advancement of technology to improve seismic performance of...

TECHNICAL CHAMBER OF GREECE – HELLENIC CONCRETE SECTIONJAPAN SOCIETY OF CIVIL ENGINEERS

20th November 2009, ELECTRA PALACE Hotel

Advancement of technology to improve seismic performance

of concrete bridge after Kobe earthquake

Hikaru NAKAMURANagoya University, Japan

Hanshin-Awaji (Kobe) Earthquake

Collapsed highway piersthe supporting columns collapsed over 600m

Date : January 17, 1995Magnitude : 7.2Type : inland type due to active faultDepth of epicenter : 14km Max. Acc. : 818cm/s2

The dead persons : 6425Economic Loss 100billion Euro

Earthquakes in Japan from 1960-2009 over magnitude 6.5

Strong earthquakes occurred many times and in all areaEarthquake mapEarthquake history

2000190019801960 1970

Impossible to avoid damage due to earthquake!

Economy loss forecast due to future earthquakes

Big earthquake riskLoss of huge moneyLoss of many human life

Probability map of earthquake

Economy loss forecast and occurrence probability

Economy loss(billion Euro)

Probability during 30

years

Inland earthquake in

Tokyo

70070%

Tonankai and Nankai

earthquake

35050%

Tokai Earthquake

200 86%

CONTENTS

Damage of concrete structuresdue to recent earthquakes in Japan

Advancement of seismic design- JSCE Standard Specifications

for Seismic Performance Verification -

Advancement of seismic performance- Seismic Retrofit method, Seismic isolation

and Vibration Control Technique -

Recent strong earthquakes concrete structures were damaged

1: Kobe, 95.1.17, M7.22: Tottori,00.10.6, M7.33: Geiyo, 01.5.24, M6.74: South of sanriku-oki,

03.5.26, M7.15: Miyagi-oki, 03.7.26, M6.26: Tokachi-oki, 03.9.26, M8.07: Niigata-ken chuetsu,

04.10.23, M6.88: fukuoka-oki, 05.3.20, M7.09: Noto Hanto,

07.5.25, M6.910: Niigata-ken chuetsu-oki,

07.7.16, M6.8

After Kobe Earthquake, the concrete structures have been damaged due to several earthquakes in Japan.

13

4

5

6

2

8

7109

Mechanism of earthquakes

150km

100km

50km

0

InterplateInland

magma reservoir Japan

trenchJapan

sea

mantle

Outbreak of magma

volcano

Intraslab

Pacifi

c pla

te

Eurasian plate

Inland type: occur at fault and epicenter is near ground surfaceKobe(M7.2) , Tottori(M7.3), Off miyagi(M6.2), Niigata(M6.8)

Interplate type: occur at interplate and epicenter is relatively deepOff Tokachi(M8.0)

Intraslab type: occur inside plate and epicenter is deepGeiyo(M6.7), South of sanriku-oki(M7.1)

Mechanism of earthquakes

Kobe Earthquake on January 17, 1995

Many Concrete Structures were collapsed.

First experience of big Inland type earthquake at city area.

Magnitude : 7.2Type : inlandDepth of epicenter : 14kmMax. Acc. : 818cm/s2

Kobe Earthquake occurred at Hyogo Prefecture in 1995.

Damage due to Kobe Earthquake onJanuary 17, 1995

Geiyo Earthquake on March 24, 2001

Magnitude : 6.7Type : intraslabDepth of epicenter : 50kmMax. Acc. : 830cm/s2

The Geiyo Earthquake occurred at Aki-nada in the Seto Inland Sea

Damage due to Geiyo Earthquake on March 24, 2001

146 piers in RC elevated bridges of Sanyo Shinkansen were damaged. The shear failure with the spalling of cover concrete was observed by 12 piers among these. Photo shows a damaged two story RC rigid frame elevated bridge. The feature of damage is that severe diagonal shear crack was observed in the middle layer beam.

Tokachi-Oki Earthquake on September 26, 2003

The feature of the earthquake ground motion was that long-period wave is dominant and the duration time is long.A fire of the oil storage tank occurred due to sloshing and the effect of the long-period wave have been paid to attention.

