EUROCODE 8
Background and Applications
Dissemination of information for training – Lisbon, 10-11 February 2011
1
Ground conditions and seismic action
Eduardo C Carvalho
GAPRES SA
Ch i
Chairman
TC250/SC8
Ground conditions
Dissemination of information for training – Lisbon 10-11 February 2011
2
Earthquake vibration at the surface is strongly influenced
b the
by
th underlying
d l i ground
d conditions
diti
EN 1998-1 requires that appropriate investigations (in situ
or in
i the
th laboratory)
l b
t
) mustt be
b carried
i d outt in
i order
d to
t
identify the ground conditions, with two main objectives:
• allow the classification of the soil profile, in view of
defining
g the ground
g
motion appropriate to the site ((i.e.
allowing the selection of the relevant spectral shape)
• identify the possible occurrence of soil behaviour
during an earthquake detrimental to the response of
th structure
the
t
t
Ground conditions
Dissemination of information for training – Lisbon 10-11 February 2011
Five ground types:
A - Rock
B - Very dense sand or gravel or very stiff clay
C - Dense sand or gravel or stiff clay
D - Loose to medium cohesionless soil or soft to
firm cohesive soil
E - Surface alluvium layer C or D, 5 to 20 m thick,
over a much stiffer material
2 special ground types S1 and S2 requiring special studies
Ground conditions defined by shear wave velocities in the top
30 m and also by indicative values for NSPT and cu
3
Ground conditions
Dissemination of information for training – Lisbon 10-11 February 2011
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Table 3.1: Ground types
Ground
type
Description of stratigraphic profile
Parameters
vs,30 (m/s)
NSPT
cu (kPa)
(blows/30cm)
 800
A
Rock or other rock-like
rock like geological
formation, including at most 5 m of
weaker material at the surface.
B
Deposits of very dense sand, gravel, or 360 – 800
very stiff clay, at least several tens of
metres in thickness,, characterised byy a
gradual increase of mechanical
properties with depth.
_
_
 50
 250
Ground conditions
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Table 3.1: Ground types
Ground
type
Description of stratigraphic profile
Parameters
vs,30 (m/s)
NSPT
cu (kPa)
(blows/30cm)
C
Deep deposits of dense or medium
mediumdense sand, gravel or stiff clay with
thickness from several tens to many
hundreds of metres.
metres
180 – 360
D
Deposits of loose-to-medium
 180
cohesionless soil ((with or without some
soft cohesive layers), or of
predominantly soft-to-firm cohesive
soil.
15 - 50
70 - 250
 15
 70
Ground conditions
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Table 3.1: Ground types
Ground
type
Description of stratigraphic profile
Parameters
vs,30 (m/s)
NSPT
cu (kPa)
(blows/30cm)
E
A soil profile consisting of a surface
alluvium layer with vs values of type C
or D and thickness varying between
about 5 m and 20 m, underlain by
stiffer material with vs > 800 m/s.
m/s
S1
Deposits consisting, or containing a
layer at least 10 m thick, of soft
clays/silts
l / ilt with
ith a high
hi h plasticity
l ti it index
i d
(PI  40) and high water content
S2
Deposits
p
of liquefiable
q
soils,, of
sensitive clays, or any other soil profile
not included in types A – E or S1
 100
((indicative)
d c ve)
_
10 - 20
Seismic zonation
Dissemination of information for training – Lisbon 10-11 February 2011
Competence of National Authorities
Described by agR (reference peak ground
acceleration
l
ti on type
t
A ground)
d)
Corresponds to the reference return period TNCR
agR modified by the Importance Factor  I to
become the design ground acceleration (on type
A ground) ag = agR . I
Objective for the future updating of EN1998-1:
p
zonation map
p with spectral
p
values for different
European
hazard levels (e.g. 100, 500 and 2.500 years)
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Seismic zonation
Dissemination of information for training – Lisbon 10-11 February 2011
8
Seismic Hazard Analysis
Attenuation relationships
valid for:
• Intraplate seismicity
seismicit (Europe)
(E rope)
• Rock sites
• 4.0 < M < 7.3
•3 km < R < 200 km
Spectral law:
log SA [g] = c1 + c2M + c4 logR
T (s)
PGA
0.10
0.20
0.30
0.40
0.50
1.00
1 50
1.50
2.00
C'1
C2
C4
h0

