The Seismic Damage Characteristics And Mechanism Of The World Cultural Heritage In The Kathmandu Valley Of Nepal, 2015

Nepal,located in South Asia mountain area,is famous for its exquisite architecture.The Kathmandu valley is in the center of Nepal,meanwhile,is the art and culture center of the nation.Nevertheless,frequent earthquakes result in sustained damage of the heritage buildings in Nepal due to the location of the country is on the Mediterranean-Himalaya earthquake belt.The earthquake on April 25 th,2015 caused severe damage to the world cultural heritage.The study on the seismic damage characteristics and mechanism of cultural heritages the Kathmandu Valley provides a theoretical basis for the post-earthquake restoration and strengthening.The analytical approaches in the paper are applicable for the similar heritages in Nepal,Meanwhile,they also have reference value to the same type heritages in China.Based on the data analysis and field investigation of the Kathmandu valley world cultural heritage,the study has combed the geological background data of the earthquake in 2015 and researched the cultural heritage protection history in the Kathmandu valley.Taking consideration of the seismic damage data both at home and abroad,cultural heritage seismic damage rating standards are delineated.According to the building history,building types,building materials,building structures and geological condition,the seismic damage distribution of the world cultural heritage sites are formed.Three typical buildings are selected for the seismic response analysis using FEM software ANSYS to study the failure mechanism under earthquakes.Some restoration and strengthening suggestions are given in final.The main conclusions of the paper are as below.(1)Three categories of cultural heritage seismic damage rating standards were defined based on the damage of structure and restoration need.The seismic damage maps of six world cultural heritage sites in the Kathmandu valley,defined by the UNESCO,are formed and then analyzed statistically.The most damaged sites were the Kathmandu durbar square and Changu Narayan temple,where the damaged buildings were more than 40% of the total heritage buildings.Boudha Stupa was less affected by the earthquake with some malposition was occurred in the main stupa.(2)Soft sediments in the valley center,where the three durbar squares located,amplified the seismic effect which resulted in the more serious damage of the structures.Swayambhunath and Changu Narayan temple located on the top of the hill,which affected the seismic damage characteristics.The structures near the slope shoulder were damaged more seriously than the structures in the center of the top hill.Short of periodic Strengthening and maintenance measures is another main factor that caused serious damage of the Kathmandu heritage during an earthquake.(3)According to the results of field investigation and data analysis,three typical structures in the Kathmandu valley,with different architectural characteristics,were selected to determine the seismic responses by ANSYS.The three structures are Kasthamandap(wooden structure),Laxmi Nayaran temple(brick-wood structure)and Vatsala Devi Temple(stone structure).Four different intensity earthquake records were selected for the comparative analysis of Kasthamandap.The seismic responses increase with the increasing of earthquake intensity.The maximum story drift ratios of the four seismic data occurred in the second floor,indicating the second floor was the structural weak layer.Site effects were considered in the analysis of the Laxmi Nayaran.The natural frequency of vibration of the structures decreased with the considerations of the site effect.The first floor was the structural weak layer of the Laxmi Nayaran temple.The structure was collapsed because the damage of the first floor.Larger deformation occurred in the conical portion of Vatsala Devi Temple.The connection part of the stone stoas and plinth,the conical portion and lower floor,the adytum on the first floor and plinth proved to be the weaker portion of the Vatsala Devi Temple.Finally,Some restoration and strengthening suggestions are given for the buildings,with the different architectural characteristics.