الفهرس 
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Abstract
This research consists of experimental and analytical studies to evaluate the behavior of composite post tensioned precast concrete girders with top slabs (the bottom part of slab is precast concrete and the top part of slab is cast-in-place concrete). The investigated variables are the shear connectors’ distribution, extending girder stirrups to act as shear connectors, the top slab width, and the concrete strength of top slabs.
The experimental program consisted of testing six composite T-girders under two-point loading. The first specimen G1 is post tensioned T-section cast monolithically and act as control specimen. In the other five specimens, the web and the flange of the girder were poured separately then connected together. The web element is post tensioned precast concrete girder supporting a reinforced concrete slab (flange). The bottom part of slab is precast concrete and the top part of slab is cast-in-place concrete. The second and third specimens (G2 and G3) have different shear connectors’ distribution along the girder span to connect the web with the slab panels however, the same total area of shear connectors by using different diameters and spaces. In specimen G2, the shear connectors are D10 @ 161 mm, while in specimen G3, the shear connectors are D12 mm @ 233 mm. In the fourth Specimen (G4), the shear connectors are replaced by full stirrups. The fifth specimen (G5) is similar to specimen G2 but the slab width is 750 mm instead of 500 mm. The sixth specimen (G6) is similar to specimen G2 but the compressive concrete strength for the top slabs is 25MPa instead of 40MPa.
The analytical study includes a numerical analysis by using non-linear finite element program (ABAQUS/CAE2020) to verification of experimental results. Moreover, using available models from literature and codes provisions used for calculating shear transfer failure load, and compared with the experimental results to determine the best correlation with the experimental results.
Based on the results of the experimental and analytical calculations, design recommendations will be proposed for the studied girders.
7.2 Conclusions
The key findings of the research may be summarized as follows:
• Shear connectors used to connect the top slabs to the girders achieved almost the full composite action as the monolithic T-section girder since the shear connectors can provide the necessary ultimate horizontal shear strength at the interface of the top slabs and the girders.
• Using the same shear connectors reinforcement ratio, larger diameter of shear connectors shows higher capacity compared to smaller diameter due to the higher stiffness of the larger diameter bars.
• Shear connectors of 10 mm diameter achieved 100% of the monolithic T-section girder but failure occurred due to slippage between girder and topping slab while using shear connectors of 12 mm diameter achieved 105% of the monolithic T-section girder and failure occurred as the monolithic T-section girder.
• Extending girder stirrups to connect the top slabs to the girders instead of using the shear connectors, achieved almost the full composite action as the monolithic T-section girder, and shows better ductility compared with using the shear connectors.
• Increasing the top slab width by 50% leads to increasing the capacity of the girder with ratio 3% and improved the ductility of the composite T-girder.
• Reducing the concrete strength of topping slabs from 40 MPa to 25 MPa leads to decreasing the ultimate capacity of the girder by 15% and increasing slippage between top slabs and girders.
• The finite element program (ABAQUS) gave a good prediction to the experimental results, and gives crack patterns almost similar to the experimental ones and the same trend of the load-deflection response.
• The Concrete Damage Plasticity method achieved the fracture parameters of experimental results for girder specimens.
• It was found that predicting equations of Mast, BS 8110, Eurocode-2, ECP 203-2020, and Patnaik represent the most conservative equations for determining the horizontal shear stress due to the conservative values for cohesion and interfacial friction. Equations of Mattock and Shaikh provide moderate conservative equations for determining the horizontal shear stress due to the high contribution of cohesion and friction in those equations. Equations of Loov, Birkeland, and AASHTO LRFD represent the least conservative equation.
7.3 Recommendations for Future Research
The following recommendations for further studies are proposed based on the outcomes of this research:
• Studying the effect of flange thickness and web width on the behavior of composite T-girders.
• Studying the effect of replacing the mechanical shear connectors with chemical adhesion on the behavior of the connection between girder and slab.
• Strengthening of composite T-girders due to slippage between girder and slab.
• Studying the effect of corrosion on shear connector in case of composite T-girders.