پديد آورندگان :
دهقاني، احسان دانشگاه قم - دانشكده مهندسي عمران , بحراني، محمدكاظم دانشگاه قم - دانشكده مهندسي عمران , افخمي، وحيدرضا دانشگاه قم
چكيده فارسي :
يكي از مسائلي كه مهندسين سازه در طراحي سازه هاي فولادي بوسيله نرم افزار هاي تجاري از قبيل SAP يا ETABS با آن مواجهند، نحوه در نظر گرفتن اثرات ناحيه همپوشاني المانها (طول ناحيه صلب انتهايي) در چشمه اتصال است. در اين نرم افزارها امكان در نظر گرفتن اين ناحيه بصورت كاملاً صلب يا نيمه صلب وجود دارد، در حالي كه اتخاذ هر يك از اين گزينه ها منجر به تفاوت قابل ملاحظه اي در نتايج و محاسبات خواهد شد. در اين تحقيق با معرفي دو مدل تحليلي متعارف در مدلسازي چشمه اتصال و تمركز روي اتصال با ورق انتهايي، به بررسي دقيقتر تاثير ميزان طول ناحيه صلب انتهايي در نتايج مدل سازي قاب هاي فولادي پرداخته شده است. براي اين منظور نتايج بدست آمده از تحليل به روش مرسوم با نتايج بدست آمده از تحليل دقيقتر بر اساس روش پيشنهادي آيين نامه يوروكد مقايسه شده اند. در نهايت پيشنهاداتي براي در نظر گرفتن ميزان صلبيت ناحيه انتهايي المانها به منظور دستيابي به نتايج دقيقتر سختي و مقاومت قاب فولادي ارائه گرديده است.
چكيده لاتين :
In the design of most of steel frames, the beam to column connections are assumed to be rigid or pinned. However, in many steel frames beam-column connections show semi-rigid behavior. Structures with semi-rigid connections contain systems with the connections in joints which are not completely rigid, but allow, usually, some relative movements in directions of general displacements. However, semi-rigid design has not received widespread attention due to its perceived complexity and the lack of effective tools for global analysis.
Early experimental studies showed the importance of shear deformations in panel zone for stable energy dissipation under cyclic loading. Modeling of panel is very important because of its role in prevention of local failure of columns under ultimate limit state.
A substantial effort has been made in recent years to characterize the behavior of semi-rigid connections. Recent studies and modern codes, especially EC3 and EC4, include methods and formulas to derive resistance and stiffness of panel zone. EC3 proposes a mechanical model for semi-rigid connection -in which each component is modeled by an equivalent linear spring. In this case, some components of the connection are showed by springs. These springs are assembled by a single bilinear (elastic–plastic) rotational spring alternating the connection, and is attached at beam-column intersection in the global analysis.
Stiffness and strength of the springs in EC3 and EC4 depend on β factor which implies an approximation of the internal forces at the joint. Therefore, adopting accurate β factor requires an iterative process at the time of performing the global analysis of the structure. Modifying EC methods; E. Bayo et al proposed a new component-based method (or cruciform element method) for modeling the internal and external semi-rigid connections. In this model, a cruciform element (a four-node element) is proposed to avoid β factor, and the inherent initial assumption and iterative process that it requires, and includes the finite size and deformation modes of the joint.
One of main problems with which structural engineer deals is considering End Length Offset in conventional software. Extended end plate connection is one of beam-column semi rigid connections that is to evaluate by its behavior, using cruciform connection model and other panel zone models.
In this paper, three 2-dimensional frames with extended end plate connections are modeled in MATLAB using cruciform element method and the results are compared with the analytical results of SAP2000 for eight cases (including four models regarding the presence of the panel zone and four models disregarding it). At one state, End Length Offset is considered just for beams and at the other, for both beams and columns (in two cases of Rigid Zone Factor: 0.5 and 1). The results show that modeling panel zones according to EC method and considering Rigid Zone Factor equal to 1 in columns and beams are the best assumptions for analyzing 2D frames with extended end plate connections. However, if the panel zones are not modeled, Rigid Zone Factor must be considered equal to 0.5 simultaneously in columns and beams - to give actual results.
