Seismic action and site effects: work in progress for the ... · Seismic action and site effects:...
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Seismic action and site effects: work in progress for the revision of Eurocode 8
Roberto Paolucci
Department of Civil and Environmental Engineering, Politecnico di Milano
PSHA Workshop
Future Directions for Probabilistic Seismic Hazard Assessment at a Local, National and Transnational Scale
5-7 September 2017Lenzburg, Switzerland
Roberto Paolucci
2Present EC8: seismic hazard representation
- seismic hazard defined in terms of a single parameter, PGA
- national territory subdivided in zones, differentiated by PGA
- each country identifies the normalized elastic spectra for design based on either the Type 1 (M>5.5) or Type 2 (M<5.5) spectral shapes
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3Present EC8: normalized elastic response spectra for design
Type 1 Type 2
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T(s)T=1s
S1
Ss
long return period / high seismicity
short return period / low seismicity
combination of Ss and S1 parameters allows one:
to tune the ERSD for high and low seismicity regions within a single country
to tune the ERSD for long and short return periods within a single site
Definition of the Elastic Response Spectrum for Design
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5Elastic response spectrum
3.1.1.1 Horizontal elastic response spectrum
(1)P For the horizontal components of the seismic action, the elastic responsespectrum Se(T) is defined by the following expressions (see Figure. 3.1):
0
e :0F
STSTT S
A (3.2)
0e :
F
TTTT
TT
STSTTT B
AAB
SBA (3.3)
SSTSTTT eCB : (3.4)
T
STSTTT 1
eDC : (3.5)
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eD :T
STTSTT D (3.6)
topography factorlong period factor
short period factor
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6Elastic response spectrum
TC/TB
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7Elastic displacement spectrum 7
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Design peak values of ground motion8
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PGV9
residuals using the EC8 formula:PGV=0.16PGATC
residuals using this draft
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10PGD values on rock in Italy according to this proposal
reference values from long period PSHA
this proposal
present EC8
Italian norms
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11Spatial distribution of PGD in Italy
according to long periodPSHA
according to EC8 draft
according to present EC8
according to NTC 08
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12Vertical spectra
short-period V/H
long-period V/H
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13Vertical spectra
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14Vertical spectra
EC8 draft
present EC8
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15Vertical spectra
this proposal
present EC8
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16Present EC8: Site classification and site amplification factors
EC8 Site classification
EC8 Site amplification factors – Type 2
EC8 Site amplification factors – Type 1
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17Site categorization
(1) The profile of the shear wave velocity vs in the ground should be regarded as the most reliable predictor of the site-dependent characteristics of the seismic action at stable sites.
(2) To account for the influence of local conditions on the seismic action, the ground materials should be characterised at least down to 30 m depth, except if the bedrock formation is at a smaller depth.
(3) As a minimum requirement for seismic characterisation, the site should be classified according to a simplified description of the shallow geological materials. Parameters retained by EN 1998 for site categorization are:
- H800, the depth of the bedrock formation identified by vs larger than 800m/s,
- vS,H, the average superficial shear wave velocity, between the surface and the depth H defined by
H= 30 m if H800 30m (vS,H is then designated as vS,30.)H= H800 if H800 < 30m.
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18Present EC8: Site classification and site amplification factors
0 20 40 60 80 100 120100
200
300
400
500
600
700
800
H(m)
Fs EC8 Type 1
VsH
(m/s
)
1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
B
C
A
E
D
?
S values for Type 1 EC8
0 20 40 60 80 100 1200
0
0
0
0
0
0
0
H(m)
Fs EC8 Type 2
1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
B
C
A
E
D
?
S values for Type 2 EC8
"at least severaltens of m"
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19Site categorization in the EC8 draft
Table 3.1 Standard site categorisation
vS,H class high medium low
Depth class 800 m/s> vS,H > 400 m/s
400 m/s> vS,H > 250 m/s
250 m/s> vS,H > 150 m/s
very shallow H800 < 5 m A A E
shallow 5 m < H800 < 30 m B E E
intermediate 30 m < H800 < 100 m B C D
Deep 100 m < H800 < 200 m B F F
very deep H800 > 200 m B F F
