تحلیل حساسیت میراگر ftmd و بررسی عملکرد آن در مقایسه با tmd در سطوح مختلف خطر لرزه ای

از جمله به‌روزترین وسایل کنترل لرزه ای، میراگرهای جرمی تنظیم شده اصطکاکی (ftmd) هستند. این نوع میراگر، ترکیبی از میراگر جرمی تنظیم شده (tmd) با سختی خطی و یک میراگر اصطکاکی خالص با رفتار غیرخطی است. در این مقاله، ابتدا به تحلیل حساسیت پاسخ های سازه مجهز به این میراگر در اثر تغییر در نسبت فرکانس، ضریب اصطکاک و نسبت جرمی میراگر پرداخته شده است؛ سپس به کمک این نتایج، پاسخ های لرزه ای برای سه سازه ی برشی 3، 5 و 10 طبقه در سه حالت سازه بدون میراگر، با ftmd و با tmd مورد بررسی قرار گرفته و در دو سطح خطر لرزه ای مقایسه شده است. تحلیل های انجام شده در نرم افزار opensees و تحت 40 شتاب نگاشت پروژه sac، در دو سطح خطر لرزه ای 1 و 2 است. نتایج به‌دست‌آمده حاکی از حساسیت بالاتر پاسخ ها به نسبت فرکانس، در مقایسه با ضریب اصطکاک و نسبت جرمی است. بهترین مقدار برای ضریب اصطکاک در سطح خطر یک عددی بین 0.1 تا 0.3 و در سطح خطر دو، 0.2 تا 0.4 است. همچنین رفتار سازه با به‌کار بردن ftmd در هر سه سازه ی 3، 5 و 10 طبقه بهتر از tmd است؛ لیکن با افزایش زمان تناوب سازه تاثیر ftmd به tmd نزدیک می شود.

Sensitivity Analysis of Friction Tuned Mass Damper and its Performance Compared to Tuned Mass Damper at Different Seismic Hazard Levels

One of the most uptodate seismic control devices are friction tuned mass damper (FTMD). This type of damper is a combination of a tuned mass damper (TMD) and a nonlinear frictional damper. In this paper, the governing equations for a singledegreeoffreedom (SDOF) structure equipped with a FTMD and effective parameters on these systems performance are expressed first. Then, SDOF structures with linear behavior equipped with a FTMD are modeled and validated in OpenSEES software. Finally, the sensitivity analysis of these models to their effective parameters is performed. The structures mass is assumed to be 10 tons, their period is 0.5 second and their damping ratio is assumed to be 2%. Nonlinear time history analyses are done for these structures using 40 strong ground motions from the SAC project. These ground motions consist of 20 records (La01La20) at design basis earthquake (DBE) level and 20 records (La21La40) at maximum considered earthquake (MCE) level for the Los Angeles area. Effective parameters on the performance of FTMD assumed in this study are the friction coefficient of the damper, the mass ratio of the damper to the structure and the frequency ratio of the damper to the structure. Average of the structures’ maximum displacement is determined for two ground motion records sets and effects of the mentioned parameters on the structural performance are discussed. Results show that the responses are more sensitive to frequency ratio rather than friction coefficient and mass ratio. The best value for the friction coefficient varies between 0.1 and 0.3 at DBE level, and varies between 0.2 and 0.4 for MCE level.Based on the results obtained for SDOF structures, application of FTMD on multidegreeoffreedom (MDOF) is discussed in the next step. This is done for short period structures because this type of damper is more effective on these structures. Three MDOF structures with linear behavior and period of 0.3, 0.5 and 1 second are selected and the seismic performance of these structures equipped with FTMD is investigated and compared with the same structures equipped with tuned mass damper (TMD). The mass of stories is uniformly distributed among structure and the mass of each story is 10 ton. In addition, the damping ratio for the main structure in all models is assumed to be 2% and the stiffness of the stories is decreased linearly with the triangular pattern. Same ground motion records are used for the nonlinear time history analysis of MDOF structures and the results for the mean maximum relative displacement of the stories under DBE and MCE levels are compared for structures with FTMD and TMD. Results show that the structures equipped with FTMD have better performance than the structures equipped with TMD, but with increasing structures period, performance of two systems approach each other. In addition, 3 and 5 story structures equipped with FTMD have better performance at DBE level while a 10story structure equipped with this damper has better performance at DBE level.