Seismic Damage of and Seismic Rehabilitiion Techniques for Railway Reinforced Concrete Structures

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Journal of Advanced Concrete Technology Vol. 7, No. 3, 287-296, October 2009 / Copyright © 2009 Japan Concrete Institute 287

Invited paper

Seismic Damage of and Seismic Rehabilitation Techniques for RailwayReinforced Concrete Structures

Tadayoshi Ishibashi1 and Daisuke Tsukishima2

Received 6 June 2009, revised 20 August 2009

Abstract

The Miyagi Prefecture Earthquake in 1978 was the first earthquake to cause serious damage to railway concrete structures

in Japan. This was followed by the South Hyogo Prefecture Earthquake in 1995, which caused shear failure of columns of

RC viaducts carrying the Shinkansen (Bullet Train) and old railroad lines predating the 1983 seismic design standard. As

the result of various concrete structures sustaining extensive damage never experienced before, the seismic design stan-

dard was greatly revised, and the seismic rehabilitation of existing structures was started on a full scale.Basic concept of seismic rehabilitation is to prevent shear failure of columns that led to the collapse of RC viaducts and

bridges catastrophically occurred in whole structural frame during the past large earthquakes. To enhance the seismic

capacity of the whole structural frame, increase in ductility of each column through seismic rehabilitation capable ofabsorbing seismic energy is needed.

As the space under many railway viaducts is used by stations and shops, negotiations regarding the relocation of busi-

nesses, the removal of large obstacles such as heavy machinery, and the development of valid seismic rehabilitationmethods to reinforce a large number of massive columns were called for. At present, we are trying to enhance seismic

capacity as much as possible for new structures in order to prevent serious damage and enable early restoration.

1. Introduction

The Miyagi Prefecture Earthquake in 1978 was the first

earthquake to cause serious damage to railway concrete

structures in Japan. As a result, the seismic design stan-

dard was revised in 1983. However, as the revision of theseismic design standard was not retroactively applied to

existing structures, these structures did not undergo

seismic rehabilitation. Afterwards, the South Hyogo

Prefecture Earthquake occurred in 1995 and columns of

RC viaducts carrying Shinkansen and old railroad lines

constructed with pre-1983 seismic design standards

suffered shear failure. As the result of various concrete

structures sustaining extensive damage never experi-

enced before, the seismic design standard was greatly

revised, and the seismic rehabilitation of existing struc-

tures was started on a full scale. The subsequent occur-

rence of several severe earthquakes further underlined

the urgency and importance of the seismic rehabilitationof existing railway structures to secure the safety of

railway transportation (Table 1). This paper describes

the damage to railway RC structures caused by earth-

quakes in Japan and various seismic rehabilitation

methods developed in the process of advancing seismic

rehabilitation.

2. Seismic damage of railway RC structure

The Miyagi Prefecture Earthquake in 1978 caused shoe

damage at many railway facilities such as RC viaducts

and RC piers (Fig. 1). In response, restrainer cables have

been installed in bridge movement joints and bracketshave been attached to abutments on all railway lines in

Japan. However, before the South Hyogo Prefecture

Earthquake in 1995, no seismic rehabilitation for RC

structures had been conducted except for measures pro-

viding against the Tokai Earthquake. In the 1980s, an RC

viaduct for the Shinkansen in the Shizuoka area was

reinforced with steel plate jacketing and a connecting

adjacent viaduct with prestressing cable.

Due to the South Hyogo Prefecture Earthquake in

1995, many columns of RC viaducts suffered shear fail-

ure (Fig. 2). As a result, the beams and bridges that hold

up railway tracks suffered serious damage. The failure

mode of these damaged structures became shear failure before yielding of the longitudinal reinforcement of

column members. Fortunately, as the earthquake oc-

curred in the early morning, accidents involving trains

falling from RC viaducts and bridges did not occur.