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20Recommended site amplification factors
Site category Fs F1
H and vs,H available Default value H and vs,H available Default value
A 1,0 1,0 1,0 1,0
B 1,20 1,60
C 1,35 2,25
D 1,50 3,20
E 1.7 3,0
F 1,35 4,0
sHsv
25,0
,
800
170,0,
800
Hsv
104
3025,0
,
800
HH
Hssv
3070,0
,1
800
H
Hsv
sHsv
25,0,
80090,0
170,0,
80025,1
Hsv
2,
3 /1021 HssRPs vS 2,1
31 /1021 HsRP vS
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21Recommended site amplification factors
100 200 300 400 500 600 700 8001
1.05
1.1
1.15
1.2
1.25
1.3
1.35
1.4
1.45
Vs,30 (m/s)
Fs
SsRP
= 0.15 g
SsRP
= 0.45 g
SsRP
= 0.75 g
100 200 300 400 500 600 700 8001
1.5
2
2.5
3
3.5
Vs,30 (m/s)F
1
S1RP
= 0.05 g
S1RP = 0.15 g
S1RP = 0.25 g
Fs F1
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10-2
10-1
100
0
0.5
1
1.5
2
2.5
3
3.5
4Vs30(m/s) = 500
Period (s)
Akkar et al. 2013 PGA0.07
Akkar et al. 2013 PGA0.14
Akkar et al. 2013 PGA0.21Akkar et al. 2014 PGA0.28
Bindi et al. 2014
10-2
10-1
100
0
0.5
1
1.5
2
2.5
3
3.5
4
Period (s)
S/S
A
Response Spectral ratios vs Class A - proposed EC8 Spectra Vs30=500 m/s
Ssg = 0.85
Ssg = 0.2EC8 - B - Type1
EC8 - B - Type2
Recommended site amplification factors
comparison with European GMPEs
Vs,30= 500 m/s
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10-2
10-1
100
0
0.5
1
1.5
2
2.5
3
3.5
4Vs30(m/s) = 300
Period (s)
Akkar et al. 2013 PGA0.07
Akkar et al. 2013 PGA0.14
Akkar et al. 2013 PGA0.21Akkar et al. 2014 PGA0.28
Bindi et al. 2014
10-2
10-1
100
0
0.5
1
1.5
2
2.5
3
3.5
4
Period (s)
S/S
A
Response Spectral ratios vs Class A - proposed EC8 Spectra Vs30=300 m/s
Ssg = 0.85
Ssg = 0.2EC8 - C - Type1
EC8 - C - Type2
Recommended site amplification factors
Vs,30= 300 m/s
comparison with European GMPEs
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10-2
10-1
100
0
0.5
1
1.5
2
2.5
3
3.5
4Vs30(m/s) = 200
Period (s)
Akkar et al. 2013 PGA0.07
Akkar et al. 2013 PGA0.14
Akkar et al. 2013 PGA0.21Akkar et al. 2014 PGA0.28
Bindi et al. 2014
10-2
10-1
100
0
0.5
1
1.5
2
2.5
3
3.5
4
Period (s)
S/S
A
Response Spectral ratios vs Class A - proposed EC8 Spectra Vs30=200 m/s
Ssg = 0.85
Ssg = 0.2EC8 - C - Type1
EC8 - C - Type2
Recommended site amplification factors
Vs,30= 200 m/s
comparison with European GMPEs
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25Recommended site amplification factors
comparison with NEHRP 2015
EC8 proposal(Ss=0.45g – S1= 0.15g)
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0 20 40 60 80 100 120100
200
300
400
500
600
700
800
H(m)
Fs EC8 Type 2
VsH
(m/s
)
1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
0 20 40 60 80 100 120100
200
300
400
500
600
700
800
H(m)
Fs
VsH
(m/s
)
B
C
D
EF
AB
C
A
E
D
?
Fs values for low seismicitySs=0.20g S1=0.05g
Fs ( S) values for Type 2 EC8
"at least severaltens of m"
Recommended site amplification factors
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0 20 40 60 80 100 120100
200
300
400
500
600
700
800
H(m)
Fs
VsH
(m/s
)
0 20 40 60 80 100 120100
200
300
400
500
600
700
800
H(m)
Fs EC8 Type 1
VsH
(m/s
)
1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
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B
C
D
EF
AB
C
A
E
D
?
Fs values for high seismicitySs=0.75g S1=0.25g
Fs ( S) values for Type 1 EC8
Recommended site amplification factors
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0 20 40 60 80 100 120100
200
300
400
500
600
700
800
H(m)
F1 EC8 Type 2
VsH
(m/s
)
1
1.5
2
2.5
3
3.5
4
0 20 40 60 80 100 120100
200
300
400
500
600
700
800
H(m)
F1
VsH
(m/s
)
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B
C
D
EF
AB
C
A
E
D
?
F1 values for low seismicitySs=0.20g S1=0.05g
F1 ( STC/TCA) values for Type 2 EC8
Recommended site amplification factors
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0 20 40 60 80 100 120100
200
300
400
500
600
700
800
H(m)
F1 EC8 Type 1
VsH
(m/s
)
1
1.5
2
2.5
3
3.5
4
0 20 40 60 80 100 120100
200
300
400
500
600
700
800
H(m)
F1
VsH
(m/s
)29
B
C
D
EF
AB
C
A
E
D
?
F1 ( STC/TCA) values for Type 1 EC8F1 values for high seismicitySs=0.75g S1=0.25g
Recommended site amplification factors
Roberto Paolucci
30Conclusions
(1) Recall that seismic norms address generic sites: a recipe suitable for whatever specific-site is impossible. Site-specific analyses should be encouraged (or enforced in some cases)
(2) Drafting European norms implies a compromise between very different points of view and constraints from Countries having conflicting interests and different approaches to the seismic problem.
(3) Also, a compromise between ease-of-use and scientific soundness should be found. This implies smoothing complexity and pinpointing those elements that, although extremely interesting from the scientific point of view, are costly to be quantified and do not imply major variations in the design solution.
(4) Finally, the compromise between safety and costs, that is at the actual basis of any seismic norm.
With so many compromises, the optimum solution is not possible!
Thank you !