University of Illinois Contribution

Jan. 23, 2009

Amr S. ElnashaiSung Jig KimCurtis Holub

Seismic Simulation and Design of Bridge Columnsunder Combined Actions, and Implications on System Response

Analytical Investigation

Effect of V/H Ratio

16 V/H ratios per earthquake record (5 stations) Axial force variation increases noticeably by up to 600% due to

vertical ground motion The slight increases in shear demand and noteworthy reductions

in shear capacity of up to 30% as V/H ratio increases.

0 0.5 1 1.5 2-30

-20

-10

0

10

V/H Ratio

Eff

ect

of

VG

M (

%)

Shear Demand

LP-COR-L

NO-SCS-LLP-COR-L

NO-SCS-L

Shear Capacity

0 0.5 1 1.5 20

100

200

300

400

500

600

V/H Ratio

Rat

io o

f C

on

trib

uti

on

of

VG

M o

nA

xial

Fo

rce

Var

iati

on

to

Dea

d L

oad

(%

)

LP-COR-L

LP-COR-T

NO-ARL-L

NO-ARL-T

NO-SCS-L

NO-SCS-T

KB-KBU-L

KB-KBU-T

KB-PRI-L

KB-PRI-T

595%

Effect of Time Interval

11 cases of arrival time intervals for each record– Results were compared against the response with coincident horizontal

and vertical peaks. The contribution of vertical ground motion to the axial force

variation tends to be reduced as time interval increases. – The effect was relatively small when compared to the effect of V/H ratio.

Although no clear correlation exists between the shear demand or capacity and the time lag, noticeable changes are noted up to 20%

0 1 2 3 4 5-15

-10

-5

0

5

10

15

20

TimeLag (sec)

Eff

ect

on

th

e S

hea

r C

apac

ity

(%)

LP-COR-L

LP-COR-T

NO-ARL-L

NO-ARL-T

NO-SCS-L

NO-SCS-T

KB-KBU-L

KB-KBU-T

KB-PRI-L

KB-PRI-T

Shear capacity

LP-COR-L

LP-COR-T

NO-ARL-L

NO-ARL-T

NO-SCS-L

NO-SCS-T

KB-KBU-L

KB-KBU-T

KB-PRI-L

KB-PRI-T

LP-COR-L

LP-COR-T

NO-ARL-L

NO-ARL-T

NO-SCS-L

NO-SCS-T

KB-KBU-L

KB-KBU-T

KB-PRI-L

KB-PRI-T

Axial Force Variation

0 1 2 3 4 5-100

-75

-50

-25

0

25

50

TimeLag (sec)

Rat

io o

f A

xial

Fo

rce

Var

iati

on

C

ause

d b

y V

GM

to

Dea

d L

oad

(%

)

LP-COR-L

LP-COR-T

NO-ARL-L

NO-ARL-T

NO-SCS-L

NO-SCS-T

KB-KBU-L

KB-KBU-T

KB-PRI-L

KB-PRI-T

Large Scale Experiments

Prototype and Test Matrix

Prototype: FHWA Bridge #4– Half scale pier (D=610mm, H=3048mm)– Rebar ratios: 2.79% for long.; 0.84 and 0.50% for spiral

Test Matrix– Hybrid Simulation: IPH and IPV

Specimen Input Control Type

IPH Horizontal ground motion

Displacement ControlIPV

Horizontal and vertical ground motions

Prototype and Test Matrix

Prototype: FHWA Bridge #4 Test Matrix

– Hybrid simulations : IPH and IPV

– Cyclic Static Tests: ICT and ICC

• Consideration of the observed axial force levels obtained during the second hybrid simulation

Specimen Input

ICTCyclic lateral displacement with constant axial tension

ICCCyclic lateral displacement with constant axial compression

• Displacement Control for Lateral

and Rotational displacements• Force Control for Axial Forces

Dx

Fy

y

Hybrid Simulation

ComponentEffect of VGM (%)

Peak Variation

Dx (mm) 6.97 4.67

Dy (mm) 25.44 27.48

Rz (rad) -9.72 -5.13

Fx (kN) -12.91 -3.60

Fy (kN) 31.70 98.01

Mz (kN-m) -9.07 -2.37

Ground Motions– Sylmar Converter Station, Northridge

Earthquake (Mw 6.7)– V/H ratio: 1.2 (ah=0.61g and av=0.73g)

No notable change in lateral displacement and moment

Significant effect on axial force variation (increases of up to 100%)– Fluctuation of lateral stiffness – Axial tension force (390 kN)

0 1 2 3 4 5 6 7-50

0

50

100

150

Time (sec)

Dx

(mm

)

IPH

IPV

0 1 2 3 4 5 6 7-1000

-500

0

500

1000

1500

Time (sec)

Mz

(kN

m)