Following this earthquake, the Ministry of Land, Infra-

structure and Transport instructed rail operators to con-

duct seismic rehabilitation to prevent shear failure of

columns. Thus seismic rehabilitation of existing RC

railway structures that were constructed based on the old

design standard officially started. At first, the target area

of seismic rehabilitation was limited to overcrowded

lines in the Sendai, Kanto, Tokai, Kinki, and Sanyo areas

and around active faults in view of the active fault size

and the influence of a damaging earthquake on human

1Head, Structural Engineering Center, East Japan

Railway Company, Tokyo, Japan2

Structural Engineering Center, East Japan RailwayCompany, Tokyo, Japan

E-mail :[email protected]


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288 T. Ishibashi and D. Tsukishima / Journal of Advanced Concrete Technology Vol. 7, No. 3, 287-296, 2009

life and living, and the regional economy (Fig. 3). Then,

following the occurrence of a series of serious earth-

quakes that damaged concrete structures after the South

Hyogo Prefecture earthquake of 1995, seismic rehabili-

tation of existing structures was conducted nationwide.For example, soon after the South Hyogo Prefecture

earthquake in 1995 occurred, East Japan Railway Co.

began conducting seismic rehabilitation of RC railway

structures on a preferential basis in areas that have

overcrowded lines in the Sendai and South Kanto areas

and active faults with a high probability of earthquakes.Then, in 2003, the Sanriku Minami Earthquake oc-

curred in an area where seismic rehabilitation was not

planned. Since this earthquake damaged RC viaducts of

the Tohoku Shinkansen, it was decided to reinforce all

Shinkansen lines regardless of the area. As the rehabili-

tation plan was underway, the Niigata Chuetsu Earth-

quake of 2004 (Fig. 4) and the Niigata Chuetsu-okiEarthquake of 2007 occurred. The Niigata Chuetsu

Earthquake caused damage at the cut-off section of the

river pier. As a result, seismic rehabilitation needed to be

accelerated. However, the space under many railway

viaducts is used for stations, shops, and other buildings.Thus seismic rehabilitation poses a number of challenges,

including the relocation of shops and the removal of

heavy machinery and other obstacles, which have to be

overcome in order to allow the reinforcement of a large

number of columns.

3. Seismic rehabilitation technique

3.1 Basic conceptThe basic concept of seismic rehabilitation is to prevent

shear failure of column members caused by large earth-

quakes resulting in the collapse of RC viaducts and

bridges, which are catastrophes that have occurred in

past earthquakes. To enhance the seismic capacity of the

whole structural frame, the aim is to increase the ductilitycapacity of column members through seismic rehabilita-

tion in order to allow better absorption of earthquake

energy, but enhancing the flexural strength of the column

members is not properly done. The reason for this is that

if the flexural strength of the column members damaged

by an earthquake is enhanced, future earthquake damage

may occur in beam members and foundation members.

Since repair and strengthening of beams and foundation

members is more difficult than for column members, it is

considered important to restrict damage after seismic

rehabilitation to column members.

3.2 Main seismic rehabilitation methods for RCviaductsIn almost all RC railway viaducts, the space under the

viaduct is used by stations, shops, and other buildings.

Therefore seismic rehabilitation must deal with various

obstructions such as partition walls and equipment. Inthis case, the construction site is a confined space, which

means restrictions on the use of large construction

equipment such as cranes. Often, construction schedule

restrictions also apply, so that a suitable method designed

taking into account the various conditions at each site

must be adopted. The main seismic rehabilitation meth-ods are outlined below.

Fig. 1 Damages to bearings during the Miyagi Prefecture Earthquake in

1978. Fig. 2 Shear failure at viaduct piers during the

South Hyogo Prefecture Earthquake in 1995.

Table 1 Main occurrences of domestic seismic damage (since South Hyogo Prefecture Earthquake in 1995).

