Damage description, material characterization, retrofitting, and dynamic identification of a complex neoclassical monument affected by the 2015 Gorkha, Nepal earthquake

Abstract

Neoclassical monuments with multiple courtyards are complex brick masonry constructions of the 19th century. They are vulnerable to seismic ground shaking. The 2015 Gorkha earthquake in Nepal damaged several such structures in Kathmandu Valley. Seismic capacity and/or vulnerability of such structures is associated with large uncertainties. Numerical modeling of such structures is challenging due to underlying uncertainties in their material properties and lack of construction details at the time of their construction. Retrofitting of such structures when damaged by earthquakes, although important for the preservation of their historical and cultural values, is challenging on many fronts. This paper presents a case study of a neoclassical monument in Nepal. A detailed description of the damage caused by the 2015 Gorkha earthquake is presented. Then retrofitting measures used to restore and enhance the structure of the monument are discussed in detail. In-situ and laboratory tests conducted to characterize material properties of the monument are also presented. Numerical models of the monument are then created to estimate its modal vibration properties. Dynamic identification of vibration frequencies of the monument before and after retrofitting is shown as a viable means to reduce uncertainties in the numerical model, a large part of which is due to inherent uncertainties in material properties of such monuments. The results show a significant increase in the stiffness of the structure after retrofitting it with measures that are compliant with the preservation of historical monuments.