PEER 2G02 – Code Usage Exercise: OpenSees Zhaohui Yang UCSD 2/15/2005.
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PEER 2G02 – Code Usage Exercise: OpenSees Zhaohui Yang UCSD 2/15/2005
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Transcript of PEER 2G02 – Code Usage Exercise: OpenSees Zhaohui Yang UCSD 2/15/2005.
PEER 2G02 – Code Usage Exercise:
OpenSees
Zhaohui Yang
UCSD
2/15/2005
Treasure Island site
0 1000 2000 3000 4000 5000 6000 7000 8000 9000Shear W ave Ve locity (ft/s)
500
450
400
350
300
250
200
150
100
50
0
De
pth
(ft
)
• Total model height: 100 m (328 ft)
• Discretized into 106 elements
• Lysmer transmitting boundary with incident motion specified as ½ of the outcropping motion given
Model base
Elastic half space
0.0001 0.001 0.01 0.1 10
0.2
0.4
0.6
0.8
1
G/G
max
0.0001 0.001 0.01 0.1 10
10
20
30
40
Dam
pin
g R
atio
(%
)
0.0001 0.001 0.01 0.1 1Cyclic Shear Strain (%)
0
0.2
0.4
0.6
0.8
1
G/G
max
0.0001 0.001 0.01 0.1 1Cyclic Shear Strain (% )
0
10
20
30
40
Dam
pin
g R
atio
(%
)
M easured
O PEN SEES M odel(use m easured M R curve)
O PEN SEES M O D EL(fit M R and dam ping itera tive ly)
T1 T1
T2 T2
G/Gmax and damping curves
• Fitted MD/damping curves (blue) were used at UCLA• Measured MR curves (red) were used at UCSD, with higher damping
Rayleigh damping employed:
Damping ratio = 1% at 1 Hz and 6 Hz
(as measured damping ratio at low strain is about 1%)
Computed acceleration Time Histories (UCSD)
Response Spectrum (5% damping)
Comments on response spectrum
• All analyses give similar spectrum shapes.
• Compared to rock outcropping motion, response at soil surface is amplified for period > 0.25 sec and de-amplified for period < 0.25 sec.
• Nonlinear analysis results are much lower than that of SHAKE at period 0.6-2 sec, due to strong nonlinearity at this soft soil site.
• UCLA response is generally higher than that of UCSD, due to lower damping curves used at UCLA.
0 1000 2000 3000 4000 5000 6000 7000 8000 9000Shear W ave Ve locity (ft/s)
500
450
400
350
300
250
200
150
100
50
0
De
pth
(ft
)
0 1000 2000 3000 4000 5000 6000 7000 8000 9000Shear W ave Ve locity (ft/s)
500
450
400
350
300
250
200
150
100
50
0
De
pth
(ft
)
Profile of maximum shear strain (UCSD)
• approximately in proportion to shear wave velocity (Gmax) profile, as lower Gmax -> lower backbone curve -> more nonlinearity -> higher shear strain
Permanent displacement profile after shaking (UCSD)
(strong correlation with shear wave velocity (Gmax) profile)
0 1000 2000 3000 4000 5000 6000 7000 8000 9000Shear W ave Ve locity (ft/s)
500
450
400
350
300
250
200
150
100
50
0
De
pth
(ft
)
0 1000 2000 3000 4000 5000 6000 7000 8000 9000Shear W ave Ve locity (ft/s)
500
450
400
350
300
250
200
150
100
50
0
De
pth
(ft
)
Location with strongest shear stress-strain response (UCSD)
• Notice permanent shear strain incurred in a single pulse
Shear stress-strain response at base (UCSD)
Shear stress-strain response near surface (UCSD)
Gilroy site
0 1000 2000 3000 4000Shear W ave Velocity (ft/s)
650
600
550
500
450
400
350
300
250
200
150
100
50
0
De
pth
(ft
)
• Total model height: 170.7 m (560 ft)
• Discretized into 173 elements
• Lysmer transmitting boundary with incident motion specified as ½ of the outcropping motion given
Model base
Elastic half space
0.0001 0.001 0.01 0.1 10
0.2
0.4
0.6
0.8
1
G/G
max
0.0001 0.001 0.01 0.1 10
10
20
30
40
Dam
pin
g R
ati
o (
%)
0.0001 0.001 0.01 0.1 1Cyclic Shear Strain (%)
0
0.2
0.4
0.6
0.8
1
G/G
max
0.0001 0.001 0.01 0.1 1Cyclic Shear Strain (%)
0
10
20
30
40
Dam
pin
g R
atio
(%
)
G1 G1
G2 G2
G/Gmax and damping curves• Fitted MD/damping curves (blue) were used at UCLA• Measured MR curves (red) were used at UCSD, with higher damping
G/Gmax and damping curves• Fitted MD/damping curves (blue) were used at UCLA• Measured MR curves (red) were used at UCSD, with higher damping
0.0001 0.001 0.01 0.1 10
0.2
0.4
0.6
0.8
1
G/G
max
0.0001 0.001 0.01 0.1 10
10
20
30
40
Dam
pin
g R
ati
o (
%)
0.0001 0.001 0.01 0.1 1Cyclic Shear Strain (%)
0
0.2
0.4
0.6
0.8
1
G/G
max
0.0001 0.001 0.01 0.1 1Cyclic Shear Strain (%)
0
10
20
30
40
Dam
pin
g R
atio
(%
)
M easured
O PE N SEES M ode l(use m easured M R curve)
O pensees M odel(fit M R itera tive ly)
G3 G3
G4 G4
Rayleigh damping employed:
• UCSD: Damping ratio = 3% at 1 Hz and 6 Hz (as measured damping ratio at low strain is about 3%)
• UCLA: Damping ratio = 1% at 1 Hz and 6 Hz
Computed Acceleration Time Histories (UCSD)
Response Spectrum (5% damping)
Significant surface amplification at 0.13-2 second periods
Comments on response spectrum
• All analyses give similar spectrum shapes.
• Compared to rock outcropping motion, response at soil surface is amplified for period > 0.13 sec and de-amplified for period < 0.13 sec.
• Nonlinear analysis results are similar to that of SHAKE, as this site is more competent (less nonlinearity).
• UCLA response is generally higher than that of UCSD, due to lower damping curves used at UCLA.
0 1000 2000 3000 4000Shear W ave Velocity (ft/s)
650
600
550
500
450
400
350
300
250
200
150
100
50
0
De
pth
(ft
)
Profile of maximum shear strain (UCSD)
• Strong correlation with shear wave velocity (Gmax) profile.
Permanent displacement profile after shaking (UCSD)
Location with maximum shear stress-strain response (UCSD)
Shear stress-strain response at base (UCSD)
Shear stress-strain response at surface (UCSD)
Influence of Rayleigh damping on surface acceleration
