Civil Engineering Reference
In-Depth Information
Table 3.1
Calculated eigen-frequencies and eigen-modes
Mode no.
f [Hz]
Character of eigen-mode
1.10
Torsion +
Horizontal
bending
1
1.63
Vertical bending
2
2.15
Vertical bending
3
4
2.49
Vertical bending
5
2.53
Torsion +
Horizontal
bending
6
3.12
Torsion +
Horizontal
bending
7
3.73
Torsion +
Horizontal
bending
8
3.76
Vertical bending
9
3.98
Torsion
+ Horizontal bending
10
4.69
Vertical bending
Fig. 3.4
First two eigen-modes of structure; (
a
) - axonometry and (
c
) - horizontal displacement of 1. lateral mode (f
¼
1.1 Hz); (
b
) - axonometry
and (
d
) - vertical displacements of 1. Vertical mode (f
¼
1.63 Hz)
frequencies, which lie in the critical vertical (1-5 Hz) and horizontal (0.5-2.5 Hz) range of the pedestrian step frequencies
are typed with bold. These eigen-frequencies and relevant mode shapes were analyzed with respect to the unacceptable
vibration. Five modes shapes of the first ten are identified as a combination of torsion and bending, the prevailing direction is
typed with italic. The first two eigen-modes are presented in Fig.
3.4
both in axonometry and in the plane view.
3.3.1 Comfort Criteria and Analysis of Human Induced Vibration
The effects of vibration on the human organism are usually expressed in terms of velocity as a function of frequency. This
approach is suitable especially for higher frequency oscillation. For lower frequencies that are characteristic for flexible
structures, the criterions are given in codes and hygienic regulations in the units of accelerations. The maximum accepted
