Seismic performance assessment of stone masonry buildings: Efficacy of various strengthening elements

Post the 2015 Gorkha earthquake in Nepal, various codes and guidelines were introduced and implemented to enhance the seismic resistance of masonry structures. These provisions encompass diverse seismic measures such as incorporating horizontal bands and vertical reinforcements to fortify structures against seismic forces. Nevertheless, a comprehensive investigation and validation of effectiveness of horizontal bands and vertical reinforcement on the performance of such buildings is still lacking. This paper addresses this gap by presenting the seismic fragility assessment of stone masonry buildings constructed with mud mortar (SMM) and cement mortar (SMC), with a case study involving three distinct building prototypes, presented in the catalogue by the Department of Urban Development and Building Construction (DUDBC), Nepal. The research evaluates the effectiveness of several strengthening components on the buildings' performance, making comparisons among four different scenarios: (a) RM (a reinforced model with all horizontal bands, vertical reinforcement, and through stones), (b) RM-WOV (a reinforced model excluding vertical reinforcement), (c) RM-WOV-St (a reinforced model excluding vertical reinforcement and stitches), and (d) URM (an unreinforced model lacking all horizontal bands, vertical reinforcement, and through stones). The cracking mechanisms reveals the importance of the horizontal bands and through stones. The fragility analysis performed for slight, moderate, extensive and collapse damage states shows that unreinforced models are more susceptible than their reinforced counterparts, irrespective of whether mud or cement mortar is used. The maximum reduction in probability of exceedance of collapse and extensive damage for SMM and SMC buildings with the introduction of horizontal bands at sill and lintel level together with through stones are around 82 % and 81 % respectively. This shows that horizontal bands at sill and lintel level play an important role in preventing the damage of the buildings. Furthermore, it is found that the effect of using vertical reinforcement and horizontal stitches is minimal in preventing the structural damage in cement mortar buildings. However, for mud mortar buildings, these measures have a noticeable effect.