مطالعه روند تغییرات پاسخ لرزه ای اسکلت های ترکیبی قاب محیطی خمشی بلندمرتبه در ساختگاه های نزدیک گسل

این پژوهش به بررسی روند تغییرات پاسخ لرزه ای اسکلت های ترکیبی قاب خمشی محیطی و مقایسه آن با سیستم پایه، بر اساس نتایج تحلیل های غیرخطی تحت مجموعه ای از رکوردهای نیرومند سه‌ مولفه ای حوزه نزدیک می پردازد. ساختارهای ترکیبی با تعبیه پیکربندی های چند طبقه ای المان های زیپر بزرگ‌مقیاس در اسکلت قاب محیطی خمشی حاصل می گردند. المان‌های زیپر بزرگ‌مقیاس، تنها در پانل های صلب سازه قاب محیطی تعبیه شده و دارای اتصال پیوسته با پانل زون‌های اسکلت مقاوم می‌باشند. پروسه مطالعاتی حاضر شامل بررسی چگونگی تغییرات پارامترهای پاسخ سه اسکلت مقاوم 30 طبقه با و بدون پیکربندی المان‌های زیپر بزرگ‌مقیاس است. طراحی سازه های مطالعاتی بر اساس ضوابط مقررات ملی ساختمان و همچنین ویرایش چهارم آیین نامه طراحی ساختمان ها در برابر زلزله (استاندارد 2800) انجام شده است. مدل سازی رفتار غیرخطی اعضا و تعریف مفاصل پلاستیک بر اساس ضوابط fema356 بوده و مجموعه تحلیل های غیرخطی تاریخچه زمانی با استفاده از نرم‌افزار sap 2000 صورت گرفته است. کاربرد المان های زیپر بزرگ‌مقیاس در سیستم قاب محیطی خمشی، سبب پخش به نسبت یکنواخت تر نیروی محوری، برش، لنگر خمشی و پیچشی دینامیکی در ستون های محیطی پلان و کاهش دامنه دوران غیرخطی اتصالات می شود. همچنین، ارزیابی پارامترهای پاسخ دینامیکی این سازه ها نشاندهنده‌ی بهره وری بالاتر سیستم سازه ترکیبی فوق بوده و کاهش نسبی پارامترهای پاسخ لرزه‌ای را در پی دارد.

Study on the Seismic Response Variations of Tall Hybrid Hramed Tube Skeletons in Near-Fault Sites

This research investigates the trend of changes in seismic response of tall hybrid framed tube skeletons according to the obtained analytical results through conducting nonlinear dynamic response history analyses (NLRH analyses) under three components nearfield earthquake records. For this purpose, three 30story structural models with framed tube resistant skeletons were selected and designed. The first resistant skeleton is classified as the basic model with a framed tube structural system. The second and third models are introduced by embedding of multilevel configurations of large scale zipper elements on the basic model, which connected to one or two columns in the first story. The existence of a designed multilevel arrangement of large scale zipper elements prevents the formation of expanded plastic mechanism and also relatively blocks the occurrence of any possible buckling in the lowerstories columns. The connection of the large scale zipper elements to the columns was defined rigid. The studied structures were loaded and designed in accordance with the notified provisions recommended by the Iranian national building codes (divisions six and ten) as well as the standard 2800 (fourth edition) [13]. The assumed hysteresis loops related to the possible formation of plastic hinges in structural elements have been adapted from the FEMA 356 [4]. These notifications were described to clarify the assigned nonlinear behavior of the elements of each studied structure. All of the analyses were conducted through SAP 2000 software [5].To perform nonlinear dynamic response history analyses, an ensemble of five earthquake records including one farfield and four nearfield ground motions contain forwarddirectivity effects, were selected and scaled according to the fourth edition of the Standard 2800. The main criterion in choosing nearfield records is the existence of distinct coherent pulses caused by the strong rupture directivity effects, which are emerged in the ground velocity time history [67]. In this research, a comprehensive numerical assessment was accomplished on the seismic response parameters of the studied structural models. The analytical evaluations are focused on the maximum interstory drift ratios, the maximum relative velocity and absolute acceleration of the floors (defined at the center of mass CM), maximum axial and shear force resultants, the upper bound of flexural and torsional moment of the columns, and also the maximum rotation of the formed plastic hinges.By comparing the configuration of the plastic hinges formed in columns and beams, it is resulted that the presence of the largescale zipper elements in the lower four stories of the structure relatively causes less damages as well as a greater time domain of dynamic stability. The use of these elements in the perimeter bays of tall framed tube structures results a more uniform distribution of the axial and shear forces, as well as bending and torsion moments in the peripheral columns. It is also resulted a noticeable reduction for the maximum inter story drift ratio of floors, the maximum relative velocity and absolute acceleration of floor levels. Moreover, by comparing the total weight of studied models, it is clear that the architectural embedding of the largescale zipper elements would cause a slight increase for this factor while reducing the average relative displacement near to 15% as well. REFERENCES1 Iranian National Building Code (2014) Design Loads for Buildings Division 6. Tehran, Iran (in Persian).2 Iranian National Building Code (2014) Steel Structures Division 10. Tehran, Iran (in Persian).3 Iranian Standard No. 2800 (2014) Iranian Code of Practice for Seismic Resistant Design of Buildings. Fourth edition. Tehran, Iran (in Persian).4 FEMA (1998) Prestandard and Commentary for the Seismic Rehabilitation of Buildings, FEMA 356. Federal Energy Management Agency.5 SAP 2000, Integrated Software for Structural Analysis and Design. Computers Structures, Inc., Berkeley, California.6 Mukhopadhyay, S., and Gupta, V.K. (2013) Directivity pulses in nearfault ground motions—I: Identification, extraction and modeling. Soil Dynamics and Earthquake Engineering, 50, 115.7 Mukhopadhyay, S., and Gupta, V.K. (2013) Directivity pulses in nearfault ground motions—II: Estimation of pulse parameters. Soil Dynamics and Earthquake Engineering, 50, 3852.