ORIGINAL ARTICLE Effects of circular openings on the compressive behaviour of R.C. columns G. Campione • C. Cucchiara • G. Minafo ` Received: 9 May 2013 / Accepted: 6 March 2014 Ó RILEM 2014 Abstract Core-drilling technique is nowadays always more frequently performed in existing rein- forced concrete (RC) structures in order to investigate on the mechanical properties of concrete and for structural health monitoring purposes. Even if the engineering practice discourages to drill columns, this can be often unavoidable. In this last case the presence of the circular opening influences the compressive behavior of the column in terms of load-carrying capacity and axial deformability. The goal of this investigation was the experimental evaluation of the effects induced by circular openings on the behavior of RC columns. Twenty-four reinforced and plain con- crete prisms in presence of circular openings were tested in compression. The effects of concrete strength, hole diameter and repairing were taken into account. Axial loads and strains were recorded during the tests in order to evaluate the effects of key parameters. Finally, analytical predictions of the load- carrying capacity were made with a strut-and-tie model available in the literature, which was also used to estimate the load-shortening curves showing good agreement with experimental data. Keywords Experimental investigation  Circular openings  Core-drilling  Drilled columns  Strut-and-tie modeling  Isostatic lines of compression List of symbols A s Area of longitudinal steel bars b Width of the specimens d Diameter of the opening F In-plane axial concentric load f c Cylinder compressive strength of concrete f t Splitting tensile strength of concrete f y Yield strength of transverse reinforcement H Height of specimens l Y-coordinate of point of origin of isostatic line of compression T Transverse tensile force t Thickness of specimens 1 Introduction Core drilling is today a very common partially- destructive testing technique adopted in existing reinforced concrete (RC) structures. It is usually performed by extracting a cylindrical concrete sample from the examined members with a drilling machine. It allows different applications able to provide useful G. Campione (&)  C. Cucchiara DICAM, University of Palermo, Viale delle Scienze, 90128 Palermo, Italy e-mail: studioingcampione@libero.it G. Minafo ` Facolta ` di Ingegneria e Architettura, University of Enna ‘‘Kore’’, Cittadella Universitaria, 94100 Enna, Italy e-mail: giovanni.minafo@unikore.it Materials and Structures DOI 10.1617/s11527-014-0288-5