Abstract:
Punching shear is one of the most critical phenomena for flat plate building
systems due to the brittle nature of this failure mode. The region of a slab in the
vicinity of a column could fail in shear by developing a failure surface in the form
of a truncated cone or pyramid. This type of failure, called a punching shear
failure, is usually the source of collapse of flat plate and flat slab buildings. It is
one of the topics of intensive research in recent years by various researchers in
the field of concrete structure. Numerous tests have been carried out to evaluate
the punching shear strength of slabs. Several theories have been put forward to
predict the strength observed in these tests.
An attempt has been made in this research to study the punching shear of
reinforced concrete flat plates. Before carrying out the systematic computational
investigation, existing literature on the relevant field based on experimental
investigation, analytical methods, numerical models and various Codes of
Practice is thoroughly reviewed. A 3-dimensional reinforced concrete flat plate
model was generated. The formulation has been checked against experimental
results of tests on slabs subjected to punching shear. From a comparison of the
numerical and the experimental results, it is concluded that the adopted model
of the Finite Element Analysis package (ANSYS)is suitable for analyzing
reinforced concrete plates. The good agreement obtained between the numerical
and the experimental results establish the validity and accuracy of the
computational model.
A systematic study is carried out to determine the punching shear capacity due
to variations of different structural parameters like span-depth ratio,
reinforcement ratio, support condition, shear reinforcement etc. The parametric
study indicated that the analysis is able to predict the influence of several of the
most commonly considered parameters on the punching shear behaviour of
slabs. From the graphical presentation of the various parameters a designer can
visualize and choose the most suitable one to enhance the punching shear
strength. The results of the analysis confirm the general understanding of the
behaviour of slabs in punching shear . .It was seen that the addition of shear
reinforcement has a significant effect on the punching shear strength of the
slab/plates. The models with shear reinforcement showed a more ductile
behavior than those without shear reinforcement. The results indicate that the
inclined stirrups are technically superior. These are also very easy to install,
and would thus seem to be a promising form of shear reinforcement for flat
plates.
This study shows that both span-depth ratio effects and the type of support
condition have significant influence on the punching shear strength in concrete
slabs. Size effect and reinforcement ratio effects are not considered in ACI 318-
02 Code (also BNBC 1993) provision; as such there is scope for review of these
codes taking all the parameters into consideration. Hence, a modification to the
ACI 318-02 Code equation is proposed and the performance of the proposed
modification is verified. Finally, based on the findings of the study, conclusion
and recommendations are put forward.