Year 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 Comment

☆ ☆

South Hyogo Prefecture Sanriku Minami Noto Hanto

Earthquake in 1995 (M7.3) Ear thquake in 2003 (M7.1) Earthquake i n 2007 (M6.9)

☆ ☆

Western Tottori Prefecture Niigata Chuetsu Iwate-Miyagi Nairiku

Earthquake in 2000 (M7.3) Earthquake in 2004 (M6.8) Earthquake in 2008 (M7.2)

☆ ☆ ☆

Geiyo Earthquake North Miyagi Niigataken Chuetsu-Oki

in 2001 (M6.7) Earthquake in 2003 (M6.2) Eart hquake in 2007 (M6.8)

☆ ☆ ☆

Tokachioki West Fukuoka North Coast Iwate

Earthquake in 2003 (M8.0)Earthquakein 2005 (M7.0) Earthquake in 2008 (M6.8)

Main

occurence

s of

domestic

seismic

damage


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T. Ishibashi and D. Tsukishima / Journal of Advanced Concrete Technology Vol. 7, No. 3, 287-296, 2009 289

List of epicenters of various earthquakes

① Miyagi Prefecture Earthquake ② South Hyogo Prefecture Earthquake ③ Sanriku Minami Earthquake

④ Niigata Chuetsu Earthquake ⑤ Niigataken Chuetsu-Oki Earthquake

Fig. 3. Epicenter of various earthquakes and target areas of seismic rehabilitation. Thicker lines are Shinkansen railways

and thinner lines are local ones. Small open circles represent main station in the area.

Fig.4 Damages to piers during the Niigata Chuetsu Earthquake in 2004.


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(1) Steel plate jacketing method (Ishibashi et al .2004, Fig. 5)This method is the most common seismic rehabilitation

technique used for railway RC viaduct columns. Jack-

eting with steel plate 6 to 14mm thick enhances the shearstrength and ductility capacity of RC viaduct columns.

After jacketing, the gap between the steel plate and ex-

isting column is grouted with non-shrink mortar, etc..

Although the joint method with site welding is common

for steel plate joints, indented joints are used to ensure

construction quality.

A method using assembled steel plate panels has also

been developed (Fig. 6). This method consists in as-

sembling precast panels with projections by using per-

forated connect plates around an existing column. Then,

after securing these members by rivets, the gap between

the steel plates and the existing column is grouted with

non-shrink mortar. Besides enabling manual assembly,this method also has the merits of low noise and vibration

levels, which makes it suitable for work under viaducts

where there are shops or other buildings. In addition, as

this method employs factory-made products, consistent

quality is ensured and design aspects can be concen-

trated.

(2) Other jacketing methods (American Con-crete Institute 2008, Fig. 7)In the case of rehabilitation work in a confined con-

struction site such as a space under a viaduct that has

shops or other buildings and is near other buildings, use

of the steel plate jacketing method, which requires theuse of large construction equipment such as cranes, is

difficult. Therefore, various other jacketing methods

including ones that apply fiber-reinforced plastics (car-

bon fiber, aramid fiber, etc.) sheets, other ones that spray

glass fiber and epoxy resin directly to the member faces

with a spray gun or combine sprayed mortar with rein-

forcing bars, and still other methods that use precast

concrete panels, have been developed.

(3) Rib-bar and rib-plate method (Ishibashi et al .2004.)The rib-bar method was developed to enhance shear

strength and ductility capacity by reinforcing bars an-chored with supporting members arranged at each corner

of RC viaduct columns (Fig. 8, Fig. 9). This method

eliminates the need to remove partition walls and enables

manual assembly in confined construction sites such as

areas under viaducts that have shops or other buildings

and facilities.

Another method, the rib-plate method, which rein-

forces RC viaduct columns with steel plate bands with

indented joints, was also developed for the same purpose

as the rib-bar method (Fig. 10, Fig. 11). The indented

joints make this method easy to use, and as the bands are

easy to fabricate, this method can be easily applied to

columns with various cross-section shapes.

(4) Thin plates attachment method (Associationof Railway Advanced Construction Technology

2008, Fig. 12)This method was developed to enhance the shear strength

and ductility capacity of RC viaduct columns by attach-

Fig. 5 Steel plate jacketing.

Fig. 7 Method using FRP sheets.

