Punching strengthening of two-way slabs using a prestressing technique

Punching shear failure normally occurs in reinforced concrete slabs subjected to concentrated loads and particularly in concrete bridge decks due to development of an internal arching action within the system. This study presents punching shear behavior of two-way slabs strengthened with transverse prestressed bars. The main purpose of this paper is to develop the use of a prestressing technique to repair or strengthen two way slabs due to construction or design errors, poor quality or inadequate materials, overloading and accidents. Eight two-way slabs (1100 x 1100 x 120 mm) with a steel reinforcement ratio of 0.94% were tested under concentric loading. In addition to a non strengthened slab, the present research was studied in two groups to examine different configuration shapes of prestressing bars around the punching area to study their effectiveness under ultimate limit states. The test results indicated a large efficiency of this method to change the mode of failure from punching shear failure to flexure failure. The strengthened slabs showed an increase of up to approximately 50% in load-carrying capacity and an increase of up to 80% in punching cracking load with respect to the un-strengthened control slab.