Although creating an opening in an existing Reinforced Concrete (RC) slab is permitted under specific circumstances, it may lead to a weakened slab. To investigate the strengthening of two-way RC slabs with an opening, six full-scale two-way RC slabs with a central opening, in addition to one reference slab without opening, were tested up to failure under monotonic and cyclic loading. These six slabs consisted of one control un-strengthened slab and five strengthened slabs. The strengthening methods used in this study were either Externally Bonded Glass Fiber Reinforced Polymer (EB-GFRP) or embedded extra steel bars at the tension side of the slabs, as proposed by ACI 318-14 (2014). Failure modes, cracking patterns, ultimate loads, and load -deflection relationships of all slabs are reported. The test results show that using GFRP strengthening method could increase the ultimate strength and flexural stiffness of the slabs significantly. Moreover, embedding extra steel bars around the opening as proposed by ACI 318-14 (2014) may not enhance the load-carrying capacity of the slab to the value of the continuous slab. The test results also show that the deflections of the strengthened slabs with opening under service loads are more than that of the slab without opening.
