PSI - Issue 57

Qingyang Wei et al. / Procedia Structural Integrity 57 (2024) 262–270 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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drop at the crack tip, accurately indicating the location of the crack. All three curves show high CCSC values in the uncracked zone and small CCSC values in the cracked zone. Nevertheless, the abnormally high values of the cracked point on the left side of the crack tips as shown in Fig. 9 (b) and Fig. 9 (c) can interfere with damage diagnosis. This interference occurs when the number of strain gauges is small, and not occurs when the number of strain gauges is enough to characterize the entire CCSC curve.

Fig. 9. Correlation coefficients of the dynamic strain curves, (a) depth=0 mm; (b) depth=20 mm; (c) depth=60 mm; (d) depth=100 mm; (e) depth=140 mm. 5. Conclusions and prospects This study presents the problem of fatigue cracks found on a steel bridge over the Danube River. The fatigue cracks at the upper seam of the vertical rib are considered and analyzed. Two damage features are used to analyze the effect of the fatigue crack on the dynamic responses of the steel bridge, which are the decrease of high-order frequencies and the weakening of local normal stress correlation. Some detailed conclusions can be drawn as follows: (1) The local impact makes the vertical rib has obvious local vibration along the impact direction. The global vibrations of the steel bridge that exist in the other two directions are caused by the secondary vibration of the impact. (2) The local vibration mode of the steel bridge is obtained by local excitation and local measurement on the vertical rib, which reflects the vibration information of the vertical rib. The local vibration frequency of the vertical rib is sensitive to its crack, and the global vibration frequency of the steel bridge is not sensitive to the minor crack on the vertical rib. (3) The existence of cracks leads to the loss of stress correlations on opposite sides near the crack, while the stress correlations on opposite sides of the uncracked zone are highly consistent. (4) The CCSC values calculated by the pairs of stress curves remain low in the cracked zone, close to 1 in the uncracked zone, and have an obvious abrupt decline at the crack tip. The study is a numerical verification of the two proposed detection strategies based on model of the Türr Istvan Danube bridge. The most urgent further work is to carry out practical validation on this bridge . For damage feature 1, an accelerometer and a force hammer are required. For damage feature 2, the loads required will be environmental