Magnitude : 8.0Type : inter-plateDepth of epicenter : 42kmMax. Acc. : 972cm/s2

The Tokachi-Oki Earthquake occurred at southeast offshore of Hokkaido and the magnitude was 8.0. Tsunami was also observed. It was typical inter-plate type earthquake.

For pier, the spalling of the concrete cover and the buckling of the longitudinal re-bars occurred.

For the floor slab at the end of girder, damage occurred due to the collision between girders.

Damage of Toshibetsu-gawa railway bridge

Damage of a pier Damage of floor slab

Typical Damage

Left photo shows the flexural failure in the piers in which spalling of concrete cover and buckling of the longitudinal re-bars were observed. Right photo shows the punching shear failure at support due to horizontal force from anchor.

Damage of Chiyoda highway bridge

Damage at a supportDamage of a pier

Damage of Uroho-gawa railway bridge

The spalling of the concrete cover and buckling of the longitudinal re-bars occurred at cut-off plane of the longitudinal re-bars.

Moment

Capacity

South of Sanriku-Oki Earthquake on May 26, 2003

The feature of the earthquake ground motion is that short-period wave is dominant.

Magnitude : 7.1Type : intraslabDepth of epicenter : 71kmMax. Acc. : 1106cm/s2

The South of Sanriku-Oki Earthquake occurred at Off Miyagi Prefecture in 2003.

The severe damages were observed in 5 one story RC viaduct of Tohoku Shinkan-sen constructed in 1977 to 1978. The feature of these damages was that the end columns are mainly damaged.

Damage due to South of Sanriku-OkiEarthquake on May 26, 2003

damaged one story RC elevated bridges

Two of the end columns failed in shear with the spalling of the cover concrete, while others were observed diagonal cracks. The damagedue to flexure hardly observed. The feature of structures is that the end columns has severe condition for shear failure, because they are shorter than intermediate columns to support simple beam between elevated bridges.

Damage of four bay one story RC viaduct of Shinkan-sen

SB（spalling of cover concrete)

SC（crack width > 1mm)SD（crack lwidth < 1mm)

No observed crack

b

a

(a) damage of end column (view from a) (b) damage of intermediate column (view from b)

Restoration procedure was (1) injection of epoxy resin to cracks, (2) restoration of cross section by shrinkage compensating mortar, and (3) steel jacketing.

Process of repair and strengthening of damaged structures

Restoration finished only in 3 days

May 26: earthquake occurMay 27: shinkan-sen start to drive slow speedMay 29: shinkan-sen drive normal speed again

Niigata-ken Chuetsu Earthquake on October 23, 2004

The earthquake occurred when a Shinkan-sen was running. Then, Shinkansen was derailed.


The Niigata-ken Chuetsu Earthquake occurred at Mid Niigata Prefecture. It was caused by inland active fault.

Left photo shows damage of end columns failed in shear. The end columns show severe damage more than intermediate columns. This failure is the same as the one explained in the South of Sanriku-OkiEarthquake.

Damage of three bay one story RC frame elevated bridge of Shinkan-sen

Dai-san Wanazu Bridge R1 of Joetsu Shinkansen

Damage of end column Column strengthenedby the steel jacketing

The spalling of the concrete cover and buckling of the longitudinal re-bars occurred at the mid height. Failure occurred at the cut-off plane of the longitudinal re-bars. Lateral ties at that location detached.

Damage of Uono-gawa Bridge of Joetsu Shinkansen

(a) Panorama of Uono-gawa bridge (b) Close-up of damaged portion

Niigata-ken Chuetsu-oki Earthquake on July 16, 2007

The earthquake occurred near nuclear power station.


The Niigata-ken Chuetsu-oki Earthquake occurred at Mid Niigata Prefecture. It was caused by inland active fault.Same type earthquake occurred 3 years ago near the place.

CONTENTS






Kobe earthquakeNiigata-ken Chuetsu Earthquake

Shear failure of RC columnThe damage due to Kobe earthquake is severer, but they are same failure type

Similar damage due to recent earthquakes

Similar damage due to recent earthquakes

We already observed similar damage for several earthquakes

Kobe(1995)Niigata-ken Chuetsu(2004)

For all structures, the spalling of the concrete cover and buckling of the longitudinal re-bars occurred at mid height in piers where the longitudinal re-bars are cut off

Most major life-line structures were constructed in 1960’s and 1970’s in Japan. Then, the knowledge and design code for seismic performance were insufficient.

