PREDICTION OF PUNCHING SHEAR RESISTANCE OF PRE-STRESSED CONCRETE FLAT SLABS

Ashraf M. EL-shihy, Hamdy A. K. Shehabeldin, Osman E. A. Shaalan, Ragab S. Mahmoud

Abstract


Punching shear of pre-stressed concrete flat slab is an undesirable mode of failure that occurs without
warning and can lead to progressive collapse of large areas of the slab or even complete structures. Modeling
the punching shear strength of pre-stressed concrete slabs is conceptually difficult as the tendons can
be bonded or unbonded, the tendon passing through the columns or not, the stress in tendons at the punching
failure is indeterminate, the tendons can be banded and the tendons can be draped resulting in beneficial
vertical components of the vertical pre-stressing force. The purpose of this study is to predict punching
shear resistance of pre-stressed concrete slab-column connection from physical analytical model, that
includes integration of the vertical component of concrete tensile strength along the inclined surface of the
inverted cone which represents the punching shear cracks, the dowel forces of supplementary bonded
reinforcement and the pre-stressing force from pre-compression and vertical component of pre-stressing
calculated by yield line theory. The comparisons of the present proposed equation with ECP 203, ACI
318, BS8810, and EC2 code provisions and Gardner equations for the previous experimental scaled studies
indicated that the proposed equation is less conservative. Finally from the proposed equation the
contribution of concrete tensile force, dowel force and pre-stressing force in the punching shear resistance
of pre-stressed concrete flat slabs can be calculated.

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