Experimental evaluation of nonlinear behavior of unreinforced masonry (URM) walls retrofitted using center-core technique

Earthquake vulnerability is the major weakness of unreinforced masonry structures. Various methods have so far been proposed to strengthen such structures against earthquakes. The recommended procedures are not especially suitable for this type of structures, that are meanwhile historically and culturally valuable. One of the adequately suitable methods of retrofitting of this particular type of structures is the center-core technique; based on which the façade of buildings with no change whatsoever. Scantly little studies have so far been conducted on structural retrofitting and the essential research carried out in this area has focused on the study of masonry piers. In this study, the in-plane nonlinear behavior of two full scale unreinforced masonry wall specimens, retrofitted with three and five reinforced cores, were tested under experimental cyclic loading; and their related hysteresis force-displacement, envelop force-displacement (backbone curve), energy dissipation and secant stiffness degradation curves, were plotted. Using envelop curves, ductility and effective stiffness parameters of each of the two specimens were extracted and the results were compared with those of the reference non-retrofitted wall specimen. The outcome results revealed that this method has led to 42% increase in ultimate strength and a 55% increase in ductility of the three-core specimens compared to 84% increase in the ultimate strength and 236% rise in ductility of the five-core sample. Also, the reinforced samples’ effective stiffness raised significantly as compared to the non-retrofitted specimen. Failure and damage patterns of the strengthened specimens showed that their failure modes, compared to the non-retrofitted reference specimen, have converted from diagonal to combination of diagonal and sliding failure mode.