Avaliação de técnicas de detecção de dano em lajes de concreto armado fissuradas

Abstract

Cracks are one of the types of pathologies that can affect an reinforced concrete structure, being the result of damage. The damage causes changes in the physical properties of the structure, which are related to the dynamic properties, so changes in physical properties also cause changes in the dynamic properties, such as natural frequency, modal forms and damping. The damage detection techniques show success in identifying the damage, but the difficulty lies precisely in the location of that damage. The objective of this work is to evaluate the applicability of the damage detection technique, known as “curvature mode shape”, in a reinforced concrete slab. The technique presented can be summarized as follows: for a healthy structure, the graph of the curvature has a smooth shape, and therefore a peak or discontinuity in the graph indicates an abnormal variation of flexibility / stiffness in the position where the discontinuity is, Then the damage can be located using this information. An experimental and a numerical model were used. By decreasing the stiffness of each element, we attempted to reproduce the cracking pattern of the experimental model, in the numerical model. To evaluate the correlation between the modes of vibration of the two models, the Modal Assurance Criterion was used. Two applications of the technique were made, one using a finite difference expression and another being in fact a function that would represent the format of the mode, and deriving it twice to find the modal curvature as a function of the position of the node. The application of the technique using finite differences could not locate the damage, already using the modal function in fact, it was possible to locate only the damage caused by the application of 8 kN. The techniques of detection and location of damages are promising and the suggestion is made for other researches that use the distributed pattern of cracks and not located in a single element, as already consolidated in the literature.