Site-Specific Seismic Studies for Optimal Structural Design - A Case Study (2012)
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Transcript of Site-Specific Seismic Studies for Optimal Structural Design - A Case Study (2012)
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Prof. Dr. Llambro DUNI
Polytechnic University of Tirana Institute of Geosciences, Energy, Water and Environment
Departament of Seismology
Dr. Faruk KABA InfraTransProject Ltd., Albania
Prof. Dr.Neki KUKA Polytechnic University of Tirana
Institute of Geosciences, Energy, Water and Environment Departament of Seismology
Site-specific seismic studies for optimal structural design: A case study
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1. Introduction Seismicity and seismic hazard of Albania
2. Code requirements for bridge design Seismic action into the KTP-N.2-89 code Seismic action requirements according to the EC8 standard
3. Application to the bridge design. A case study Assessment of the horizontal and vertical UHRS Deaggregation of seismic hazard at the Viaduct site construction Development of ground motion time histories
Site-specific seismic studies for optimal structural design: A case study
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Introduction: Seismicity and seismic hazard of Albania
Distribution of the earthquake epicenters in Albanian and surrounding area (510 B.C.31/12/2010, MW4.0),
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Introduction: Seismicity and seismic hazard of Albania
Intense microseismic activity (1.0 < M 3.0) Many small earthquakes (3.0 < M 5.0) Seldom by moderate size earthquakes (5.0 < M 7) Very seldom by strong earthquakes (M > 7.0)
From the evidences we possess today, it results that Since the period of IIIII century B.C. up to now, Albania was striken by: 55 strong earthquakes with intensity Io VIII degree
15 of them have had intensity of Io IX degree From these 55 earthquakes of a period of more than
2000 years, 36 belongs to the 19-th century
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Introduction: Seismicity and seismic hazard of Albania
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Introduction: Seismicity and seismic hazard of Albania
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Seismic zonation map of Albania
(Sulstarova et al., 1980)
Probabilistic Seismic hazard map of Albania
(Duni & Kuka 2010)
Introduction: Seismicity and seismic hazard of Albania
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The seismic action in the KTP-N.2-89 design code is expressed by an elastic ground acceleration response spectrum:
Sa(T) = kE (T) g kE is the so-called seismic coefficient, (T) is the dynamic coefficient , g is the acceleration gravity Both kE and (T) are dependent on local soil conditions Introducing the coefficients kr (building importance coefficient) and (ductility and
damping structures coefficient), the design acceleration values are obtained. Values of various parameters defining the spectral shape of (T) curves
Code requirements for bridge design:Seismic action into the KTP-N.2-89 code
00.5
11.5
22.5
3
0 1 2 3T(sec)
Dyn
amic
coe
ffici
ent
Category ICategory IICategory III
Soil category TC(sek) TD(sek) ( 0TTC ) (TCTTD) (TDT)
I 0.30 1.08 2.3 0.7/T 0.65 II 0.40 1.23 2.0 0.8/T 0.65 III 0.65 1.69 1.7 1.1/T 0.65
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The structure design is performed following two methods: (i) the response spectrum method; (ii) acceleration time-history method Acceleration time history selection is recommended to be based on site-specific
seismic studies. The amplitude of the chosen accelerograms should not be lower than the value kEg.
For lifeline systems (railways, roads, bridges, etc.) some specifications are introduced: The value of the vertical component of acceleration should be specfied in the case of
bridge design Specific engineering-seismological studies for the definition of kE and parameters for
the tunnels with large length, etc. are recommended
Code requirements for bridge design:Seismic action into the KTP-N.2-89 code
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The seismic hazard is described in terms of reference peak ground acceleration on type A ground, agR, with reference return period (RP) 475 years of the seismic action for the no-collapse requirement.
The effect of soil conditions on the seismic action is accounted for through seven ground types A, B, C, D, E, S1 and S2
The earthquake motion at a given point on the surface is represented by: (i) an elastic ground acceleration response spectrum, called elastic response spectrum o Two types of spectra are recommended: Type 1 and Type 2. If the earthquakes, that
contribute most to the site seismic hazard, have a surface-wave magnitude Ms not greater than 5.5, it is recommended that the Type 2 spectrum is adopted.
o Recommendations are given in EC8 for the five ground types A, B, C, D and E and values of the parameters S, TB, TC and TD, as well.
Code requirements for bridge design: Seismic action requirements according to the EC8 standard
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The earthquake motion at a given point on the surface is represented by: (ii) time-history of the earthquake motion.
For this kind of presentation, artificial, recorded or simulated accelerograms of the earthquake motion can be used.