-1.48
-0.84
-1.21
-1.55
-1.94
-2.25
-3.17
-3 61
-3.61
-3.79
0.27
0.22
0.28
0.34
0.38
0.42
0.51
0 52
0.52
0.50
-0.92
-0.95
-0.92
-0.93
-0.89
-0.91
-0.89
-0 82
-0.82
-0.73
3.50
4.50
4.20
4.20
3.60
3.30
4.30
3 00
3.00
3.20
0.25
0.27
0.27
0.30
0.31
0.32
0.32
0 31
0.31
0.32
agR - reference
e peak ground accelera
ation
Sample law: Ambraseys et al. [1996]
320
Mag=5.0
M
50
Mag=6.0
280
240
Mag=6.5
M 70
Mag=7.0
200
160
120
80
40
0
10
100
Distância [km]
1000
Spectral shape
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Se ((g)
Effect of Magnitude on Response Spectra (Rock, 5% damping)
0.35
0.30
R = 30 km
0.25
Magnitude
0.20
5
0.15
6
6,5
0.10
7
0.05
0.00
0
0.5
1
1.5
Period T (s)
2
Spectral shape
Dissemination of information for training – Lisbon 10-11 February 2011
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Se //ag
Effect of Magnitude on normalised shape (Rock, 5% damping)
3.00
2.50
R = 30 km
Magnitude
2.00
5
1.50
6
1.00
6,5
7
0.50
0.00
0
0.5
1
1.5
Period T (s)
2
Spectral shape
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Effect of Epicentral Distance on Response Spectra
Se (g)
(Rock, 5% damping)
0.30
0 25
0.25
M=6
0.20
Distance (km)
0.15
15
30
0.10
50
100
0.05
0.00
0
0.5
1
1.5
Period T (s)
2
Spectral shape
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Effect of Epicentral Distance on normalised shape
Se /a
ag
(Rock, 5% damping)
2.50
2.00
M=6
Distance (km)
1.50
15
30
1.00
50
100
0.50
0.00
0
0.5
1
1.5
Period T (s)
2
Basic representation of the seismic action in Eurocode 8
Dissemination of information for training – Lisbon 10-11 February 2011
Elastic response
p
spectrum
p
Common shape
p for the ULS and DLS verifications
2 orthogonal independent horizontal components
Vertical spectrum shape different from the
horizontal spectrum (common for all ground types)
Possible use of more than one spectral shape (to
model different seismo-genetic
seismo genetic mechanisms)
Account of topographical effects (EN 1998-5) and spatial
variation of motion (EN1998-2) required in some special cases
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Definition of the horizontal elastic response spectrum
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Four branches
0  T  TB
Se (T) = ag . S . (1+T/TB . ( . 2,5 -1))
TB  T  TC
Se (T) = ag . S .  . 2,5
TC  T  TD
Se ((T)) = ag . S .  . 2,5 ((TC /T))
TD  T  4 s
Se (T) = ag . S .  . 2,5 (TC . TD /T 2)
Se (T)
ag
TB TC TD
S

elastic
l ti response spectrum
t
design ground acceleration on type A ground
corner p
periods in the spectrum
p
((NDPs))
soil factor (NDP)
damping correction factor ( = 1 for 5% damping)
Additional information for T > 4 s in Informative Annex
Normalised elastic response spectrum
Dissemination of information for training – Lisbon 10-11 February 2011
Standard shape
Control variables
• S, TB, TC, TD (NDPs)
(
)
• ( 0,55) damping
correction for   5 %
Fixed variables
• Constant acceleration,
acceleration
velocity & displacement
spectral branches
• acceleration spectral
amplification: 2,5
15
Normalised elastic response spectrum
Dissemination of information for training – Lisbon 10-11 February 2011
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  10 / 5     0,55
Corre
ection facto
or η
Correction for damping
1.6
14
1.4
1.2
1
0.8
0.6
0.4
0.2
0
0
5
10
15
20
25
30
Viscous damping ξ (%)
To be applied only to elastic spectra
Elastic response spectrum
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Two types of (recommended) spectral shapes
Depending on the characteristics of the most
significant earthquake contributing to the
local hazard:
• Type
yp 1 - High
g and moderate seismicity
y regions
g
(Ms > 5,5 )
ype 2 - Low
o seismicity
se s c ty regions
eg o s (Ms  5,5 );
• Type
near field earthquakes
Optional account of deep geology effects (NDP) for the definition
of the seismic action
Recommended elastic response spectra
Dissemination of information for training – Lisbon 10-11 February 2011
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Normalised shape for Type 1 and Type 2 seismic action (rock)
3.00
Se /ag
R = 30 km
M
Magnitude
it d
2.50
5
2.00
6
1.50
6,5
7
1.00
EN1998 1 type 1
EN1998-1
0.50
EN1998-1 type 2
0.00
0
0.5
1
1.5
2
Period T (s)
Recommended elastic response spectra
Dissemination of information for training – Lisbon 10-11 February 2011
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Recommended parameters for the definition of
th response spectra
the
t for
f various
i
ground
d types
t
Seismic action Type 1
Seismic action Type 2
Ground
Type
yp
S
TB (s)
TC (s)
TD (s)
S
TB (s)
TC (s)
TD (s)
A
1,0
0,15
0,4
2,0
1,0
0,05
0,25
1,2
B
,
1,2
0,15
,
0,5
,
2,0
,
1,35
,
0,05
,
0,25
,
1,2
,
C
1,15
0,2
0,6
2,0
1,5
0,1
0,25
1,2
D
1,35
0,2
0,8
2,0
1,8
0,1
0,3
1,2
E
1,4
0,15
0,5
2,0
1,6
0,05
0,25
1,2
Recommended elastic response spectra
Dissemination of information for training – Lisbon 10-11 February 2011
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Se/ag
Se/ag
5
4
E
4
D
C
3
3
B
A
2
1
0
0
0
1
2
A
2
1
0
D
E
C
B
3
T(s) 4
Type 1 - Ms > 5,5
1
2
3
4
T(s)
Type 2 - Ms  5,5
Recommended elastic response spectra
Dissemination of information for training – Lisbon 10-11 February 2011
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4
Se/ag
E
D
C
3
B
A
2
1
0
0
1
Type 1 - Ms > 5,5
2
3
T (s)
4
Recommended elastic response spectra
Dissemination of information for training – Lisbon 10-11 February 2011
Se/ag
5
22
D
E
C
4
B
3
A
2
1
0
0
1
Type 2 - Ms  5,5
2
3
T (s)
4
Definition of the vertical elastic response spectrum
Dissemination of information for training – Lisbon 10-11 February 2011
Four branches
0  T  TB
Sve (T) = avg . (1+T/TB . ( . 3,0 -1))
TB  T  TC
Sve (T) = avg .  . 3,0
TC  T  TD
Sve ((T)) = avgg .  . 3,0 ((TC /T))
TD  T  4 s
Sve (T) = avg .  . 3,0 (TC . TD /T 2)
Sve (T)
vertical elastic response spectrum
avg
vertical design ground acceleration on type A ground
TB TC TD corner periods
i d iin th
the spectrum
t
(NDP
(NDPs))

