2.7 Logarithmic Decrement
55
Prob. 2.28
2.29 A one-storey building is idealised as a rigid girder having total weight W
and weighless columns. During the jacking operation while carrying out a
free vibration test, a horizontal force of 100 kN displaces the girder laterally by 0.5 cm. After the instantaneous release of this initial displacement,
the maximum displacement at the end of the first cycle is 0.4 cm. and the
time period is 1.4 s. Determine (a) the effective weight W of the girder, (b)
undamped frequency of vibration, (c) damping coefficient and (d) amplitude
after first 5 cycles.
Prob. 2.29
2.30 A system shown in the Fig. having k 1 = k 2 = 8 × 10
4 N/m and k 3 = 3 × 10
5
N/m and m = 250 kg. Determine the natural frequency of the system.
55
Prob. 2.28
2.29 A one-storey building is idealised as a rigid girder having total weight W
and weighless columns. During the jacking operation while carrying out a
free vibration test, a horizontal force of 100 kN displaces the girder laterally by 0.5 cm. After the instantaneous release of this initial displacement,
the maximum displacement at the end of the first cycle is 0.4 cm. and the
time period is 1.4 s. Determine (a) the effective weight W of the girder, (b)
undamped frequency of vibration, (c) damping coefficient and (d) amplitude
after first 5 cycles.
Prob. 2.29
2.30 A system shown in the Fig. having k 1 = k 2 = 8 × 10
4 N/m and k 3 = 3 × 10
5
N/m and m = 250 kg. Determine the natural frequency of the system.