Tokachi-oki(2003)

Change of JSCE Specification for Design

Before 1986, the allowable stress design method was applied in JSCE Specification. Then, the allowable shear stress is large value and the minimum web reinforcement ratio is small value.

Therefore, structures constructed in 1960’s and 1970’s do not have sufficient shear capacity. This is the reason that many concretestructures failed in shear.

year1940

1.2

Allow

able shear stress

60 80 2000

0.8

0.4 Effective depth 3mMain bar ratio 0.5％

0

year

Minim

um w

eb reinforcem

ent ratio(%)

19400

0.1

JSCERailwayHighway

60 80 2000

0.2

0.3

Example for square section of 1m length(D32)

Allowable shear stress Min. web reinforcement ratio

Many concrete structures were failed roadways, railways, the port, and other lifelines

Underestimation of design seismic loadsUnderestimation of shear capacityInsufficient structural details

detaching of lap splices of web re-bar buckling of longitudinal re-barbreaking of longitudinal re-bar at spliced portion

New seismic design concept had been adopted in Japanese code after Kobe earthquake

Three major reasons why many structures were damaged

Change of JSCE Specification for Design

Allowable Stress design

Limit state design

Performance based design

1986

2002

19961995 KOBE earthquake

Seismic design

Seismic performance verification

Design

Structural performance verification

Structural design

Seismic design

Design(one chapter)

Performance based design

At 1986, limit state design was adopted, then seismic design was described as one chapter in the specification for design. After Kobe earthquake, seismic design code was established based on the performance based design. At 2007, it was included in design code again.

2007Design

Change of JSCE Specification for Seismic Performance Verification

2002 JSCE standard specification for Seismic performance verification

1996 JSCE standard specification for Seismic designThe methods for seismic performance verification of concrete structures was described basically. It includes definition of seismic performance, definition of design earthquake ground motion, modeling and analytical method and Structural details

Definition of seismic performance, definition of design earthquake ground motion are same. The items of (1)earthquake ground motion in verification, (2) evaluation for the effect of ground, (3) verification technique(analytical method) were enhanced based on the knowledge of seismic performance and the advancement of the analytical technique. Moreover, it was systematized that the more reasonable seismic performance verification becomes possible.

2007

Procedure to verify the seismic performance based on ‘Seismic Performance Verification’

Verification

Response Analysis

Setting Structure

Modeling of Structure and Ground

Setting Seismic Performance

Setting Limiting Values

Setting Ground Motion

Estimation of Response Values

END

In the specification, the methods how to consider these items are described.

Nonlinear analysis

nonlinear finite element analysis

standard technique to verify seismic performance

Seismic Performance 1

Function of the structure during an earthquake is maintained, and the structure is functional and usable without any repair after the earthquake.


Function of the structure can be restored within a short period after an earthquake and no strengthening is required.


There is no overall collapse of the structural system due to an earthquake even though the structure does not remain functional at the end of the earthquake.

Seismic Performance

Seismic performance is classified into 3 cases

The damage is allowable for strong earthquake. Performance 1 : serviceabilityPerformance 3 : safetyPerformance 2 : serviceability and restoration ability

from social and economic points of view

Concept

Important point is to make clear damage for restoration process

Limit values for membersWhen the seismic performances of structures are verified, limit values of response should be determined to assure the defined seismic performance.


displacement of a member does not exceed the yield displacement


shear and torsional capacity of a member, and ultimate displacement of a member are not reached


shear capacity of vertical members and self-weight support capacity is not exceeded

An example of skeleton curve of memberDisp.

yieldload

Load

yield disp. ultimate disp.

Shearfailure

shear failureafter yielding

flexuralfailure

Performance 3Performance 2Performance 1

Level 1 Design Earthquake Ground Motion

earthquake ground motion that is likely to occur a few times within the lifetime of a structure.

Level 2 Design Earthquake Ground Motion

very strong earthquake ground motion that has only a rare probability of occurrence within the lifetime of a structure.

Earthquake ground motion in verification

Before Kobe Earthquake, the design seismic coefficient was assumed as 0.2 and it was considerably small compared with the earthquake ground motion at the location that structures damagedin the Kobe Earthquake.

