Comparison of Strengthening Techniques for Typical Stone Masonry in Mud Mortar (SMM) Walls Popular in Rural Nepal

Nepal suffered a massive devastating earthquake in April 2015, resulting in colossal loss and significant injuries to thousands of lives which was majorly due to poorly built houses. With reference to Post Disaster Needs Assessment (PDNA) conducted in 2015; in total 10,48,574 houses were affected across Nepal and 73% of those houses were estimated to be unreinforced stone masonry in mud mortar (SMM) exposing the vulnerability of those houses under seismic effects. Many of these traditional houses are built with low-strength, random rubble load-bearing masonry walls in mud mortar and timber diaphragms offered poor resistance for out-of-plane forces. Hence strengthening these houses by adopting a suitable retrofitting technique is a must to prevent potential damage due to future earthquakes. Due to limitations in available resources, technology, and financial constraint of homeowners, only a few techniques can be implemented in rural Nepal. Strongback and splint and bandage retrofitting technologies are among those applicable and have been widely used. To analyze the performance of the strongback and splint and bandage retrofitting technologies, a detailed analytical model of SMM walls strengthened with these techniques was established. The model has inputs based on mechanical experimental results of the materials, samples. Strongback technology uses reinforced concrete and timber explicitly as load-carrying members whereas splint and bandage technology use galvanized iron wire mesh as well as steel rebars with concrete as load-carrying members. The research analyzes the simulation results and compares the strongback and splint and bandage technologies in terms of in-plane and out-of-plane load-taking capacity of SMM walls, joint drift and displacement. It recommends favorable strengthening solution for rural SMM houses in Nepal.