Experimental tests on masonry walls strengthened with an innovative C-FRP sheet

A lot of tuff masonry buildings have been built in the past decades and generally need to be repaired and/or strengthened to improve their seismic performance. Tuff masonry buildings are generally dimensioned and detailed for vertical loads; for this reason strengthening upgrade is generally required for horizontal actions. In the last years composite materials have been utilised for such a purpose instead of more traditional techniques consisting, for example, in casting two thin r.c. plates at both the faces of the masonry wall obtaining a sort of sandwich structures. On one hand, using the usual CFRP tissues, even if applied in discrete strips, generally results in over-dimensioning; on the other hand epoxy resins usually utilised with such composite materials are not so suitable and very expensive for gluing FRP tissues to the masonry. For this reasons, epoxy bonded FRP unidirectional or bidirectional tissues, suitably utilised for r.c. members strengthening, can be substituted by other specific materials and techniques in masonry wall strengthening. The present paper deals with experimental tests carried out on tuff masonry walls strengthened with an innovative composite material consisting in a low-density bidirectional carbon-fiber tissue that can be applied to the masonry wall by means of an special cement-based mortar. A series of masonry walls have been tested under diagonal compression at the Laboratory of Structures of the University of Salerno, according to the ASTM E519/81 standard. Both unreinforced and reinforced walls have been considered in order to quantify the influence of such a new strengthening technique with respect to the bare masonry behaviour in terms of strength and ductility. Various arrangements of the material have been considered (single side versus double side strengthening, number of tissue layers, etc.) in order to point out the influence of the various parameters of the final behaviour. The tests described in the present paper is part of a research project dealing with experimental tests of tuff masonry reinforced with C-FRP materials. The results obtained on tuff element and column specimens have been presented in a companion paper and one of the first conclusions regarding with the tests reported in the present one is that the increase in relative strength on reinforced walls is generally higher than the corresponding values observed for the other tests on single tuff elements