرخ ه ای میراگر یاد شده در مقایسه با میراگرهای رقیب (مانند adas و tadas) رفتار مناسب تری را نشان داده است.

Evaluating Seismic Performance of Steel Structures Equipped with MADAS Dampers in Comparison with Moment-Resisting Frames

One of the effective methods to improve dynamic response of steel structures is using adjunct elements among which metal yielding dampers are the most common. The working mechanism of these dampers in the lateral loadresisting structural system is related to the fact that development of inelastic strains in metallic dampers as the fuse elements results in dissipating the earthquake input energy imparted to the structure in a major seismic event. On the other hand, the aim of implementation of such damping devices is to substantially reduce the seismic demand in main structural systems, such as beams and columns, and hence, these members remains essentially elastic. One of the types of metallic yielding dampers is Added Damping and Stiffness (ADAS) metal damper that is a series of Xshaped steel sheets, which can be efficient in dissipating seismic energy but have shown apparent weakness due to the buckling resulted from development of axial forces in the dampers.The objective of the present paper is to investigate the characteristics of a Modified Added Damping and Stiffness (MADAS) damper to be used as a supplementary device to improve seismic performance of low and midrise steel structures. In MADAS damper, Xshape plates are configured in a way that their displacement along vertical axis is quite free, and hence, no axial force is developed in such metallic dampers. In this paper, a numerical Finite Element (FE) model of MADAS damper was simulated in ABAQUS and used to compare the predicted numerical results to those of experimental results of the MADAS damper subjected to cyclic displacements. It should be noted that, the experimental cyclic tests have been conducted by previous researchers for MADAS dampers, and, have shown superior cyclic performance compared to conventional metallic dampers such as Triangular Added Damping and Stiffness (TADAS) dampers.In addition, three 4, 5, and 6story buildings with steel momentresisting frames have been studied, as the representative of the low and midrise structures. For each building, two design alternatives, one for the case of conventional Steel MomentResisting Frame (MRF) and the other alternative is the one equipped with MADAS dampers, have been designed to be studied using numerical models. The structural members of the adopted buildings equipped with metallic MADAS dampers are designed according to ASCE/SEI 710 design code. The behavior of the numerical models has been investigated regarding seismic parameters including the Response Modification Factor, R, and Overstrength Factor, (Ω). The application of metallic dampers have shown to provide an increase of about (50%80%) in the Response Modification Factor, R, and about (10%20%) in the Overstrength Factor, (Ω). Pushover analyses for the numerical models have been conducted to obtain Base shearDisplacement curves. Based on the obtained pushover results, a maximum decrease of about 20% was noticed in the interstory drifts of the numerical models in the Collapse Prevention (CP) performance level.In addition, to investigate the seismic performance of analysis cases, timehistory analyses of the numerical models subjected to 1940 ElCentro, 1994 Northridge, and 1978 Tabas earthquakes have been conducted. The earthquake records have been scaled to Maximum Credible Earthquake (MCE) and Design Based Earthquake (DBE) intensity levels. Based on the obtained timehistory results, a decrease of about (40%50%) has been observed in the peak interstory drift values due to the application of metallic MADAS dampers compared to that of momentresisting steel frames. In addition, regarding the results of timehistory analyses, the values of equivalent damping has been observed to be in the range of about (15%20%) for the analysis cases. The obtained results indicate significant improvement in the seismic response of the structures equipped with MADAS dampers compared to the same buildings utilizing Steel MomentResisting Frames (MRFs) as their lateralresistant structural system.