Seismic Damage To Residential Buildings In Ms 8.1 Gorkha Earthquake And Seismic Capacity Analysis Of Owner-Built RC Frame Structure In Nepal

An earthquake of Ms8.1 hit the Gorkha district,Nepal,on April 25,2015,has caused great catastrophic deaths,injuries and economic losses.After the earthquake,my team rushed to the earthquake area and experts in Nepal carried out building seismic damage investigation work together.According to the results of seismic damage investigation,the main research contents and results are presented as follows:(1)In order to analyze the seismic damages of the owner-built dwellings along mountainous highway in Nepal earthquake sequence,the field survey was taken along the highway from Kathmandu to Zhangmu port.Firstly the structural characteristics of reinforced concrete frames and masonry structures in Nepal were described.Then the characteristics of the seismic damages to the two types of residential structures were summarized and the damage ratios of the structures were given according to the direct disasters and secondary disasters.The basic intact ratio of frame structures is more than three times masonry structures,but the proportion of moderate damage and serious damage and destruction is about half of the masonry structures.Based on the damage investigation and the statistical analysis,it is concluded that many owner-built frame structures were not properly designed as the requirements of the building codes of Nepal and their construction quality is coarse,but the damage degree of the frame structures is much less than that of the masonry structures.Moreover,as the elevation increases along the highway,the seismic damage to the dwellings has a tendency of increase.Finally,secondary disasters resulted from this earthquake aggravated the seismic damage of dwellings.(2)The seismic capacity of typical owner-built RC frame structures that represent the local practice in Nepal are investigated through nonlinear static analysis of 3-,4-,5-and 6-story prototype structures,and is compared with that of confined masonry structures that are designed in accordance with the Chinese seismic design code.The results show that the owner-built RC frame structures in Nepal exhibit higher strength and ductility than confined masonry counterparts in China,which have the similar structural layout,masonry properties and amount of reinforcement.In seismic ability,seismic capacity of 3-story Nepalese owner-built RC frame structure is equivalent to the 8 degrees(0.3g)of confined masonry structure.Seismic capacity of 4-story Nepalese owner-built RC frame structure is between confined masonry structure of 8 degrees(0.2g)and 8 degrees(0.3g),and more near to 8 degrees(0.3g)area.Seismic capacity of 5-story Nepalese owner-built RC frame structure is equivalent to the 7 degrees(0.15g)confined masonry structure.Seismic capacity of 6-story Nepalese owner-built RC frame structure is between confined masonry structure of 7 degrees(0.15 g)and 8 degrees(0.2g),and more close to 7 degrees(0.15 g).