Experimental and numerical study on the compressive behaviour of partially accessible concrete columns strengthened by a layer of high-performance concrete

In this paper, a novel reinforcement system for partially accessible concrete columns is studied experimentally and numerically. This technique involves the application of a layer of high-performance mortar only on one side of the existing concrete columns with built-in shear connectors that, together with the concrete-mortar interface, transfer the load between the two components. In the experimental campaign, three different fibre-reinforced high-performance mortars have been used for the reinforcement of a concrete column. The influence of the thickness and the material of the reinforcement layer on the increase of the bearing capacity of the columns have been assessed. In addition, a novel finite-element formulation for a multi-layer beam allowing for plastic deformation (and failure) of the layers and mixed-mode delamination between them is proposed to model the reinforced columns. The model has been capable of simulating the complex structural behaviour of the experimental testing with low computational burden and robust solution procedure, allowing to conclude that the amount of the interlayer relative displacements strongly influences the effectiveness of the reinforcement technique.