Design Criteria for FRP Seismic Strengthening of Masonry Walls

Abstract eng:
Masonry structures have been the primary building typology for millennia in many countries and also nowadays many masonry buildings are realized. Seismic events have shown their vulnerability to in-plane actions even if they behave properly for gravity loads. This often requests to retrofit masonry walls for in-plane loads and a sound solution is provided by fiber-reinforced polymer (FRP) materials. FRP have emerged as a valid alternative to traditional materials used for retrofitting unreinforced masonry (URM) walls. Recent guidelines give information on the use of such FRP systems and recommendations on the design and construction of FRP systems used to strengthen URM structures. URM walls are usually strengthened applying FRP strips along the diagonals of the wall or in the direction parallel to the mortar joints. The shear resistant mechanism of strengthened walls with FRP strips along the diagonals of the wall is also discussed in this paper. The lateral strength of FRP strengthened walls can significantly increase if anchor systems are installed at the ends of FRP strips. This is due to the fact that the failure mode of strengthened walls could change from intermediate to end debonding if FRP strips present anchors at the ends. An assessment of design formulas for evaluating lateral strength of unreinforced and FRP reinforced masonry walls is presented. A comparison between theoretical predictions and experimental data is performed using outcomes of shear-compression tests on URM and FRP strengthened masonry available in literature. The study points out that the evaluation of the design FRP strains at failure could be dependant also on the masonry typology.

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