Experimental and numerical evaluation of coring effects in reinforced concrete columns

The knowledge of in-situ material properties is the first step in the assessment process of existing structures and, where needed, in the design of the consequent strengthening interventions. In order to achieve this goal, destructive (DT; e.g., cores) and non-destructive (NDT; e.g., ultrasonic, rebound) test methods are generally adopted, either alone or combined. Although many literature papers and guidelines propose to minimize the number of cores in the estimation of the concrete strength in reinforced concrete structures, the European and Italian codes prescribe that the estimation of in-situ strength has to be mainly based on cores drilled from the structure (DT). In this framework, the paper reports results of an experimental program aimed at evaluating the effects of core tests on RC columns, as well as the effectiveness of the structural restoration of drilling holes. Specifically, three sets of column specimens have been considered: (i) drilled columns, (ii) drilled and subsequently restored columns, and (iii) reference not drilled (as-built) columns. Compression tests have been carried out on each column and the results have been compared with the prediction based on codes or other literature approaches. This helped to recognize the main phenomena affecting the column members behavior under axial loads. At the same time, the authors calibrated detailed finite element models based on the experimental results of the tests carried out on column specimens. An advanced Fem tool was used to set-up 3D models. Numerical simulations aimed at better understanding the failure mechanism, especially in the presence of the hole related to the core extraction. The role of longitudinal and transverse reinforcement has been evaluated, highlighting that concrete crushing in the areas around the hole causes the early buckling of rebars, leading to premature failure of drilled column specimens.