Thin layers of mortar reinforced with steel fibers can be applied on one or both sides of bearing walls as an effective seismic strengthening of existing masonry buildings. To assess the effectiveness of this technique, an experimental study on masonry sub-assemblages was carried out at the University of Brescia. This paper summarizes and discusses the main results of the investigation, which included mechanical characterization tests on masonry and its components as well as on the Steel Fiber Reinforced Mortar (SFRM) used to retrofit the masonry samples. Uniaxial and diagonal compression tests were carried out on both unstrengthened wallets and masonry samples retrofitted with 25 mm thick SFRM coating. Both single-sided and double-sided retrofitting configurations for application on wall surfaces were considered. The results highlighted the ability of the technique to improve the compressive and the shear behavior of masonry, even in case of single-sided strengthening. Moreover, no premature debonding of coating was observed. Lastly, the manuscript presents the results of a numerical investigation that was performed both to simulate the diagonal compression tests described in the first part of the paper and to predict the response of panels with different strengthening configurations.

A constitutive model for simulating the compressive response of unreinforced brick masonry subjected to cyclic loading is presented and discussed. The developed formulations are consistent with the smeared rotating crack approach and may be easily implemented in finite element codes for nonlinear analysis. The analysis approach includes different features such as nonlinear curves for capturing the shape of the unloading/reloading branches, both in case of full unloading from the envelope curve and partial unloading/reloading. A unified model for predicting the residual plastic strain as a function of the strain recovered during unloading is also proposed. Particular attention is paid to the stiffness degradation occurring during reloading and to the prediction of the stress and strain values at which the reloading branch intersects the envelope. The calibration of most of the proposed formulations is based on experimental results reported in the literature, as well as from two uniaxial cyclic compression tests carried out within the present work. Finally, the model effectiveness is tested with some verification examples.