No. 42 August 2014

STEEL CONSTRUCTIONTODAY & TOMORROW

http://www.jisf.or.jp/en/activity/sctt/index.html【 h a s h i 】“橋 (hashi)” in Japanese, or bridge in English

Bridges constitute the most important element of social
infrastructure. This issue, No. 42, discusses the emerging
trends in the design standards for bridges, the maintenanceof steel highway and railway bridges, and the retrofitting of
RC slab bridges to steel deck bridges.

In this issue.....
1 Design Standards for Civil
Engineering Structures

4 Report on Repair of

Fatigue Cracks of the
Orthotropic Steel Decks in
the United Kingdom

8 Maintenance andPublished Jointly by

The Japan Iron and Steel Federation

Photo: Metropolitan Expressway Co., Ltd.

Reinforcement of Steel
Bridges on the Tokaido
Shinkansen

12 Maintenance of Metropolitan Expressways
16 Replacement of RC Slabs with Steel Decks on Mikawaohashi
BridgeJapanese Society of Steel Construction

Back cover Conference on Recent Technologies for Steel
Structures 2014 in Phnom Penh

Design Standards for Civil Engineering Structures

Design Standards for Civil Engineering
Structures-Performance- and Reliability-based Designs, and Future Directionsby Yusuke Honjo
Professor, Faculty of Engineering, Gifu University
This article discusses the design standards
for civil engineering structures in Japan
with the following two objectives: to briefly
introduce the trends of the last 15 years andto prospect future directions. The key termsof this discussion are performance-based
design and reliability-based design.
Here, the term “performance-based design” conforms to the definition provided in JGS4001-20041), which states, “Performance-based design: a design concept inwhich structures are not designed based on
descriptive characteristics, but are designedby specifying the performance required bysociety.”
Details of Reliability- and Performance-based Designs• Introduction of Design Standards
Based on Reliability-based Design
The introduction of reliability-based design, or the limit state design method, dates
back to the 1970s. At that time, efforts werelaunched in Europe to prepare design standards for buildings and infrastructure facilities that were commonly used throughout the European community of nations.
The standard thus prepared is the currently prevailing Structural Eurocode. Based on

the concept of “putting new wine into freshwineskins,” the Eurocode introduced a verification method based on reliability-based
design, which had just been compiled. It is
well known that the Eurocode was completed and put into effect in 2010 after nearly 40
years of preparation.
Established in 1983 in North America,
the Ontario Highway Bridge Design Code(OHBDC) is a full-scale design standard
based on reliability-based design. Triggeredby the establishment of this code, preparation began in the latter part of the 1980s on
Bridge Design Specifications (BDS), which
was issued by the American Association ofState and Highway Transportation Officials(AASHTO) and is the most influential design standard in the field of civil engineering structures in North America. Then in
1995 the LRFD (load and resistance factor
design)-version of AASHTO BDS was issued and has since undergone regular revision.
In spite of steady movement in Europe
and North America, Japan trailed far behindin the establishment of design standards that
rely on partial factor-type verification formulae based on the reliability-based design
method. It was the Technical Standards forFig. 1 Two Basic Roots in Performance-based Design
Nordic 5 Level
SystemNew ZealandAustralia

UK

CanadaGoals

Objectives

Objectives

Goal

Objectives

Functional
requirements

Functional
requirements

Functional requirements

Functional
requirements

Functional
requirements

Operational
requirements

Performancerequitemens

Verification
methods

Verification
methods

Acceptable
solutions

Acceptable
solutions

Performancerequirements

1 Steel Construction Today & Tomorrow August 2014

Deem tosatisfy
Performance
Techinicalsolutions
Alternative
approaches

Acceptable
solutionsPort and Harbor Facilities in Japan issued
in 2007 that was Japan’s first design standard for civil engineering structures clearlybased on reliability-based design.
Specifications for Highway Bridges, themost influential reference for the design ofcivil engineering structures in Japan, currently does not adopt the partial factor design method. However, it is now under vigorous revision that will likely be completed
in the near future and will widely incorporate verification formulae based on the
LRFD approach.
Japan lags behind Europe and North
America in the introduction of reliabilitybased design in design standards, but in its
introduction in Japan there is a feature thatdiffers distinctly from other countries. Thatis, in Japan’s design standards, great importance is attached to the framework called
performance-based design, and then the reliability-based design is positioned as theperformance verification method and incorporated into the standards. Introduction of
performance-based design is explained in
the following:• Details in Introduction of Performance-based Design
When examining design standards worldwide, there are at least two basic roots in performance-based design. One originates in theNordic 5 Level System2) (Fig. 1). In order topromote international harmonization of building standards, in its concept, the required performances are stratified and divided into twolayers: mandatory requirements and supporting documents (guidance). This concept
is closely related to a statement in the Agreement on Technical Barriers to Trade of World
Trade Organization (WTO/TBT Agreement):“technical regulations based on product requirements in terms of performance rather
than design or descriptive characteristics (Article 2.8).” Another concept originates in the
proposal for a required performance matrix(Fig. 2) that is shown in Vision 2000 of theStructural Engineers Association of Califor-

Seismic performance level

Earthquake design level (return period)

Fully operational

OperationalLife safe

Near collapse

Frequent(43 years)
Unacceptable performance(for new construction)

Occasional(72 years)

Es

Ba

se

Rare
(475 years)

Very rare(970 years)

Sa

fet

yc

sic

riti

nti

ca

al/

lo

ha

bje

za

rdo

us

cti

ob

ob

jec

jec

tiv

e

WTO/TBT
Agreement
Specification
by performance

Respect forinternational
standards(ISO2394 etc.)tivePerformance-based
designReliabilitybased
designmethod,
LSD, LRFD