Level 2 ground motion is chosen from the ground motion caused by an inland type beneath or close to the site and by large scale inter-plate type occurring in the neighborhood of land.

design earthquake ground motion was classified into two level

Earthquake ground motion in verification

The earthquake ground motion used for seismic performance verification is expressed as the time history waveform of acceleration.This is examples of simulated earthquake ground motion waveforms at the engineering base layer for inland type and inter-plate type. Inland type has very large acceleration and Inter-plate type has long duration time.

0 20 40 60 80-800-600-400-200

0200400600800

Acceleration(gal)

Time（S）

Max. Acc. 749 gal

Examples of an inland type Level 2 earthquake ground motion

0 20 40 60 80-400

-200

0

200

400

Max. Acc. 347 gal

Acceleration(gal)

Time（S）

Examples of a off-shore type Level 2 earthquake ground motion

Example of combination with seismic performance and earthquake level

Damage location

Level 1 earthquake – seismic performance 1 (no repair)

Rotation angle of all members should be less than θy

Level 2 earthquake – seismic performance 2 (short time repair)upper andunderground beam

less than θn

column less than θnpile less than θm

Rotation angle of pile is limited to smaller value in comparison with other members, because pile is difficult to repair.

Railway frame structure

Moment

Rotation angle

Yield point

Maximum moment

Ultimate deformation

My,MnMm

θc θy θm θn

Evaluation for the Effect of GroundMethods to analyze the structure with ground

The response of a structure during an earthquake is strongly affected by neighboring ground and others. Therefore, the whole structural system including foundation or neighboring ground should be analyzed.

Engineering base layer

ground


To consider the effect of ground, a coupled analysis modeled forstructure and ground should be use to obtain the response of structure. Input place of the earthquake ground motion is at the engineering base layer.

Evaluation for the Effect of GroundMethods to analyze the structure and the ground independently

According to types or characteristics of structures and ground, dynamic interaction between structures and ground can be neglected. Then, the responses of the structures and the ground may be analyzed independently.

First, only ground model is solved for input earthquake ground motion at the engineering base layer and obtain the wave form at the base part of structure.

Then, only structure is solved for obtained ground motion at the base part of structure.


Base part ofstructures

Subsurface grounds

Input tostructures

Earthquake ground Motion for verification

Earthquake ground motionat ground surface

Verification technique(analytical method)

The seismic performance is verified by a nonlinear analysis based on finite element method.

linear member beam element

planar member plate or layered shell element

x

z

y

Fiber modelbeam element is divided into many cells with fiber technique In which material stress-strain relationships are considered.

Mechanical model using nonlinear analysis

The constitutive model of concrete, reinforcing bar, and soil should be described with those hysteresis.

Stress strain relationship shall includesoftening branch after peak stressresidual plastic strain stiffness degradation on loading and reloading path.

A simplified hysteresis model of concrete

( )a,a τ−γ− Hysteresis curve(unloading)

skeleton curve( )a,a τγ

yτ0G

( ) ( )( ) 1ry0

ra

a0aG2aG−γ

τ+τ−γ+γ=τ−τ

1G

yγ

Hysteresis curve(loading)

dynamic shear stress-strain curve of the soil

Structural Details

It was observed many damages that are related to insufficient structural details in Kobe Earthquake. Therefore, structural details were greatly revised from 'Seismic Design(1996)’.

Revised points

Development of longitudinal re-bar

Splices of longitudinal re-bar

Spacing of Lateral Re-bar

Splices of Lateral Re-bar

Anchorage of Lateral Re-bar

Development of longitudinal re-bar

Tensile re-bar shall be anchored into concrete sections not subjected to tensile stresses. It may, however, be anchored intoconcrete sections subject to tensile stresses, when the moment and shear capacity are sufficiently greater than design shear force.

Vu : shear forceVydl : design shear capacity at termination point of re-barMu : flexural momentMl : flexural moment at termination point of re-barMudl : design flexural moment at termination point of re-bar

Cut off plane

Damage due to insufficient development

Splices of longitudinal re-bar

For the splices of longitudinal re-bar, the longitudinal re-bar shall be spliced in a manner that the splices perform satisfactorily evenunder repeated stress in plastic hinge zone.

