معرفی و بررسی رفتار یک مهاربند فولادی جدید با قابلیت مرکزگرایی و استهلاک انرژی

سیستم های مقاوم مرسوم در برابر نیروهای لرزه ای، اغلب از طریق تغییرشکل های غیرارتجاعی در برخی از اعضا و اجزای سازه ای، انرژی ورودی زلزله را مستهلک می کنند. در این سیستم ها بعد از وقوع زلزله تغییرمکان ماندگار زیادی مشاهده می شود که هزینه های بازسازی را بالا برده یا تخریب سازه را ایجاب می کند. استفاده از سیستم های مرکزگرا که در ده سال اخیر بسیار مورد توجه مجامع علمی معتبر بوده است، باعث کاهش قابل ملاحظه یا حذف تقریبا کامل تغییرشکل های ماندگار در سازه پس از زلزله می شود. سیستم مرکزگرای بررسی شده در این مقاله، یک مهاربند فولادی جدید است که در آن از کابل های فولادی پیش تنیده به عنوان مکانیزم بازگرداننده برای کاهش تغییرشکل پسماند استفاده شده است. همچنین از میراگرهایی به شکل دندانه- شانه ای که به صورت درون صفحه ای عمل می کنند، برای تامین استهلاک انرژی بهره گرفته شده است. این مهاربند مرکزگرا را می توان به جای مهاربندهای معمول در قاب های فولادی ساده مورد استفاده قرار داد. بررسی معادلات تحلیلی این مهاربند و نیز مدلسازی اجزای محدود نشان می دهد که قابلیت مرکزگرایی و استهلاک انرژی موردنظر می تواند به میزان مطلوبی توسط آن تامین گردد. همچنین تحلیل های غیرخطی تاریخچه زمانی در نمونه هایی از سازه های 6 طبقه برای شتاب نگاشت های مختلفی انجام گرفته که بیانگر رفتار قابل قبول این سازه ها در صورت استفاده از این مهاربند است.

Introduction and Investigation of a New Steel Brace with Self-Centering and Energy Dissipating Capabilities

Current design philosophy for conventional lateral resisting systems is that the frames should not collapse during major earthquakes, however significant structural damage in elements such as beams, braces and sometimes columns may occur. The presence of residual drift due to inelastic deformations may hinder building occupancy or functionality after major earthquakes, and may increase associated repair costs significantly. During last two decades, practicing engineers and researchers have tried to develop seismic resisting systems that can minimize and potentially eliminate residual drift due to earthquakes. Proposed structural systems utilize the socalled ldquo;selfcentering rdquo; systems that can improve the seismic behavior, provide higher resiliency and overcome the significant residual drift of conventional systems. Selfcentering (SC) seismic resistant systems, introduced in the literature are developed for both steel and concrete structures. For the steel structures, they may be categorized into three primary groups: SC moment frames, SC rocking systems and SC braced frames. The most important similarity between selfcentering systems is that the lateral load resistance of the system has a flagshaped hysteretic loop. That is the characteristic of systems that selfcenter after large lateral displacements. Considering the normal practices of construction industry in Iran, it is more feasible and favorable to use metal yielding dampers instead of viscous or friction dampers. Also considering the economic issues, selfcentering mechanisms which use pretension tendons are more feasible compared to shape memory alloys. A yielding metallic damper called combteeth damper (CTD) provides energy dissipation mechanism. CTD is made of steel plates and includes a number of teeth that dissipate energy through inplane flexural yielding. The new self centering brace (SCB) can substitute the conventional braces to provide desired seismic performance and to reduce residual deformations and repair costs. The proposed brace can be easily disassembled in the field which provides the possibility of inspection of the core after a large earthquake. Parameters of this system should be selected so that they can provide appropriate stiffness, strength and energy dissipating capacity. In this paper, initially the overall mechanical behavior of the device has been defined in terms of its internal components, based on an analytical approach. The mechanical equations for the SCB were decomposed into two portions, which are the pretension tendons that cause the selfcentering behavior and the CTD links that support the energy dissipation mechanism. Also finite element analysis has been conducted to verify the hysteretic responses and mechanics of the proposed SCB. Based on the results, the characteristics of finite element responses have good similarity with the analytical results and show that either of the approaches are reasonable to predict the SCB behavior. Then a parametric finite element analysis has been conducted by varying the mechanical properties of steel elements to optimize the properties of the system. The results show that the desired self centering and energy dissipating capacities would be achieved using the new SCB. Lastly, nonlinear time history analyses have been performed to investigate the characteristics of some 6 story steel buildings equipped with the new SCBs. The results confirm the feasibility of using the new SCBs in braced frame structures.