پيش بيني رفتار گسيختگي شاه‌تير مركب با سخت‌كننده‌ي طولي و پيشنهاد روش برآورد ظرفيت برشي

Ultimate Shear Strength of Steel-Concrete Composite Plate Girder with Longitudinal Stiffeners Loaded in Shear

در اين پژوهش رفتار و بيشينه‌ي ظرفيت برشي شاه تيرهاي مركب بتني-فولادي با سخت كننده‌ي طولي در جان، تحت بارگذاري برشي به صورت تحليلي و عددي مورد بررسي قرار گرفته است. روش تحليلي با درنظرگرفتن عملكرد ميدان كششي در جان شاه تير، گسيختگي برشي دال بتني، و محل قرارگيري سخت كننده هاي طولي با موقعيت هاي مختلف در جان رابطه‌سازي شده است. براي توسعه‌ي روابط فرض شده است كه هر پانل شاه تير، مقاومت برشي مربوط به خود را ارايه مي دهد. اين فرض دربررسي هاي المان محدود مختلف به اثبات رسيده است. دقت روش پيشنهادي با استفاده از تحليل-هاي اجزاء محدود انجام‌گرفته بر روي شاه تيرهاي مركب، كه چيدمان هاي مختلفي از سخت كننده هاي طولي دارند، سنجيده شده است. رفتار غيرخطي مصالح و هندسه‌ي شاه تيرهاي مركب با يك مدل سه بُعدي اجزاء محدود شبيه سازي شده است. نتايج اين تحليل ها نشان مي دهد كه وجود سخت كننده‌ي طولي در جان شاه تير علاوه بر افزايش مقاومت كمانشي، مقاومت نهايي برشي شاه تير را نيز افزايش مي دهد. همچنين مقايسه‌ي نتايج به‌دست‌آمده از روش تحليلي با مدل هاي اجزاء محدود نشان مي دهد كه روش تحليلي قابليت پيش بيني ظرفيت برشي نهايي شاه تيرهاي با سخت كننده‌ي طولي، دقت قابل قبولي دارد.

The contribution of longitudinal stiffeners to the shear capacity of composite plate girders has not been studied. This paper aims to investigate, both analytically and numerically, the ultimate shear strength of longitudinally stiffened simply supported steel-concrete composite plate girders under shear loading. In this study, a theoretical formula is proposed to estimate the ultimate shear strength of such girders. The proposed method is approximate, simple, does not require any complex mathematical operations and can be applied to composite plate girders at the preliminary stages of design. The proposed analytical method considers the tension field action within the plate girder web panel and the shear failure of the concrete slab. The method incorporates the effects of the concrete slab, composite action, and web shear buckling of the composite girder. The ultimate shear capacity of the composite plate girder may be considered as the combined shear strength resisted by the steel part of the girder and that by the concrete slab. These two components can be computed separately and summed up to obtain the shear strength of the composite girder. The method used to determine the shear strength of the steel part is similar to the Cardiff model, in which the web panels are assumed simply supported along the longitudinal and transverse edges. On the basis of previous experimental studies and detailed information obtained from finite-element studies, it may be considered that each individual subpanel in the longitudinally stiffened composite plate girder can develop its own tension field independently of adjacent subpanels. Furthermore, the web panels are assumed simply supported along the longitudinal and transverse edges. Three different locations of longitudinal stiffeners are investigated and appropriate analytical methods are proposed for each case. These locations are: close to the compression flange of the steel girder, near to the tension flange of the steel girder and in the middle of the plate girder. Several validated finite element models of the composite plate girders having different configurations of longitudinal stiffeners are also generated to verify the proposed method and compare 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 longitudinal stiffeners, which have been tested by other researchers, and, afterwards, different configurations of longitudinal stiffeners are added to the models. The calculated ultimate shear strengths using the proposed method are in good agreement with both numerical and experimental values. This indicates that the proposed analytical equations can be applied to predict the ultimate shear strength of the girders for design office use. In comparison with the un-stiffened girders, it is also observed that longitudinal stiffeners are able to reduce the buckling effects of the web steel plate, increase the elastic shear buckling strength, and, therefore, the ultimate shear capacity of the girders.