PSI - Issue 42

Taško Maneski et al. / Procedia Structural Integrity 42 (2022) 1503–1511 T. Maneski at al/ Structural Integrity Procedia 00 (2019) 000 – 000

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outside the robots’ work space. Therefore, in the next step of the theoretical study, we determined the transfer function in the frequency domain. The dynamic gains of the amplitude of static deformations for the selected excitations were calculated. The location in the support structure of the excitation and where the appropriate responses were measured is shown in Figure 4 (red circle). The results obtained are shown in Figures 6 and 7. Figure 6 shows the responses in the three directions, and the total response, resulting from excitation in the x-direction.

Response in x- direction

Response in y- direction

Response in z- direction

Total response

Figure 6. Transfer functions from excitation in x-direction (horizontal axis shows the frequency in Hz, corresponding gain is on the vertical axis)

Excitation in the x-direction produced the highest response in the vertical y direction, about 60, while the response in the z -direction was half that intensity. Figure 7 shows the responses resulting from excitation in the y direction and in the z -direction.

Response in x- direction

Total response

Response in x- direction

Total response

Transfer functions from excitation in y direction

Transfer functions from excitation in z direction

Figure 7. Transfer functions from excitation in y and z directions (horizontal axis - frequency in Hz, corresponding gain - vertical axis)

Excitation in the vertical direction caused a large increase in deformation in the horizontal longitudinal direction, while much smaller increases occurred in the other two directions. Excitation in the z -direction also produced great deformation in the longitudinal direction. It was noticeable that the corresponding frequencies were mostly between 5 Hz and 20 Hz, which was in accordance with the previously presented calculated frequencies. Figures 6-7 show that the dynamic gain factor of the excitation forces in all three directions was extremely large, which again indicated the support structure had very poor dynamic behavior. 3. Visual inspection of the structure During the first visual inspection of the support structure, some deficiencies in the construction were noticed. Figure 8 shows the extremely large, plastic deformation of the upper horizontal flange of an I-girder, and it was clear that no welded joints had been made along the entire length of this girder during the installation of the upper plate. There were numerous screw connections on the construction that could and had loosened over time, and a large number of them were located inappropriately, so they could not be adequately tightened. There were numerous unwelded joints along the entire length of some girders in places where welding was clearly necessary, while in other places, welding had been only partially done. In several places, the vertical flanges of supporting beams had been cut, and had been left without the addition of ribs in order to strengthen them; some of these steel flanges were already quite plastically deformed.