Fiber reinforced polymer (FRP) systems have been increasingly used for the strengthening of slabs, beams and columns. This paper presents the results of an experimental programme that investigated the punching shear behaviour of RC flat slabs externally bonded with FRP systems. Four square slabs measuring 1.75 min width and 120 mm in thickness, with a tension steel ratio of 1.19% in each direction, were loaded to failure. One un-strengthened slab served as a control specimen and the others were externally bonded on their tension face with CFRP sheets. Each slab was simply supported along its edges and subjected to a concentrated load over a square area at its centre. The slab deflection and strains in the internal steel reinforcement and external CFRP sheets were monitored during the test. All slabs failed by punching shear. The load-deflection response of the strengthened slab was characterized by three regimes: un-cracked regime, cracked regime, and post-peak regime. The punching shear strength of flat slabs was enhanced by the addition of bonded CFRP sheets. The British Standard BS8110 equation for punching shear strength of RC slabs was modified for the slabs bonded with FRP system by transforming the area of FRP reinforcement into an equivalent area of steel reinforcement based on the modular ratio, and using an effective depth to the reinforcement. The modified equation was found to predict the present and previous test results with good accuracy. Also, a strength enhancement factor is proposed to evaluate directly the increase in punching shear resistance due to externally bonded FRP system.
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