Strengthening of RC one-way slabs including cut-out using different techniques q H.M. Afefy ⇑ , Tarek Mohamed Fawzy Structural Engineering Dept., Faculty of Engineering, Tanta University, Tanta, Egypt article info Article history: Received 15 July 2013 Revised 6 September 2013 Accepted 9 September 2013 Available online 8 October 2013 Keywords: Cut-outs Carbon Fiber Reinforced Polymer (CFRP) anchors CFRP sheet Engineered Cementitious Composites (ECC) Near Surface Mounted (NSM)-steel bar RC slabs Strengthening abstract Often, it is essential to introduce a cut-out in an existing reinforced concrete slab for facility require- ments. That cut-out poses a break in the continuity of the slab loading trajectories. Hence, a great atten- tion has to be paid to the adopted strengthening approach in order to restore the flexural resistance of the slab included cut-out. To investigate the structural flexural performance of strengthened one-way rein- forced concrete slab included cut-out, six slabs including cut-out adjacent to the central patch load in addition to one slab without cut-out as a reference slab were tested up to failure under incremental monotonic loading. The six slabs including cut-outs contained one control un-strengthened slab along with five strengthened slab. These slabs were strengthened using either Near Surface Mounted (NSM) steel bars or Externally Bonded Carbon Fiber Reinforced Polymer (EB-CFRP) at the tension side, while four out of them were strengthened by either NSM-steel bars (one slab) or an overlay of Engineered Cemen- titious Composites (ECC) material (three slabs) at the compression side. It can be concluded that end anchors for the EB-CFRP sheets along with the surface preparation before installing the ECC overlay are very important parameters in order to guarantee the optimum utilization for both the EB-CFRP sheets and the ECC overlay material. In addition, the test results showed that the hybrid strengthening tech- nique incorporated NSM-steel bars in tension side along with ECC overlay in compression side showed its superiority among all proposed strengthening schemes. It is not only allowed the slab included cut- out to restore its flexural resistance, but also it enabled the slab to outperform its structural performance compared to that of the slab without cut-out. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Introducing cut-outs in an existing reinforced concrete slab is necessary in some circumstances as the installation of escalators, elevators or utilities such as air conditioning, heating or wiring ducts. These cut-outs have the advantages of improved air circula- tion, aesthetics, and improved lighting. However, these cut-outs pose a break in the continuity of the slab causing weak points in the whole structure. They thus require special attention in remod- eling of the slab in order to capture the actual behavior of the new slab including cut-out [1–4]. Broad applications of the fiber-reinforced polymer (FRP) materials as new construction strengthening materials have been recently accomplished. FRP materials are lightweight, high strength, and non-corrosive materials. By virtue of these advanta- ges, there are wide ranges of recent, current, and potential applica- tions of these materials that cover both new and existing structures. Among different types of FRP materials, a Carbon Fiber Reinforced Polymer (CFRP) is used extensively in the structural engineering field. The Externally Bonded Reinforcement (EBR) technique has been more generally applied due to its simple instal- lation procedure. Design guidelines and specifications have also been established well for this system [5]. In particular, their prac- tical implementations for strengthening by epoxy bonding are sev- eral [6–10]. When compared to the Externally Bonded Reinforcement (EBR) technique, the Near Surface Mounted (NSM) technique assures a higher anchoring capacity to the CFRP reinforcing material. In con- sequence, a high tensile stress can be mobilized in the CFRP, as long as the member load carrying capacity is not limited by a premature failure mode [11–13]. The Near-Surface Mounted (NSM-CFRP) strengthening technique has been used in the recent years, with remarkable efficiency, in order to increase the flexural strength [14,15]. The use of FRP rods for this application is very new and the Near Surface Mounted (NSM) steel rods have been in Europe for strengthening of RC structures dated back to 1948 [16]. 0141-0296/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.engstruct.2013.09.013 q The experimental work had been conducted at Tanta University’s Concrete and Heavy Structures Laboratory. ⇑ Corresponding author. Address: 34 Ahmed Farouk Ali Ezzat, Smouha, Alexandria, Egypt. Tel.: +20 3 4298 793, mobile: +20 106 177 3174. E-mail addresses: hamdyafefy@hotmail.com (H.M. Afefy), telakrat1@yahoo.com (T.M. Fawzy). Engineering Structures 57 (2013) 23–36 Contents lists available at ScienceDirect Engineering Structures journal homepage: www.elsevier.com/locate/engstruct