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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Roberto Paolucci

3Present EC8: normalized elastic response spectra for design

Type 1 Type 2

Roberto Paolucci

4

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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Roberto Paolucci

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)

21

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

8

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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.

Roberto Paolucci

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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Roberto Paolucci

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

Roberto Paolucci

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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Roberto Paolucci


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 PGA0.21Akkar 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)




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


Ssg = 0.85

Ssg = 0.2EC8 - C - Type1

EC8 - C - Type2


Vs,30= 300 m/s


Roberto Paolucci

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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)




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


Ssg = 0.85

Ssg = 0.2EC8 - C - Type1

EC8 - C - Type2


Vs,30= 200 m/s


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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"


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Roberto Paolucci

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


Roberto Paolucci

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

)

28

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


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Roberto Paolucci

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


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 !

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