Curvature based DAD-method for damage localization under consideration of measurement noise minimisation

Structural components like bridges are essential elements in any infrastructure system for easy transportation. Lately, there has been a great need to enhance infrastructure repair, maintenance and preservation techniques to align with the current needs in terms of cost, safety, and functionality. Whereas bridges are susceptible to various modes of failures, the influence of the weight of transitions of different axles on the structural dynamics has recently attracted research attention. Therefore, appropriate and reliable methods for bridge inspection are highly desirable.

Through static loading and dynamic excitation tests, the impact of bridge damages on the structural responses which influences their load-bearing capacities have been observed. Recently, various researchers have embraced this concept in developing long term structural monitoring concepts, with the ability to control structural changes and predict possible changes by comparing the newly obtained data and the existing data. However, this has not been fully achieved especially for long term monitoring of structures due to several drawbacks: difficulty in integrating the measured data with the bridge model, unfavorable method for assessing the bridge condition and the aging effects. Despite the advantages of static loading as compared to other methods, there is a need for more improvements to enable effective damage assessment. Additionally, noise emanating from the measuring techniques have also produced considerable effects which should be managed.

Curvature evaluation has recently emerged as a promising approach for detecting damages in infrastructure by minimizing noise effects. This method takes into consideration the length of curvature interval and the noise to damage ratio. With the current advancement in technology, digital measurement techniques such as digital photogrammetry have been developed for inspecting structures so as to overcome the currently experienced challenges. This pioneered the development of the deformation area difference (DAD) method for damage localization due to the depended on the structural curvature on the stiffness.

At the University of Luxembourg the researchers Dolgion Erdenebat (PhD candidate) and Ass.-Prof. Danièle Waldmann from the Institute of Civil and Environmental Engineering developed a deformation area difference method for improved identification and localization of local damages. This research is published in the Journal Engineering Structures. The presentation was generally theoretical based on the static load deflection tests on bridges. Two laboratory experiments were used to validate the results. They included a reinforced concrete beam loaded to achieve failure in the compression zone and a steel beam locally damaged at three positions by increasing the degree of damage. The authors aimed at identifying and localizing the crack areas using the information of the measured deflection line and to evaluate the capability of the method in terms of measured degree of the damage.

The work of University of Luxenberg scientists successfully identified cracked areas from the measurement of the deflection line using the DAD-method attributed to the reduction in stiffness due to increase in the load increase that led to cracking. In their study a high level of accuracy measurement was required for the deflection line which was quite challenging. However, the use of digital photogrammetry proved effective in enhancing accuracy. Furthermore, various possible solutions: use of polynomial regression to smoothen data, variation and standard variation were proposed to improve minimization of the noise effects. Altogether, successful localization of cracking in concrete beam makes the DAD-method a promising technique for practical applications of damage assessment.