Research On The Shape Detection Method Of Long-span Precast Concrete Members Based On BIM Technology

With the acceleration of China’s modernization construction,in the field of rail transit engineering,as an important part of engineering structure,the size and appearance quality of long-span precast concrete members will directly affect the overall quality and service life.At present,the traditional detection methods and means are still used to detect the shape of long-span precast concrete members,which has low detection efficiency and low accuracy.In this paper,the rail beam members in rail transit engineering are taken as the research object,and the shape and size of large-span precast concrete members with complex shapes are detected by using BIM technology and close-range photogrammetry technology.Firstly,the forward Revit model of prefabricated components is established according to the design drawings,and then the reverse 3D real-life model of prefabricated components is established by collecting the image information of prefabricated components at the site or construction site.Finally,the reverse model and the forward model are compared and analyzed,and the dimensional deviation between the two models(that is,the dimensional deviation of prefabricated components)is obtained.By applying this method to practical engineering cases,a complete set of inspection methods for the dimensions of precast members is formed,which improves the inspection efficiency and accuracy of the dimensions of large-span precast concrete members with complex shapes.Main contents of this thesis:1.Image acquisition and data processing.In order to establish the reverse 3D model of components,it is necessary to collect images and process data of prefabricated components.Using the theory of optimization method,the best shooting parameters,shooting mode and overlap between adjacent images are obtained to ensure the original image quality of prefabricated components;Then,the camera is corrected for distortion and the image is processed for uniform light and color to eliminate the distortion caused by the camera and the influence of external conditions on the image.2.Establishment of 3D model about components.Firstly,according to the design drawings of prefabricated components,the forward BIM model of the components is established by using Revit software.Then,using close-range photogrammetry technology,the reverse 3D real-life model of prefabricated parts is established,and a method based on sequential 3D reconstruction strategy is proposed to assist the 3D calculation,which improves the accuracy of 3D calculation.3.Quality analysis of reverse 3D model.It is necessary to analyze the quality of the reverse model before comparing the reverse model with the forward model.The model quality is mainly analyzed from two aspects,appearance quality and model accuracy.The appearance quality analysis is mainly judged by direct observation with naked eyes,and the model accuracy analysis mainly analyzes the accuracy of the reverse 3D model from two aspects of point accuracy and geometric accuracy through experiments.The results show that the average mean error of point accuracy of the model is 1.256 mm,and the geometric accuracy error of the model is mainly between 0.9mm and 2.0mm.4.Comparison between reverse model and forward model.In order to get the dimension deviation of components,it is necessary to compare the reverse model with the forward model.Firstly,the two models are preliminarily aligned by using the seven-parameter method,and then the two models are accurately aligned by using ICP algorithm.Finally,the deviation of dimensions between the reverse model and the forward model of prefabricated components is obtained by comparative analysis.The results show that the deviation of dimensions between XOZ plane and XOY plane of prefabricated components is within the range of-1.298mm～1.298 mm,which meets the requirements of relevant standards.