PSI - Issue 44

Paola Sorrentino et al. / Procedia Structural Integrity 44 (2023) 1300–1307 Paola Sorrentino et al. / Structural Integrity Procedia 00 (2022) 000–000

1302

3

a maximum spectral acceleration of 0.92g at 0.25s (Figure 1a) and a maximum spectral displacement of 31.53cm at 3s (Figure 1b).

4

140

1940, Imperial Valley - El Centro (S90W) 1940, Imperial Valley - El Centro (S00E)

1940, Imperial Valley - El Centro (S90W) 1940, Imperial Valley - El Centro (S00E)

3.5

120

1952, Kern County - Taft Lincoln School Tunnel (S69E) 1952, Kern County - Taft Lincoln School Tunnel (N21E) Envelope

1952, Kern County - Taft Lincoln School Tunnel (S69E) 1952, Kern County - Taft Lincoln School Tunnel (N21E) Envelope

3

100

2.5

80

2

60

1.5

acceleration (g)

40

1

20 displacement (cm)

0.5

0

0

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3

T (s)

T (s)

(b)

(a)

Figure 1. Trevor Kelly (2001) spectra: pre 1971. Spectral accelerations (a); Spectral displacements (b).

The second category, the post 1971 motions, consists of earthquake records in which ground accelerations are much higher. The increasing in the number of seismic arrays for recording ground motions and the consequent availability of the number of strong motion data showed unexpected values, with several accelerations exceeding 1g. The strong motion data chosen by Kelly are from 1979 El Centro, 1985 Mexico City, 1989 Loma Prieta, 1992 Landers, 1994 Northridge events. Their acceleration response spectra (Figure 2a) show completely different forms, having: peaks also for period between 2 and 3s (1979 El Centro Earthquake, Array 6 Station and 1985 Mexico City Earthquake, SCT1 Station); constant values for period between 2 and 4s (1992 Landers Earthquake, Lucerne Station); spectral accelerations exceeding 2.5g at short periods and exceeding 0.5g at longer periods (1994 Northridge Earthquake, Sylmar County Hospital Station). The envelope of displacement response spectra (Figure 2b) shows a trend increasing with the period, with a maximum spectral displacement of 116cm at 3s.

1979, Imperial Valley - Array 6 (230) 1979, Imperial Valley - Array 6 (140)

4

140

1985, Mexico City - SCT1850919BL.T (S00E) 1989, Loma Prieta - Hollister - South & Pine (90) 1989, Loma Prieta - Hollister - South & Pine (00) 1992, Landers - Lucerne (00) 1992, Landers - Lucerne (270) 1994, Northridge - LA Sepulveda (270) 1994, Northridge - LA Sepulveda (360) 1994, Northridge -Sylmar County Hospital (90) 1994, Northridge -Sylmar County Hospital (360) Envelope

3.5

120

3

100

2.5

80

2

60

1.5

40

1 accelerazione (g)

20 displacement (cm)

0.5

0

0

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3

T (s)

T (s)

(b)

(a)

Figure 2. Trevor Kelly (2001) spectra: post 1971. Spectral accelerations (a); Spectral displacements (b).

2.2. FEMA307 (1999)

In FEMA307 (1999), the ground motions have been chosen with the aim of identifying possible effects of duration and forward directivity on the response of damaged structures. For this reason, three categories of ground motions were established: Short Duration (SD), Long Duration (LD) and Forward Directivity (FD). For each category, they have been chosen records familiar to the research community. The acceleration response spectra of the short duration category (Figure 3a) exhibit peak values at different range period: 2.30g at 0.3s (1992 Big Bear Earthquake, Civic Center Grounds Station), 1.38g between 0.55 and 0.8s (1989 Loma Prieta Earthquake, Corralitos Station) and 0.77g at 0.7s (1979 Imperial Valley Earthquake, Array 7 Station). The displacement response spectra (Figure 3b) show constant values for periods higher than 1s, with the exception of the 1979 Imperial Valley spectrum, in which the values increase with increasing periods. The maximum spectral displacement is equal to 41.35cm at 3s.