[Univ of Cambridge] [Dept of Engineering]

Punching shear in high strength steel fibre
reinforced concrete slabs

 B M Kiilu


Abstract:

Punching shear failure in high strength concrete flat slab-column connections occurs in a sudden and brittle manner.  This phenomenon can be prevented by addition of high strength steel fibres which act as three-dimensional shear reinforcement into the concrete.

This dissertation presents investigations into the behaviour of high strength steel fibre reinforced concrete (HSFRC) slabs subjected to concentrated loads. Improvement in the punching shear strength and ductility of slab - column connections due to addition of high strength steel fibres is investigated.  Further, the validity and applicability of the upper bound plastic theory of punching in HSFRC slabs is examined.

The experimental results obtained from one third model scale HSFRC slabs show substantial increase in the ultimate punching shear strength with addition of fibres.  An optimum volume fraction of fibres of 0.5% is found to transform the failure from sudden brittle failure to flexural - punching failure and to enhance the ultimate punching shear capacity by approximately 70%.  The upper-bound plastic theory is found to give fairly accurate predictions of the ultimate punching shear capacity as long as the correct efficiency factors of concrete are used.

Keywords:  High strength concrete, steel fibres, punching shear, ductility, plasticity theory, composite tensile strength, compressive strength, fibre orientation factors, and length efficiency factors.

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