Lap splices shall not be provided in plastic hinge zones subjected to repeated stress.

Damage due to insufficient splices

Longitudinal reinforcement broke at pressure welding portion in Kobe earthquake.

Therefore, provision about splices greatly revised.

Spacing of lateral re-bar

For spacing of lateral re-bar, it is necessary to provide sufficient amount of lateral re-bar, because the lateral re-bars restrain the progress of diagonal cracks, increase shear capacity, prevent buckling of longitudinal re-bars, and also provide confinement of core concrete.

Damage due to insufficient amount of lateral re-barShear failure Buckling

ties(diameter φt)

(diameter φl)

ties

a≦bs≦a/2 and s≦12φl

Anchorage and splices of lateral re-bar

The ends of ties shall be acute-angle hooks enclosing the longitudinal re-bars and anchored in the core concrete.

For splices of ties, the ties should transmit full strength, even if the spalling occurs. Considering this requirement, flare welding or mechanical coupler are recommended.

lap splices with standard hooks

flare welding

Acute-angle hook

web re-bar did not transmit stress after spalling

Damage due to insufficient detailsTies are detachedShear crack open greatly

CONTENTS






CONTENTS

Seismic Retrofit Technique of Concrete Piers

Seismic Isolation and Vibration Control Technique


Shear Failure of Reinforced Concrete ColumnsShear Strength Enhancement

Buckling and Fracture of Re-barDuctility Enhancement(Confinement Effect)

Damage from Re-bar Cut Off PlaneDuctility and Shear Strength Enhancement

We observed three typical damage.


There are three major methods for seismic retrofit of reinforced concrete piers.reinforced concrete jacketingsteel plate jacketingfiber sheets jacketing (Carbon / Aramid)The best method is determined among them considering cost, vicinity of construction site, and handling of jacketing materials etc.

Additional cross section is thin.

Retrofit materials is light ( possible to transport by human power )

Additional cross section is thin.

Cheep for construction and maintenance.

Thick additional cross section is need for retrofitting.

t= 10～20mmt= 40mmt=250mm

FRP jacketingSteel plate jacketingRC jacketing

Injected mortar

Steel plate

RC jacket at the root

longitudinal direction

Hoop direction

Top coat

Fiber

RC jacket

footing

pier

superstructure

Rebar

Examples of Retrofit MeasureCrane

Girder

Steel plate

Cofferdam

Scaffold

River

2m

River

Scaffold

Light, High-

Strength Fiber

Girder

2m

Cut-off Section

Anchor

Steel Jacketing FRP Jacketing

Purpose of Seismic Retrofit

Retrofit of Cut-off Zone

Enhancement of Ductility

Vertical Gap between Jacket and Top of Footing

H-beam Retrofit in Plastic Hinge Zone

Enhancement of Flexural Strength by Anchor Bars

Retrofit of Cut-off Zone

Enhancement of Ductility

Vertical Gap between Jacket and Top of Footing

H-beam Retrofit in Plastic Hinge Zone

Enhancement of Flexural Strength by Anchor Bars

In order to enhancement only shear strength and ductility, there is vertical gap between jacket and top of footing.

In order to enhancement of flexural strength, jacket is anchored to footing.Then, the effect of basement should be considered.

RC Jacketing

Reinforced concrete jacketing has the advantage of cost for construction and maintenance compared with the other two methods.

So if there is no restriction, reinforced concrete jacketing will be adopted.

Usual method

Steel Jacketing

DEMERIT

• Retrofit materials is heavy

It will be often adopted to piers in urban site considering the merits

MERIT

• Additional cross section is thin

• Construction period is short

FRP Jacketing

• Additional cross section is thin• Retrofit materials is light and possible to transport by human power.

It will be adopted to narrow site, cut-off section in middle height of piers, or high-pier.

Special Technique for Seismic Retrofit of Concrete Piers

There are three major methods for seismic retrofit of reinforced concrete piers. reinforced concrete jacketingsteel plate jacketingfiber sheets jacketing (Carbon / Aramid)

Several special technique have been proposed considering construction work.

Special Technique – Coupler Joint Steel jacket

No welding workGood joint qualityNo scaffold

short construction time

Merit

Quality of steel jacket method depend on welding work.

