Experimental qualification of seismic strengthening of URM buildings in Nepal

Nepalese buildings are typically constructed using unreinforced masonry (URM) as the lateral load-bearing system. In the 2015 Nepal Gorkha earthquake several URM buildings suffered heavy damage. The limited economic resources available in the country and the challenge of strengthening a large portfolio of buildings highlight the need for low-cost retrofitting techniques. This paper presents a large-scale experimental campaign aimed at quantifying the seismic performance of a typical URM wall when strengthened with splints and bandages. This represents one of the retrofit techniques that are most widely-used in Nepal. A 5 x 3 m URM wall was constructed using 1:6 cement-sand mortar as per the mechanical properties identified by material testing in Nepal. The URM wall was tested under a two-way ramp cyclic loading. Typical crack patterns associated with URM were observed. The wall was subsequently retrofitted with 8 mm rebars as splints and bandages and tested to failure. The results show that the strength of the retrofitted wall is almost twice that of the URM wall. The observed crack damage improved from EMS-98 Grade 2, with horizontal and diagonal shear cracks in the mortar bed, to Grade 1, with hairline cracks on the rendered splints and bandages. Overall, the experiment demonstrated the efficiency of this practical, low-cost retrofitting technique that is tailored to traditional Nepalese URM buildings. This work can be used to advise local stakeholders in the construction industry as well as to act as a benchmark to improve the reliability of fragility functions for URM buildings in Nepal.