Assessment of structural damage using operational time responses and finite element simulation

This paper presents a damage detection technique based on operational response monitoring. The technique utilizes finite element and linear elastic fracture mechanics (LEFM) analyses. The main novel feature of this technique is its ability to identify structural damage completely. The technique is based on monitoring the changes in internal data variability measured by a test statistic χ02 value. Structural normality is assumed when the χ0m2 value calculated from a fresh set of measured data falls inside the limits prescribed by a threshold value χ0TH2. The extent of damage is quantified by matching the χ0m2 value calculated from the measured data with the corresponding χ0p2 values predicted by using a benchmark finite element model. The use of χ02 values has been found to provide better sensitivity to structural damage than the natural frequency shift technique. The findings are illustrated in the case of a numerical case study of a simulated steel cantilever beam and an experimental cantilever beam. The analysis done on the numerical study showed that the sensitivity of the proposed technique ranged from three to 1000 times as much as the sensitivity of the natural frequencies. The results obtained from a laboratory structure showed that the extent of damage and the remaining service life could be accurately assessed up to a crack size corresponding to 0.55 of the material's thickness. It was observed that this crack size corresponded to the limiting crack size for the applicability of linear elastic fracture mechanics theory.