damping correction factor ( = 1 for 5% damping)
Soil factor not influencing the vertical response spectrum
23
Definition of the vertical elastic response spectrum
Dissemination of information for training – Lisbon 10-11 February 2011
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Recommended parameters
Sve/a
ag
3
2.5
EN1998-1
Vertical Elastic
Seismic
action
avg/ag TB (s) TC (s) TD (s)
Type 1
0,90
0,05
0,15
1,0
Type 2
0,45
0,05
0,15
1,0
2
1.5
1
Type 1
Type 2
0.5
0
0
1
2
3
Period T (s)
Displacements

TD
TC
S

ag

5
2
0
,
0
Design ground displacement
dg
Dissemination of information for training – Lisbon 10-11 February 2011


Elastic displacement response spectrum in Informative
Annex A of EN 1998-1
1998 1
Soil
TE
(s)
TF
(s)
A
4,5
10,0
B
50
5,0
10 0
10,0
C
6,0
10,0
D
6,0
10,0
E
6,0
10,0
25
Design spectrum for elastic analysis
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Derived from the elastic spectrum
0  T  TB
Sd (T) = ag . S . (2/3+T/TB . (2,5/q -2/3))
TB  T  TC
Sd (T) = ag . S . 2,5/q
TC  T  TD
Sd ((T)) = ag . S . 2,5/q
, q . ((TC /T))
  . ag
Sd ((T)) = ag . S . 2,5/q
, q . ((TC . TD /T 2 )
  . ag
TD  T  4 s
Sd ((T)) design
g spectrum
p
q
behaviour factor

lower bound factor (NDP recommended value: 0,2)
Specific rules for vertical action: q  1,5
Design spectrum for elastic analysis
Dissemination of information for training – Lisbon 10-11 February 2011
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Derived from the elastic spectrum but:
Correction factor for damping η not included
Values of the behaviour factor q already account for
the influence of the viscous damping being different
from 5%
The behaviour factor q is an approximation of the ratio of
the seismic forces that the structure would experience if its
response was completely elastic with 5% viscous
damping to the seismic forces that may be used in the
damping,
design, with a conventional elastic analysis model, still
ensuring a satisfactory response of the structure.
Design spectra for elastic analysis
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2.5
Sd
(cm/s2)
2.0
EN1998-1
EN1998
1
Soil C
1.5
Behaviour factor
1,5
2
1.0
3
4,5
0.5
0.0
0
0.5
1
1.5
2
2.5
T (s)
3
Alternative representations of the seismic action
Dissemination of information for training – Lisbon 10-11 February 2011
Time history representation (essentially for NL
analysis purposes)
Three simultaneously acting accelerograms
• Artificial accelerograms
Match the elastic response spectrum for 5% damping
Duration compatible with Magnitude (Ts  10 s)
Minimum number of accelerograms: 3
• Recorded or simulated accelerograms
Scaled to ag . S
Match the elastic response spectrum for 5% damping
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