Special Technique – Rib Plate Method

The method is possible to construct by human. It will be applied to narrow site.

Steel plate with coupler joint is arranged out side of columnSteel plate with coupler joint is arranged out side of column

補強鋼板

かみ合わせ継手

Steel plate

Couplerjoint

モルタル材


補強鋼板

鋼板取付け用弾性（ゴム）材

等辺山形鋼

モルタル材


補強鋼板

鋼板取付け用弾性（ゴム）材

等辺山形鋼

rubber

Coupler joint

mortar

Steelplate

Steel Jacket Steel plate

When bottom part of piers is retrofitted, the parts are usually underground or underwater. Then, excavation work is needed.

Special Technique – retrofit underground or underwater parts

RCjacket

soil

water

RC jacket

cofferdam

Therefore, the retrofit technique without excavation work is required for easy and quick construction work.

The retrofit of pier bottom in a ground is constructed without excavation work.

Steel pipe between hold concrete and footing is played as compression strut to increase neutral axis and to reduce compressive deformation.

Special Technique – Steel Pipe Strut Method

Strut( steel pipe)

RCjacket

Hold concreteof steel pipe

Steel pipe driving in a ground to footing

Construction of hold concrete and RC jacket on the ground

Special Technique – Steel Pipe Strut Method

Steel pipe

hold concrete

Steel pipe driving

Hold concrete construction

Special Technique – Steel Sheet Pile Method

Pier in water is enclosed by steel sheet piles.

The space between pier and steel sheet piles is excavated and is filled by concrete.

Construction of RC jacket on the water surface.

RC 巻き

River surface

River bed

RC JacketSteel Sheet Pile

footing

Infilled concrete

The retrofit of pier bottom in a water is constructedwithout cofferdam and excavation work.


soil

water

RC jacket

cofferdam

soil

water

RC jacket

Steel sheet piles

The method will be applied to the case of piers in water or the difficult location of excavation.


RC jacket

Steel sheet piles

Special Technique – Girder Collision Method

JacketPermit collision of Girder to abutment using energy absorption material. Then, the deformation of pier in water can be decrease.

Usual method

Several retrofit methods are proposed for pier in the water. Easiest method is no-retrofit of pier in water.

Reduce damage of pier in water

BIG Damage small damage

Other feature of damage at Kobe Earthquake

Unseating caused by bearing failures were observed.

Unseating Prevention System (Fail-safe System)

Girders are connected by cable, and restrainers of displacement are set.

Peldampers are set at several place in order to reduce the effect of collision.

CELL TYPE

Unseating Prevention Devices

PELDAMPER

Connection cable

HONEYCOMB TYPE

Restrainers

Unseating Prevention Devices

Connection cable

Restrainers

Increase of seat width

peldamper

Utilization of Seismic Isolator

Retrofit ConceptElongation of natural periodEnhancement of damping

Seismic Isolation

72

Seismic Isolator

Super-High Damping Rubber BearingPb Rubber Bearing

Several isolators as bearing have been proposed.

Vibration Control System

Expansion jointUsual DesignIsolationbearing

Dumper

Vibration ControlVibration control dumper is applied

Reduction of displacement

Scale down of expansion joint

Omission of unseating prevention device

Reduction of seismic force

Scale down of isolation bearing

Scale down of piers

unseating prevention device

Isolationbearing

Expansion joint

Example of Damper

Low yield stress steel damperBingham material damper

Damping using the effect of filler(silicon resin)

Damping using yielding behavior

Combination with bucking prevention system

Several isolators have been proposed for buildings. The technique is applied to bridge.

Vibration Control of Railway Viaduct

The method was developed in order to control of displacement of railway viaduct.

X shape damper brace method

damper

brace

Brace and damper are combined.

CONCLUSION

Following contents were presented.


Advancement of seismic design

Advancement of seismic performance

Japan has big earthquake risk and it is difficult to prevent thedamage due to earthquake perfectly.

As fundamental aspects of design method, accurate evaluation of dynamic response and design system from construction to restoration after earthquake are required.

Seismic retrofit greatly advanced after KOBE earthquake. Isolation and vibration control technique will be important topic.

Thank You Very Much for Your kind Attention !

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