Issue 49

E.U.L. Palechor et alii, Frattura ed Integrità Strutturale, 49 (2019) 614-629; DOI: 10.3221/IGF-ESIS.49.56 618 Figure 6 : Damage positions in Case 2. The additional masses (M) add together 3.366 kg for Case-1 and 24.718 kg for Case-2. Supports The two beam specimens (Figs. 3 and 4) are simply supported. For that, the left and right ends of the beam are supported by two steel rollers held over thick steel plates. The right steel plate is plain, but the left steel plate has a notch to accommodate the steel roller. Details of these two supports can be seen in Figs. 7a and 7b. Observing these figures, the right support constraints displacements in X and Y directions and allows free translation in the Z-direction and the X-axis. The left support allows no translation just rotation around the X-axis. (a) Left Support. (b) Right support. Figure 7 : Detail for the simple supports at beam ends. It is important to emphasize that the supports constitute a fundamental part of the structure, restricting the degrees of freedom necessary for the stability of the beam. In this research, the two supports are fundamental for the process of damage identification, due to the influence of residual noise signals generated at the supports at the ends of the beam specimens. Such noises are caused by friction between the roller and the beam despite lubrification. The roller surfaces at the supports are kept at the same condition to avoid extra unknown noise sources [19]. Instrumentation In order to carry out the dynamic tests the following tools are used:  Signal Conditioner (Fig. 9a);  Accelerometer model 352C34 (Fig. 8a)  Accelerometer model 352C33 (Fig. 8b);  Instrumented hammer PCB model 086C0, with steel tip (Fig. 9b).  Computer with Lab-View software for data acquisition Fig. 10 shows details of the test scheme assemblage the steel beams in the Laboratory of Vibration and Dynamics of Systems of the University of Brasília. For the tests, two accelerometers are used, one of the accelerometers is located in the middle of the span (L / 2) and the second accelerometer is located at L / 4. (Fig. 11).