Other
designmethods

Performancerequirement

Fig. 3 WTO/TBT Agreement and Performanceand Reliability-based Designs

Designverification

Fig. 2 Performance Matrix in Vision 2000 of SEAOC

venia (SEAOC, 1995)3). Triggered by the damage experienced in both the Northridge andLoma Prieta Earthquakes, the proposal was
worked out as a means to promote dialogue
between building owners and structural engineers regarding seismic resistance.
Currently in Japan, there is a movement
to establish a design standard that primarily incorporates the verification of structures by means of reliability-based designthat is based on the performance-based design concept. It can be said that the firststep in this movement was attributable tothe WTO/TBT Agreement that went into effect in 1995. Taking this opportunity, theJapanese government implemented a wider deregulation policy. As a link in deregulation, several policies were promoted suchas the international conformance of various
industrial standards in Japan, specificationof performances and elimination of repetitive inspections.
To meet such trends, the Japanese engineering societies quickly responded to the
movement to introduce the performancebased design concept proposed in the WTO/TBT Agreement into Japanese design standards. Among the practical attainments inthis field were Geo-code 21 that was established by the Japanese Geotechnical Society in 2004 and the code PLATFORM4) by
the Japanese Society of Civil Engineers in
2003, both of which affected subsequent revisions of various design standards.
Fig. 3 conceptually shows the position of
performance- and reliability-based designs
in the design standards and the relation between them and the WTO/TBT Agreement

and ISO standards. The performance-based
design framework is based on the agreement in terms of international commerce
policies. Accordingly, it is believed that, inthe future preparation of design codes, theperformance requirements of structures will
be indicated by performance criteria, andthat the verification of performance criteria will use the reliability-based design approach prescribed in ISO2394 and other international standards.
Current Design Standards for Civil
Engineering Structures in JapanAs stated above, the Technical Standards
for Port and Harbor Facilities in Japanwas revised in 2007 and enforced, whichbasically adopts performance verification
by means of the partial factor method basedon the reliability-based design approach. An
outline of the revision has already been introduced, for example, in an English technical paper by Nagao et al. (2009)5) and istherefore not discussed in this article.
Revision work is underway on Specifications for Highway Bridges in Japan, a technical standard for the highway structuresthat account for the largest share of civil engineering structures in Japan. In this connection, the major concepts in the revisionof the Specifications are introduced here6):
Fig. 4 shows the concept of performance
specifications for highway bridges, shownin the draft for the current revision of theSpecifications. While the figure shows theconcept that specifies the performance pertaining to the loading capacity of bridges,
the performance requirements of bridges

are shown using a performance matrix composed mainly of two conditions: the bridge
limit state (description of the performanceat the limit state) and the design situation(i.e. the loading conditions to be taken into
account in the design work: combination of
permanent, variable and accidental loading
conditions). Then, it is required that the performance requirement be satisfied by meansof “specified assurance” within the design
service period (normally 100 years). The
specified assurance described here means
the reliability, and it is understood that theperformance specification in the Specifications under revision is based on the conceptof reliability-based design.
The lower section of Fig. 4 shows theconcept of performance verification bymeans of the partial factor method, and the
combination of design situation and limit state specified in the matrix is verified
by means of the verification formulae using the partial factor method. The format
used in the verification formulae is preparedbased on load and resistance factor design(LRFD).
Currently, revision of the Specificationsfor Highway Bridges is being promoted
based on the concept shown in Fig. 4. Specifically, the work is underway to develop
the practical verification criteria of the required performance defined in the matrix
in Fig. 4 pertaining to each structural member. Diverse engineering judgments are required in the process. To this end, the concept “deem to satisfy” is emphasized in thecourse of the revision. The term refers towhether or not a specifically required perAugust 2014 Steel Construction Today & Tomorrow 2

Fig. 4 Concept of Performance Specification for Highway Bridges Shown in
Revision of Specifications for Highway Bridges in Japan
Performance matrix of loading capacity
Bridge limit state

Loading condition
to be taken into accountin design

No occurrence ofdeterioration anddamage even inpartial section ofentire bridge;
and no impairment offunction as a bridge(service limit state)Occurrence ofdeterioration anddamage even in partial
section of entire bridge,
but limited effect on
function as a bridgeand quickly recoverable
in function(recovery limit state)

Considerable
impairment of function
as a bridge and difficultin quick recovery offunction, but not fatalin bridge collapsing(ultimate limit state)

Permanently governing
To be satisfied with specified assurance
at optional time in design service period

Variably governing
Accidentally governing

Performance verification by means of partial factor design method

Performance required for bridge
Loading condition taken
into account in design

Limit state taken into
account in design

Indication of required performanceusing performance matrix

Deem to satisfy

Load combination

Performance verification(partial factor design method)

