Strengthened Unreinforced Masonry (URM) structures with Ultra High Performance Fibre Reinforced (UHPFRC) layers under axial in-plane and horizontal out-of-plane loading

The structural upgrade of existing Unreinforced Masonry (URM) buildings is an area with increasingly interest worldwide and especially in low-middle income countries and in earthquake prone areas. The deficiency of the existing URM has been highlighted through collapses and severe damages during recent earthquakes which could be considered as one of the greatest causes of fatalities and economic losses during major earthquakes.

The structural upgrade of existing URM has always been a quite challenging task which is mainly attributed to the relatively poor bond between the ‘new’ material and the existing structures. In this study a novel technique has been investigated by the addition of Ultra High Performance Fibre Reinforced Concrete (UHPFRC) layer together with partial repointing of the conventional mortar in order to increase the shear strength at the interface between masonry and UHPFRC. Numerical analyses have been conducted using Finite Element Analysis (FEA) models that have been calibrated in previous studies using experimental data for UHPFRC. Analyses have been conducted using different values for the thickness of the layer while the mortar-to-bricks and the UHPFRC-to-masonry interfaces have also been simulated. Numerical analyses have been conducted to investigate the axial in-plane and the horizontal out-of-plane behaviour of the strengthened URM specimens.

The numerical results demonstrate that the proposed technique can considerably improve the axial load strength of URM elements. In case of out-of-plane loading, the addition of UHPFRC has been proved to be quite efficient for the improvement of the stiffness and the maximum strength of existing URM structures.