The general rules for their use are as follows: 1. Artificial accelerograms shall be generated so as to match the elastic response
spectra for 5% viscous damping ( = 5%). 2. Duration of the accelerograms shall be consistent with the magnitude and the other
relevant features of the seismic event underlying establishment of ag. 3. When site-specific data are not available, the minimum duration Ts of the stationary
part of the accelerograms should be equal to 10 sec.
Code requirements for bridge design: Seismic action requirements according to the EC8 standard
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4. The suite of artificial accelerograms should observe the following rules: 4.1 a minimum of three accelerograms should be used; 4.2 the mean of the zero period spectral response acceleration values (calculated
from the individual time histories) should not be smaller than the value of agS for the site in question;
4.3 in the range of periods between 0.2T1 and 2T1, where T1 is the fundamental period of the structure in the direction where the accelerogram will be applied; no value of the mean 5% damping elastic spectrum, calculated from all time histories, should be less than 90% of the corresponding value of the 5% damping elastic response spectrum.
Code requirements for bridge design: Seismic action requirements according to the EC8 standard
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Bridge design has some specific requirements A site-dependent, horizontal and vertical elastic response spectrum should be specified
for the design. The horizontal component depends on the ground type and should be applied at the
foundation of the supports of the bridge. Near source effects, describing the directivity phenomenon of the earthquakes when
the site is located within 10 km horizontally of a known active seismogenic fault that may produce an event of moment magnitude higher than 6.5, should be assessed.
At least three pairs of horizontal ground motion time-history components shall be used.
The ensemble spectrum shall be scaled so that it is not lower than 1.3 times the 5% damped elastic response spectrum of the design seismic action, in the period range between 0.2T1 and 1.5 T1, where T1 is the natural period of the fundamental mode of the structure in the case of a ductile bridge, or the effective period (Teff.) of the isolation system in the case of a bridge with seismic isolation.
Code requirements for bridge design: Seismic action requirements according to the EC8 standard
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Near source effects, describing the directivity phenomenon of the earthquakes when the site is located within 10 km horizontally of a known active seismogenic fault that may produce an event of moment magnitude higher than 6.5, should be assessed
Code requirements for bridge design: Seismic action requirements according to the EC8 standard
-40
-20
0
20
40
0 0.5 1 1.5 2 2.5 3
Koha (sek)
Nxi
timi (
cm/s
/s)
TIR-04-1 E-W komp (TIR3)
-70
-35
0
35
70
0 0.5 1 1.5 2 2.5 3
Koha (sek)
Nxi
timi (
cm/s
/s)
TIR-04-1 E-W komp (TIR2)
0.01
0.1
1
10
0.01 0.1 1Perioda (sek)
PSRV
(cm
/sec
)
TIR-04-1(TIR3)
Earthquake Code
Station Code
Acceleration(cm/s/s) Velocity (cm/s) Displacement (cm)
Z E-W N-S Z E-W N-S Z E-W N-S
TIR-04-1 TIR2 27.88 -46.87 -3.99 -0.358 0.639 -0.081 -0.009 -0.011 -0.003
TIR-04-1 TIR3 4.05 35.47 7.33 -0.101 1.121 -0.248 -0.004 -0.043 -0.010
0.01
0.1
1
10
0.01 0.1 1Perioda (sek)
PSRV
(cm
/sec
)
TIR-04-1 (TIR2)
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0.01
0.26
0.51
0.76
0.1 0.35 0.6 0.85
Period (sec)
PSRV
(cm
/sec
)
Map of active faults of Albania (Aliaj et al, 2000) Blue: Middle Pleistocene-Holocene; Green: Pliocene-Lower Pleistocene; Red:Pre-Pliocene, active also during Pliocene-Quaternary
-0,6
-0,3
0
0,3
0,6
0 2 4 6 8 10 12
Acce
lera
tion
(g)
Time (sec)
E - W comp
-0,2
-0,1
0
0,1
0,2
0 2 4 6 8 10 12
Acce
lera
tion
(g)
Time (sec)
N - S comp
Code requirements for bridge design: Seismic action requirements according to the EC8 standard
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48 m high and 160 m long viaduct at Bulqiza-Ura e Vashes road section.
