PEER 2G02 – Code Usage Exercise: OpenSees Zhaohui Yang UCSD 2/15/2005

Treasure Island site

100 150 0 50 200 250 300 Model base 350 400 Elastic half space 450 500 0 1000 2000 3000 4000 5000 6000 Shear Wave Velocity (ft/s) 7000 8000 9000 • 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

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 1 4 0

T 1 T 1

0 .8

3 0 0 .6

2 0 0 .4

1 0 0 .2

0 0 .0 0 0 1 1 0 .8

0 .0 0 1 0 .0 1 0 .1

T 2

1 0 .6

0 .4

0 .2

M e a s u re d O P E N S E E S M o d e l ( u s e m e a s u r e d M R c u rv e ) O P E N S E E S M O D E L ( fit M R a n d d a m p in g ite ra tiv e ly ) 0 0 .0 0 0 1 0 .0 0 1 0 .0 1 0 .1

C y c lic S h e a r S tr a in (% )

1 0 0 .0 0 0 1 4 0

T 2

3 0 0 .0 0 1 2 0 1 0 0 .0 1 0 .1

0 0 .0 0 0 1 0 .0 0 1 0 .0 1 0 .1

C y c lic S h e a r S tr a in (% )

1 1

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.

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 0 0 50 50 100 100 150 250 200 300 250 350 450 350 500 0 400 1000 2000 3000 4000 5000 6000 Shear Wave Velocity (ft/s) 7000 8000 9000 450 500 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 Shear Wave Velocity (ft/s)

Permanent displacement profile after shaking (UCSD) (strong correlation with shear wave velocity (Gmax) profile) 0 0 50 50 100 100 150 250 200 300 250 350 400 300 450 350 500 0 400 1000 2000 3000 4000 5000 6000 Shear Wave Velocity (ft/s) 7000 8000 9000 450 500 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 Shear Wave Velocity (ft/s)

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 50 100 150 500 550 600 650 0 350 400 450 200 250 300 Model base Elastic half space 1000 2000 Shear Wave Velocity (ft/s) 3000 4000 • 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

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 1 4 0

G 1 G 1

0 .8

3 0 0 .6

2 0 0 .4

1 0 0 .2

0 0 .0 0 0 1 1 0 .8

0 .6

0 .4

0 .0 0 1 0 .0 1 0 .1

0 .2

0 0 .0 0 0 1 0 .0 0 1 0 .0 1 0 .1

C y c lic S h e a r S tr a in (% ) G 2

1 1 0 0 .0 0 0 1 4 0

G 2

0 .0 0 1 3 0 2 0 1 0 0 .0 1 0 .1

0 0 .0 0 0 1 0 .0 0 1 0 .0 1 0 .1

C y c lic S h e a r S tr a in (% )

1 1

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 1 4 0

G 3 G 3

0 .8

3 0 0 .6

0 .4

2 0 M e a s u re d O P E N S E E S M o d e l (u s e m e a s u re d M R c u rv e ) O p e n s e e s M o d e l (fit M R ite r a tiv e ly ) 1 0 0 .2

0 0 .0 0 0 1 1 0 .8

0 .0 0 1 0 .0 1 0 .1

G 4

1 0 0 .0 0 0 1 4 0

G 4

0 .0 0 1 3 0 0 .0 1 0 .1

1 0 .6

0 .4

0 .2

0 0 .0 0 0 1 0 .0 0 1 0 .0 1 0 .1

C y c lic S h e a r S tr a in (% )

1 2 0 1 0 0 0 .0 0 0 1 0 .0 0 1 0 .0 1 0 .1

C y c lic S h e a r S tr a in (% )

1

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.

Profile of maximum shear strain (UCSD) • Strong correlation with shear wave velocity (Gmax) profile.

0 400 450 500 550 600 650 0 50 100 150 200 250 300 350 1000 2000 Shear Wave Velocity (ft/s) 3000 4000

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