Abstract:
Punching shear is an important consideration in the design of reinforced concrete flat plates,
flat slabs, and column footings. Present design rules for punching shear failure of reinforced
concrete slabs, given in various Codes of practice, are largely based on studies of the behaviour
and strength of simply-supported, conventional specimens extending to the nominal line of
contraflexure. As punching shear provisions incorporated in various Codes of practice are a
direct result of the empirical procedures, they do not usually provide an accurate estimate of
the ultimate punching load capacity of a slab with its edges restrained against rotation. This is
because no direct account is taken of the significant enhancement of punching capacity due to
the in-plane restraint in many types of reinforced concrete slab systems.
The present study describes punching tests conducted on reinforced concrete slabs with their
edges restrained as well as unrestrained. Here, edge restraint has been provided, by means of
edge beams of various dimensions, to mimic the behaviour of continuous slabs. A total of 16
model slabs have been tested in an effort to ascertain the influence of the degree of boundary
restraint, percentage of steel reinforcement, and slab thickness of the slab models on their
structural behaviour and punching load-earrying capacity. The cracking pattern and loaddeflection
behaviour of the slabs tested have also been monitored closely. The test program was
carried out to provide basic information on the real punching behaviour of restrained slabs
subjected to concentrated loading and may also be usefully applied in the assessment of
existing structures with laterally restrained slab construction.
The significant positive effect of edge restraint on the punching failure load, resulting in
enhancing the ultimate punching strength, has been noticed. The code-specified strength of the
specimens was calculated in accordance with the American, British, Canadian and European
codes. It became apparent that no code-specified method predicts an enhancement in the
punching shear strength of a restrained reinforced concrete slab with an increase in the degree
of such restraints. Present Codes do not recognize the role of percentage oflongitudinal steel on
the punching strength effectively either. It has been understood that inclusion of the findings of
the study in the design Codes will result in a rational design of structural sy~ems where
punching phenomenon plays a vital role.
