Volume 39, Issue 4 (July 2011)
A Photogrammetric System Design to Determine the Load-Deflection Behaviors of Materials in Civil Engineering
This paper defines a photogrammetric system developed to automatically measure displacements at a large number of points on structural elements in static or quasi-static load experiments. The system consists of hardware and software. Basically, the hardware component includes online image acquisition system with three charge coupled device (CCD) cameras and the software comprises the photogrammetric processing of the obtained image data. The computational approach of the system involves initially determining the camera calibration parameters, then calculating three-dimensional (3D) object coordinates of signalized points on the test object during the load test. The measurements are performed in near real-time (<1 s), continuously for previously defined time periods or for a single measurement session after every loading by user intervention. For testing purposes, the system was used in the unconfined compression tests on different cohesive soil samples and load tests on a steel beam. Sub-millimeter object point precision was obtained for the 3D object coordinates in all the measurement sessions of both experiments. The axial deformations of cohesive soil samples were measured with a dial gauge and the comparison of the results obtained from both measurement systems indicated that the proposed photogrammetric system is sufficiently reliable and accurate to monitor the deflection behavior of materials under loading conditions.