ANALYSIS OF THE SEISMIC PERFORMANCE OF A STRENGTHENED PAGODA TEMPLE DURING GORKHA EARTHQUAKE

An earthquake of magnitude Mw 7.8 struck mid-western Nepal on April 25th 2015, followed by hundreds of aftershocks. This earthquake level is not uncommon in Nepal, where several events of magnitude 8 or even greater have occurred in the past. The earthquake destroyed approximately half a million houses and damaged another quarter million; it also damaged or destroyed part of the seven Cultural World Heritage Sites located in the Kathmandu Valley. Following the seismic event, several field surveys were performed, which provided clear evidence to construction technologies commonly employed in the earthquake stricken areas. Specifically, interesting data have been collected about the use of wood and bricks: two kinds of bricks of different quality are traditionally employed for the masonry internal side and for the external one, respectively; masonry walls, indeed, are normally constituted by three layers, with the middle core filled with lower quality material. In relation to the use of wood as a construction material, timber elements are widely present both in vernacular and monumental architecture as well, mainly because of the large material availability; they are typically used not only for floor and roof structures, but also for the framing of openings. All this applies to the case of temple structures as well, which are extremely significant from both the historical and architectural point of view, since they reflect high quality handcraft and the use of the best materials and workmanship available at the time of construction. In this work, attention is focused on the specific case of pagoda temples, which were destroyed in a limited number of cases, whereas most of them survived the earthquake with limited damage. A specific building technology has been observed in these structures, which deserves special attention. Pagoda temples, indeed, exhibit specific characteristics, related to the response to earthquake motion: lack of continuity of the masonry walls in the vertical direction, conical configuration of the internal masonry structure, open spaces at the ground level, poor connections between structural elements. In order to interpret the dynamic behavior of a pagoda in a Buddist monastery in Lalitpur, Kathmandu Valley, information on recent renovation interventions have been collected. On the basis of available information on the structure geometry, construction details and material properties, a numerical model has been developed. Dynamic analyses performed in the linear range indicated the interest for more sophisticated computations, based on the recognition and the analysis of specific local collapse mechanisms.