Specific and limit
value of material→→

Loading effect →Limit state of bridge→→

Working → Specificworking value

Load coefficient

Resistance factor

formance that is satisfactorily verified by
the use of a specified verification method isdeemed to satisfy the performance requirement. At the same time, it is important that
there remains some allowance in the meaning of “deem to satisfy.” That is, the specified verification method is not necessarily the only verification method, but, rather,other verification methods that are deemed
to be appropriate by structural designers canalso be applied.
Future Directions
A widely prevailing trend in the design
standards for major civil engineering structures in Japan is that performance-based design is basically incorporated in the design
standards and that performance verificationis conducted employing the partial factor
method that is based on the reliability-based
3 Steel Construction Today & Tomorrow August 2014

design approach and the load and resistancefactor design (LRFD) method. The concept“design standards based on performancebased design” is peculiar to Japan and is
not found in the Eurocodes or the Standard Specifications for Highway Bridges of
AASHTO.
As discussed above, this concept was
initially introduced as a link in the deregulation policies taken by the government asa result of the enactment of the WTO/TBTAgreement and has continued to develop
since then. However, when examining therevision of the Specifications for Highway
Bridges in Japan now underway, it seems
that the framework of the concept is developing in new directions.
Like the United States and other advanced nations, Japan possesses a hugestock of social infrastructure. Their con-struction accelerated from the 1960s andreached massive numbers in the period of
rapid economic growth from the 1970s to
1980s. Currently, it is widely accepted thatthe maintenance of these massive social infrastructure facilities will be of great concern in the future.
Given this situation, it seems that those
who are responsible for maintenance at the
Ministry of Infrastructure, Land, Transport
and Tourism and at other government agencies foresee difficulty in uniformly maintaining these superannuating infrastructures
at identical levels. In this connection, it isconsidered that the concept of performancebased design will potentially allow the formation of a social consensus in discriminating the performance of various structures,
which should not be overlooked when prospecting the future development of performance-based design.
￭
References
1) The Japanese Geotechnical Society (2004):
JGS4001-2004 General Principles of Foundation Design Founded on Performancebased Design Concept (Popular name: Geocode 21).
2) NKB (1978): Nordic Committee on Building Regulations (NKB), Structure for Building Regulations, Report No. 34, Stockholm
3) SEAOC (1995): Vision 2000-Performancebased Seismic Engineering of Buildings4) JSCE(2003): Principles, Guidelines andTerminologies for Structural Design CodeDrafting Founded on the Performance-based
Design Concept, Code PLATFORM (Popular name: Code PLATFORM ver.1)
5) Nagao, T., Y. Watabe, Y. Kikuchi and Y.
Honjo (2009): Recent Revision of JapaneseTechnical Standard for Port and Harbor
Facilities Based on a Performance-based
Design Concept, Geotechnical Safety and
Risk (Proc. of IS-Gifu) (eds. Y. Honjo, M.
Suzuki, T. Hara and F. Zhang), CRC Press,
pp. 39-50
6) Tamakoshi T.: Performance Specification
and Future Prospect for Specifications for
Highway Bridges, Journal of Japanese Society of Civil Engineers, Vol. 98, No. 3,
pp. 28-29
7) CEN (2004): “EN 1997-1 Eurocode 7 Geotechnical Design – Part 1: General Rules.”8) AASHTO (2004): “LRFD Bridge Design
Specifications,” SI Unit, 3rd Edition

Repair of Fatigue Cracks of Orthotropic Steel Decks

Report on Repair of Fatigue Cracksof the Orthotropic Steel Decks in the
United Kingdom

by Shigeyuki Hirayama, Highway Technology Research Center; Susumu Inokuchi, Yokogawa Bridge
Corporation; Daisuke Uchida, Mitsui Engineering & Shipbuilding; and Atsunori Kawabata, JFE
Engineering Corporation
Fatigue cracks around the welded joints between deck plate and trough rib of orthotropic steel bridges which initiate at weld
root and propagate through weld bead canbe seen in Japan. Recently, these cracks
which are called as bead-through cracks occurred at the bridges suffered from severe
traffic condition. Sometimes they can propagate toward trough rib or deck plate andmake damage to bridge function.
The first observation of bead-throughcracks in Japan was reported by Hanshin Expressway in 1993. As the accuracy and technique of bridge inspection were improved,
the number of bead-through cracks has been
increased. Many organizations have conducted experimental or analytical studies
for them. On the other hands, the first observation of bead-through cracks in the world
was reported at Richemont Bridge, France,
in 1970’s. Also Severn Bridge in England isfamous as the bridge where bead-throughcracks occurred at the same term and they
have been repaired by re-welding. We also have studied about the initiating mechanism or the repair method for bead-throughcracks. Then ten-day field visit about the repair for fatigue cracks of orthotropic steel
bridge such as Severn Bridge in the United Kingdom was carried out in April 2011.
The field visit at Severn Bridge and Erskine
Bridge was carried out. This paper reports
field visit on the fatigue problem of orthotropic steel bridges in the U.K.

Photo 1 Severn Bridge

Fig. 1 Cross Section of Severn Crossing

Outline of Severn Bridge and Wye
BridgeSevern Bridge is the suspension bridgecrossing Severn River in southwest of U.K.
Severn Bridge is called as Severn Crossing
with Wye Bridge, Aust Viaduct and Beachley Viaduct which cross the boundary between England and Wales. Severn Bridge
was opened in 1966. The bridge lengthis 1,600 m and main span length is 988
m (Photo 1). The box girder with streamAugust 2014 Steel Construction Today & Tomorrow 4

lined section was adopted as stiffening girders based on results of the wind tunnel testing. Pedestrian and bicycle lanes are locatedeach side of the main girder and they are also used as lanes for maintenance vehicles(Fig. 1). Thickness of deck plate is 11.5 mm
and shape of trough rib is (B) 305 mm ×(t) 6 mm × (H) 230 mm. Inner diaphragms
are located every 4,600 mm and trough ribs
are welded round with inner diaphragms.
Field joints of deck plate are welded joints
in the each longitudinal and transverse direction. Surfacing is mastic asphalt of 35
mm thickness. Wye Bridge is the singleplane cable stayed bridge with twin towers and their structural dimension is sameas Severn Bridge.
In 1977 when eleven years have gone
after opening of Severn Bridge, fatigue
cracks were observed at orthotropic steel
deck. These cracks could be classified into
three by its locations, (1) welded joints between deck plate and trough rib, (2) crosssection between trough rib and cross beam,and (3) welded joints between bottom oftrough rib and floatation diaphragm (Fig.
2). Floatation diaphragms were attachedeach end of box girder block in order toprevent water leakage into it when floatedto transport on the water of Severn River.
Because they were not removed away after construction, they caused fatigue cracks

