59 Crack Detection in a Concrete Beam using Two Different Camera Techniques D. Lecompte, 1, * J. Vantomme 1 and H. Sol 2 1 Royal Military Academy, Department of Materials and Construction Renaissancelaan 30, PO Box 1000, Brussels, Belgium 2 Free University of Brussels, Mechanics of Materials and Constructions Pleinlaan 2, PO Box 1050, Brussels, Belgium The study presents an application of two different optical measurement techniques for the detection of cracks at the surface of a realistically sized concrete beam subjected to flexural loading conditions. Both techniques provide displacement measurements in a discrete number of points on the surface. Based on these displacement fields, deformations are calculated by means of the Green–Lagrange strain expression. The study deals with the relationship between cracks and the concept of deformation and it examines which of the two methods presented appears to be the most suitable for crack prediction or detection. The study shows that it is possible to detect the appearance and evolution of cracks, even before the cracks become visually detectable, with both methods and reveals their complementarities. Keywords concrete beam  damage-detection  optical measurements  non-contact measurements 1 Introduction The present study is defined in the framework of the FWO-Flanders-project Nr G.0266.01, where the objective is to evaluate the behavior of a realistically sized prestressed concrete beam, during static and dynamic loading, using a four- point bending disposition in which the two bending points (position of the loading jacks) are decoupled (see Figure 6). Classical experimental validation techniques that use strain gauges, extensometers, etc., do not allow a correct apprehension of the local damage mechanisms, which lead to the failure of the structure, due to the heterogeneous nature of concrete. A more relevant modeling of these mechanisms can be assisted by a full field measuring technique focused on a given region of interest of the loaded specimen. The question is whether it is possible to predict crack develop- ment before a crack becomes visually detectable and whether the crack evolution during the process can be monitored. In this article, two different measurement techniques are used to measure the displacements of a discrete number of points on the surface of a beam during loading. The first technique is based on the compar- ison of a number of digital images, taken during the loading of the beam. It uses a given speckle pattern, exhibited by the surface of the specimen or obtained by a paintspray, combined with *Author to whom correspondence should be addressed. E-mail: David.Lecompte@rma.ac.be Copyright ß 2006 SAGE Publications, Vol 5(1): 0059–10 [1475-9217 (200603) 5:1;59–10 10.1177/1475921706057982] Copyright ß 2006 SAGE Publications, Vol 5(1): 0059–10 [1475-9217 (200603) 5:1;59–10 10.1177/1475921706057982] by guest on October 19, 2016 shm.sagepub.com Downloaded from