Fig. 6 Assembled steel plate panels.


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ing thin plates about 0.8 mm thick by adhesion bond. The

purpose of this method is the same as that of the rib-bar

and rib-plate methods. This method has the advantage

that following column reinforcement, the increase in

member section thickness is only 20 to 30 mm, comparedto 40 to 50 mm for the jacketing steel plate method. This

minimizes space reduction for shops and other buildings

under viaducts.

(5) Method using concrete segment and steelstrand wire (Okamoto et al . 2006)This method, which consists in attaching four

washboard-shaped precast concrete segments to the

member faces and banding them with galvanized spiral

strand wire was developed for the same purpose as the

previously described methods (Fig. 13). Advantages of

this method include the use of factory-made reinforcing

products enabling stability and easy control in quality,and visual inspections of existing column corners leading

to rapid and easy emergency checkup at daily or

post-earthquake operations.

(6) Single-face method (Ishibashi et al . 2004, Fig.

14, Fig. 15)

This method, which uses a steel plate and reinforcing bars, is applied to only one face of the RC column for the

same purpose as the previously described methods. This

method is suitable when only one face of RC viaduct

columns is exposed due to adjacent shops, storage sheds,

etc., under a RC viaduct. This method eliminates the

need to remove shops and suspend business during re-

habilitation work.

(7) Method using steel damper and braces(Shimada et al . 2005, Fig. 16)This method uses steel dampers and braces to reinforce

mainly building frames. The role of the steel braces is to

control deformation of the RC viaduct columns, whilethe role of the damper placed at the center is to absorb

energy. In cases when it is impossible to apply a jacketing

Fig. 8 Conceptual diagram of rib-bar method. Fig. 9 End of rib-bar retrofit.

Fig.10 Conceptual figure of rib-plate method. Fig. 11 End of rib-plate retrofit.

Supporting member

Reinforcing bar

Steel plate band

Indented joint


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method owing to the presence of walls, etc., a pair of

steel dampers and their respective braces can be placed

inside the RC viaduct in the track direction and the di-

rection perpendicular to the track, respectively, for

seismic rehabilitation.

3.3 Main seismic rehabilitation methods for RCpiersRC piers can also be reinforced using a number of

methods for seismic rehabilitation. RC piers have a

cut-off in their main longitudinal reinforcements. This

cut-off area is a weak point of RC pier when an earth-

quake occurs. The cross section of RC piers is larger than

that of RC viaduct columns. Wall type piers and piers

with an elliptic cross section have different cross sections

in the track direction and the direction perpendicular to

the track, making it impossible to adopt the same seismic

rehabilitation methods as for RC viaducts.Therefore, concrete or steel jacketing is used to in-

crease the flexural and shear strength of the cut-off area

to protect this area from damage. So the seismic reha-

bilitation concept is based on enhancing the shear

strength and ductility capacity of piers to avoid shear

failure and absorb the energy generated by earthquakes

through ductility capacity. Further, the concept that pre-

vents the flexural strength of RC piers from increasing

and suppresses the influence on other structural members

is the same as for RC viaducts.

The main seismic rehabilitation methods are outlined below.

(1) Reinforced concrete jacketing method (Fig.17)Reinforced concrete jacketing for RC piers increases

shear and flexural strength around the cut-off area and

enhances the shear strength of RC pier as the whole and

the ductility capacity of the pier base. This method can be

used to reinforce the area around the cut-off, the base of

the pier, and other areas in need of seismic rehabilitation

depending on the seismic capacity of the existing RC pier.

As a result, it is possible to end seismic rehabilitation

after reinforcing only the area around the cut-off. The jacketing thickness is on the order of 200 mm. Further-

more, for the seismic rehabilitation of RC piers situated

in valleys in mountain areas and near houses or along a

road, a construction method using elevating scaffolds for

workability and safety has been developed. (Association

補強薄板Thin plates

Fig. 12 Conceptual diagram of thin plates attachment

method.

