Contents lists available at ScienceDirect Engineering Structures journal homepage: www.elsevier.com/locate/engstruct Punching shear strengthening of RC slabs using L-CFRP laminates Haifa Saleh a,b, ⁎ , Robin Kalfat a , Kamiran Abdouka a , Riadh Al-Mahaidi a a Faculty of Science, Engineering and Technology, Swinburne University of Technology, Hawthorn, VIC 3122, Australia b Tikrit University, Tikrit, Iraq ARTICLE INFO Keywords: Carbon fibre Laminate Punching shear Strengthening ABSTRACT This paper evaluates the behaviour of reinforced concrete (RC) slabs strengthened in shear with prefabricated L- shaped carbon fibre–reinforced polymer (CFRP) laminates. Four large scale slabs were tested; one slab was kept without strengthening and the other three slabs were strengthened with L-CFRP laminates using different configurations. The behaviour of the slabs strengthened with L-CFRP laminates was compared with that of a similar slab without shear reinforcement. The details of the strengthening methods implemented in the study, experimental setup and parameters of all the material used are provided. The experimental results are presented including deflection, strain readings and rotation as well as the crack pattern of each specimen. The test results reveal that using post installed L-CFRP laminates can significantly improve the punching shear capacity and deformation capacity of RC slabs. Further, the strengthening technique can also be used to prevent sudden collapse of buildings after punching shear failure by increasing the post punching deformation of slabs. The experimental results were compared with the theoretical results predicted by ACI 318 (2011), Eurocode 2 (2004) and Fib Model Code (2010). 1. Introduction Many residential and commercial buildings are comprised of flat slabs due to their suitability as a suspended flooring system offering simpler formwork and faster site operations. However, one of the dis- advantages of flat slabs are their susceptibility to punching shear failure. Punching shear failure can occur suddenly without warning and sometimes it results in the catastrophic collapse of the building [1]. Punching failure happens due to formation of a shear cone comprising a truncated pyramid of concrete cracks encircling the column and causing the column to be pushed out of the slab. This form of failure is usually addressed during the design process either by increasing concrete strength, the thickness of the slab, the dimensions of the column or by providing vertical steel stirrups or stud rails in order to prevent the formation of inclined shear cracks. However, many existing flat slabs are being subjected to increased loading due to changes in use which may necessitate punching shear strengthening requirements in order to accommodate a higher loading case. Design or construction errors are another reason punching shear strengthening is needed in many in- stances. Recently, fibre reinforced polymers (FRPs) have become one of the most effective materials for strengthening of RC structures. CFRP is a composite material made of a polymer matrix embedded with fibres and its use as externally bonded or near surface mounted reinforcement has largely replaced traditional strengthening methods such as: ex- ternally bonded/mechanically fastened steel plates and/or concrete/ steel jacketing. This is due to FRP’s many advantages as a strengthening material such as: high tensile strength, light weight and ease of in- stallation. FRP is a composite material made of a polymer matrix em- bedded with fibres. The mechanical properties of the composite are influenced by many factors including type of fibre, volume and direc- tion of the fibres [2]. Additionally, FRP can be produced in different forms such as bars, sheets or laminates. To date, a significant amount of research has been done in the area of strengthening or repairing of existing slabs to delay or prevent the occurrence of punching shear failure. Methods of strengthening methods of slabs against punching shear can be divided into 2 categories: indirect and direct method. The indirect method which involved indirectly increasing the punching shear capacity of the slab through directly increasing the flexural ca- pacity by adding FRP sheets or laminates to the tensile face of the slab [3–13]. However, for punching shear strengthening, the use of steel bolts installed within predrilled holes in the concrete remains the most popular and effective strengthening method [14–17]. A comprehensive review has been done by Saleh et al. [18], where it was found that this method can increase the punching load by 33–133% [19,20]. However, the installation of post installed steel bolts is labour intensive, requires https://doi.org/10.1016/j.engstruct.2019.05.050 Received 20 December 2018; Received in revised form 16 April 2019; Accepted 18 May 2019 ⁎ Corresponding author at: Faculty of Science, Engineering and Technology, Swinburne University of Technology, Hawthorn, VIC 3122, Australia. E-mail address: hsaleh@swin.edu.au (H. Saleh). Engineering Structures 194 (2019) 274–289 Available online 29 May 2019 0141-0296/ © 2019 Elsevier Ltd. All rights reserved. T