الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Punching shear failure of reinforced concrete flat slabs is a sudden one that has a catastrophic outcome. Recent failures of punching shear-reinforced concrete flat slabs have raised a question mark on the reliability of the current understanding of the punching shear design. Slabs with large dimensions may be subjected to in-plane tensile forces due to concrete shrinkage or temperature change, accompanied by restraint provided by large columns or shear walls. There is a lack of agreement between various design codes regarding the significance of in-plane tensile forces on the two-way shear strength. In this respect, experimental tests were conducted to investigate the effect of axial tensile forces on the punching shear behavior of five pre-cracked slabs with and without shear reinforcement.
The test program incorporated two stages. The first stage involves pre-cracking the specimens by applying only axial tensile forces to the cross-section of the slab. The second stage deals with fixing the axial tensile forces on the slab cross-section and vertically loading the specimens until failure. The tested slabs consisted of five specimens having the same cross-sectional dimension (1500 mm x 1500 mm x 150 mm depth) and the same reinforcement ratio, the only difference being the value of axial tensile force and whether shear reinforcement was present or not. Only four of the five specimens were tested under simultaneous axial tension with punching shear, and one specimen was tested under punching shear only as a reference specimen. The results showed the significance of the effect of axial tensile forces on the punching shear behavior of flat slabs, as the punching shear capacity of the slabs decreases significantly as the tensile forces increase.
A rational analysis based on the critical shear crack theory was conducted to study the effect of axial tensile forces on the punching shear resistance on flat slabs. In this study, the experimental results for this thesis were used in addition to the previous experimental results that were conducted in this research point. A proposed equation was developed to calculate the punching shear capacity of flat slabs, taking into account the effect of axial tensile forces. In addition, a coefficient was proposed to predict the full behavior of flat slabs subjected to simultaneous axial tension and punching shear. The results using the proposed equation and the proposed coefficient showed good agreement with the experimental results. The experimentally measured strength from current and previous studies was compared with that calculated using different design codes. The results showed that the EC-2 was the most accurate in predicting the punching shear capacity under axial tensile forces, followed by the ACI 318-19, and then a proposed modification factor was added to the ACI 318-19, taking into account the effect of axial tensile forces. The proposed modified ACI-318-19 code shows a more conservative result than the original equation, which could be used in design as it will be safer.