رفتار گسيختگي و برآورد ظرفيت برشي شاه تيرهاي مركب بتني- فولادي با سخت كننده‌ي قطري

Behavior and Ultimate Shear Strength of Composite Plate Girder with Diagonal Stiffener

در اين مطالعه، يك روش تحليلي جديد براي تخمين ظرفيت برشي در شاه تيرهاي مركب بتني- فولادي كه سخت كننده‌ي قطري دارند، ارايه شده است. اين روش بر مبناي عملكرد ميدان كششي در جان شاه تير فولادي و سازوكار خرابي تاوه‌ي بتني رابطه‌سازي شده است. دقت روش پيشنهادي با استفاده از تحليل هاي اجزاء محدود شاه تيرهاي مركب، كه چيدمان هاي مختلفي از سخت كننده هاي قطري دارند، سنجيده شده است. در الگو سازي هاي اجزاء محدود، كه به صورت سه بُعدي انجام شده است، رفتار غير خطي بتن و فولاد با استفاده از الگو هاي رفتاري موجود تعريف شده است. نتيجه‌هاي به‌دست‌آمده از روش تحليلي و الگو هاي اجزاء محدود بيان‌گر آن است كه روش تحليلي پيشنهادي مي تواند با دقت قابل قبولي ظرفيت برشي نهايي شاه تيرهاي مركب را برآورد كند. همچنين نشان داده شده است كه سخت كننده هاي قطري از يك سو اثرهاي كمانشي پانل برشي شاه تير را كاهش مي‌دهند و از سوي ديگر مي توانند باعث افزايش استحكام كمانش برشي كشسان و افزايش ظرفيت برشي نهايي شاه تير شوند.

The contribution of diagonal stiffeners in the shear capacity of composite plate girders has not been studied so far. In this study, the behavior of diagonally stiffened simply supported composite plate girders is investigated and a theoretical formula is proposed to estimate the ultimate shear strength of such girders. The proposed analytical method considers the tension field action within the plate girder web panel and the shear failure of the concrete slab. Several validated finite element models of the composite plate girders, having different configurations of diagonal stiffeners, are also generated to verify the proposed method by comparing the analytical and numerical outcomes. These three-dimensional finite element models are developed to account for the geometric and material nonlinear behavior of composite girders. The models are first verified by experimental values obtained for girders with no diagonal stiffeners tested by other researchers and afterwards different configurations of diagonal stiffeners are added to the models. A total of four tested specimens are selected from previous studies. Based on the results of finite element analyses, a design method is proposed which incorporates the effects of the concrete slab, the composite action, and the web shear buckling of composite girders. The proposed method is approximate, simple and does not require any complex mathematical operations and can be applied to composite plate girders at the preliminary stages of design. The calculated ultimate shear strengths using the proposed method are in good agreement with both numerical results and experimental values, which indicates that the proposed analytical equations can be applied to predict the ultimate shear strength of girders for design office use. In comparison with un-stiffened girders, it is also observed that diagonal stiffeners are able to reduce the buckling effects of the web steel plate, increase elastic shear buckling strength and therefore the ultimate shear capacity of the girders.