DOE/NRC DOE/NRC Natural Phenomena Hazards WorkshopOctober 23-24, 2018, Rockville, Maryland
INFRASTRUCTURE
MINING & METALS
NUCLEAR, SECURITY & ENVIRONMENTAL
OIL, GAS & CHEMICALS
New Approach for Seismic Vertical SSI analysis of Structures with Embedded FoundationsFarhang Ostadan, Nan Deng
Presented by Lisa Anderson
Bechtel Earthquake Engineering Center
EPRI Report 3002011804March 2018
A literature survey was conducted to review the recent findings for vertical motion
It was noted that some researchers attribute the vertical motion to shear wave propagating in an angle which produces both horizontal and vertical motion upon reflection and refraction
It was also noted that researchers have avoided preforming PSHA analysis for vertical motion because most often it results in controlling events quite different from controlling events attributed to the horizontal motion at the same return period
BNL report BNL-107612-2015-IR (2015) provides valuable insight on vertical to horizontal spectral ratio at shallow depth
Data from the 696 KiK-Net stations was analyzed
The borehole depths from 696 KiK-Net stations vary from 99 m to 3,510 m
Literature Survey and Review
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Literature Survey and Review (696 KiK-Net stations)
Histogram plot of the number of the records used for different depth ranges
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Histogram plot of the number of the records used for different VS30 ranges
Literature Survey and Review (696 KiK-Net stations)
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Mean (V/H)d / (V/H)s for the five binned VS30 categories
Literature Survey and Review (696 KiK-Net stations)
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Mean (V/H)d/(V/H)s for the four binned depth values of the sensor location.
Literature Survey and Review (696 KiK-Net stations)
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V/H)d/(V/H)s for three binned mean surface horizontal PGAs
Literature Survey and Review (696 KiK-Net stations)
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V/H)d/(V/H)s for three binned mean surface horizontal PGAs
Literature Survey and Review (BNL-107612-2015-IR)
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V/H)d/(V/H)s for three binned mean surface horizontal PGAs
Literature Survey and Review (BNL-107612-2015-IR)
Current Models for Spectral V/H Ratios for Ground Surface Motion
RG 1.60 provides site-independent H and V spectra and the ratio of V/H
NUREG/CR 6728 is widely used. This document provides V/H ratios for Western and Eastern US based on the maximum acceleration (PGA)for rock sites
In appendix J, NUREG/CR 6728 provides a procedure for V/H ratio for soil sites for WUS sites. The ratio still needs to be modified for CEUS soil sites
Literature Survey and Review
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Literature Survey and Review
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In order to demonstrate the anomalies associated with vertically propagating P-wave, a deep soil site in Central Eastern US (CEUS) was selected for analysis
The PSHA has been performed for the site and the seismic hazard data for the hard rock at a depth of approximately 1,000 ft are available
The site best estimate shear wave velocity profile has been simulated into 60 profiles in order to include the variability of the velocity data in the site amplification analysis
For site response P-wave analysis, the P-wave velocity profiles corresponding to the 60 simulated shear wave velocity profiles are obtained using the Poisson’s ratio
Using the hard rock PSHA data and the applicable V/H ratio for the hard rock at the subject site, the vertical response spectrum for the Uniform Hazard Spectrum at 1.0E10-4 MAFE corresponding to the de-aggregated high frequency ARS was obtained
The site amplification using P-wave was also performed. The acceleration response spectra at the surface (total of 60 spectra) and the median spectra were obtained
Issues with Vertically PropagatingP-Wave
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Issues with Vertically PropagatingP-Wave
Vp Profiles for CEUS Deep Soil Site
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Issues with Vertically PropagatingP-Wave
Vertical response spectra at the ground surface
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Issues with Vertically PropagatingP-Wave
Vertical response spectra at the ground surface from two methods