IPH

IPV

0 1 2 3 4 5 6 7-3000

-2000

-1000

0

1000

Time (sec)

Fy

(kN

)

IPH

IPV

-60 -40 -20 0 20 40 60 80 100 120-800

-600

-400

-200

0

200

400

600

800

Dx (mm)

Fx

(kN

)

IPH

IPV

IPH and IPV

IPH IPVBlue: IPH

Red: IPV

Left Front Right

Crack and Strain

Crack Longitudinal strain and curvature – No significant effect Spiral strain

– Significant increase up to 200% when vertical ground motion is included

0 0.002 0.004 0.006 0.008 0.01 0.012 0.0145

10

15

20

25

30

35

40

45

50

55

60

Spiral strain

% o

f P

ier

Hei

gh

t

1st peak

2nd peak3rd peak

4th peak

5th peak

6th peak7th peak

Yield strain

Thin line: IPHThick line: IPV

IPH

IPV

IPH and IPV

Cyclic Tests

Loading Scenario– Positive cyclic lateral displacement with constant axial load– ICT: 222 kN (50 kips), ICC: -1112 kN (250 kips)

ICT: ductile behavior and strength increase by 4% ICC: brittle shear failure and strength degradation by 56%

ICT ICC

-50 0 50 100 150 200 250-500

-250

0

250

500

750

1000

Dx (mm)

Fx

(kN

)

ICT

ICC

56%

ICT and ICC

Conclusions

The hybrid simulations results confirmed that the vertical motion can significantly affect pier behavior

Significant increase (up to 100%) of axial force variation leads to more severe cracking and damage

Spiral strains increased by 200% when vertical ground motion is included

The cyclic tests confirmed that the different axial load level can impact the pier behavior and change the failure mode

Small Scale Experiments

Small Scale Testing Program

Experimental Setup (1/10 Scale)

Small Scale Testing Program

28 specimens 1/10 scale of

ICC and ICT Various lateral

and vertical loading patterns and magnitude

Test Matrix

Pseudo-DynamicMonotonic 1-Sided Cyclic 2-Sided Cyclic GM

High Tension 1 10

Low Tension 2 10 - CABER 3 11 22

Zero 3 12

Low Compression 4 11 - CABER 4 13 23

Moderate Compression 5 14

High Compression 6 15

T-C-C 16

C-T-C 17

C-C-T 18

V/H #2 7 19

V/H #3 8 20

V/H #4 9 21

No Vertical 24

V/H #1 25

V/H #2 26

V/H #3 27

V/H #4 28

StaticLateral LoadingCABER PIER (h/d = 2)

Flexure/Shear Failure

Ve

rtic

al

Lo

ad

ing

Co

nst

an

tP

seud

o-D

ynam

icA

ltern

ate

C

ycle

sH

igh

F

requ

en

cy

Small Scale Testing Program

30% axial compression Cyclic lateral loading

Preliminary Test

-0.2 -0.1 0 0.1 0.2 0.3-1.5

-1

-0.5

0

0.5

1

1.5

Displacement, inch

For

ce,

kip

ExperimentUCSD Limit

Failure Load Error

Experiment 1.33 kip NA

UCSD Model 1.32 kip -0.750%

Response 2000 (MCFT)

1.37 kip +3.01%

Publications

Journal– Kim, S. J., Holub, C., and Elnashai, A., “Analytical Assessment of the Effect of Vertical

Earthquake Motion on RC Bridge Piers”, ASCE Journal of Structural Engineering, (in review)– Holub, C., Kim, S. J., and Elnashai, A., “Aspects of Multi-Axial Pseudo Dynamic Testing of

RC Members”, Earthquake Engineering and Engineering Vibration, (to be submitted)– Holub, C., Kim, S. J., and Elnashai, A., “Behavior of RC Bridge Piers Subjected to Vertical

Earthquake Motion—Part 1: Experimental Framework”, Engineering Structures, (to be submitted)

– Kim, S. J., Holub, C., and Elnashai, A., “Behavior of RC Bridge Piers Subjected to Vertical Earthquake Motion—Part 2: Experimental Results”, Engineering Structures, (to be submitted)

Conference– Elnashai, A., Kim, S. J., and Holub, C., “Assessment of RC Bridges under Horizontal and

Vertical Earthquake Motion”, 3rd International Conference on Concrete & Development, Tehran, Iran, April, 2009

– Kim, S. J., Holub, C., and Elnashai, A., “The Analytical and Experimental Investigation of the Effect of Vertical Ground Motion on RC Bridge Pier”, 14th World Conference on Earthquake Engineering (14WCEE), Beijing, China, Oct, 2008

Report– Kim, S. J. and Elnashai, A., “Seismic Assessment Of RC Structures Considering Vertical

Ground Motion”, Mid-America Earthquake Center, Report No. 08-03, 2008. Download url: http://hdl.handle.net/2142/9454