Nondestructive deformation measurements and crack assessment of concrete structure using close-range photogrammetry

Reliable measurement of deformations and crack assessment of concrete structural elements under loading is essential for evaluating the performance and durability of these elements. Traditionally, structural elements are monitored under loading with strain gauges, deflectometer, and data acquisition systems. Limited studies have investigated the potential of close-range photogrammetry and three-dimensional (3D) modeling in analyzing deformations, internal stresses/strains, and crack propagation. This research proposes an innovative four-phase testing method to develop 3D models of the concrete beam with close-range photogrammetry and image processing techniques. The proposed method entails the capabilities of analyzing deformations, internal stresses/strains, and monitoring crack propagation. The main phases of the proposed method are as follows: 1) preparing the test setups, beam preparation, photogrammetry preparation, and surveying preparation; 2) testing the beam under loading while recording deformation data, collecting high-resolution images, and conducting ground-controlled surveying from nine points around the beam; 3) performing photogrammetric processing of the images to generate a textured 3D model of the beam; and 4) comparing the results from both the 3D model and the direct measurements. For triangulation accuracy, the overall RMSE of the generated model is 4.974 mm. While for product accuracy, the RMSE is 9.303 mm. Moreover, the RMSE for deformations is 0.115 mm, indicating acceptable accuracy of measurements through the model. In addition, a photogrammetric-based deformation model can be generated for the beam surface, and cracks area, length, and width are efficiently extracted and monitored.