Out-of-plane closed-form solution for the seismic assessment of unreinforced masonry schools in Nepal

Traditional unreinforced masonry (URM) constructions still represent an important part of the school building stock in several low-income countries including Nepal. Unfortunately, their intrinsic vulnerability impacts negatively on the resilience of cities and local communities. Observations after major seismic events have shown that the predominant mode of failure is the out-of-plane (OOP) of the weak and loosely connected perimeter masonry walls which typically leads to partial or global collapse. Starting from this evidence, a closed-form analytical approach is presented aimed at deriving the OOP force-displacement response of URM walls for different boundary conditions and vertical loads. The novel analytical solution is successfully validated with the results of seventeen OOP experimental tests on URM walls available in the literature. Then, referring to a case-study Nepalese school building, capacity curves of the constituting walls are derived and adopted for the vulnerability assessment of the structure through the Capacity Spectrum Method (CSM) where equivalent hysteretic damping is calibrated with available OOP shaking table test results. Lastly, PGA capacities for different damage states are successfully compared with median values from observational fragility curves.