# Post-Earthquake Building Evaluation Using UAVs: A BIM-Based Digital Twin Framework

## TL;DR

This paper introduces a digital twin framework using UAVs and BIM to evaluate building safety after earthquakes by integrating image and 3D data.

## Contribution

A novel BIM-based digital twin framework for post-earthquake building evaluation using UAV imagery and 3D point cloud change detection.

## Key findings

- The framework enables component-wise damage identification and association with BIM components.
- 3D point cloud change detection successfully identifies nonstructural damage in synthetic environments.
- BIM-guided image selection improves the accuracy of component identification from UAV imagery.

## Abstract

Computer vision has shown potential for assisting post-earthquake inspection of buildings through automatic damage detection in images. However, assessing the safety of an earthquake-damaged building requires considering this damage in the context of its global impact on the structural system. Thus, an inspection must consider the expected damage progression of the associated component and the component’s contribution to structural system performance. To address this issue, a digital twin framework is proposed for post-earthquake building evaluation that integrates unmanned aerial vehicle (UAV) imagery, component identification, and damage evaluation using a Building Information Model (BIM) as a reference platform. The BIM guides selection of optimal sets of images for each building component. Then, if damage is identified, each image pixel is assigned to a specific BIM component, using a GrabCut-based segmentation method. In addition, 3D point cloud change detection is employed to identify nonstructural damage and associate that damage with specific BIM components. Two example applications are presented. The first develops a digital twin for an existing reinforced concrete moment frame building and demonstrates BIM-guided image selection and component identification. The second uses a synthetic graphics environment to demonstrate 3D point cloud change detection for identifying damaged nonstructural masonry walls. In both examples, observed damage is tied to BIM components, enabling damage to be considered in the context of each component’s known design and expected earthquake performance. The goal of this framework is to combine component-wise damage estimates with a pre-earthquake structural analysis of the building to predict a building’s post-earthquake safety based on an external UAV survey.