Steel plate

Reinforcing bar

Wall

Existing column

Fig. 14 Conceptual figure of single-face method.

Fig. 13 Using Concrete segment and Steel strand wire

method.

Fig. 15 End of retrofit.


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of Railway Advanced Construction Technology. 2008,

Fig 18, 19)

(2) Steel plate jacketing method (AmericanConcrete Institute 2008; Tamai et al . 1999.)Steel plate jacketing for RC piers increases the shear and

flexural strength around the area of the cut-off and en-

hances the shear strength of RC pier as the whole as well

as the ductility capacity of the pier base. The thickness

including the steel plate is 40 to 50 mm. Since the in-

crease of the cross section after seismic rehabilitation by

steel plate jacketing is smaller than RC jacketing, this

method can be applied to constrained site conditions.And similarly to RC jacketing, it is possible to end

seismic rehabilitation after reinforcing only the area

around the cut-off, and depending on the type of pier, the

base of RC pier can be confined for enhancing ductility

after seismic rehabilitation.

(3) FRP sheet jacketing method (AmericanConcrete Institute 2008)A fiber reinforced plastics (carbon fiber, aramid fiber,

etc.) sheets jacketing method has been developed and is

used for RC piers. A method that uses fiber reinforcedsheets pre-impregnated with ultraviolet curable resin for

jacketing has also been developed. As FRP sheets arelightweight, they are easily carried to the construction

site. As the resin becomes hard with ultraviolet, the

sheets do not have to be impregnated with a curative

agent, contributing to shorter construction time.

(4) Method using concrete filled tube (Associa-tion of Railway Advanced Construction Tech-nology 2008, Fig. 20, 21)After removing any sediment inside steel tubes inserted

into the ground, concrete is cast into the tubes. The con-crete filled tubes then serve as strut members supporting

an cantilever concrete block attached to the RC pier. As a

result, this structure mainly enhances the ductility capacity of the pier base.

Compared to the jacketing method with reinforced

Fig. 16 Method using steel damper and braces. Fig. 17 Method using RC jacketing.

Fig. 18 Example of RC pier in valley.

Fig. 19 Elevating scaffold.


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concrete and steel plate after sediment excavation, this

method reduces construction cost since large sediment

excavation and temporary works are not needed for this

method.

(5) Method using steel sheet pile (Associationof Railway Advanced Construction Technology2008, Fig. 22)After removing any sediment inside a steel sheet pile

inserted into the ground around an RC pier, mortar

casting is conducted into the space between the RC pier

and the steel sheet pile to enhance the shear strength and

ductility capacity of the RC pier. Since steel sheet plates

are used as reinforced members for RC piers, temporary

works need not be constructed in rivers, which signifi-

cantly cuts down construction cost.

4. Considerations for the design of newstructures

Next, we refer to matters that should be considered for

new structures based on consideration of seismic damage

and restoration. Figure 23 shows an example of the

elasticity acceleration response spectrum applied to the

current seismic design standard. The basis of the design

is that the response displacement calculated by elasto- plasticity response analysis is below the ductility capac-

ity of the structure. However, as the evolution of the

seismic design standard shows, the demanded seismic

capacity has grown with each new occurrence of earth-quake damage. Given this fact, there is a good possibility

that the seismic design standard will again change in the

future. Therefore, if construction costs remain un-

changed, enhancing the seismic capacity as much as

possible is desirable. Enhancing the strength of a struc-

ture requires reinforcement of all the members including

the foundation. However, the cost of construction would

increases excessively as a result. On the other hand,

enhancing the ductility capacity of the structure can be

done by reinforcing only the plastic hinge part, for a

minimal increase in construction cost. Therefore, the

reinforcement arrangement for enhancing the ductility

capacity should be designed in the plastic hinge zone.To this end, regardless of the level of ductility capac-

ity required for the design, spiral reinforcement is ar-

ranged inside the longitudinal reinforcements in the 1D

area of the column of a new RC viaduct (D is the height

of the cross section of the column) (Fig. 24, 25). Figures

26 and 27 show the situation of the cyclic loading ex-

periment and the relationship between the load and dis-

CFT (strut member)

Existing pier

Concrete block

CFT (strut member)

Existing pier

Concrete block

Fig. 21 Conceptual diagram of concrete. filled tube

method.