Fig. 2 Fatigue Cracks Observed at Severn Crossing

Fig. 3 Original Cutting Machine

5 Steel Construction Today & Tomorrow August 2014

around welded joints between bottom oftrough rib and floatation diaphragm. At
first, fifteen fatigue cracks at welded joints
between deck plate and trough rib wereobserved, and then over 160 cracks wereobserved by 1985. All cracks were located under the first traffic lane where almost
large vehicles pass.
Re-Welding Repair at Severn Bridge
and Wye Bridge
Many studies were conducted by TRRL
(Transport and Road Research Laboratory) to decide the method to repair fatigue
cracks. These studies indicated that fatigue
strength of the welded joints between deckplates and trough ribs was improved by increasing throat thickness. Then re-welding
repair at Severn Bridge started in the latter half of 1980’s in order to keep enoughthroat thickness.
When fabricated, the edges of troughrib were cut to be parallel to the under faceof deck plate. In re-welding process, they
were cut (not grooved as we did usually)again to be vertical to it in order to makepartial penetrate welding and keep enoughthroat thickness. The original cutting machine was developed (Fig. 3). This cutting
machine could move longitudinally every one meter and the cutter supported by
two independent guide flames was locatedin order to follow to deformation of deckplate and web of trough rib. The welding
conditions were decided by the field trial
tests of fifty one times with thirteen conditions and re-welding repair was conduct-

Fig. 4 Macro Etching Test for Welded Joints of Original and Re-Weldeded to keep throat thickness of 7.5 mm withthree welding passes according to the results of these tests (Fig. 4). The total lengthof re-welding became to be about 20 km,
which had been conducted for the welded joints located under the position of vehicle’s wheels. The repair was carried out
while the traffic lanes were limited in order to avoid traffic inconvenience by traffic
closing, then the period for repair became
to be eighteen months.
Field Visit at Severn Bridge and Wye
BridgeIn the field visit at Severn Crossing, we observed the condition of re-welded joints inthe box girder and the condition of asphalt
surfacing. We felt that the traffic volume
was very little. The reason is that the traffic volume of about 70% may pass throughSecond Severn Bridge which was opened in
1996 at the downstream of Severn Bridge.
Many patches by re-casting of asphalt surfacing which was re-cast in 1991 could beseen at the position of vehicle wheel (Photo 2). In the field visit inside the box girder, we observed the condition of re-welded joints between deck plate and troughrib, and also between trough rib and diaphragm, welded joints between bottom oftrough rib and floatation diaphragm which
had been repaired (Fig. 5).
For re-welding by three passes, it
seemed that dispersion of weld size between deck plate and trough rib was smaller and their quality was better than theoriginal. Welding repair with the metalbacking plates had been carried out for thefatigue cracks at the cross section between
trough rib and diaphragm. To repair thelarger fatigue cracks at the welded joint between trough rib and floatation diaphragm,
the bottom of trough rib was cut away partially and metal bypass materials were at-tached. The flotation diaphragms had been
removed away when the fatigue problem
came out.
The general inspection every two years
and the principal inspection every six years
are conducted for the long span bridges in
the U.K. such as Severn Bridge. Fatigue
cracks or defects found by general inspection are repaired in each occasion. Although number of fatigue cracks which areobserved newly has decreased because of

decrease of traffic volume by open of Second Severn Bridge, about fifty cracks or
failures are still repaired every year.
Outline of Erskine Bridge
Erskine Bridge is the single-plane cablestayed bridge which is located over Clyde
River in West Glasgow of Scotland (Photo 3). The length of bridge is 1,321 m andit was opened in 1971. This bridge consistsof the main route toward Scotland and thenPhoto 2 Condition of surfacing at Severn Bridge

Fig. 5 Repair of Fatigue Cracks at
Severn Bridge

Photo 3 Erskine Bridge

August 2014 Steel Construction Today & Tomorrow 6

the traffic volume is over 4,000 per day.
It was clear that this bridge did not satisfy the criteria shown later by Merrison Report and reinforcing and re-strain of the cables were carried out from 1970’s to 1980’s
and in 2004 (Photo 4). As orthotropic deck
system in Erskine Bridge, thickness ofdeck plate is 12.7 mm and V-shaped rib isused as longitudinal rib of 5 mm thick. Surfacing is mastic asphalt of 38 mm thick assame as Severn Bridge.
Field Visit at Erskine Bridge
Fig. 6 shows the main three types of fatigue cracks which had been observed at
Erskine Bridge; (1) welded joint between
deck plate and trough rib, (2) welded joints
between trough rib and end diaphragm, and(3) welded joint between deck plate andvertical stiffener. Over 1,200 cracks or defects including also ones observed without
orthotropic deck have been repaired in Erskine Bridge. In the field visit, we observed
these fatigue cracks of three types.
Photo 5 shows the sample of crack
which occurred at the weld bead which
we call “bead-through crack.” About ten
bead-through cracks have been observedin this bridge and some of them have been
repaired by cutting the edge of trough rib
and re-welding by three passes as same as
Severn Bridge. Although the length of thefatigue crack shown in Photo 5 is over 700
mm, the crack does not propagate toward
the web of trough rib as the case observedin Japan. The reason seems to be that welding condition and cutting at the welded
joint between deck plate and trough rib anddimension or stiffness of trough rib are different between the U.K. and Japan and soon.

