Nonlinear Performance and Potential Damage of Degraded Structures Under Different Earthquakes

The 5th Tongji-UBC Symposium on Earthquake Engineering “Facing Earthquake Challenges Together” May 4-8 2015, Tongji University Shanghai, China

Case study of ground motion and response spectra comparison of the Wenchuan (2008) and Lushan (2013) earthquakes

Yuxin PanStructural & Earthquake Engineering / Dr. Carlos E Ventura

M.Phil | The Hong Kong University of Science and Technology, Hong Kong (2012)

PhD Candidate | The University of British Columbia, Canada (2013 - Present)

May 7th, 2015

Background & Objectives

General Seismicity of Selected Stations

Numerical Model of Equivalent SDOF System

Analysis Results & Discussions• Inelastic hysteretic response

• Arias intensity vs. drift limit

• Elastic & inelastic response spectra

Conclusions & Future Works

Outline

Research background

Crustal EQs

Intraplate EQs

Interplate EQsCascadia Seismic Sources

Historical Eqs in Canada

SI_for_Kobe 72 SI_for_Llayllay 81

cm Max_DiplacementLlayllay 15cm Max_Diplacement_Kobe 20

0 10 20 30 40 50 60 7020

10

0

10

20

Time (s)

Dis

plac

emen

t (cm

)

0 10 20 30 40 50 60 7020

10

0

10

20

Time (s)

Dis

plac

emen

t (cm

)

cm / sMax_Velocity_Kobe 74cm / sMax_Velocity_Llayllay 73

0 10 20 30 40 50 60 70100

50

0

50

100

Time (s)V

eloc

ity (

cm/s

)

0 10 20 30 40 50 60 70100

50

0

50

100

Time (s)

Vel

ocity

(cm

/s)

cm/s2 Max_Acceleration_Llayllay 605cm/s2 Max_Acceleration_Kobe 587

0 10 20 30 40 50 60 701000

500

0

500

1000

Time (s)

Acc

eler

atio

n (c

m/s

/s)

0 10 20 30 40 50 60 701000

500

0

500

1000

Time (s)

Acc

eler

atio

n (c

m/s

/s)

Crustal Eq. vs Subduction Eq.

1995 Kobe eq. 1985 Chile eq.

Research background

Research background

0.5 1 1.5 2 2.5 3 3.5 40

0.5

1

1.5

2

2.5

KOBELLAYLLAY

Spectral Acceleration (g)

T (sec)

SA

(g)

0.5 1 1.5 2 2.5 3 3.5 40

50

100

150

200

250

300

KOBELLAYLLAY

Spectral Velocity (cm/s)

T (sec)

SV

(cm

/s)

0.5 1 1.5 2 2.5 3 3.5 40

10

20

30

40

50

60

KOBELLAYLLAY

Spectral Displacement (cm/s)

T (sec)

SD

(cm

)

5% damping

Crustal Eq. vs Subduction Eq.

SA spectra

SV spectra SD spectra

Research background

Rule Based Hysteretic Models & Backbone Curves

Research background

Arias Intensity

Research background

Directivity is an effect of a fault rupturing whereby earthquake ground motion in the direction of rupture propagation is more severe than that in other directions from the earthquake source.

8

5249150 0 150

150

150Particle Velocity (cm/s)

E/W direction

N/S

dire

ctio

n

150 0 150

150

150Particle Velocity (cm/s)

E/W direction

N/S

dire

ctio

n

200 0 200

200

200Particle Displacement (cm)

E/W direction

N/S

dire

ctio

n

S 1

200 0 200

200

200Particle Displacement (cm)

E/W direction

N/S

dire

ctio

n

Research background

Fig. Intensity map for Wenchuan and Lushan EQs

In 2008, there was an big earthquake with Mw of 7.9 occurred in Wenchuan, Sichuan Province of China. Five years later, in 2013, another earthquake with Mw of 7.0 took place at the same region (Lushan, Sichuan Province) along the Long Men Shan fault.

Wenchuan Earthquake (2008):Epicenter: 31.000N 103.400E Depth: 14 KM Duration: 350 SEC

Lushan Earthquake (2013): Epicenter: 30.299N 103.000E Depth: 13 KM Duration: 80 SEC

Objectives

This study mainly analyzed the ground motion records at same stations from both earthquakes, and compared the elastic and inelastic response spectra for a typical SDOF in-filled reinforced concrete (RC) structure by considering the stiffness and strength degradation. Response of different capacity levels’ structures (100% Fy, 75% Fy, … 10% Fy) will also be investigated.