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Issues with Vertically PropagatingP-Wave
V/H spectral ratio at the ground surface from two methods
Recent Method for develop of V/H Spectral Ratio for WUS Sites
The paper by Gulerce and Abrahamson (2011) provides the methodology for development of spectral V/H ratios for WUS sites
The key input parameters needed for Gulerce/Abrahamson model are the magnitude and distance of the controlling events, which are readily available from PSHA data for horizontal motion and the Vs30 reflecting the average shear wave velocity in the upper 30 m of the site profile
The V/H ratio can be adjusted for different Vs30 values
Most Recent Approach to Developing Vertical Design Motion Used by the Industry Today
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Most Recent Approach to Developing Vertical Design Motion Used by the Industry Today
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V/H ratio from magnitude 7 vertical strike-slip earthquakes 5 km away from the fault (Rrup ¼ 5 km) and 30 km away from the fault (Rrup¼ 30 km) for (a, left figure) 20 Hz, and (b, right figure) 1 Hz, Gulerce and Abrahamson (2011) at 5% spectral damping
Task 2. Model of Vertical Ground Motions for SSI Analysis
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SASSI Model Layout forStructure SSI Analysis
Interaction Nodes Input Motion
Layered Soil Profile
Halfspace
ExcavatedSoil
SASSI uses the Flexible Volume method to combine the substructures of building structure, excavated soil volume, and the free-field impedance
SASSI works in frequency domain, i.e., at each frequency, the response of the system is computed, and the results of all frequencies are combined to produce the final SSI responses through inverse FFT (For time-history approach), or through inverse PSD (for RVT approach). All terms in the SASSI Equations of Motion are frequency dependent
The soil strata is modeled as a perfectly layered visco-elastic profile overlaying a uniform half-space
The free-field motion is defined at the layer interfaces and is first determined through site response analysis
SASSI Methodology
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While for horizontal motions the assumptions fit reasonably well with the field observations, this is not the case for vertical motion. As discussed before, the assumption of P-wave propagation produced a vertical motion both inconsistent with recorded motion and overly conservative, resulting in challenges for design of SSCs and for seismic stability evaluation
It is observed that the P-wave incidence assumption is introduced only for the convenience of numerical solutions of site response analysis. We should introduce new assumptions consistent with current field observation and the practice for development of vertical design motion Since the current seismological and engineering practice is to use the site-and-magnitude-specific V/H ratios to produce vertical rock outcrop motions, it is natural that we should use the same V/H approach to produce the vertical input motions for SSI analysis
The V/H approach has been implemented in the updated version of SASSI that maintains the site applicable V/H ratio in the free-field solution
SASSI Methodology
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Standard Plant LMSM Vertical SSI Analysis
─ SSI analyses of the LMSM (published version of the nuclear island model) are performed. The model has 40 ft embedment. The vertical ARS responses due to P-wave and V/H approach generated vertical motions were compared at the key nodal points
─ The analyses results presented is for a CEUS deep soil profile with RG 1.60 input motions and a CEUS rock site with site-specific motion
Parametric Study on Vertical Motion SSI Analysis
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Structural Model –LMSM
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Program on Technology Innovation: Effect of Seismic Wave Incoherence on Foundation
and Building Response EPRI Report TR-1013504 November 2006
The model is embedded to 40 ft. in the subsurface profile with a rigid wall built around the perimeter
Soil Profile
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0
200
400
600
800
1000
1200
0 2000 4000 6000 8000 10000 12000
Dep
th fr
om G
rade
(ft.)
Wave Velocity (ft./sec)
Deep Soil Profile - Wave Velocity
Vs
Vp
0
200
400
600
800
1000
1200
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04
Dep
th fr
om G
rade
(ft.)