Photo 4 Reinforcement based on Merrison Report

Fig. 6 Fatigue Cracks Observed at Erskine Bridge

Conclusions
We could know fatigue problem of orthotropic decks and stance for maintenanceof them in the U.K. through this field visit. Especially for the long span bridges wevisited, private companies have engaged inmaintenance work for long periods, and we
felt their stance that they kept watching thebridges intently in the future. It is meaningful that the same engineers can conduct
usual observation, inspection, and repair
work systematically, and we should referthem in Japan.
￭

Photo 5 Bead-through crack at Erskine Bridge

7 Steel Construction Today & Tomorrow August 2014

Maintenance of Steel Railway Bridges

Maintenance and Reinforcement of Steel
Bridges on the Tokaido Shinkansen
by Hideki Kaji, Shinkansen Operations Division, Kazuya Takahashi, Chuo Shinkansen Promotion
Division and Yuichi Ito, General Technology Division, Central Japan Railway Company
A total of 22.1 km of steel railway bridges are
installed on the Tokaido Shinkansen (bullet
train line). The construction of these bridges features the extensive use of fully weldedsteel structures, the first full-scale adoptionof this method in Japan.
Because steel bridges respond more dynamically to train loads than concrete bridges and because the trains are now running at agreater frequency compared to when the line
opened, the task of dealing with weld zone
fatigue and durability is emerging as an important issue. In particular, because the total
length of the longitudinal weld beads (hereinafter referred to as longitudinal beads) of
the major structural members is extensive, it
is difficult to focus on only specified sections
during inspection. Further, once a crack initiates in a bead, it quickly propagates. For thisreason, it is essential in steel bridge maintenance to suppress the occurrence of fatigue
cracks in longitudinal beads (Fig. 1).

To achieve this goal, fatigue loading tests
and three-dimensional FEM analysis were
implemented using a full-scale bridge model or the members of existing steel railway
bridge at the Komaki Research Laboratories
owned by the Central Japan Railway Company. This led to the development of newsteel bridge reinforcement techniques foruse in preventive maintenance, such as thereinforcement of floor system joints, the replacement and reinforcement of bearing supports, and the insertion of additional sleepers. These techniques are to be adopted in alarge-scale project to retrofit the steel railway
bridges of the Tokaido Shinkansen and are
introduced below.
Then, following the implementation ofthese countermeasures to suppress degradation, the company plans to confirm the service conditions of the affected bridge structures and then determine the intervals at
which the members of these structures should

be replaced as a general retrofitting measure.
Maintenance and Reinforcement of
Steel Railway Bridges• Assessment of Longitudinal Beads
It is known that the fatigue strength of a longitudinal bead is affected by internal defects
in the weld zone. According to the resultsof surveys of actual bridges using ultrasonic testing and as a result of the dismantlingof actual bridges removed from the Tokaido
Shinkansen, it is accepted that the existenceof a certain level of blowholes is an undeniable fact.
At the Komaki Research Laboratories, fatigue tests were conducted in the following
two cases: one test using a steel bridge thatwas in service for more than 35 years following the startup of the Shinkansen and removed after installation of the new Shinagawa Station in the fall of 20031); and anothertest using a large girder specimen that was in-

Fig. 1 Longitudinal Weld Bead

Longitudinalbead

Fatigue strength of longitudinal bead (resistance to cyclic loading)
Large effect of weld internal defect (blowhole)• Difficulty in specifying crack occurrence position• Quick crack propagation rate

Difficulty in treating crack in inspection

andEffect of crack occurrence on train operation

Replacement and other physical measures

August 2014 Steel Construction Today & Tomorrow 8

tentionally infused with blowholes (Photo 1).
The test results for both the full-scale bridge
specimen and the girder specimen satisfy the“Class D” designation prescribed in the fatigue design guidelines of the Japanese Society of Steel Construction and other organizations (Fig. 2). And the developed stressmeasured in all the steel bridges on the Tokaido Shinkansen falls below the Class D fa-(a) Test for floor systemtigue limit, even when taking into accountthe variation coefficient of the train wheelloads commonly forecasted in train operations. However, in cases when a bridge structure undergoes changes due to other types ofdamage and, as a result, the developed stressincreases and in cases when shocking fluctuations in wheel load occur depending on themaintenance conditions of the rails, sleepers(b) Test for single main girder

Photo 1 Fatigue testing condition

Fig. 2 Fatigue Test Results for Longitudinal Bead
Full-scalespecimenStress range (MPa)Memberspecimen

No. of loading cycles up to crack occurrence (cycles)

