ENHANCEMENT OF THE SEISMIC PERFORMANCES OF HISTORIC MASONRY BUILDINGS THROUGH GLASS FIBER-REINFORCED MORTAR

The study investigates on the behavior of a strengthening technique for unreinforced masonry based on the application, on both the sides of the wall, of a 30 mm thick mortar coating with Glass Fiber-Reinforced Polymer meshes embedded. The effectiveness of this technique, called Glass Fiber Reinforced Mortar (GFRM), for the enhancement of both the in-plane and out-of-plane performances of masonry walls is proved through experimental tests and numerical simulations, which are here described and discussed in detail. In particular, a contextualization of the study is presented in the introduction section (2), describing briefly the behavior of historic unreinforced masonry buildings subjected to seismic actions and evidencing the main critical aspects to be considered so to ensure an adequate safety against horizontal loads. Furthermore, an overview on the state-of-art in the field of reinforcement techniques for masonry structures is reported, focusing, in particular to modern strategies employing composite materials. In section 3, the considered reinforcement method is described and the experimental results of different characterization tests are shown. Section 4 concerns the in-plane behavior of GFRM reinforced masonry. The characteristic and the results of a wide number of diagonal compression tests carried out in laboratory field are presented and discussed. Some considerations on the influence of different parameters on the technique effectiveness, based on experimental evidences, are also reported. The tests permit to investigate on the reinforced masonry equivalent diagonal tensile strength, shear modulus and deformation capacity. Analytical formulation, based on the experimental findings, are then proposed to predict the stiffness and the resistance of reinforced masonry specimens; a simple numerical Finite Element model is elaborated so to check the influence of some parameters. At last, a preliminary study aimed to the evaluation, at the whole building scale, of the seismic performance improvement due to the application of the reinforcement is performed by applying a simplified modeling method (Equivalent Frame Method). The application of the modified Capacity Spectrum Method permitted to compare the performances of reinforced and unreinforced structures also in terms of maximum resisting ground acceleration. In section 5, the out-of-plane behavior of GFRM reinforced masonry is investigated. In analogy with the approach adopted for in-plane behavior, the results of some experimental tests (four-point bending) on unreinforced and reinforced full-scale masonry samples of different types are presented and compared, allowing an evaluation of the technique effectiveness in terms of both resistance and displacement capacity. The interpretation of the results permits also to purpose simple formulations for the evaluation of the cracking and ultimate bending resistance of reinforced masonry walls. A numerical Finite Element model is then presented to simulate the experimental tests and perform a parametric analysis, varying the main masonry and reinforcement parameters (such as thickness, stiffness and resistance). Some typical configurations of masonry walls of historic buildings subjected to out-of-plane bending are also analysed numerically to evaluate the actual performance improvements. Moreover, the numerical model is applied for the numerical simulation of the behavior of unreinforced and GFRM reinforced masonry vaults subjected to horizontal loads acting in the transversal direction. Each section ends resuming the respective contents and results. Moreover, the main findings of the study, the final remarks and the future developments of the research are summarised in the conclusion section (6).