In this thesis, we present the experimental results of tests on stone masonry spandrel walls and piers. The materials, samples, sites, and methods of testing are described. We compared the response of unstrengthened and strengthened walls. For strengthening, we used a 30 mm thick mortar layer, strengthened with a GFRP mesh and Experimental results were analyzed and compared to the strength as calculated using available analytical models. Because very few models are available in literature in foreign standards, and even those that exist are for brick, not stone masonry, no model could be used directly. Therefore an existing model was sensibly adjusted for the present case. We also analyzed the results of the life-sized pilot building investigation. The building was built using the same materials and building techniques that were used for the spandrel walls and piers. A numerical model was created for his building using Sap2000 and the discoveries made during the test of the single walls and the calculated response were compared with the experimental results. A numerical model for the prediction of the strength of the same building strengthened on one side was created.