ضریب رفتار چند سطحی سیستم ترکیبی قاب خمشی فولادی و دیوار برشی بتنی درزدار

تامین شکل‌پذیری زیاد موجب کاهش سختی سازه و افزایش تغییرشکل‌های جانبی و متعاقب آن آسیب به اجزای غیرسازه‌ای میشود. هر چند افزایش مقاطع قاب خمشی فولادی سختی سازه را افزایش می‌دهد ولی اقتصادی نخواهد بود. بدین منظور ترکیب قاب خمشی و دیوار برشی بتنی می تواند یک راه حل جهت افزایش سختی باشد. اما در سازه‌های کوتاه استفاده از این سیستم ترکیبی باعث کاهش شکل‌پذیری و استهلاک انرژی در زلزله‌های متوسط تا قوی می‌گردد. استفاده از درزهای قائم در دیوار بتنی کوتاه و متوسط این نقص را بهبود می‌بخشد. این درزها رفتار برشی دیوار بتنی را به رفتار خمشی شکل‌پذیر تعدادی اجزاء ستونی تبدیل نموده و می‌توانند شکل‌پذیری را افزایش دهند. عدم درج ضریب رفتار در آیین‌نامه‌های طراحی لرزه‌ای از چالش‌های استفاده از این سیستم نوظهور می‌باشد. بیان چند سطحی ضریب رفتار و استخراج آن با توجه به میزان تقاضای زلزله و میزان آسیب قابل قبول به عنوان سطوح عملکردی مورد انتظار از نوآوری های این مطالعه می‌باشد. در این تحقیق ضرایب رفتار طلب و ظرفیت قاب خمشی فولادی با دیوار برشی بتنی درزدار و بدون‌درز در ارتفاع 5 و 10 طبقه با کمک تحلیل بارافزون و تحلیل دینامیکی افزایشی، محاسبه شده‌اند. بررسی نتایج نشان داد، اگرچه سختی اولیه ارتجاعی در سازه ترکیبی قاب خمشی و دیوار برشی بتنی درزدار و بدون‌درز اختلاف چندانی ندارد، اما به علت تغییر رفتار دیوار بتنی از برشی به ستونک های خمشی جذب انرژی بیشتر و لذا ضریب رفتار بزرگ‌تر و شکل‌پذیری بیشتری را برای نوع با درز به ارمغان می‌آورد.

MultiLevel Behavior Factors for Steel Moment Frame Accompanied with RC Slit Shear Wall System

Earthquake loads induce significant damages and cause widespread failures into buildings. Having appropriate system against seismic loads is a minimum necessary requirement for a structure. Moment Resisting Frame Systems (MRFS) are one of the common seismic resisting systems against lateral seismic loads. Ductility is the most important properties of these kinds of systems; but increase in ductility leads to decrease stiffness and increase lateral deflections and hence induces damages to nonstructural components. Although stiffness can be magnified through increasing section sizes of members, but it would not be economical. To compensate this deficiency, the combination of these systems with reinforced concrete (RC) shear walls may be useful. Although in general, this combination (RC shear walls and MRFS) decreases the section size and increase stiffness; but in low rise structures using this combined system cause decrease in ductility and dissipation of energy under moderate/strong earthquakes.This deficiency can be improved by using vertical slits in RC shear walls of low to moderate height. These slits invert shear behavior of RC shear wall into flexural behavior of several columns and are able to increase ductility. So, for the first time in this paper, a study was conducted on introducing behavior factor (R) for Steel Moment Frame (SMF) with reinforced concrete slit shear wall system at two levels of demand and supply. In view of existing concerns about precise of behavior factors in seismic design codes, due to developing these factors based on engineering judgment from observing seismic performance of structures subjected to past earthquakes besides the lake of these information in current seismic design codes causes the seismic design of RC slit shear wall system needs more research works. The behavior factors are used to reduce the linear elastic design spectrum to account for the energy dissipation capacity, overstrength and redundancy of the structure. The most distinctive feature of this study respecting to similar studies is multilevel definition of behavior factors and their extraction with respect to seismic intensity, and accepted damage level as expected performance levels in designing RC slit shear wall structural system. Hence, the demand/supply behavior factors are determined with a more accurate attitude involving the effective parameters such as ductility, overstrength, redundancy, seismic hazard level, performance levels, etc. In this study, to determine the appropriate behavior factor, static pushover analysis along with Incremental Dynamic Analysis (IDA), are used. The behavior factors in two levels of demand and supply are obtained with two procedures: At the first, the pushover analysis was applied on case study structures and then relationship for SDOF system of Newmark and Hall, Nassar and Krawinkler, and Miranda to evaluate behavior factor for MDOF structures were used. At the second stage both pushover and incremental dynamic analysis were used to achieve directly the behavior factor for MDOF structures. In this paper, two 5 and 10story steel moment resisting frame with RC slit and ordinary shear wall systems were designed by ETABS software. These structures were designed in which their behavior factors were the same values. Then the pushover and IDA were conducted on sample structures using nonlinear analysis software PERFORM. Results show that, although initial elastic stiffness has not been considerably changed in slit RC shear wall systems, but they show higher behavior factor relative to regular RC shear wall systems. Converting the shear behavior of RC ordinary shear wall to ductile flexural behavior of a series of wall pieces as columns by providing slits in shear wall may be considered as the reason for achieving more ductility and dissipating high seismic energy in this innovative systems.