Challenges for the Next Generation of Seismic Codes - Earthquake Engineering for Structural Design - page 504

Figure 10.26 Influence of number and succession of velocity pulses
(Gioncu et al, 2000)
The frame of Figure 10.20a (with periods T 1 = 0.90sec, T 2 = 0.26 sec and T 3 =
0.13 sec), designed for acceleration of code 0.16g, was analyzed using different
velocity pulses (Fig. 10.28) One can see that for very short pulse period (0.20 sec),
a medium value between second and third structure periods, the plasticization
began at the top of frame and the global collapses mechanism occurs at 1.6g, ten
times of design acceleration. For higher velocity pulse period (0.50 sec), a medium
value between first and second vibration modes, the collapse acceleration is 0.45g,
2.8 times the design acceleration. Contrary, for the highest pulse period,
corresponding to the first period, the collapse acceleration is 0.22g, only 1.38 times
the design spectra. This analysis clearly shows the importance of the highest
vibration modes in determining the behavior of structures under low to moderate
earthquakes.