Fig. 3 Outline of Measures toControl Degradation

Replacement andreinforcement ofbearing support

9 Steel Construction Today & Tomorrow August 2014

Reinforcement offloor system joint

and other structures, it is possible that the developed stress will surpass the fatigue limitof the longitudinal beads2).
Two approaches have been developed tosuppress the increase of stress in longitudinalbeads by preventing the occurrence of the deficiencies that cause changes in bridge structure. One is to reinforce the joints of the floor
system (stringers and cross girders) and theother is to replace and reinforce the bearing
supports (Fig. 3). These approaches are introduced below:
Reinforcement of Floor System
Joints
It has been confirmed in surveys of actual
bridge conditions thus far conducted that fatigue cracking has occurred in the floor system joints of part of the through truss and thethrough plate girders. The through truss, forexample, has cracks that initiates in the boxing weld zone at the stringer pedestal and in
the boxing weld zone within the slit at thecross section of the pedestal and the vertical stiffener or cross beam. It has been confirmed by means of three-dimensional FEM
analysis that such cracks increase the longitudinal bead stress and tend to induce cracks
that initiates in the longitudinal beads. In response, we proposed a reinforcement method to suppress the occurrence of cracks at thefloor system joints3).
• Reinforcement of Floor System
Joints of the Through Truss
It was previously confirmed that several kinds of cracks develop because of problems involving the details of the floor system
joints.
First, stresses were measured and the conditions that produced fatigue cracks wereanalyzed, and then the structural safety issues related to treating fatigue were examined. As a result, it became clear that fatigue
cracks could possibly occur in the floor system joints and that the cracks would initiate
from two sections: the weld zone at the crosssections of the stringer pedestals and the upper end of the vertical stiffeners, and the boxing weld zone within the slit at the cross sections of the stringer pedestals and the cross
beams (Fig. 4).
Next, we proposed a reinforcement method (Photo 2) to control the deformation behavior that caused the above-mentioned
cracks. Specifically, static loading and fatigue tests were conducted using a full-scale
test specimen of the floor system joints towhich reinforcing members were attached.
The effectiveness of the attachments wasFig. 4 Fatigue Crack in Floor System Joint (Through Truss)

Fig.5 Open Deck-type Through Plate Girder

Cross beam
Floor system joint
Stringer(a) Crack occurring from stringer pedestal(b) Crack occurring from boxing weldzone within slit of cross section

Stringer
Cross beamStringer

Cross beam

Fig. 6 Fatigue Crack in Floor System
Joint (Through Plate Girder)
Stringer
Crack type①

Crack type③

Crack type②(a) Before reinforcement(b) After reinforcement

Cross beam

Photo 2 Floor system joint before and after provision of reinforcing measurethen confirmed as a means to improve fatigue
strength, and finally the confirmed method ofeffective reinforcement was applied to an actual bridge to measure the stress before andafter reinforcement. As a result, it was confirmed that, by attaching reinforcing members, stress is reduced to a level below thefatigue limit in the weld zone at the cross section of the stringer pedestals and the upper
end of the vertical stiffeners and in the neighborhood of the boxing weld zone within theslit at the cross section of the stringer pedestals and the cross beams.
• Reinforcement of the Floor System
Joints of Through Plate Girders
It is reported that fatigue cracks have occurred in the joints of the stringers and thecross beams of open deck-type through plate
girders (Fig. 5).
It is known that three types of fatigue
cracks have occurred in these joints: ①
cracks in the notch section of stringer upper flanges, ② cracks at the notch section ofstringer lower flanges, and ③ cracks at the
rivet holes of stringer webs (Fig. 6). In cases when these cracks propagate, the structuralcontinuity of the stringers that sandwich thecross beams will be lost, and as a result, it isconsidered that the stress in the longitudinalbeams will increase as the stress increases inthe through truss mentioned above.
To solve this problem, a static loading test
was conducted to examine methods to reinforce the joints of stringers and cross beams.
Then the reinforcing structure that was foundto be most effective in reducing stress was selected. Specifically, it was confirmed that by
attaching boat-shaped brackets and other reinforcing members to the floor system joints(Photo 3), the stress occurring at the three positions shown in Fig. 6 can be reduced.
Countermeasures for Girder Bearing
Supports
It is known from stress measurements at actual bridges that when the functionality of the
bearing supports or shoes declines, it is likely
to cause a considerable increase in longitudinal bead stress. In particular, in steel bridges
in which the sole plate is attached to the girders by welding, stress occurs in the sole plate
weld zones and the resulting stress-induced
fatigue damage penetrates into the flanges
and webs of the main girders, which is cited
as a serious deficiency in steel bridge maintenance.

(a) Before reinforcement
Reinforcing
connection
memberReinforcing
wear plate
Boat-shapedbracketReinforcing angle(b) After reinforcement
Photo 3 Reinforcement measure employing
boat-shaped bracket (through plate
girder)August 2014 Steel Construction Today & Tomorrow 10

Fig. 7 shows the position where stress wasmeasured on the front surface of the sole plate
weld zone before and after shoe replacement,
and Fig. 8 shows the measured results. Large
stress occurred at the front surface of the sole
plate weld zone, and torsion was generated in
the lower flange. The stress measured at the
shoe before replacement was about 10 times
higher than after replacement. Therefore, itis necessary to maintain the soundness of theshoes4).
Improvement of the Service Life andDurability of Steel Railway Bridges
Fatigue cracks that originate in a longitudinal bead quickly propagate after initiation
and are difficult to find during inspection.

to control wheel load fluctuation by installing a plate bearing support structure on therailway in which additional sleepers are inserted among the existing sleepers. A detailed
explanation of this new system will be discussed separately.
The service life and durability of the steel
bridges on the Tokaido Shinkansen will be
improved in the future by applying the diverse reinforcing measures thus far developed. Meanwhile, as regards the necessity
to replace railway bridge members, Central
Japan Railway Company will continuously
monitor the replacement effect and examine
the replacement period if the need arises. ￭As an effective measure of dealing with suchcracks, it was conventionally considered necessary to quickly replace the affected member. However, as a result of our research, we
believe that the service life of steel railway
bridges can be prolonged and durability canbe improved by the floor system joint reinforcement that suppresses the degradation of
those floor system joints and, also, by carrying out measures to maintain the girder bearing supports.
In addition, because exceptionally large
wheel loads occur in slab-less railway steel
bridges, it is very important to prevent its occurrence. The conventional approach to solving this problem was to thoroughly change
the railway structure. But now it is possible

Fig. 7 Stress Measurement Position at Sole Plate Weld Zone
Sectional drawing of steel girder

