PSI - Issue 64

Pavel Ryjáček et al. / Procedia Structural Integrity 64 (2024) 228 – 237 Pavel Ryjacek / Structural Integrity Procedia 00 (2019) 000 – 000

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For detection by advanced methods, it can be stated that they are designed to locate areas of reduced stiffness. Thus, for the temperature change of the structure, this localization is not relevant. However, these methods have been used to see if they can have an effect on failure localization when multiple effects are combined. The cooling was seen as an increase in the stiffness of the structure and influenced the modal flexibility matrix [  ], see Fig. 7. As for the manifestation of the second derivative of the change of the diagonal terms of the modal flexibility matrix [  ] or to the change of the curvature of the CAMOSUC(j),x, the manifestation is minimal. 8. Effect of end segment support stiffness Furthermore, the model was modified by changing the rotational stiffness of the end segments. This is based on the fact that over time the elastomer of the bearings ages and its elastic modulus increases, while flooding may have caused blockage of the narrow gap at the bearings. Also, the inspection in 2013 also states that some bearings have been moved or displaced or the bridge could get to the contact with bearings (as originally, the bridge was probably supposed to lift from them due to the prestressing force, unfortunately, no photo is available). It is evident that failure is shown in the change of the 6th and 7th mode shape. see Fig. 8.

Fig. 8 Comparison of the 7th mode shape for 3 variations of the end segment support stiffness with the undamaged model

A very strong correlation is seen with the change in the measured 7th eigenmode between 2010 and 2013. According to the comparison, it can be concluded that the vertical stiffness of the support has been increased to about 400%, see Fig. 9.

Fig. 9. Visual comparison of the measured mode shape f 8 = 1.53 Hz and the 7th measured shape from November 2010, f 7 = 1.62 Hz

For detection by advanced methods, the shapes are compared when the vertical support stiffness was increased to 400%. This effect resulted in an increase in stiffness in the edge spans near the supports. The increased values of the second derivative of the change in the diag. members of the modal flexibility matrix [  ] for the model with 86 sections indicate the location of the defect, but for the model with 24 sections, these values are significantly lower. Also, the values of CAMOSUC(j),x. indicate the location of the defect for the 86-section variant, but these values are again lower for the 24 sections. The highest effect is shown for the 8 th and 10 th shape, see Fig. 10.