Evaluation of Limit States of RC Columns in Performance-Based

Seismic Design of Bridges

Jun-ichi Hoshikuma

Center for Advanced Engineering StructuralAssessment and Research (CAESAR)

Public Works Research Institute

What’ is the Public Works Research Institute

Public Works Research Institute is one of Japanese representative research institutes under MLIT (Ministry of Land, Infrastructure, Transport and Tourism) jurisdiction.

PWRI’s mission is to develop public works technologies including prevention/mitigation of natural disasters, improvement of living environment, new materials/construction methods etc.

・ Collection of Data of Design, Construction, Maintenance of Bridges and Damage/Trouble Experiences

・ Technical Counsel for Bridge Administrators・ Technical Emergency Assistance for Bridge Administrators after

Disaster and Accidents

Advanced Researches for On-site Technical Needs of Bridges

Researches for Development of Design Criteria・ Investigation of Cause of Damage and Trouble with Bridges・ Clarification of Lessons Learned form Damage and Trouble Experiences ・ Study of Prevention or Mitigation of Damage and Development of

Design Criteria, Construction Manual for Bridges ・ Clinical Research Approach with Decommissioned Bridge Elements

Center for Advanced Engineering StructuralAssessment and Research

Center for Advanced Engineering StructuralAssessment and Research

Earthquake Engineering Research Team Development of Seismic Design Methods for Bridges Assessment of Seismic Performance of Existing Bridges Development of Seismic Retrofit Technique for Existing Bridges

Seismic Performance for Bridges in Japan

Type of Ground Motion

Level 1 EQHigh Probability to Occur

SPL 1: Undamaged to befully operational

Type-I EQInterplate

(Kanto EQ)Level 2 EQLow Probability to Occur

Type-II EQNear-fault(Kobe EQ)

Class-A(Standard Br.)

Class-B(Important Br.)

SPL 3:Prevent critical damage

SPL 2:Retain limited damage to recover ope-ration soon

Importance

Required seismic performance for bridges specified by MLIT 2012 Interplate EQ（cIz=1.0）2012 Interplate EQ（cIz=1.2）

.1 10.2 0.5 2 530

0

0.1 10.2 0.5 2 5300

00

0.1 10.2 0.5 2 53Natural Period T (s)

Standard Design Response Spectra (m/s2)

Soil Profile Type I Soil Profile Type II Soil Profile Type III

2002 Interplate EQNear-Fault EQ

50

30

20

10

75

3

2

10.1

Standard Design Response Spectra

JCI Paper #3

Design earthquake ground motion (Type-I) corresponding to interplate earthquakes zones was revised with consideration of the 2011 great east Japan earthquake & the anticipated great earthquake along the Nankai Trough.

Structural planning for bridges with the risk of tsunami inundation

Clarification of Requirements for seismic structural elementsof bridges

Recent research accomplishments on seismic design limit state of structural elements

Revised in 2012 based on knowledge derived from recent extreme earthquakes and research accomplishments

Latest Revision of Seismic Design Criteria

2011 Great East Japan EQ

M9 EQs were taken into account for revision of Cz.

Major Interplate Earthquakes near Japan

9

cIz cIIz1.2     1.0

1.0     1.0

1.2     0.85   

1.0     0.85

0.8     0.7

cIz : Interplate EQ.cIIz : Near fault EQ.

Seismic Risk Hazard Map (Zone Factor Cz)

SPL Safety ServiceabilityRepairability

Short Term Long TermSPL 1: Prevent Damage

Prevent Unseating of Superstructure

Same Function as before Earthquake

Needless of Repair for Function Recovery

Simple Repair Work

SPL 2: Limited Damage for Function Recovery

Prevent Unseating of Superstructure

Possible Early Function Recovery

Function Recovery by Temporary Repair

Possible Permanent Repair Work

SPL 3:Prevent Critical Damage

Prevent Unseating of Superstructure

Seismic Performance Level for Bridges

11

Rubber Bearing

Bearing: Elastic Limit

Columns: RepairableLimit

Abutment: Elastic Limit

Foundation: Limited Nonlinear Behavior

Footing: Elastic Limit

General Continuous Multi-Span Bridge

Engineering Limit States of Bridge System to Satisfy Requirement of SPL2

12

Superstructure: Limited Nonlinear BehaviorAbutment:

Elastic Limit

Column: Repairable Limit

→ Support Live Load Directly / Difficult to repair

Foundation: Limited Nonlinear Behavior

Engineering Limit States of Bridge System to Satisfy Requirement of SPL2

Frame-type PC Bridge

JCI Paper #3

Cyclic Loading Test for Full Scale Model

1/2 Scale Model

1/4 Scale Model

Experimental Verification for RC Columns

水 平 力

水 平 変 位

耐 震 性 能 １耐 震 性 能 ２ 耐 震 性 能 ３

耐 震 性 能 １に 対 す る限 界 状 態

耐 震 性 能 ２に 対 す る限 界 状 態

耐 震 性 能 ３に 対 す る限 界 状 態

SPL3SPL2SPL1

Lateral displacement

Late

ral F

orce

Limit state for SPL1

Limit state for SPL2

Limit state for SPL3

Engineering Limit States for RC Columns

水平力

水平変位

1) 2) 3)4)

1) Flexural cracksYielding of rebar

2) Residual cracksStable hysteresis loop

3) Onset of Buckling of rebarDegradation of lateralforce during cyclic loading

4) Onset of Fracture of rebar

LateralDisplacement

Lateral force

Damage Observation of RC Bridge Column

Limit State for SP2

Limit State for SP3

Tension

Compression

Strain

Stress

Limit State of RC columns for SP2 is represented by tensile strain of longitudinal rebars.