Fraction of Critical Damping
Deep Soil Profile - Damping
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.1 1 10 100
V/H
Rat
io
Spe
ctra
l Acc
eler
atio
n (g
)
Frequency (Hz)
Input Motion - RG 1.60 H and V ARS at Grade. Scaled to 0.3g
RG 1.60, H
RG 1.60, V
V/H
Task 3.1A: Input Motion
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Vertical Input Motions
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0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.1 1 10 100
Spec
tral A
ccel
etio
n, 5
% d
ampi
ng
Frequency (Hz)
At Grade
Depth of 10 ft
Depth of 20 ft
Depth of 30 ft
Depth of 40 ft
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.1 1 10 100Sp
ectr
al A
ccel
erat
ion,
Dam
ping
Frequency (Hz)
Grade
Depth of 10 ft
Depth of 20 ft
Depth of 30 ft
Depth of 40 ft
By P-Wave By V/H Approach
V/H Ratios for Input Motions
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0
0.2
0.4
0.6
0.8
1
1.2
0.1 1 10 100
V/H
Ratio
s
Grade
Depth of 10 ft
Depth of 20 ft
Depth of 30 ft
Depth of 40 ft
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0.1 1 10 100
V/H
Ratio
Frequency (Hz)
At Grade
Depth of 10 ft
Depth of 20 ft
Depth of 30 ft
Depth of 40 ft
By P-Wave By V/H Approach
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Vertical ARS on SCV Stick
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.1 1 10 100
Spe
ctra
l Acc
eler
atio
n (g
)
Frequency (Hz)
Vertical ARS at Node 34
Vert. - P-Wave Input
Vert. - V/H Input
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0.1 1 10 100
Spe
ctra
l Acc
eler
atio
n (g
)
Frequency (Hz)
Vertical ARS at Node 45
Vert. - P-Wave Input
Vert. - V/H Input
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0.1 1 10 100
Spe
ctra
l Acc
eler
atio
n (g
)
Frequency (Hz)
Vertical ARS at Node 145
Vert. - P-Wave Input
Vert. - V/H Input
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Vertical ARS on ASB Stick
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.1 1 10 100
Spe
ctra
l Acc
eler
atio
n (g
)
Frequency (Hz)
Vertical ARS at Node No. 1
Vert. - P-Wave Input
Vert. - V/H Input
0
0.2
0.4
0.6
0.8
1
1.2
0.1 1 10 100
Spec
tral A
ccel
erat
ion
(g)
Frequency (Hz)
Vertical ARS at Node No. 118
Vert. - P-Wave Input
Vert. - V/H Input
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.1 1 10 100
Spec
tral A
ccel
erat
ion
(g)
Frequency (Hz)
Vertical ARS at Node 212
Vert. - P-Wave Input
Vert. - V/H Input
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Vertical ARS on CIS Stick
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.1 1 10 100
Spe
ctra
l Acc
eler
atio
n (g
)
Frequency (Hz)
Vertical ARS at Node No. 26
Vert. - P-Wave Input
Vert. - V/H Input
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.1 1 10 100
Spe
ctra
l Acc
eler
atio
n (g
)
Frequency (Hz)
Vertical ARS at Node No. 229
Vert. - P-Wave Input
Vert. - V/H Input
CEUS Rock Profile
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0
20
40
60
80
100
120
0 5000 10000 15000 20000
Dep
th [f
t]
Wave Velocity [ft/sec]
EPRI - BE Rock Site Profile
Rock Vs
Rock Vp
0
20
40
60
80
100
120
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Dep
th [f
t]
Damping Ratio [%]
EPRI - BE Rock Site Profile
Rock Damping
Input Motion
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0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0.1 1 10 100
V/H
Rat
io
Spe
ctra
l Acc
eler
atio
n (g
)
Frequency (Hz)
Input Motion - EPRI HF Rock H and V ARS at Grade
Horizontal ARS
Vertical ARS
V/H Ratio
Vertical Input Motions
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0
0.2
0.4
0.6
0.8
1
1.2
1.4
0.1 1 10 100Ve
rtica
l AR
S, 5
% D
ampi
ng
Frequency (Hz)
At Grade
Depth of 10 ft
Depth of 20 ft
Depth of 30 ft
Depth of 40 ft
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0.1 1 10 100
Verti
cal A
RS
, 5%
Dam
ping
Frequency (Hz)
At Grade
Depth of 10 ft
Depth of 20 ft
