Targetless image-based method for measuring displacements and strains on concrete surfaces with a consumer camera

Abstract

9Measurement of concrete strain through non-invasive methods is of great importance in civil 10 engineering and structural analysis. Traditional methods use laser speckle and high quality 11 cameras that may result too expensive for many applications. Here we present a method for 12 measuring concrete deformations with a standard reflex camera and image processing for 13 tracking objects in the concretes surface. Two different approaches are presented here. In the 14 first one, on-purpose objects are drawn on the surface, while on the second one we track small 15 defects on the surface due to air bubbles in the hardening process. The method has been tested 16 on a concrete sample under several loading/unloading cycles. A stop-motion sequence of the 17 process has been captured and analyzed. Results have been successfully compared with the 18 values given by a strain gauge. Accuracy of our methods in tracking objects is below 8 m, in 19 the order of more expensive commercial devices. 20 21 22

Parametric Study of the Errors Obtained from the Measurement of the Oscillating Movement of a Bridge Using Image Processing

“…Measuring the movement from a distance of 10 m and in laboratory conditions, the error obtained was below 0.1 mm. Using this procedure, the strain in a concrete surface was measured with good agreement with strain gauges measurement [9]. A similar method has been used by Chen et al [10] to measure the vibration of some stay cables.…”

“…In [9] the tracking performance of a low-cost consumer camera is compared with that from a high resolution camera. Low cost cameras introduce JPEG compression in the video sequence, thus degrading the final quality of the image.…”

Development and Laboratory Testing of a Multipoint Displacement Monitoring System

“…used for obtaining video images limits the range of the system. Ferrer et al [11] successfully measured displacement on a concrete surface using consumer grade cameras, but were unable to verify their work under field conditions due to problems with illumination conditions.…”

Concrete Characterization through digital image processing techniques

“…Lately, methods for the testing of compressive strength and measurement of concrete deformation based on non-contact techniques have been developed, mainly through vision systems or the shooting of pictures and their following processing, favored by the ongoing improvement in photography and computers ability [5]. These techniques, which imply and improvement in respect to the traditional use of sensors such as strain gages, are not affected by variation due to weather conditions, something which happens with the last-mentioned ones; they also avoid residue generation and the final cost associated with disposing, among other aspects.…”

“…Currently, there are records of stress and displacement in concrete based on digital images processing among them, some authors make use of Moiré sampling method, [6] others, opt for labeling the surface of the tube to measure [7]. In the case of [5], it is done using measuring techniques based on video sequences from a standard photography camera. In all these cases, the measurement is done placing the structure or the analyzed specimen under a specific loading state.…”