رفتار اتصال هاي لوله‌يي X شكل مقاوم شده با حلقه خارجي تحت بار محوري فشاري

Behavior of tubular X-joints retrofitted with external ring subjected to compressive loading

در پژوهش حاضر، اثر سخت‌كننده‌ي حلقوي خارجي در مقاومت نهايي اتصال‌هاي لوله‌يي X شكل تحت بار فشاري مطالعه شده است. براي اين هدف، ابتدا مدل عددي ساخته و دقت آن با نتايج آزمايشگاهي مقايسه شده است. سپس، 117 مدل المان محدود جهت بررسي پارامتريك مشخصات هندسي اتصال و سخت‌كننده‌ي حلقوي ساخته شدند. در مدل‌هاي عددي مذكور، اثر غيرخطي هندسه و مصالح لحاظ شده است. همچنين، جوش متصل‌كننده‌ي اعضاء فرعي به عضو اصلي مدل‌سازي شده است. نتايج نشان داده است كه سخت‌كننده‌ي حلقوي خارجي مي‌تواند مقاومت نهايي اتصال را تا 367٪ افزايش دهد.علي‌رغم اثر محسوس سخت‌كننده در مقاومت نهايي اتصال، تاكنون هيچ رابطه‌يي جهت محاسبه‌ي مقاومت نهايي اتصال‌هاي X شكل با سخت‌كننده‌ي حلقوي خارجي استخراج نشده است؛ بنابراين، پس از انجام مطالعات پارامتريك در پژوهش حاضر، فرمول تحليلي براي محاسبه‌ي مقاومت نهايي اتصال‌هاي سخت شده تحت بار فشاري ارائه شده است.

Tubular structures are made of hollow steel members with circular cross-sections and connecting them is one of the major challenges in their design. So far, some techniques to improve the performance of tubular connections have been proposed. Most of these methods (e.g., internal ring, doubler plate) can only be used for structures during the design, but there are only a few techniques (e.g., external ring, FRP) which can be applied during both fabrication and service. This paper investigates the ultimate strength of circular hollow section (CHS) X-connections stiffened with external ring subjected to axially compressive load. The SOLID186 in ANSYS was used to establish the finite element (FE) models. In these models, both geometric and material non-linearity were considered. Moreover, the welds joining the chord and brace members were modeled. The validation of the FE model with several experimental data indicated that the proposed FE model can accurately predict the static behavior of the ring-stiffened X-joints under compression. In the next step, 117 FE models were created and analyzed to evaluate the effect of the connection geometry and external ring size on the static capacity through a parametric study. Results indicated that the external ring can considerably increase the initial stiffness. Moreover, the ultimate strength of the ring-reinforced X-joints under brace compression can be up to 367% to that of the strength of the corresponding unreinforced joint. Despite these significant differences between the ultimate strength of un-stiffened and ring-stiffened X-connections under compressive load, the investigations on this type of stiffened joints have been limited to only three X-joint tests. Also, no design equation is available to determine the ultimate strength of X-connections stiffened with the external ring. Hence, the parametric study was followed by the nonlinear regression analysis to propose a theoretical equation for the static design of X-connection stiffened with the external ring in compressive load.