Seismic enhancement of community housings in Nepal’s mid-Himalayas: Retrofitting and reconstruction scenarios

Nepal lies within the Himalayan seismic belt, making it one of the most earthquake-prone regions globally. Non-engineered masonry structures, though widely used, are highly vulnerable to seismic disasters. Replacing these structures is impractical and culturally insensitive due to their deep traditional and cultural significance. Retrofitting is a practical and culturally appropriate approach to enhance a building’s strength and safety against earthquakes. This study evaluates retrofitting and reinforcement techniques for unreinforced masonry (URM) structures in Nepal's mid-Himalayan region through numerical modelling, non-linear static analysis, and fragility assessment. Pushover analysis revealed that reconstruction models significantly improve base shear capacity compared to the URM model. Although gabion wire retrofitting has a limited effect at the initial stage, it significantly improves strength at larger displacements. Vertical reinforcements and horizontal bands in the reconstruction model consistently enhance performance. The URM model exhibits concentrated cracking near openings and corners, while the retrofitted model improves stress distribution and reduces crack widths. Additionally, the reconstruction model confines cracks within bands, preventing vertical propagation and ensuring superior structural integrity. Fragility curves reveal that reinforcement significantly enhances seismic performance, as the retrofitted model improves resistance across damage states, with exceptional collapse resistance due to its ductility, allowing energy absorption and delayed failure. The reconstruction model offers consistent protection with lower probabilities of damage across all states, underscoring its reliability during seismic events. Although the reconstruction model incurs higher costs than the retrofitted model due to its extensive reinforcement features, both models provide substantial seismic benefits compared to the base URM model.