بررسي تجربي و تيوري كاربرد مهاربند كابلي در مقاوم سازي قاب هاي خمشي فولادي

Experimental and Theoretical Investigation of Steel Moment Frames Retrofitting Using Cable Bracing

قاب‌هاي خمشي فولادي با شكل پذيري مناسب و جذب انرژي بالا، تغييرمكان هاي جانبي زياد در برابر نيروهاي زلزله دارند. در اين نوشتار، امكان استفاده از مهاربند كابلي براي كنترل تغييرمكان جانبي و افزايش مقاومت قاب‌هاي خمشي، ضمن حفظ شكل پذيري آنها بررسي شده است. با انجام آزمايش و تحليل اجزا محدود نمونه‌ي قاب خمشي، قاب خمشي مقاوم‌سازي‌شده با مهاربند كابلي واگرا و قاب خمشي با مهاربند كابلي ضربدري، نيروي محوري ستون ها و رفتار چرخه ‌يي برش پايه- جابجايي قاب ها بررسي شده است. همچنين در قاب مهارشده با مهاربند كابلي واگرا، تاثير موقعيت اتصال كابل به تير در شكل پذيري و مقاومت قاب مورد توجه قرار گرفته است. بررسي ها نشان داده است كه مهاربند كابلي واگرا با افزايش مقاومت و سختي جانبي قاب خمشي فولادي، كاهش قابل توجهي در شكل پذيري قاب ايجاد نمي‌كند و رفتار مناسبي نسبت به مهاربند كابلي ضربدري دارد، و نيز افزايش نيروي محوري ستون ها در قاب خمشي با مهاربند واگرا به اندازه‌ي قابل توجهي كمتر از قاب با بادبند ضربدري است.

Steel moment frames have both suitable ductility and high ability to absorb earthquake energy. However, due to insufficient lateral stiffness, under high lateral forces, they undergo large displacements. In this paper, the possibility of using cable bracing to control lateral displacement and to strengthen steel moment frames were studied, including the desire to retain their ductility. In this research, some experimental tests were carried out and several finite element analyses were undertaken for the steel moment frame; retrofitted moment frames with X, and eccentric cable bracing. Frame displacement, base shear hysteresis behavior and column axial forces were also investigated. First, the behavior of the steel moment frame and the moment frame retrofitted by eccentric cable bracing under static loads, was investigated experimentally. Then, the moment frame finite element model was prepared using ABAQUS software, and the results were verified by experimental data. Three models were created, one for the moment frame, one for the moment frame retrofitted by X, and the last for eccentric cable bracing. In these models, the force-displacement hysteresis behavior and frame column axial forces under cyclic loading were determined and compared with each other. Next, ten models were prepared for the moment resisting frame; the moment frame retrofitted with the eccentric and concentric cable bracings. For these frames, the influence of the cable bracing connection to the steel beam situation on frame ductility and its strength was studied. It was observed that the eccentric bracing cables, by maintaining steel moment ductility, created strength, while it was increasing lateral stiffness. It was realized that they had suitable behavior compared with X-bracing cables and, by retrofitting moment frames with eccentric cable bracing, the increasing rate of column axial force was much less than in those retrofitted by X-bracing cables. It means that by using eccentric cable bracing to retrofit steel moment frames, there is little need to retrofit boundary members, such as columns, column bases and foundations.