1 PhD student, University of Minho, ISISE, j.almeida@civil.uminho.ptÂ

2 Assistant Professor, University of Minho, ISISE, eduardo.pereira@civil.uminho.pt

3 Professor, University of Minho, ISISE, barros@civil.uminho.pt


Among the strengthening techniques available to address the seismic vulnerability of masonry elements, one recently developed is considered of great potential and consists on the application of an FRP mesh embedded in a fibre reinforced mortar overlay. In order to assess the effectiveness of this strengthening system, and considering that the seismic action is involved, one important component of the structural behaviour is the in-plane cyclic response. In this research the applicability of the diagonal tensile test, as described by the ASTM-E519-02, for the assessment of the cyclic response of strengthened masonry is evaluated. The results obtained allowed to assess the contribution of the strengthening system in terms of load carrying capacity of the masonry elements, as well as to evaluate the damage evolution under cyclic loading.

The pure shear stress state was imposed to masonry specimens by means of the diagonal tensile test and the evolution of the shear stress, shear strain and modulus of stiffness during loading were obtained. The original experimental procedure, as indicated in the ASTM-E519-02, was altered in order to allow the assessment of the structural behaviour of the strengthened models under cyclic loading. Initially, the local crushing and splitting of the external strengthening layers was observed at both loading edges of the specimen. To avoid this premature local failure mechanism, two steel plates were added at the opposite surfaces of the specimens near each support, which were transversely connected with steel rods crossing the section. The contribution of the strengthening system to the in-plane structural response of the masonry elements was evaluated by comparing the responses of unstrengthened and strengthened specimens.

The proposed strengthening system has increased the shear strength in approximately 2.3 times. The adoption of cyclic diagonal tensile tests in the experimental characterization of masonry elements allowed the evaluation of the stiffness degradation during cyclic loading. In general, the failure modes of the reference specimens were the typical ones expected for diagonal tensile tests. In contrast, the failure modes and crack patterns of the strengthened specimens were characterized by a first phase at which the normal diagonal tensile cracks were developing gradually, followed by the delamination of the strengthening mortar right before failure. The evolution of damage in the strengthened specimens was accompanied by significant deformation capacity and energy dissipation before failure, in contrast with the reference specimens, where damage development occurred in a sudden manner.

Keywords: masonry, rehabilitation, high ductility, bonding properties, experimental characterization