PSI - Issue 61

Adil Ziraoui et al. / Procedia Structural Integrity 61 (2024) 171–179 Adil Ziraoui et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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2.2. Ground motion record The seismic response of structures to ground motions is a crucial area of earthquake engineering. This response can be classified into two distinct displacement history models, which are closely dependent on the seismic rupture process and the associated directivity effect (Deierlein et al. 2003, Moehle et al. 2004). The first model concerns forward directivity. When seismic rupture propagates towards a given site and the direction of slip on the fault is aligned with the location of the site in question, ground motions oriented in the direction of forward directivity can generate seismic pulses. These pulses are characterized by a long period, short duration, and high amplitude. In other words, they manifest themselves as intense seismic jolts that occur at the start of the seismic record. Forward directivity occurs when the fault rupture propagates at a speed close to that of shear waves. Under these conditions, the displacement associated with this shear wave velocity is greatest in the direction normal to the fault, particularly for strike-slip faults (Spacone et al. 2004). This characteristic is generally observed in seismic records of velocity or displacement. The second model relates to lateral directivity. In contrast to forward directivity, lateral directivity occurs when the seismic rupture propagates laterally in relation to the site location. In this case, ground motions are predominantly horizontal and can generate seismic shocks that are more prolonged in time, but with a generally lower amplitude than those associated with forward directivity. Lateral directivity is often observed when the speed of rupture propagation is lower than the speed of shear waves (Mazza et al. 2010, Smerzini et al. 2014), To carry out a non-linear analysis of the temporal evolution of the seismic response of a structure, it is essential to have precise data on the ground motion generated by the earthquake under study. In this case, we have used a series of ground motions from a magnitude 6.9 earthquake (Figure 5). The key values associated with this ground motion are PGA = 0.35 g, PGV = 27.38 cm/s, and PGD = 9.7 cm (Table 3).

Table 3. Information of the selected Kobe waves.

Event

Date sss

eSdtation

M w 6.9

PGA (g)

PGV (cm/s)

PGD (cm)

Kobe, Japan

16/01/1995

Kakogawa

0,35

27,38

9,7

0.3

1.2

0.4

0.25

0.3

1

0.2

0.2

0.8

0.1

0.15

0.6

0

0.1

Sa (g)

0.4

0

10

20

30

40

Power amplitude

-0.1

0.05

Acceleration [g]

0.2

-0.2

0

0

0

2

4

6

8

10

0

1

2

3

4

-0.3

Frecency (Hz)

Time (s)

Time (s)

(a) Acceleration time history curve

(b) Acceleration response spectrum Fig. 5. Characteristics of Kobe waves.

(c) Energy spectrum

3. Analytical Results To facilitate comparison, various seismic responses including storey displacement, base shear, column forces, overturning moment, and inter-storey drift are computed. Tables 4 and 5 present significant results for different parameters across various building models. It appears that base isolation proves effective, as evidenced by the seismic responses in base-isolated structures compared to those in fixed base RC buildings. It is essential to note that the building benefiting from base isolation has a significantly lower maximum storey displacement compared to traditional reinforced concrete construction with a fixed base. This significant difference can be clearly seen in the data provided in Figure 6, demonstrating the effectiveness of the base isolation approach in reducing undesirable seismic movements and thus improving building stability and safety.