Quantitative Analysis Of Earthquake Building Damage Information Based On Ground-based LiDAR Data

Earthquakes have a serious impact on people’s lives and properties,and their damage to building structures is the main cause of human casualties and economic losses.Investigation of the extent of building damage and determination of the earthquake damage level after an earthquake is crucial to disaster damage assessment,emergency response disposal,and rescue operation planning.The accuracy of building damage information discrimination directly affects the accuracy of building damage classification.Terrestrial Laser Scanning(TLS),as an emerging active remote sensing technology,is the main way to obtain high-precision LiDAR(Light Detection and Ranging)point cloud data of ground-based targets.Using terrestrial LiDAR data to detect building information is an important development direction at present,which has not been realized in the quantitative analysis of building damage level determinatio.In view of the lack of quantitative analysis and judgment indicators in the current method of terrestrial LiDAR-based building damage information extraction and the ambiguity in the identification of buildings with basic intactness,minor damage and moderate damage in the seismic field examination,this paper,considering the perspective of practical application,carries out a study on the quantitative analysis of building damage information based on terrestrial LiDAR point cloud data after the earthquake.The paper aims to promote the development of the application of terrestrial LiDAR data in the quantitative identification and analysis of building damage information,improve the accuracy of post-earthquake building damage determination,and provide technical support for post-earthquake building damage assessment and safety identification.This paper focuses on the terrestrial LiDAR point cloud data characteristics of masonry buildings.In order to study the correspondence between quantitative identification of earthquake damage information and earthquake damage level based on terrestrial LiDAR high-precision data of post-earthquake buildings,and to establish quantitative determination indexes and quantitative determination criteria of earthquake damage level of buildings,the following related researches are carried out in this paper:(1)Both the coordinate system conversion method of terrestrial LiDAR building single independent wall point cloud and the building LiDAR point cloud data were established.Through the statistical analysis of the data on the walls of new,basically intact masonry buildings and basically intact frame buildings,a reasonable interval of LiDAR data background values for the walls of masonry and frame buildings in rural residential areas around Lushan,Sichuan Province,is 0cm-0.45 cm.In the study of the background values of LiDAR data on the walls of the building,it was found that the study based on LiDAR data was not suitable for the building because of the deformation distortion and unevenness of the walls due to the characteristics of the wood frame building itself.(2)Based on LiDAR point cloud proximity curvature,pinch angle and normal vector threshold setting a method for automatic extraction of seismic damage information of buildings was proposed.Moreover,based on the fitted plane contour of the point cloud of the building wall,the verticality(flatness)of the wall,the standard deviation of the profile,and the pinch angle of the profile,the correspondence between identification feature parameters and seismic damage level was established.With the statistical analysis of the independent wall curvature of masonry and frame structure buildings collected in the earthquake zone of Lushan,Sichuan Province,in 2013,we got to know the wall curvature threshold of buildings in this study was0.0015.When the expected value of normal distribution of wall curvature is less than0.0015,the flatness of the building wall is high.If the threshold value for the angle of the proximity point is set to greater than 1.5 degrees,this method is suitable for buildings with high flatness of wall surface and small misalignment of wall crack displacement;When the expected value of normal distribution of wall curvature is greater than 0.0015,the flatness of the building wall is low.If the threshold value of the angle of the proximity point is set to be greater than 6 degrees,this method is suitable for the building with poor surface flatness of the wall and large misalignment of the wall crack displacement.In the study of automatic extraction of seismic damage information of buildings,the seismic damage of frame structure buildings is mainly judged by the seismic damage phenomena of load-bearing members such as structural columns,load-bearing beams and frame shear walls,and the infill walls between the structural columns are non-load-bearing walls.The seismic damage of infill walls does not affect the safety of the overall building,and the seismic performance of this building structure type is good,and fewer frame structure buildings with seismic damage were collected in the earthquake area after the Lushan earthquake;the masonry structure is a joint loadbearing of walls and structural columns.Therefore,in this study,the quantitative analysis is carried out mainly for the masonry structures,which account for a large proportion of the earthquake damage determination.(3)The quantitative determination indexes and criteria for determining the earthquake damage level of terrestrial LiDAR buildings was established.Based on the automatic extraction of seismic damage information of masonry buildings,this paper carries out a study on the quantitative determination criteria of seismic damage information of buildings in order to solve the correspondence between the seismic damage information and the seismic damage level.For the masonry building anomaly value area,a seismic damage information analysis model is established,and the seismic damage point cloud characteristic values are extracted by the method of profile analysis.Based on the analysis of LiDAR point cloud background values and wall verticality(flatness)of masonry buildings,the quantitative determination indexes of the standard deviation of the profile of 0.45 cm and the angle of the profile of 1 degree were established,and the criteria for determining the earthquake damage level of masonry buildings was also established.The innovations of this paper can be summarized as follows:(1)For the first time,LIDAR technology was combined with seismic field work building damage level determination,solving the problem of ambiguous recognition and determination between basically intact and slightly damaged buildings in seismic field scientific examination.(2)A quantitative analysis method for earthquake damage information of masonry buildings was established.(3)The quantitative determination indexes and criteria for determining the earthquake damage level of terrestrial LiDAR buildings were established.The new method and criteria for quantitative analysis of earthquake damage information of buildings based on ground-based LiDAR data established in this paper are of great value for the application of ground-based LiDAR data in the identification and extraction of earthquake damage information and determination of earthquake damage level of buildings after an earthquake.In this paper,the quantitative determination indexes and determination criteria of earthquake damage information established in the study were examined using 299 stations of terrestrial LiDAR masonry building point cloud data acquired after the Ms7.0 magnitude earthquake in Lushan County,Sichuan Province(30.3 N,103.0 E)on April 20,2013.Solve the problem of tilt,bulge,external flash and other features in the earthquake damage level of minor damage and moderate damage determination ambiguity.The quantitative analysis method based on the foundation LiDAR data for masonry building seismic damage information established in this paper is applicable to the post-earthquake masonry building damage level determination.