تاثير قسمت كاهش يافته اتصال فولادي RBS روي مقطع كامل

Effect of Reduced Section of RBS Connection on Intact Section

يكي از اتصالاتي كه با فلسفه ضعيف تر كردن تير به كار مي رود، اتصال خمشي تير با مقطع كاهش يافته (RBS) مي باشد. ايده تضعيف بر اين پايه است كه قسمت هايي از بال تير در ناحيه نزديك به اتصال تير به ستون بريده مي شود و با تشكيل مفصل پلاستيك در ناحيه RBS، اين ناحيه به عنوان يك فيوز شكل پذير عمل مي كند. در اين مطالعه عملكرد چرخه اي اتصال خمشي تير با مقطع كاهش يافته در محيط نرم افزار آباكوس مورد بررسي قرار گرفته است. اتصال مورد بررسي يك اتصال يك طرفه مي باشد كه محل اعمال بار انتهاي تير مي باشد. در اين اتصال، طول تير به اندازه نصف دهانه مورد نظر در يك سازه طراحي شده مي باشد. در مدل سازي اين اتصال براي دو سر ستون شرايط مرزي مفصلي در نظر گرفته شده است و از حركت خارج از صفحه تير جلوگيري به عمل آمده است. براي بارگذاري چرخه اي از قرارداد بارگذاري پيشنهاد شده در آيين نامه AISC استفاده شده است. در تحليل پارامتريك اين اتصال تاثير تغيير ابعاد ناحيه برش در رفتار اتصال بررسي شده است. نتايج به دست آمده نشان مي دهند كه ظرفيت خمشي اتصال RBS از اتصال با مقطع كامل بيشتر مي باشد اما در در اتصال با مقطع كامل مفصل پلاستيك ايجاد نمي شود.

Structural design for huge seismic events must explicitly consider the nfluences of response after the elastic range. The special moment frame (SMF) steel structures are designed such that the frame beam–column joists are able to absorb substantial energy through large rotational deformation. In this way, a major contribution occurs in the displacement ductility capacity of the system. One of the connections which is designed based on the concept of weakening the beam is the Reduced Beam Section (RBS) connection. The beam is weakened near its end, by trimming some parts of the flanges near the column face. In this way, the formation of the plastic hinge forcefully occurs in this region, because the RBS area acts as a fuse. Recent experimental results on RBS steel moment connections revealed that these connections tend to perform poorly by the early brittle fracture of the beam flange at the weld access hole. The measured strain data imply that the higher probability of base metal fracture in bolted web joints is -partly- related to the increased demand on the beam flanges. This demand is created due to the slippage of web bolt and the actual load transfer mechanism which is different from the one expected in connection design. Improvement methods include: using a better welding material and controlled welding process, using haunches at the beam-column interface (primarily intended for retrofitting of damaged frames), using cover plates on the beam flanges at the beam-column interface, and using a reduced beam section (RBS) at a prescribed distance from the column face. The RBS appears to be the most economic method and is already being used by structural engineers for welded SMRF structures in seismic zones. In this study, cyclic performance of RBS connection is studied in the numerical environment of ABAQUS. The investigated connection is a half-scale single-sided beam-to-column assembly. The cyclic load is applied at the tip of the beam. Pinned boundary condition is applied at the top and bottom of the column and is restricted out of plane displacement of the beam. The loading protocol proposed by AISC is used for cyclic loading. In parametric study of this connection, the effects of changing dimensions of the reduced area are investigated. Although the model gives reasonable predictions for the material deformation in the RBS, the designer must consider the material limit states, as this model does not predict local buckling or fracture in the RBS. Results reveal that the moment capacity of RBS connection is less than the moment capacity of a corresponding intact section connection. However, no plastic hinge is formed in intact section connection.