Four main stations were selected for comparison, both east-west (EW) and north-south (NS) ground motions were analyzed, as seen in Figure. They are 51YAM, 51LSF, 51QLY and 51YAL. These four stations recorded the maximum PGA of Lushan Earthquake.

Fig. Elastic spectra comparison

Fig. Arias Intensity and significant duration (5%-95%)

Elastic spectra & Arias intensity

Directivity

12

51LSF

Location 30.021N 102.895E

Site Condition Soil

Distance to Wenchuan Epicenter

119.3 KM

PGA of Wenchuan EQ 124.1 CM/S2 (EW)

Distance to Lushan Epicenter 32.6 KM

PGA of Lushan EQ 387.4 CM/S2 (EW)

13

51QLY

Location 30.407N 103.266E

Site Condition Soil

Distance to Wenchuan Epicenter 67.2 KM

PGA of Wenchuan EQ 199.8 CM/S2 (NS)

Distance to Lushan Epicenter 28.2 KM

PGA of Lushan EQ 315.5 CM/S2 (NS)

Directivity

Equivalent SDOF System

Experimental Test

Reinforced Concrete Partially Infilled Frames; OpenSees modeling: Hysteretic material; Strength and stiffness degradation; No pinching effect was considered; 10% collapse drift limit

Reference: Anil, Özgür, and Sinan Altin. "An experimental study on reinforced concrete partially infilled frames." Engineering Structures 29.3 (2007): 449-460.

-0.06 -0.04 -0.02 0 0.02 0.04 0.06-600

-400

-200

0

200

400

600

Hysteretic Curve of Equivalent SDOF

Fy0.75Fy0.5Fy

Rotation

Mom

ent

Zerolength element

Rigid column

Mass

Numerical model in OpenSees

Inelastic hysteretic response

51YAM_Lushan_EW

51YAM_Wenchuan_EW

Short Period (T=0.5s)

51YAM_Lushan_EW

51YAM_Wenchuan_EW

Medium Period (T=1.0s)

Inelastic hysteretic response

Inelastic hysteretic response

51YAM_Lushan_EW

51YAM_Wenchuan_EW

Long Period (T=2.0s)

Drift limit vs. Significant duration

51YAM_Lushan_EW 51YAM_Wenchuan_EW

Elastic & inelastic response spectra

For each station, both N-S and E-W directions were studied. The design earthquake spectra and rare earthquake spectra (2% in 50 years)

based on Chinese Code for Seismic Design of Buildings (CCSDB) were also plotted for comparison.

CCSDB 51YAM 51LSF 51QLY 51YAL

Design Intensity 7 7 7 7

Design EQ Acceleration 0.10g 0.15g 0.10g 0.15g

Rate EQ Acceleration 0.50g 0.72g 0.50g 0.72g

Characteristic Period 0.45s 0.40s 0.45s 0.45s

Site Category II II II II

Design EQ Category 3rd 2nd 3rd 3rd

Damping Ratio 5%0 0.5 1 1.5 2 2.5 3 3.5 4

0

0.3

0.6

0.9

1.2

1.5

Design Acceleration from CCSDB

Design EQ - 51LSFRare EQ - 51LSFDesign EQ - 51YAMRare EQ - 51YAM

Period (s)

Sa (g

)

Elastic & inelastic response spectra

51YAM (N-S)

Elastic & inelastic response spectra

51LSF (E-W)

Conclusions

For the four selected stations, the Lushan Earthquake has much higher PGA, but larger drift demands resulted from the Wenchuan Earthquake;

Both elastic and inelastic spectra from Lushan Earthquake are higher than the local design spectra, and could be higher than rare earthquake spectra;

Overall, long period structures have larger displacements, but this trend varies with different capacity levels;

For the Wenchuan Earthquake, as expected, elastic system performed better than those weaker systems. However, for the Lushan Earthquake, elastic systems generated larger displacement at different period ranges.

Future work

Sensitivity Studies

• Degradation• Capacity level

Structures• Gravity system• High-rise building• Incremental Dynamic Analysis (IDA)

Ground Motion

• Ground motion characteristics• Ground motion Selection & Scaling

Thank you

Certificate of Structural Engineering Program