كليدواژه :
اتصال تير به ستون درختي , وصله پيچي , عملكرد لرزه‌اي , پيش پذيرفتگي , آباكوس
چكيده فارسي :
استفاده از اتصالات تير به ستون درختي در قاب‌هاي خمشي فولادي، به دليل انجام جوشكاري قسمت‌هاي بحراني در كارخانه و سهولت نصب در كارگاه، بيش از گذشته موردتوجه طراحان و مجريان قرارگرفته است. اين در حالي است كه تاكنون تأثير نوع روش طراحي وصله پيچي در پيش پذيرفتگي اين نوع از اتصالات به‌منظور استفاده در سيستم‌هاي قاب خمشي ويژه بررسي نشده است. هدف اصلي تحقيق حاضر، بررسي تأثير نوع روش طراحي وصله پيچي در عملكرد لرزه‌اي و پيش پذيرفتگي اتصالات تير به ستون درختي است. بدين منظور در اين مطالعه، سه روش طراحي وصله پيچي موجود در آيين‌نامه‌هاي طراحي كه عبارت‌اند از: طراحي بر اساس اتصال لغزش بحراني، طراحي بر اساس اتصال پيش‌تنيده و طراحي بر اساس وصله ضعيف با استفاده از تحليل المان محدود غيرخطي در نرم‌افزار آباكوس موردبررسي قرارگرفته است. نتايج تحليل‌هاي انجام‌شده نشان داد كه نوع روش طراحي وصله تأثير بسزايي در مقاومت خمشي اتصال ندارد. درحالي‌كه نوع وصله در تعيين پيش پذيرفتگي اتصال، ميزان انرژي مستهلك‌شده و مقدار شاخص‌هاي خسارت ناشي از زلزله در محل اتصال تير ريشه به ستون نقش مهمي ايفا مي‌كند. در اين تحقيق، نمونه اتصال‌هاي تير به ستون درختي طراحي‌شده بر اساس لغزش بحراني و اتصال پيش‌تنيده جزء اتصالات پيش پذيرفته طبقه‌بندي شدند. درصورتي‌كه اتصال تير به ستون درختي طراحي‌شده بر اساس وصله ضعيف، به دليل نيمه صلب بودن، نمي‌تواند به‌عنوان يك اتصال پيش پذيرفته در نظر گرفته شود. درنهايت، به‌منظور بهره بيشتر از لغزش پيچ‌ها به‌عنوان يك مود شكل‌پذير، جهت كاهش شاخص‌هاي خسارت ناشي از زلزله، پيشنهاد مي‌شود كه وصله تير بر اساس اتصال پيش‌تنيده طراحي شود.
چكيده لاتين :
Moment resisting steel frames (MRSFs) are widely used as a lateral load resisting system in steel structures in
very high seismic regions. The seismic performance of this system depends mainly on the behavior of beam-tocolumn
moment connections such that trivial damages in the connections may lead to the collapse of the whole
structure or at least post-earthquake demolition of the structure. In the 1994 Northridge earthquake, beam-to-column
connections in the MRSFs damaged noticeably and unexpectedly. Several researchers then proposed various
suggestions to improve the seismic performance of beam to column connections. One of these suggestions was
using a column-tree system to avoid the low-quality field-welded moment connections. These days, column-tree
connections are widely used in the special moment resisting frames (SMRFs) buildings due to their well-known ease
of installation and inspection of welding zone, especially in the high seismic areas. However, the prequalification
and seismic behavior of these connections had not been evaluated well prior to this research; hence the structural
designers usually consider these connections as the prequalified connection for using in the SMRFs without
following a robust and validated approach. Therefore, in this study, the effect bolted splice design method on the
prequalification and cyclic response of the column-tree connections were investigated using experimentally
validated finite element analysis in ABAQUS FEA software. The column-tree connection must be designed such
that the ductile failure modes occur prior to the brittle failure modes. This may be achieved through an appropriate
design approach. Based on the bolted joint type in the AISC specification (i.e., pre-tensioned joint and slip-critical
joint) and removing plastic hinge from the column edge (weakened bolted splice), there are three bolted splice
design methods available. These are bolted splice design methods based on the slip critical joint, pre-tensioned joint,
and weak splice plates. This research studied three samples to evaluate the effects of the bolted splice design
methods on the prequalification and seismic behavior of the connection. The results show that the column-tree
connection prequalification depends on the bolted splice design methods; moreover, the bolted splice design method
influences the monotonic and cyclic behavior, strength, stiffness, fracture tendency, ductility, and energy dissipation
characteristics of the connection. Also, it is observed that based on the moment strength and rotational stiffness of
the bolted splice, the column-tree connection is classified as a rigid or semi-rigid moment connection. This is a
significant point that needs to be taken into account in the column-tree moment frame design. The structural
designers should consider these effects in their design approach for the column-tree connections. The column-tree
connection with its bolted splice designed based on the pre-tensioned joint exhibits a reduction in the fracture
tendency and increase in the ductility of the connection and also a smaller number of required bolts. For these
reasons, it is recommended that the pre-tensioned joint method be implemented in designing a bolted splice instead
of the slip-critical joint method.
