Improved Thermography Technique for Identifying Structural Elements under Ambient Conditions

Infrared thermography is an interesting non-contact evaluation technique which relies on surface thermal gradient. It is used to identify dissimilarity in geometry or material property. The application of this method in civil engineering is limited, as concrete components are heavy and require large amount of heat to reveal differential thermal gradients. Hence, the present work focuses on assessing the applicability of the infrared thermography technique for civil engineering structures under ambient conditions using solar heat. For the study, the exterior frames in real structures have been chosen, wherein the reinforced concrete and masonry members are not explicitly visible to the eye. The initial studies showed that the thermograms revealed different temperature gradients corresponding to the main beams and masonry walls, thus aiding in their identification. However, when the method was extended to multi-storey framed structures, the thinner elements like lintel beams could not be identified. The application of improved thermography technique using wavelet packet analysis to two test structures showed that lintel beams could also be identified. Also, the possibility to evaluate the geometric dimensions of structural members and floor heights, using the thermogram and a reference dimension, has been studied on two test structures. The geometric dimensions could be evaluated with more than 90% accuracy.