بررسی و مقایسه رفتار لرزه ای مهاربندهای نوین فلزی به روش تحلیل دینامیکی فزاینده

نوع مقاله : پژوهشی اصیل (کامل)

نویسندگان
رامین مردی
مهدی قاسمیه
دانشکده مهندسی عمران - دانشگاه تهران
10.22034/23.2.12
چکیده
مهاربندهای کمانش‌تاب (BRB) نوعی سیستم جدید مقاوم لرزه‌ای می‌باشند که به دلیل کارایی آن‌ها و همچنین عملکرد لرزه‌ای بهتر از مهاربندهای مرسوم، استفاده از آن‌ها در حال گسترش‌ است. مهاربندهای BRB معمولاً در قاب‌های مهاربندی‌شده همگرا به کار می‌روند. در مهاربندهای BRB به دلیل اینکه از کمانش هسته فولادی جلوگیری می‌شود، سازه رفتار بسیار پایدارتری از خود نشان می‌دهد. در این نوع مهاربندها، عملکرد هیستریک مهاربند مشابه عملکرد هیستریک مصالح هسته است. از دیگر ویژگی‌های این مهاربندها این است که شکل پذیری مصالح فولادی در طول قابل توجهی از مهاربند اتفاق می‌افتد. مهاربندهای BRB علی‌رغم آن‌که قادر به اتلاف مقداری زیادی از انرژی می‌باشند، قادر به حذف کرنش‌های پسماند خود نیستند. به عبارت‌دیگر، فاقد ویژگی خودبازگشتی می‌باشند که این امر منجر به عدم بازگشت سازه، در صورت نبود مکانیسم بازگرداننده، به موقعیت اولیه خود پس از پایان زلزله می‌شود. بنابراین تغییرشکل‌های ماندگار زیادی در هنگام زلزله در سازه ایجاد می‌شود. برای فائق آمدن بر این نواقص، راه‌حل‌های نوآورانه مختلفی در ساخت مهاربندهای فولادی انجام گرفته شده‌است که از جمله این راه‌حل‌ها استفاده از آلیاژهای حافظه‌دار‌شکلی (SMA) که دارای دو ویژگی بارز حافظه­دار بودن و رفتار ابرکشسان هستند و می‌توانند پس از باربرداری در کرنش‌های بزرگ به وضعیت اولیه خود باز‌گردند؛ است. در سال‌های اخیر از آلیاژهای حافظه‌دار‌شکلی بر پایه آهن که مزیت‌های زیادی نسبت به آلیاژهای قبلی دارند و همچنین هزینه آن‌ها کمتر است، در زمینه ساخت و ساز استفاده می‌شود. در این پژوهش به مقایسه رفتار لرزه‌ای سازه‌های دارای مهاربندهای کمانش‌تاب و سازه‌های فولادی دارای مهاربندهای آلیاژ حافظه‌دارشکلی بر پایه آهن و بر پایه نیکل می‌پردازیم. برای مدل کردن این سیستم‌ها از نرم‌افزار SeismoStruct استفاده شده‌است و تحلیل دینامیکی فزاینده بر روی یک سازه هفت طبقه مجهز به مهاربندهای ضربدری انجام شده است. نتایج این تحقیق نشان می‌د‌هد که سازه‌های مهاربندی شده با آلیاژهای حافظه‌دار پایه ‌آهن در مقایسه با سازه‌های مهاربندی شده با نیتینول جابجایی‌های حداکثر و جابجایی ماندگار کمتری را متحمل می‌شوند و عملکرد مطلوب‌تری را نشان می‌دهند. لیکن این ساز‌ه‌ها در مقایسه با سازه مهاربندی شده کمانش‌تاب جابجایی‌های حداکثر بیشتری را تجربه می‌کنند؛ در صورتی که هیچگونه جابجایی ماندگاری برجای نمی‌گذارند.

کلیدواژه‌ها

موضوعات

عنوان مقاله English

Seismic Behavior of Innovative Braces Using Incremental Dynamic Analysis

نویسندگان English

R. Mardi
M. Ghassemieh
School of Civil EngineeringUniversity of Tehran
چکیده English

BRBs are a new type of seismic resistance system that is being used extensively nowadays due to their enhanced seismic performance than conventional braces. In BRB braces, because the buckling of the steel core is prevented, the structure shows more stable behavior. In this type of bracing, the hysteresis performance of the bracing is similar to the hysteresis performance of the core material. Another feature of these braces is that the ductility of the steel material occurs over a considerable length of the brace. Although BRB braces are capable of dissipating large amounts of energy, they are unable to eliminate their residual strains. In other words, they do not have the property of self-centering. This leads to the non-return of the structure and to its original configuration after the seismic excitations; in the absence of a return mechanism. There may arise many permanent deformations in the structure during an earthquake. To overcome these permanent deformations, various innovative solutions have been developed in the construction of steel frames, including the use of shape memory alloys (SMA) that have two prominent features of shape memory and superelastic behavior and can return to their original position after subjected to the various loadings condition. In recent years, beside the Nitinol shape memory alloy (NiTi), Iron-based shape memory alloys (SMA-Fe), which have many advantages over previous SMAs and particularly due to their lower cost, have been introduced and being used in many construction projects.

In this research, the seismic behavior of structures braced with BRB, and iron-based shape memory alloy and Nitinol shape memory alloys has been investigated. Seismostruct finite element software has been used to model these systems. Incremental dynamic analysis (IDA) has been performed on seven story structures equipped with X braces with different materials.

The results of this study show that braced structures with iron-base shape memory alloys undergo less maximum displacement and permanent displacement compared to nitinol-braced structures. However, these structures experience more maximum displacement than BRB braced structure. The more the structures enter the nonlinear stage (in the maximum values of the relative inter-floor displacement demand) the more the dispersion of the results increases and the structure is more affected by the input accelerometers. The structure with buckling bracing will reach instability later than the two structures with shape memory alloy bracing.

It is also observed that the elastic stiffness (slope of the linear behavior region) in all 3 braced frames is equal to each other. And finally, the IDA curve of the BRB structure is higher than the two shape memory alloy structures, and at equal acceleration, it is clear that the displacement of the shape memory alloy structures is more than the buckling structure, and it can also be seen that the iron-based shape memory alloy brace has a favorable performance and its curve is slightly higher than the NiTi shape memory alloy. Also, two shape memory alloy structures move almost together and reach instability at one point. According to the curves, it seems that the braced structures with shape memory alloys have performed well and until these structures reach instability.

کلیدواژه‌ها English

Iron-Based shape memory alloy
Buckling Restrained brace
Nitinol
Seismostruct
Incremental dynamic analysis
Superelasticity
Residual deformation
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مهندسی عمران مدرس
دوره 23، شماره 2
خرداد و تیر 1402
صفحه 177-192