R e s p o n s e a c c e l e r a t i o n s p e c t r u m ( g a l )

Period (s)

R e s p o n s e a c c e l e r a t i o n s p e c t r u m ( g a l )

Period (s)

Fig. 23 Example of elasticity acceleration responsespectrum (Gn shows ground classification (ground dif-

ference)).

Fig. 20 Method using concrete filled tube.

Water level

Ground level

Existing pier

RC or steel plate

jacketing

Steel sheet pile

Water level

Ground level

Existing pier

RC or steel plate

jacketing

Steel sheet pile

Fig. 22 Conceptual diagram of steel sheet pile method.


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placement of a column with spiral reinforcement inside

the longitudinal reinforcements. The placement of insidespiral reinforcement enhances the ductility capacity

greatly compared to when sufficient hoop reinforcements

are provided (Kanno et al. 2009). The fact that the in-

ternal concrete in the plastic hinge zone breaks up out-

ward through being freed from binding force by buckling

of the longitudinal reinforcements and associate break oftie hoops causes rapid impairment of the flexural capac-

ity of the column and settling down of the column (Sato

and Ko 2008). Thus providing spiral reinforcement in-

side the longitudinal reinforcements shackles the internal

concrete inside the longitudinal reinforcements, pre-

venting the collapse of the internal concrete and en-

hancing the ductility capacity greatly.

Since it involves the construction of new structures, it

is important for seismic design to enhance the seismic

capacity as much as possible. It does not suffice for the

response displacement calculated by response analysis to

be lower than the acceptable value; since the plasticity

rotation capacity in the plastic hinge zone can be greatly

boosted without an increase in cost, this bears consid-

eration during actual design. Although restoration is

extremely onerous after a structure collapses, the amount

of displacement has little influence on the difficulty of

restoration as long as the structure has not collapsed.

Thus it is important to enhance the ductility capacity of

columns as much as possible in order to prevent the

collapse of a structure. Such consideration prevents se-

rious damage and enables early restoration in addition to

significantly boosting safety, even in the event of an

earthquake that is larger than predicted.

5. Conclusion

Seismic design and rehabilitation techniques evolve

along with earthquake occurrences. In other words, the

experience of a number of earthquakes drives the de-velopment of various new technologies and techniques

inside spiral reinforcement

１D区間１D区間1D section

inside spiral reinforcement

１D区間１D区間1D section

Fig 25 Example of RC viaduct fitted with inside spiral

reinforcement.

Fig. 26 Situation of cyclic loading experiment (after load-

ing up to 20δy).

The colum with hoop reinforcement outside the axial reinforcements

The colum with spiral reinforcement inside the axial reinforcements

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

-30 -20 -10 10 20 30

plasticity rate δ/δyeild

S t r e n g t h r a t i o P / P y

e i l d

The colum with hoop reinforcement outside the axial reinforcements

The colum with spiral reinforcement inside the axial reinforcements

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

-30 -20 -10 10 20 30

plasticity rate δ/δyeild

S t r e n g t h r a t i o P / P y

e i l d

Fig. 27 Example of relationship between strength ratio

and plasticity rate during cyclic loading.

Fig. 24 Example of arrangement of spiral reinforcement

inside longitudinal reinforcements.

Column with hoop reinforcements outside of the longitudinal reinforcements

Column with a spiral reinforcement inside of the longitudinal reinforcements


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for seismic design and seismic retrofitting and the sys-

tematic seismic rehabilitation of existing structures. The

authors hope that the various technologies and tech-

niques introduced here will prove helpful for everyone.

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approved for public relations.”

http://www.rail-act.org/ (in Japanese)

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Documents

Seismic Damage of and Seismic Rehabilitiion Techniques for Railway Reinforced Concrete Structures