انتخاب بهينه‌ي جابجايي تسليم ميراگرهاي فلزي جاري‌شونده در ساختمان‌هاي قاب خمشي فولادي

Optimum Selection of Yield Displacement of Metallic-Yielding Dampers in Steel Moment Resisting Frames

ميراگرهاي فلزي جاري‌‌شونده همانند المان‌هاي افزاينده‌ي ميرايي و سختي، از جمله متداول‌ترين ابزار اتلاف انرژي براي كنترل و كاهش پاسخ ديناميكي سازه‌ها محسوب مي‌شوند. انتخاب مناسب پارامترهاي طراحي اين نوع ميراگرها تاثير زيادي در رفتار غيرخطي سازه دارد. يكي از اين پارامترها، جابجايي تسليم ميراگر است. براساس پژوهش‌هاي پيشين، از ميان پارامترهاي طراحي اين نوع ميراگرها، جابجايي تسليم بيشترين تاثير را در تقاضاي شكل‌پذيري سازه دارد. در اين نوشتار روشي براي انتخاب اين مشخصه‌ي طراحي ميراگر در طبقات مختلف قاب‌هاي خمشي فولادي پيشنهاد شده است، تا نياز شكل‌پذيري طبقات مختلف يكنواخت شود. با استفاده از الگوريتم پيشنهادي در چند مثال شامل قاب‌هاي خمشي 3، 5، و 10 طبقه ملاحظه شده است كه كاهش قابل ملاحظه‌‌يي در انديس خرابي قاب‌هاي ساختماني ايجاد مي‌شود. همچنين رفتار چرخه‌‌يي ميراگرها بهبود مي‌يابد و ميراگرهاي كليه‌ي طبقات مشاركت موثري در استهلاك انرژي ورودي زلزله از خود نشان مي‌دهند.

A metallic yielding type of damper is one of the oldest and most widely used passive energy dissipation devices to decrease the dynamic response of buildings subjected to strong ground motion, such as Added Damping and Stiffness (ADAS) elements. The proper selection of design parameters of these devices has an important effect on the structural inelastic behavior. One of these parameters is yield displacement. Previous studies have shown that the yield displacement of ADAS elements is a more effective factor than other design parameters in controlling the ductility demand of a structure. In this paper, a new method for optimum selection of this design parameter of metallic yielding dampers, in different stories of a moment resisting building frame, is proposed, using the concept of the uniform distribution of ductility demands. Three frame models, including 3, 5, and 10-story moment resisting frames, were used for nonlinear dynamic analyses. The obtained results showed that using a fixed amount of yield displacement of dampers for all stories might not lead to uniform distribution of the ductility demand. Therefore, the employment of such distribution for this design parameter does not guarantee the optimum use of dampers in the nonlinear range of behavior. In the modeling of the frames, it was assumed that all elements remained elastic and behaved linearly except damper devices. The nonlinear behavior of the damper devices was modeled with a bilinear elastic-plastic shear spring with kinematic hardening behavior. Using the proposed method, it was demonstrated that a great decrease in damage index occurred after the optimization procedure for the device yield displacement. In all models, the coefficient of variation (cov) of the ductility demand distribution along the building height, in the initial step, is large, indicating that the distribution of story ductility demand is not uniform. However, after the optimization procedure, the cov becomes small enough and a state of rather uniform height-wise distribution of ductility demand prevails. Furthermore, damper hysteretic behavior is improved and all dampers participate in the earthquake input energy dissipation after the optimization.