Strain distributionStrain distribution

Lateral Displacement

Late

ral

Forc

e

Stress-strain of rebar

Compression Tension Tension

Compression

Rebar buckling occurs in compressive loading step after tensile loading

Buckling Behavior in Plastic Hinge

Ultimate Strength

Allowable Displacement

ls：Curvature at design limit state at base sectiony：Yield curvature at base sectionLp：Plastic hinge length

hMP ls

u

2/ppylsyls LhL

Plastic Deformation

Evaluation of Limit State for SP2 & SP3

Section Size:2.4×2.4 m

600m

m

Lp＝ 0.5D

ConventionalEquation

1.2

m

Buckling Behavior of Longitudinal RebarProperties of rebar

・ Resistance of hoops・ Resistance of cover concrete

3/16/15.9 nsypL

in which Lp ≦ 0.15h

n

sy ’

ProposedEquation

779

mm

Evaluation of Plastic Hinge Length

JCI Paper #3

sy

s=Ess

sy ：Yield of steel bars ：Stress of steel barEs ：Young’s modules of steel barst ：Allowable tensile strain

Idealization by Elasto-Plastic Envelope

Strain-hardeningBauschinger Effect

sy st22.02.015.015.0

2 025.0 cospst L

22.02.015.015.03 035.0 cospst L

Buckling Behavior of RebarDiameter of rebarResistance of hoopsResistance of cover concretePlastic hinge length Lp

s

co

Stress-Strain Model of Longitudinal Bar

Confinement Effectsysckcc 8.3

ck

syscc

033.0002.0

018.04

sdAh

s

Volume ratio of lateral confining reinforcement

ck：Design strength of concretesy ：Yield of lateral confining

reinforcementAh ：Sectional area s ： Spacing d ：Effective length ccl ：Allowable Compressive strain

sysdes

ckE 2

2.11

cc

ccbt

cc

cccdesccc E

111

n

ccc

ccc nE

cu

cc

ccl

Stress

Strain

descc

ccccl E

5.0

Stress-Strain Model of Confined Concrete

0

100

200

300

0 100 200 300

Exp

erim

enta

l （m

m）

Estimated (mm)

SD490 SD295, SD345

Estimated Lateral Displacement for SP2Comparison of Estimated Lateral Displacement for SP2 with Experimental Results

Applicability:

Solid Section (Hollow section excluded) Longitudinal Steel Ratio: less than 2.5%

(SD345,SD390,SD490) Lateral Steel Ratio: less than 1.8%

(SD345) Compression Stress at Base

: less than 3N/mm2

Concrete Strength: 21-30N/mm2

Reinforced concrete hollow columns

Seismic Design of RC Hollow Column

Applied for Tall column Reduction of inertia force and mitigation of load to foundation Section with high longitudinal steel ratio and high axial stress Invisible inside-face concrete and difficult to repair Remarkable failure mode for seismic loading

How should Limit State for SP2 be determined for RC

hollow columns?width(w)

thickness(t)

Some hollow columns with t/w<0.1

Lateral actuator

Axial load apparatus

• 1/7 scaled models• Effective aspect ratio : 4.3• Axial stress: 4.4 N/mm2 →specimen-1

1.0 N/mm2 →specimen-2

Damage Observation of RC Hollow Column

Cyclic Loading Test

-1500

-1000

-500

0

500

1000

1500

-300 -200 -100 0 100 200 300

Late

ral f

orce

(kN

)

Displacement (mm)

Specimen-2

A

B

C

A C B

-1500

-1000

-500

0

500

1000

1500

-300 -200 -100 0 100 200 300Displacement (mm)

Late

ral f

orce

(kN

)

Specimen-1

A

B

A

B C

C

D

A: Yielding of long. Bar,B: Spalling of outside face concrete,C: Spalling of inside face concreteD: Fracture of long.bar

Damage Observation of RC Hollow ColumnHigh Axial stress: 4.4 N/mm2 Low Axial stress: 1.0 N/mm2

JCI Paper #3

• 3δ0 : No damage at inside, spalling of cover concrete at outside• 4δ0 : Buckling of long. steel bar arranged at both sides faces.

90 degree hook of cross-ties for inside face was unhooked, while135 degree hook for outside face was still hooked effectively.