Depth of 30 ft
Depth of 40 ft
By P-Wave By V/H Approach
V/H Ratios for Input Motions
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0
0.2
0.4
0.6
0.8
1
1.2
0.1 1 10 100V
/H R
atio
Frequency (Hz)
At Grade
Depth of 10 ft
Depth of 20 ft
Depth of 30 ft
Depth of 40 ft
0
0.5
1
1.5
2
2.5
3
0.1 1 10 100
At Grade
Depth of 10 ft
Depth of 20 ft
Depth of 30 ft
Depth of 40 ft
By P-Wave By V/H Approach
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Vertical ARS on SCV Stick
0
0.5
1
1.5
2
2.5
3
0.1 1 10 100
Spe
ctra
l Acc
eler
atio
n (g
)
Frequency (Hz)
Vertical ARS at Node No. 34
Vert. - P-Wave Input
Vert. - V/H Input
0
2
4
6
8
10
12
14
16
0.1 1 10 100
Spe
ctra
l Acc
eler
atio
n (g
)
Frequency (Hz)
Vertical ARS at Node No. 45
Vert. - P-Wave Input
Vert. - V/H Input
0
2
4
6
8
10
12
14
16
0.1 1 10 100
Spe
ctra
l Acc
eler
atio
n (g
)
Frequency (Hz)
Vertical ARS at Node No. 145
Vert. - P-Wave Input
Vert. - V/H Input
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Vertical ARS on ASB Stick
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.1 1 10 100
Spe
ctra
l Acc
eler
atio
n (g
)
Frequency (Hz)
Vertical ARS at Node No. 1
Vert. - P-Wave Input
Vert. - V/H Input
0
1
2
3
4
5
6
0.1 1 10 100
Spe
ctra
l Acc
eler
atio
n (g
)
Frequency (Hz)
Vertical ARS at Node No. 118
Vert. - P-Wave Input
Vert. - V/H Input
0
0.5
1
1.5
2
2.5
3
0.1 1 10 100
Spe
ctra
l Acc
eler
atio
n (g
)
Frequency (Hz)
Vertical ARS at Node No. 212
Vert. - P-Wave Input
Vert. - V/H Input
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Vertical ARS on CIS Stick
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0.1 1 10 100
Spe
ctra
l Acc
eler
atio
n (g
)
Frequency (Hz)
Vertical ARS at Node No. 26
Vert. - P-Wave Input
Vert. - V/H Input
0
1
2
3
4
5
6
7
8
0.1 1 10 100
Spe
ctra
l Acc
eler
atio
n (g
)
Frequency (Hz)
Vertical ARS at Node No. 229
Vert. - P-Wave Input
Vert. - V/H Input
Regulatory Guide 1.208 (March 2007), recommends a performance-based approach to define the site-specific earthquake ground motion, provides specific recommendations for development of horizontal and vertical motion from the PSHA to site amplification and development of the performance-based response spectra
In Section 5.2, vertical spectrum, it states: Vertical response spectra are developed by combining the appropriate horizontal response spectra and the most up-to-date V/H response spectral ratios appropriate for either CEUS or WUS sites
For CEUS soil sites, NUREG/CR 6728 describes a procedure to determine a WUS-to-CEUS transfer function that may be used to modify the WUS V/H soil ratios
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Regulatory Constrains
SRP 3.7.1 Rev 4 (Dec 2014) in the section for defining FIRS states: “the FIRS for the vertical direction is obtained with the vertical to horizontal (V/H) ratios appropriate for the site”. Similar guidance has been provided for definition of vertical PBSRS. Similar guidance is provided in Interim Staff Guidance ISG-17 as it relates to the vertical spectrum
As noted above the methodology of using V/H ratio to develop vertical motion is fully consistent with the regulatory guidance and maintains the latest development that is appropriate for the site for spectral V/H ratio
In this regard no regulatory constraint is expected for adoption of the V/H methodology for SSI analysis
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Regulatory Constrains
The proposed method for vertical SSI analysis maintains the consistency between the method used in developing the vertical design motion and its application to SSI analysis for embedded structures. It avoids the anomalies associated with vertically propagating P-waves and results in a more realistic responses for structural and equipment design
Summary
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