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 precracked slabs with and without shear reinforcement.
The test program incorporated two stages. The first stage involves precracking the specimens by applying only axial tensile forces to the crosssection 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.