2015 Nepal earthquake: seismic performance and post-earthquake reconstruction of stone in mud mortar masonry buildings

The residential building typology of Stone in Mud Mortar (SMM) masonry contributed significantly to the seismic losses caused by the 2015 Nepalese seismic sequence, also known as the 2015 Gorkha earthquake. SMM masonry is the most common construction type in Nepal, and notwithstanding the extensive damage, this has persisted in the post-earthquake reconstruction. This paper provides first an overview of the extent of damage and typical failure modes suffered by this typology. Some pressing issues in the ongoing post-earthquake reconstruction, such as building usability, construction quality are then discussed. The results of seismic analyses on both the pre-earthquake (PRE-SMM) and post-earthquake built (POST-SMM) typologies, using the applied element method employing a modelling strategy that accounts for the random shape of stone units, are then presented and discussed in terms of capacity curves and failure mechanisms. As per the seismic design code of Nepal, seismic performance assessment is conducted to understand the seismic design levels of these constructions. Finally, seismic fragility and vulnerability functions for both the PRE-SMM and POST-SMM typologies, considering the uncertainty in ground motions and material quality, are presented and discussed. Considering the seismic hazard in Nepal, the PRE-SMM typology is found to be highly vulnerable and seismic strengthening of these buildings is urgent. On the other hand, the POST-SMM typology has adequate seismic capacity and performs within the serviceability limit, given the quality of both the construction materials and workmanship are not compromised.