50mm
Dial gauge③

Strain
gauge

④
Right

30mm

10mm
Left
①

②

10mm

Stress before replacement/Stress after
replacement

Fig. 8 Stress Ratio Before and After Shoe Replacement① Left-side
upper
surface② Left-side
lower
surface

11 Steel Construction Today & Tomorrow August 2014

③ Right-side
upper
surface④ Right-side
lower
surface

Reference
1) Y. Ito, M. Seki, Y. Natori, C. Miki and A.
Ichikawa: Demolition Surveys of Weldedstructure Steel Railway Bridge with 35-year
Service, Journal of Japanese Society of Civil Engineers, No. 724/I-62, pp. 37-48, 2003
2) A. Tanabe, M. Seki and A. Matsuura: Assessment of Effect of Exceptionally Large
Wheel Load on Steel Truss Bridge Employing Three-dimensional Dynamic Analysis,
Proceedings of Structural Engineering, Vol.
56A, March 20103) Japanese National Railways: Journal of Tokaido Shinkansen Construction: Civil Engineering Works, Japan Railway Civil Engineering Association, 1965
4) C. Miki, K. Tateishi and Y. Tokuno: Local Stress and Fatigue at Plate Girder Sole
Plate, 47th Annual Lecture Meeting of Japanese Society of Civil Engineers, September 1992

Repair and Reinforcement of Highway Bridges

Maintenance of Metropolitan
Expressways

by Masasumi Okada, Kanagawa Operation Bureau, Metropolitan Expressway Co., Ltd., Takao
Mizoguchi, Kanagawa Construction Bureau, Metropolitan Expressway Co., Ltd., and Tomohiko Aikawa,Engineering Department, Metropolitan Expressway Co., Ltd.
The Metropolitan Expressway is a network of
expressways constructed to alleviate chronic
traffic congestion in Tokyo, Japan’s capital,
and in its surrounding areas. In 1964 when
the Tokyo Olympic Games were held, about
33 km had already been put into service. In
the nearly fifty years since then, expressway
construction paralleled national economic
development and in 2010 had reached a total operational length of 301.3 km. In thatyear, the Metropolitan Expressway registered
the highest level of traffic volume in Japan(115,000 vehicles per 12 hours, or 11,000 vehicles per hour).
Maintenance of the 301.5 km-long Metropolitan Expressway is summarized in the following.
Expressway Features
From 1958, the Metropolitan Expressway

Public Corporation—which in 2005 was reestablished due to administrative reform as
Metropolitan Expressway Co., Ltd., a privatecompany—has managed the construction,
operation and maintenance of the Metropolitan Expressway.
The 301-km expressway network is divided into two types of roadway: four-lane (twolanes in each direction) and six-lane (threelanes in each direction).
The Metropolitan Expressway was constructed by maximum use of areas above existing rivers, canals, highways and other public sites. As a result, in terms of the structuresthat comprise the expressway, flat roads account for only 5% of the total extension,
while viaducts, bridges and tunnels accountfor 95%. Meanwhile, viaducts and bridges
account for 80% of the total length, with a total number of 11,800 spans (7,770 composed

Fig. 1 Inspection and Repair System
Plan

Inspection

Assessment

Measures

Ranking A(need for emergency measure)

Emergency measure(permanent measure)Ranking B(need for measure)

Repair/reinforcement

Ranking C(no need for measure)Ranking D(no abnormality)
Input ofinspection results

Next periodical
inspection

Input ofmeasures taken

Database(Metropolitan Expressway Maintenance Technical Information
System: MEMTIS)

Ranking A

Damage requiring emergency measure (fear to third-party damage)Ranking B

Damage requiring planned maintenanceRanking C

No need for measure because of slight damage (damage is recorded)

Ranking D

No damage (inspection is recorded)of steel girders/RC slabs, 1,340 of steel girders/steel decks, and 2,690 of PC and RC girders), and a total of 8,680 piers (2,885 steelpiers and 5,795 RC piers).
Currently, 1.8 million people per day use
the Metropolitan Expressway, as do one million vehicles, of which full-sized vehicles
number 100,000. However, the traffic volume differs according to the section of theexpressway network, ranging from 80,000
vehicles/direction/day on six-lane sections to
1,500 vehicles on four-lane sections.
In order to safely inspect, repair and reinforce the expressways, it is necessary to secure workspace by temporarily closing lanes.
Further, in order to ease maintenance-induced traffic congestion as much as possible, work conducted in heavily traveled sections is scheduled to avoid daytime hours andis carried out at night when traffic volume isrelatively light.
The cost of maintaining and operating theMetropolitan Expressway was ¥61 billion in
2012. Of this amount, the cost of inspection
and repair/reinforcement was ¥42 billion,
and that of operating the toll roads was ¥19
billion.
Inspection and Repair/Reinforcement
Systems
In order to continuously carry out inspection and repair/maintenance work on its expressway network, Metropolitan Expressway Co., Ltd. follows the systematic process
shown in Fig. 1: inspection plan→inspec
tion→assessment→execution (repair andreinforcement)→inspection plan.
Inspections are divided into three types
depending on aim and frequency: routine inspections (vehicular patrol and walking inspections), periodic inspections (close-range
and instrumental inspection), and emergency
inspections (in response to earthquakes etc.).
• Routine Inspections
These are conducted to observe structural condition and to check for falling objects
on roads. The frequency of these inspections
varies-from patrol inspections basically every two hours to walking inspections of exAugust 2014 Steel Construction Today & Tomorrow 12pansion joints and other devices every five
years.
• Periodic Inspections
In order to acquire a detailed understanding of the state of structural condition, closerange inspections of structures are, as a rule,conducted every five years. These are themost fundamental and important inspections.
• Emergency Inspections
These inspections are conducted to check forstructural damage and to assess damage levels after the occurrence of great earthquakes
and torrential rainstorms.
The sections to be repaired are determinedby assessing and ranking the inspection results in accordance with our database (METIS: Metropolitan Expressway MaintenanceTechnical Information System). After the repairs are completed, the repair record is input
into the database and saved as data for use
in working out subsequent inspection and repair plans.
A routine patrol inspection is shown in
Photo 1, a close-range walking inspection in
Photo 2, a close-range periodic inspection in
Photo 3, and an instrumental inspection in
Photo 4.