Application to the bridge design: A case study Assessment of the horizontal and vertical UHRS
Probabilistic evaluation of seismic hazard for rock conditions expressed in the form of: (i) horizontal peak ground acceleration (PGA), (ii) vertical PGA, (iii) 5% damped, uniform hazard response spectra (UHRS)
Period
(sec)
Spectral acceleration, g
RP=95 years
RP=145 years
RP=475 years
RP=975 years
RP=2475 years
PGA 0.179 0.202 0.270 0.316 0.383
0.10 0.259 0.299 0.432 0.527 0.677
0.20 0.344 0.395 0.560 0.682 0.860
0.30 0.304 0.348 0.499 0.613 0.781
0.50 0.196 0.227 0.334 0.415 0.543
1.00 0.082 0.096 0.146 0.185 0.248
2.00 0.044 0.052 0.079 0.100 0.133 0 0.2 0.4 0.6 0.8 1
0.1 0.3 0.5 0.7 0.9
Nxitimi spektral, g
1E-005
0.0001
0.001
0.01
0.1
1
Frek
uenc
a vj
etor
e e
tejk
alim
it
LegjendaPGASA 0.1sSA 0.2sSA 0.3sSA 0.5sSA 1.0sSA 2.0s
PP 975 vjet
PP 475 vjet
PP 95 vjet
PP 2475 vjet
PP 5000 vjet
PP 145 vjet
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 1 2 3 4 5
Perioda (sek)
Nxi
timi s
pekt
ral (
g)
Spektri elastik horizontal i reagimit i Tipit te Isipas EC8 per truallin e tipit A; Ag=0.270 g;Shuarja 5%Spektri elastik horizontal i reagimit me rrezikuniform (RP=475 vjet)
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Identification of the earthquake scenarios (distance-magnitude pairs) through the procedure known as seismic hazard deaggregation.
This analysis was performed for two periods of vibrations: SA=1.0 sec and SA=2.0 sec, vibration periods of the viaduct: T1=1.815 sec on the transversal direction and T2=1.428 sec on the longitudinal one.
Application to the bridge design: A case study Deaggregation of seismic hazard at the Viaduct site
SA
Modal event Mean event
Magnitude Distance Epsilon Magnitude Distance Epsilon
SA 1.0 s 6.8 4.6 1.03 6.62 5.2 1.41
SA 2.0 s 5.8 5.8 0.93 6.26 21.5 1.15 Probabilistic Seismic Hazard Deaggregation
Rruga e Arberit - Viadukti (9+850)(Lat=41.4648N, Lon=20.1373E)SA period 1.0sec. Acceleration 0.146 gMean Return Period: 475 yearsMean (R,M,e 0) = 5.2 km, 6.62, 1.41 Modal (R,M,e 0) = 4.6 km, 6.80, 1.03 from peak R,M binMean (R,M,e*) = 4.6 km, 6.80, eps interval: 1 to 2 sigma %c=9.1Binning: DeltaR=10km, deltaM=0.2, deltae=1.0
c)
Probabilistic Seismic Hazard DeaggregationRruga e Arberit - Viadukti (9+850)(Lat=41.4648N, Lon=20.1373E)SA period 2.0 sec. Acceleration 0.079 gMean Return Period: 475 yearsMean (R,M,e 0) = 21.5 km, 6.26, 1.15 Modal (R,M,e 0) = 5.8 km, 5.80, 0.93 from peak R,M binMean (R,M,e*) = 6.1 km, 5.80, eps interval: 1 to 2 sigma %c=3.3Binning: DeltaR=10km, deltaM=0.2, deltae=1.0
d)
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Application to the bridge design: A case study Development of ground motion time histories
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Generally, for important projects, input not covered by Code guidelines is required.
The structural engineer may perform time domain analysis that requires acceleration time histories instead of the spectral acceleration input.
When soil-structure interaction is accounted for, typically a profile of ground accelerations and displacements versus depth is required.
The same holds for evaluation of slope stability risk and calculation of dynamic earth pressures.
In cases of liquefiable soils, analyses would be performed to study the effects of this phenomenon on a proposed structure.
In all this examples, a site-specific study would be necessary to provide the required input.
Site-specific seismic studies for optimal structural design: A case study CONCLUSIONS
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A site-specific seismic hazard analysis using the probabilistic approach is
performed for a viaduct site construction at the Bulqiza-Ura e Vashes road section. Besides calculation the uniform hazard response spectra for different safety levels,
the earthquake scenarios that have high likelihood of occurrence at this site are also identified.
Then, the earthquake ground motion time histories are developed using the stochastic point-source method.
The obtained results can be used to derive structural design parameters for each usage and performance of the structure.
Site-specific seismic studies for optimal structural design: A case study CONCLUSIONS
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Thank You !
Site-specific seismic studies for optimal structural design: A case study
Slide Number 1Slide Number 2Slide Number 3Introduction: Seismicity and seismic hazard of AlbaniaIntroduction: Seismicity and seismic hazard of AlbaniaIntroduction: Seismicity and seismic hazard of AlbaniaIntroduction: Seismicity and seismic hazard of AlbaniaSlide Number 8Slide Number 9Slide Number 10Slide Number 11Slide Number 12Slide Number 13Slide Number 14Slide Number 15Slide Number 16Slide Number 17Slide Number 18Slide Number 19Slide Number 20Slide Number 21