Experimental and numerical investigation on strengthening of RC flat slabs with central opening

Slab openings occur quite often in practice to provide a convenient path for utility ducts. However, introducing an opening into a reinforced concrete flat slab causes local cracking in the vicinity of the opening leading to a reduction in stiffness and capacity of the slab. In this paper, different methods of strengthening flat slabs with central openings are investigated experimentally and numerically. The experimental program consists of six slab specimens with dimensions of (1100 × 1100 × 100) mm with cut out openings of (300 ×300) mm. Two slabs were considered as reference specimens and tested without strengthening; one of them had no opening, and the second had a central opening. The remaining four slabs had openings and were strengthened with different techniques. These include adding Near Surface-Mounted (NSM) steel bars, steel strips with anchor bolts, carbon fiber laminates (CFL), and an overlay of engineered cementitious composite (ECC) material reinforced with welded wire mesh. The results show that using different strengthening techniques leads to an increase in load-carrying capacity for all the strengthened slabs. The reinforced ECC overlay strengthening method achieved the largest increase in the capacity by 31% compared to the reference slab with central opening. The finite-element analysis is carried out to validate the experimental results. Good agreement between the finite-element analysis and the experimental results is obtained confirming many of the findings of this study.