GSA Southeastern Section Meeting Southeastern Section Meeting February 10-11, 2014 Blacksburg,...
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Morgan Eddy, PE, MSc, Mark Tilashalski, Elizabeth Godfrey, Guney Olgun, PhD, Sharmin Shamsalsadati, Martin Chapman, PhD, & James Martin, PhD 1 GSA Southeastern Section Meeting February 10-11, 2014 – Blacksburg, Virginia, USA
Transcript of GSA Southeastern Section Meeting Southeastern Section Meeting February 10-11, 2014 Blacksburg,...
Morgan Eddy, PE, MSc, Mark Tilashalski, Elizabeth Godfrey, Guney Olgun, PhD, Sharmin Shamsalsadati, Martin Chapman, PhD, & James Martin, PhD
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GSA Southeastern Section MeetingFebruary 10-11, 2014 – Blacksburg, Virginia, USA
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PiedmontGeotechnical, Inc.
Ø Motivation and Background
Ø NEHRP/IBC Seismic Design Provisions
Ø DC Region Geology and Study Sites
Ø Reston Fire Station Recordings
Ø Conclusions
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Ø Wide usage of NEHRP/IBC model based on WUS experience
Ø Unique CEUS Geology
§ Hard rock (Vs > 2,000 m/s) close to the ground surface
§ Deep sediment stack on hard rock
Ø Higher than realized seismic risk
Ø Lack of seismic experience in CEUS
Ø Mineral EQ damage focused to Coastal Plain unreinforced masonry
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F a
A B
C D
E
MAPPED SPECTRAL ACCELERATION, S (g)0.25 0.50 0.750 1.251.00
SS
S1
3.0
0
2.0
1.0
3.0
0
2.0
1.0
4.0
ABCDE
NEHRP/ IBC SITE CLASS
F v
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Vs & SPT data for
> 1,000 sites
COASTAL PLAIN
PIEDMONT
FALL LINE
Reston Fire Station
Potomac River
District of Columbia
20km10km
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Near-Surface Soil to Hard Rock Model:Ø Depth to the weathered zone is relatively simple
to define in the Piedmont…uncertain for Fall Line and Coastal Plain
Ø 60m thick weathered zone:§ Top: Vs = 2,000m/sec , ɣ = 25kN/m3
§ Base: Vs = 3,000m/sec, ɣ = 27kN/m3
Ø Reference site (Hashash et al., 2014): § Vsref = 3,000m/sec§ ɣref = 27kN/m3
Ø Hard rock transitions from 3,000 to 3,500m/sec
Ø Hard rock halfspace: § Vr = 3,500m/sec§ ɣr = 27kN/m3
§ 0.03% damping§ linear
Input
Surface
DEPTH OFTEN UNCERTAIN ON COASTAL PLAIN AND FALL LINE
Weathered Zone
Site Investigation
Hard Rock Halfspace
Hard Rock Transition
Reference Site
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Darton (1944)
Ground Surface EL = 40±
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0
25
50
75
100
125
150
0 1000 2000 3000 4000
Dept
h (m
)
Shear Wave Velocity, Vs (m/s)
Deconvolute recorded ground surface motions to 3,500 m/s hard rock à use to analyze DC region study sites
Reference
0
0.1
0.2
0.3
0.4
0.01 0.1 1 10
Spec
tral
Acc
eler
atio
n (g
)
Period, T (sec)
RecordedReference3,500 m/s Rock
0
0.1
0.2
0.3
0.4
0.01 0.1 1 10
Spec
tral
Acc
eler
atio
n (g
)
Period, T (sec)
E-W
N-S
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0
25
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75
100
125
150
0 1000 2000 3000 4000
Dept
h (m
)
Shear Wave Velocity, Vs (m/s)
0
100
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400
500
0 1000 2000 3000 4000De
pth
(m)
0
25
50
75
100
125
150
0 1000 2000 3000 4000
Dept
h (m
)
Shear Wave Velocity, Vs (m/s)
0
25
50
75
100
125
150
0 1000 2000 3000 4000
Dept
h (m
)
Class A Class B
Class C Class D
Piedmont
Coastal Plain
Fall Line
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0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.01 0.1 1 10
Spec
tral
Acc
eler
atio
n (g
)Period, T (sec)
0.0
0.1
0.2
0.3
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0.5
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0.01 0.1 1 10
Spec
tral
Acc
eler
atio
n (g
)
Period, T (sec)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.01 0.1 1 10
Spec
tral
Acc
eler
atio
n (g
)
Period, T (sec)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.01 0.1 1 10
Spec
tral
Acc
eler
atio
n (g
)
Period, T (sec)
Piedmont
Coastal Plain
Fall Line
Class A Class B
Class C Class D
NEHRP/IBC
Equivalent linear – 5% damping spectra – 500 year NEHRP/IBC spectra
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0
2
4
6
8
10
0.01 0.1 1 10
Ratio
of R
espo
nse
Spec
tra
Period, T (sec)
0
2
4
6
8
10
0.01 0.1 1 10
Ratio
of R
espo
nse
Spec
tra
Period, T (sec)
0
2
4
6
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10
0.01 0.1 1 10
Ratio
of R
espo
nse
Spec
tra
Period, T (sec)
0
2
4
6
8
10
0.01 0.1 1 10
Ratio
of R
espo
nse
Spec
tra
Period, T (sec)
Piedmont
Coastal Plain
Fall Line
Class A Class B
Class C Class DFa
Fv
Divide ground surface response by reference response
500-yr NEHRP/IBC
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0.0
1.0
2.0
3.0
4.0
5.0
0 500 1000 1500 2000
F a
Vs30
Piedmont (EW)Piedmont (NS)Fall Line (EW)Fall Line (NS)Coastal Plain (EW)Coastal Plain (NS)
0.0
1.0
2.0
3.0
4.0
5.0
0 500 1000 1500 2000F v
Vs30
Piedmont (EW)Piedmont (NS)Fall Line (EW)Fall Line (NS)Coastal Plain (EW)Coastal Plain (NS)
D
D
E
E
CC B B AA
Ø NEHRP/IBC fall below predicted Fa values
Ø NEHRP/IBC envelope predicted Fv values § except for class D Coastal Plain sites
Ø Damage generally focused to Coastal Plain unreinforced masonry
Ø NEHRP/IBC does not capture unique CEUS geology
Ø Hard rock close to surface amplifies short period motions
Ø Deeper stacks amplify long period motions
Ø Fa and Fv need region-specific adjustment
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