اثر متغيرهاي هندسي در رفتار سيستم مهاربند كابلي با آرايش Y شكل

The Effect of Geometrical Parameters on the Behavior of Y-Shaped Cable Bracing Systems

در سيستم‌هاي مهاربند كابلي، پايين‌بودن شكل‌پذيري و همچنين عدم مشاركت هم‌زمان تمامي كابل‌ها در تامين مقاومت سازه، از جمله چالش‌هاي پيش رو در اين سيستم‌هاست. مطالعات صورت‌گرفته بر روي آرايش Y شكل در مهاربندهاي كابلي نشان مي‌دهد كه اين نوع آرايش مي‌تواند بدون به‌كاربردن اتصالات ويژه، تمامي كابل‌ها را در بازه‌ي مشخصي از جابجايي‌ها تحت كشش نگه دارد و از بروز شل‌شدگي در كابل‌ها جلوگيري كند. همچنين اين نوع سيستم مهاربندي مي‌تواند باعث افزايش شكل‌پذيري و پايداري قاب شود. در اين نوشتار به كمك برنامه‌نويسي در نرم‌افزار MATLAB، نحوه‌ي عمل‌كردن اين نوع آرايش در تحت كشش نگه‌داشتن هم‌زمان كابل‌ها و همچنين اثر متغيرهاي هندسي در رفتار سيستم مورد تحليل و بررسي قرار ‌گرفته و ملاحظه شده است كه با مقادير مشخصي از متغيرهاي هندسي، كابل ها همواره در كشش باقي مي‌مانند و سختي لازم در برابر نيروي جانبي ايجاد مي‌شود.

In earthquake-prone regions, steel moment frames are a desirable choice for constructing structures, due to their appropriate ductility and high energy dissipation capacity. The main weakness of moment frames is the possibility of excessive displacement when subjected to forces resulting from powerful earthquakes, which may lead to total destruction of a structure. In recent years, using cable as a bracing system for moment frames has become an issue of interest to many researchers. Cable bracings, unlike steel bracings, are not subjected to complex phenomenon such as inelastic buckling and, due to their high tensile strength and the possibility of high pre-tensioning, create considerable stiffness. The main weakness of this system is the occurrence of slacking phenomenon in the cables when redirecting the lateral force, which has a dynamic impact on the system. Researchers have proposed solutions, including the use of special tools and connections, and different arrangements of cables and dampers in the cable bracing system. Using these methods, it is possible for the system to use its total capacity at the same time. Also, by keeping all cables stretched, slacking would be prevented when redirecting the lateral force. Studies on Y-shaped cable bracing systems show that all cables in this system participate in providing the lateral resistance of the frame, without requiring any special tools and connections. Moreover, Y-shaped bracing systems are not active in small displacements; they do not affect the elastic behavior of the moment frame and do not reduce flexibility. However, when large displacements occur in the frame, this system is activated, which, hence, increases the ductility and stability of the moment frame. In this paper, for investigating the Y-shaped cable bracing system operation, in order to keep all cables under tension, and the effect of geometrical parameters on system behavior, a program was written in MATLAB software. Considering there was no possibility of having limit points in the force-displacement curve of the system, this program was written based on the Newton-Raphson incremental-iterative method for non-linear analysis of structures, which can draw the pushover curve of the bracing system and apply its various geometric parameters as a variable. The results of system modeling in this program indicate that the arrangement causes high flexibility, and changing system stiffness is easily possible (by changing the length of the connecting cable and cable diameter). It was also observed that with a specific amount of geometric parameter, the system had maximum lateral stiffness and the most durability against any incidence of cable slacking.