PSI - Issue 81

Mykhailo Hud et al. / Procedia Structural Integrity 81 (2026) 486–492

489

Fig 4. First form oscillations of basic frame model

Frequency (Hz)

10 12 14 16

0 2 4 6 8

Frequency (Hz)

1

2

3

4

5

6

7

8

9

10

11

Mode

Fig 5. Frequencies of 1 opening frame model The graph (Fig. 5) shows the increase in the natural frequencies of the frame structure with an opening in the floor slab depending on the mode number. The initial frequencies, ranging from 1.331 to 1.342 Hz, establish a compact low-frequency range, a characteristic feature of the initial global vibration modes. The frequencies then increase gradually and steadily from 2.160 Hz up to around 8.06 Hz, with no sharp jumps, indicating smooth transitions between the vibration modes. The highest frequencies, ranging from 12.584 to 12.834 Hz, are associated with stiffer, more localized modes and more complex structural deformations. It is evident from the spectrum that the structure possesses adequate rigidity, with a seamless transition from global to local modes, devoid of any aberrant fluctuations or abrupt changes in its dynamic behaviour.

Fig 6. First form oscillations of 1 opening frame model