بررسي تاثير ابعاد و شكل صفحه‌ي اتصال سوراخ‌دار در عملكرد لرزه‌يي مهاربند هم‌گرا

Research into the Effect of Size and Shape in Perforated Gusset Plates on Seismic Behavior of CBFs

در اين نوشتار با ايجاد سوراخي در صفحه‌ي اتصال چند نمونه مهاربند قطري، سعي در تامين شكل‌پذيري و بهبود عملكرد لرزه‌يي قاب شده و عملكرد نمونه‌ها با انجام تحليل استاتيكي و ديناميكي غيرخطي با استفاده از نرم‌افزار اجزا محدود ABAQUS بررسي شده است. جهت جلوگيري و يا تعويق كمانش در اعضا مهاربندها، سوراخ‌هايي روي صفحات اتصال به نحوي طراحي شده است كه قبل از رسيدن مهاربند به بار بحراني كمانشي خود، به تسليم برسد و به جذب و استهلاك انرژي زلزله كمك كند .همچنين تاثير شكل سوراخ‌ها و نيز آثار زلزله‌ي حوزه‌ي دور و نزديك نيز مورد ارزيابي قرار گرفته است. نتايج تحليل، گوياي منحني‌هاي هيسترزيس پايدارتر و استهلاك انرژي بيشتر در نمونه‌هاي پيشنهادي است، به طوري كه در منحني رفتاري نمونه‌هاي منتخب تا تغييرمكان حدود 2 سانتي‌متر نيز افت عملكردي مشاهده نشده است، اما مهاربند معمولي در تغيير‌مكان چرخه‌يي كمتر از 1 سانتي‌متر دچار كمانش شده و افت عملكرد آن مشهود است. همچنين نتايج به‌دست‌آمده از تحليل تاريخچه‌ي ‌زماني، گوياي افزايش تغييرمكان نهايي حدود 13-43 درصدي و كاهش برش پايه‌ي 19-37 درصدي طي بارگذاري لرزه‌يي است.

Concentrically braced frames, CBFs, are among common lateral load carrying systems and their relative advantages, such as ease of implementation and lower cost compared to moment resisting frames, has led to their widespread usage. Experiences of past earthquakes indicate that the inherent defects and brittle behavior due to the buckling of compressive braces are the cause of the main damage in structures. In this paper, by making a hole in the gusset plates of diagonal bracing samples, it was endeavored to provide more ductility and improve the seismic performance of CBF through nonlinear static and dynamic analyses using ABAQUS software. For this purpose, holes were designed to have less axial capacity than the brace critical buckling load to help earthquake energy dissipation. The effects of hole shape and dimension and, also, the effect of near and far field earthquakes, were studied. Concentration of inelastic response in the hole neighborhood, results in high energy dissipation and prevents nonlinear behavior in other elements. The hysteresis curves show ductile behavior, enhancing energy dissipation during cyclic loading of the final specimens and postponing the occurrence of buckling in the brace members until lateral displacement at about 2cm. Normal braces buckle in 1cm displacement, leading to brittle behavior. The increase of the frame final displacement between 13-43% and base shear reduction between 19-37% demonstrate the superior seismic behavior of the proposed system. Moreover, equivalent damping ratios in the proposed samples are significant by about 20% The proposed model is relatively easy to implement in a variety of braces, such as X-braces, chevron and diagonal configurations, without too much cost. In this research, by a slight change in the common system and without using complicated devices, energy dissipation is provided. This is one of its distinctive features compared to other research projects. It should be noted that due to the appropriate results obtained in numerical analysis, specimen fabrication and experimental work should be on the agenda to verify the results in the next stage of research.