نوع مقاله : پژوهشی اصیل (کامل)
کلیدواژهها
موضوعات
عنوان مقاله English
نویسندگان English
Damage occurrence is always inevitable in structures. So far, many examples of damage types in engineering structures have been recorded with many losses of human and financial. For this reason, the detecting of structural damages during its exploitation to provide safety with the lowest cost has been the subject of many researchers in the last two decades. In this regard, the wavelet transform is a powerful mathematical tool for signal processing, has attracted the attention of many researchers in the field of health monitoring of structures. Wavelets are a combination of a family of basic functions that are capable of detecting signals in the time (or location) and frequency (or scale) range. In fact, wavelet transform is based on the principle that any signal can be transformed into a set of local functions called wavelets. Any local feature of a signal can be analyzed using the corresponding wavelet functions. The wavelet transforms to the singularities points in the signals are sensitive and can be used to detect abrupt changes in modes, which often indicate damage. In this study, free vibrations of a four-story building with specified boundary conditions have been investigated and monitored the health of the building basis on experimental results using the continuous wavelet analytical method are studied and the damage that may occur in these structures has been evaluated and analyzed. Building modeling is done in finite element software using the sandwich model. In this four-story building, eight-layer sandwich panel (polystyrene, concrete, steel, concrete) is used symmetrically. The fourteen natural frequencies of the sandwich structure were compared with the experimental model. and the main modes of the structure obtained to influence the health of the structure. An error of less than 2.5% reveals a good match between the results of the two models. Changes in the values of natural frequencies and also the inconsistency of the modes shape، based on Modal Assurance Criterion (MAC) and the angle between modes of shape confirm the damage of the structure. Precast panel health monitoring results show that based on the experimental results, the damage location using the coif5 function with scale parameter 8 has been successfully identified and shows a higher perturbation of the coefficients at the damage locations than the other functions. Thus, the relative maximum and minimum jumps in the wavelet coefficients occurred at the location of the damage and considering the maximum or minimum wavelet coefficients generated at the damage location as the center of damage, the damage center can be identified with an error of less than 8%. The disturbance of the wavelet coefficients of each of the damage locations are independent of the other damage locations with different intensities. Also, the effect of higher modes is more pronounced in the damage intensity index as in the torsional modes of the structure, the maximum wavelet coefficients are greater and the intensity of the damage is increased. In addition, in the process of reducing the structural stiffness, the first and second stories play a more important role, and around the openings are the critical points of the structure.
کلیدواژهها English
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