The project focuses on using laser scanners capable of measuring large objects in space, an important attribute for structural assessment after an earthquake event. A 3D point cloud representing the structure?s surface is delivered as the outcome of the laser scanning. We will have all laser scans geo-referenced at surveying grade accuracy allowing us to create a combined database of photo images and the laser scans. We will scan an array of buildings in different damage states, particularly in two of the sample blocks in Port-au-Prince previously surveyed by both the World Bank from the aerial photos and by two members of the team using on-the-ground surveillance. There are approximately 45 buildings in these two city blocks with a range of damage states. One objective of this effort is to see if the scanning would be an appropriate way to corroborate damage from aerial surveys.
The project will provide information for the first time on the use of high definition laser scanning and the merits and difficulties of using this advanced technology in a reconnaissance effort after a major disaster. This unique deployment of field measurements will provide an important benchmark for image-based remote sensing evaluation and future advancement of our capabilities for damage assessment of structural systems using the collected detailed data in this project. The laser scanning and other conventional data, e.g. material properties and collection of design data will improve our preparedness in situations of similar disasters in the US or worldwide. The information gathered will be instrumental in guiding the delivery of US aid for the reconstruction of Haiti.
This project explored the capabilities and advantages of laser scanners used for structural engineering applications in laboratory tests and in assessing structural damage in the post-earthquake field survey. High definition laser scans (HDS) have many advantages over conventional instrumentation in both the field survey and in a laboratory setting: (1) capture 3-D deformation with accuracy, (2) reduce measurement error resulting from linearization assumption in conventional instrumentations, (3) enable easier access to objects , and (4) reduce workload for instrumentations. Due to these advantages, high definition laser scans have been successfully used in laboratory tests and several case studies are studied in this project to validate the accuracy of laser scanner measurements. This project alsomade the first attempt to demonstrate the use of the high-definition laser scanning technology in field surveys of structures damaged in the January 2010 Haiti earthquake. A damage assessment was performed on several buildings using the scans, and the results were compared to the qualitative results of the visual ground survey. The techniques of gathering and disseminating critical information employed in this project is expected to have a major impact on future earthquake engineering laboratory tests and post-earthquake reconnaissance in the US and worldwide. From the research conducted in this project, the following concluding remarks are made: The laser scanner used in the above studies delivers individual point accuracy of 4.0 mm, and other devices are capable of much higher accuracies. Accuracy of the point cloud can be further increased by best-fitting sections of the point cloud to lines or surfaces. In-house study at the University of Califoria, Berkeley showed that the error margin of points on a surface can be reduced to as low as 1 mm. For most purposes, these accuracies are comparable to the accuracy of conventional lab instruments like displacement transducers and inclinometers. The quantitative damage assessment from the laser scans of structures in Haiti showed good correlation with the qualitative visual damage assessment and conventional quantitative reconnaissance approaches. The main limitations of laser scanners are: a) It can only acquire data from visible surfaces, b) It is relatively slow to use in real-time structural testing and rapid reconnaissance efforts. Advances in HDS technology will most likely reduce this problem in the future. With pre-made programming scripts, the post processing of scan data can be performed in a few days. After processing, data is in a convenient format that is easy to work with, enabling fast and efficient data-sharing across the Internet.
