Punching shear in normal and lightweight aggregate reinforced concrete slabs.
The results of an experimental and theoretical
investigation into the behaviour of reinforced concrete
flat slab-column connections are presented.
In the experimental programme 33 lightweight and
8 normal weight slabs were failed in punching shear.
The specimens were simply supported and loaded vertically
through central, monolithic column stubs.
Three lightweight aggregates were used, and the concrete
strength and section depth varied. It was found that
slabs made with Lytag, Solite and limestone aggregates
failed at similar loads, but slabs made with Leca
aggregate concrete failed at approximately 70% of the
former group (other variables being equal).
In the theoretical investigation an analysis was
developed to model the various stages of the slabs'
behaviour under increasing load. The analysis enabled
the critical pre-failure and punching loads to be calculated.
Satisfactory agreement was established between
the pre-failure values. The load at which failure
occurred in the compression zone was computed using one
of two methods designed to accommodate the differing
characteristics of the concretes used. The methods
depend on an idealisation of the behaviour of the shear
crack which enables the compression zone stresses to be.
established. Comparison of these stresses with a
criterion of failure gives the concrete failure load.
The ultimate punching load includes the enhancing effects,
on the concrete failure load, of inplane stresses and
dowel action. Good agreement between the theoretical,
and. experimental punching values was established.
The thesis includes a review of previous experimental
and analytical work performed on normal and lightweight
aggregate slabs. The existing empirical data is shown
to be limited in several areas, especially for lightweight
aggregate concrete tests. The application of
existing formulae to the present experimental work does
not provide a satisfactory agreement with the results.
Three of the equations axe re-evaluated to pr6vide a
closer fit with the present test results and for a wider
based group of lightweight aggregate tests. The provisions
of ACI 318-71 and CP. 110 : 1972 are also applied
to the slabs of the present test series, and are shown to
be conservative. Finally recommendations for
future work are given.