07/07/2012,Thrissur: The Institution of Engineers (India), Thrissur local centre organised a technical presentation on the topic "Health Assessment of Structures" by Er. P. Harikrishnan, a post graduate in Structural Engineering from IIT, Kanpur in the hall of Association of Engineers Kerala today. The following is the nutshell of the presentation. Health Assessment of Structures Vibration-based damage detection is an emerging field of research, which promises to provide a way of rapid condition assessment at a very low cost. Some of the target applications of this vibration-based damage detection are the safety assessments of structures after natural hazards, continuous health monitoring of important structures etc. Although many methodologies have been developed so far for this purpose, most of them often fail to perform satisfactorily in terms of damage characterization and localization for real-life civil engineering structures. Here, a new algorithm is proposed for damage localization and characterization of frame structures. The proposed algorithm estimates the modal parameters of a structure from the ambient responses using Natural Excitation Technique coupled with Eigen-system Realisation Algorithm (NExT-ERA). The curvature values of the fundamental mode shape are then evaluated through central difference approximations. Since various damage conditions alter these curvature values differently, the differences in these curvature patterns are then used for damage localization and characterization. The proposed method is capable of distinguishing between a beam or a column damage. In addition, damage is quantified in the proposed method using the inverse of maximum change of curvature. To validate the proposed method, simulation studies are carried out on a three-bay twelve-storey steel moment-resisting building frame subjected to simulated ambient excitations. It has been shown that the proposed method is capable of handling noisy and damped responses for several damage situations. The efficiency of the proposed algorithm is also demonstrated through laboratory shake-table experiments on a scaled model of a three-storey single-bay steel moment-resisting frame. The method is found to be successful in localizing and distinguishing between beam and column damage conditions. In addition, a field experiment was performed (without obstructing the regular traffic) on the Jajmau-Ganga Bridge, located near Kanpur. The proposed method is found to successfully localize and identify the bearing damage even with limited number of sensors. In general, it is found from these studies that the uncertainty in the damage localization increases with an increase in the level of noise and a high level of noise may lead to even false detection of damage. Further, a quantification of damage is found to be satisfactory. It is however concluded that an improvement of the algorithm is desirable for more generalised applications.