Damage Observation of RC Hollow ColumnHigh Axial stress: 4.4 N/mm2

Damage Observation of RC Hollow ColumnHigh Axial stress: 1.0 N/mm2

• 4δ0 : No damage at inside, spalling of outside face cover concrete• 5δ0 : Onset of spalling of inside face cover concrete• 6δ0 : Buckling of long. steel bar arranged at both sides faces

90 degree hook of cross-ties for inside face was unhooked, while135 degree hook for outside face was still hooked effectively.

Structural Details of RC Hollow Column

Details of Reinforcement for Hollow Section

Solid Section

Haunch Section

Solid Section

Potential Plastic Hinge Region

Hoop for Corner Confinement

2012 Seismic Design Specifications for Highway Bridges Seismic Retrofit has been firstly targeted to prevent following failure modes observed during 1995 Kobe Earthquake.

Seismic Retrofit for RC Columns at Section of Cut-off of Longitudinal Rebars

Seismic Retrofit for Unseating Prevention System at Deck-end

Failure Modes Resulted in Fatal Damage

有効高さd 有効高さd

計算上不要となる部材断面

「十分な定着長」慣用的に重ね継ぎ手長la（軸方向鉄筋径φの30～35倍程度）

柱とフーチングの接合部や軸方向鉄筋量が大きく変化する位置（段落とし部など）では15cm程度

（一般の位置における規定量の２倍程度）

30cm程度（全高）

水平力

・d+20φ（折り曲げる時）

・鉄筋の引張応力度が　許容応力度の1/2以下　となる断面（下限値はla）

　　（伸ばす時）

水平力

30cm程度（一般部）

有効高さd 有効高さd

計算上不要となる部材断面

「十分な定着長」慣用的に重ね継ぎ手長la（軸方向鉄筋径φの30～35倍程度）

柱とフーチングの接合部や軸方向鉄筋量が大きく変化する位置（段落とし部など）では15cm程度

（一般の位置における規定量の２倍程度）

30cm程度（全高）

水平力

・d+20φ（折り曲げる時）

・鉄筋の引張応力度が　許容応力度の1/2以下　となる断面（下限値はla）

　　（伸ばす時）

水平力

30cm程度（一般部）

Before 1980 Design Code

1980 Design Code

300 mm Spacing

150 mm Spacing

150 mm spacingaround cut-offpoint

Development Length

Develop-ment

Length

300 mmSpacing

Revision of Reinforcement Details in 1980

Steel Jacketing for Pier Body and Unseating Prevention Devices

Seismic Retrofit for RC Columns at Section of Cut-off of Longitudinal Rebars

Seismic Retrofit for Unseating Prevention System at Deck-end

Concrete Jacketing for Pier Body and Unseating Prevention Devices

Damage experiences indicated the most vulnerable section in existing bridges designed in old Japanese codes.

Seismic Retrofit Strategy for Existing Bridges

JCI Paper #3

Retrofitted（Designated, Route 4）（3 3-span cont. girders）（Designed in 1974）

Damage at Cut-off Section Caused Bridge Close for about 3 Months.

Oshu city, IWATE

Trace of Seismic Behavior in Movable Bearing

Seismic Retrofit by RC Jacketing

Shear Crack

Retrofitted/Unretrofitted Bridge Piers Located Close Unretrofitted（Local Route）（9-span cont. girders）（Designed in 1972）

(Photo Provided from Tohoku Regional Development Bureau)

(Photo Provided from Tohoku Regional Development Bureau)

1995 Kobe EQ 2011 Great East Japan EQ

Research Projects in PWRIExperimental Researches for Seismic Retrofit

1982 Urakawa‐oki EQ

Seismic Retrofit Improved Seismic Performance Well

Retrofit

LESSONS

･Increase of Design Acceleration･ Improvement of Ductility

Revision

of

Design

Code

Unretrofitted

Unretrofitted Bridges Repeated Similar Damage Observed in Past EQs

Retrofitted Bridges Suffered Minor Damage except a Few Bridges

写真提供：茨城県

写真提供：茨城県

Extension of Seat Length Successfully Prevented Superstructure from Unseating!

2011 Great East Japan Earthquake

Reference: Ogasawara et., 67th JSCE Annual Meeting, VI-572, 2012.9

Released by Tohoku Regional Development Bureau, MLIT

Operation“TEETH OF COMB”

Route 4 and 11 east-west routes to coast area were serviceable to emergency vehicle up to March 12.Seismic retrofit for bridges in these important routes contributed to the quick recovery of highway network.

Resilient Design for Extreme Seismic Events

Seismic Assessment of Existing Foundation

Seismic Behavior of Foundation in Liquifiable Soil Based on Large-scale Shake Table Tests

Seismic Retrofit Technique with reducing post-anchored bars

Tsunami Effect on Bridges

Ongoing Seismic Research Project for Bridge

・ Damage-control approach to minimize the function damage

・ Capacity of Existing Piles and Evaluation of Limit State of Foundation

・ Seismic Retroifit of Foundation in Liquifiable Soil

・ Connection between Existing Section and Post-anchored Devices

・ Assessment of Existing Bridges for Tsunami-induced Force・Structural Planning for Mitigating Tsunami Effect on Bridges

JCI Paper #3