Issue 49

E.U.L. Palechor et alii, Frattura ed Integrità Strutturale, 49 (2019) 614-629; DOI: 10.3221/IGF-ESIS.49.56 628 Figs. 25 and 26 show the graphs corresponding to DWT applied to the signal in Fig. 24 and considering the use of the four mother wavelet functions (rbio2.6, bior6.8, sym6, db5). In the previous figures (Figs. 25 and 26), it can be observed that the biggest peak was generated between nodes 24 and 29, matching the damage located in between nodes 26 and 28, corresponding to Damage-1 and Damage-2, respectively. The techniques of signal interpolation with the cubic spline in the frequency domain and the method of main lobe correction showed good results. C ONCLUSIONS his research paper presented a new experimental methodology to locate damages in steel beams with simulated damages. The proposed methodology used just the measure of the fundamental frequency of a vibrating beam with an added mass positioned at different points along the beam. Two cases were analyzed in this research: Case-1 and Case-2, respectively, with 5m along and 6m in Beam-1 and Beam-2 respectively, with 5 m and 6 m long. Both beams are steel I-section available in the market made of steel. Beam-1 was 5 m long and Beam-2 6 m long. The damage can be detected observing the peaks of the Discrete Wavelet Transformation (DWT) of the signal representing the variation of the fundamental frequency vs. the Added Mass Positions (AMP). The method was tested with small and big simulated cracks. A set of one or more cracks was considered a damage and, in practice, it may be thought of as an equivalent deterioration of a beam cross section. The best result was achieved in Case 1 of Beam-1 for the detection of the biggest damage which center is located at 1.5 m to the left end of Beam-1. This damage corresponds to a cluster of notches of 3 mm straight cuts made at the beam flanges and spaced 2.5 cm one each other. This damage can be seen in Fig. 2. Beam-1 was subdivided in 26 nodes, spacing between nodes equal to 20 cm. The damages are located between nodes 8-9 and 23-24, respectively. Along those positions, the added mass was positioned. It was possible to clearly identify the damage using just the first frequency and the proposed methodology with an added mass of 3.266 kg. The detection was possible observing the peaks signal of the first frequency vs. the added mass position; i.e., DWT-f1 vs. AMP curve. Such curve also shows noises of DWT-f1 signals at the extremes of Beam-1. These false peaks are noises due to the natural discontinuity of the beam at its ends. Concerning smaller damages, the paper tested the proposed methodology for the detection of Damage-2. This damage corresponds to just one third of Damage-1. It was located also closed to a region showing noise signals, the region next to the right end of Beam-1. Again it was possible to detect the damage just observing the peaks of the curve DWT-f1 vs. AMP. For Case-2 in Beam-2, two clusters of damages were located close to the supports of the beam. Beam-2 was subdivided in 31 nodes with the same space of 20 cm as used in Beam-1. Along those nodes the added mass was positioned. Damage-1 and Damage-2 were located, respectively and exactly, over node 26 and node 28. Such positions correspond, respectively, to 0.6 m and 1.0 m away from the right end of the beam. In Case-2, as in Case-1, the curves DWT-f1 vs. AMP were built and the signal peaks observed. The added mass employed in Case-2 was 24.718 kg. The results showed peaks from node 21 to node 29, and big spikes next to the real positions of the simulated damages (Damage-1 and Damage-2). In Case-2, the locations of the Damage-1 and Damage-2, despite not being detected precise by as in Case-1, narrow down the spans one might be concerned to find damages. The experimental study shows it is possible to detect the exact damage position and the position near the damaged area using the proposed methodology. Therefore, with the proposed methodology it is possible to help to find the location of damages along steel beams just using the fundamental frequency of the damaged beams without the previous knowledge of the response of the undamaged structure. R EFERENCES [1] Aktan A. E, Farhey D. N, Helmicki A. J. (1997). Structural Identification for Condition Assessment: Experimental Arts. Journal of Structural Engineering., 123, pp. 1674–1684. DOI:10.1061/(asce)0733-9445(1997)123:12(1674) [2] Breysse D, Klysz G, Dérobert X, C. et al. (2008). How to combine several non-destructive techniques for a better assessment of concrete structures. Cement and Concrete Research., 38, pp. 783–793. DOI:10.1016/j.cemconres.2008.01.016. [3] Schabowicz K. (2010). State-of-the-art non-destructive methods for diagnostic testing of building structures – anticipated development trends. Archives of Civil and Mechanical Engineering., 10, pp. 8–9. DOI:10.1016/s1644-9665(12)60133-2 . T