Fig. 2 Occurrence Position for Fatigue Cracking in the Corner of Steel
Bridge Pier

Failure occurrence position

Examples of Repairs and Reinforcements
Repair and reinforcement include the replacement of pavement that exhibits rutting and cracking, and the repainting of steel
structures to prevent the corrosion. Recent
concerns have focused on the repair and reinforcement of fatigue phenomena in steel
structures. Examples of fatigue failure andappropriate countermeasures are introduced
below.

Photo 5 Occurrence of fatigue cracking (observed in weld line where beam andcolumn cross)• Fatigue Cracking in the Corners of

Photo 1 Patrol inspection (confirmation of structural condition using a patrol vehicle
while running on the expressway)

Photo 3 Close-range inspection (inspection bycherry picker; daytime inspection isavailable at sites where traffic flow is
not adversely affected)

Photo 2 Walking inspection (walking inspectionof structures by inspectors in areas ofrestricted traffic flow during nighttime)

Photo 4 Instrumental inspection (ultrasonic testing of welds of steel structures)

13 Steel Construction Today & Tomorrow August 2014

Steel Bridge Piers
In 1997, fatigue cracking was found in thecorner of a steel bridge pier. A detailed investigation confirmed that this kind ofcracking is the result of propagation of fatigue. Then, the cause of fatigue condition
was assumed by implementing a fatigue
test on a full-scale test specimen. As a result of further examinations, a method was
adopted that joins splice plates with existing bridge piers using high-strength bolts inorder to ease the stress concentration in areas where cracks occur.
Fig. 2 and Photo 5 show the position
where fatigue cracking occurs, and Photo
6 shows the reinforcement method using
steel plate.
• Fatigue Cracking in Steel Decks
Fatigue failure is often found in steel decks.
In particular, there are confirmed cases inwhich fatigue cracks that occur in the weldsof steel deck plates and trough ribs propagate in the direction of the deck plate thickness and then penetrate into the deck plate.
As a countermeasure against such fatigue

• Fatigue Countermeasure for RC

Photo 6 Reinforcement of steel bridge pier by splicing steel plate to piercracks, a method has been adopted that uses steel fiber-reinforced concrete (SFRC),
having a larger elastic modulus than asphalt
pavement, to suppress by means of the rigidity thus obtained the strain that occurs insteel deck welds and trough ribs.
In order to confirm the reinforcing effectprovided by the use of SFRC, it was necessary first to decide the material and struc-ture to be applied. Then, the fatigue test
was conducted using the adopted paving
method that called for 8 cm-thick asphalt
pavement to be replaced by 5 cm-thick layer of SFRC over which a 3 cm-thick layerof asphalt was laid.
Photo 7 shows the SFRC placement andthe pavement structure used by this method.

Slabs
In order to reinforce RC slabs, two methods
have conventionally been adopted to ease thebending moment produced by the live loadthat occurs in RC slabs: 1) the additional installation of one or two stringers between
the main girders and 2) the joining of steel
plates to RC slabs in the expectation that,when joined, the steel plate and the existing
RC slab will mutually resist the bending moment occurring in the RC slabs. However, because steel products are used for these methods, rigid scaffolding was required and it wasnecessary to pay special attention to the handling of the members to be attached.
Later, it became clear that the development of RC slab damage is caused by a fatigue phenomenon attributable to vehicle
traffic. In response, a method of reinforcement using a new material was established.
This method pastes carbon-fiber sheeting to
the rear surface of RC slabs to mitigate RC
slab fatigue.
Photo 8 shows an RC slab that is reinforced by a carbon-fiber sheet that was pasted to the rear of the slab and then painted, andthe reinforcing work underway.

Surface layer: Asphalt
pavement
Basic layer: SFRC
pavement
Steel deck

Photo 7 Provision of countermeasure for fatigue in steel deckby means of SFRC paving (blue section: epoxy resin)

Photo 8 Reinforcement of RC slab with carbon-fiber
sheet (sheet is pasted in the direction rectangular to slab; coating is provided to prevent deterioration of epoxy resin)
August 2014 Steel Construction Today & Tomorrow 14

Examination of Large-scale Renewalof Expressway Facilities
Metropolitan Expressway Co., Ltd. has systematically and regularly implemented inspections of its various expressway structuresand conducted the necessary repair work demanded by the inspection results. However,
the total length of the Metropolitan Expressway network is now 301 km, of which 30%(or 100 km) consist of structures with 40 or
more years in service since startup. As a result, damages have occurred in numerous expressway structures that have supported vehicle traffic for many years, and further serious
damages have been found in some of thesestructures.
Given this situation, Metropolitan Expressway Co., Ltd. has worked out a largescale renewal plan for specified sections of
the 301-km expressway. This plan calls forbridge reconstruction and the replacement offloor slabs in an 8 km-long section where serious damage has been found, as well as therenewal of structures where necessary; andthe repair of entire structures in a 55 km-longsection where large-scale repair is required.
Meanwhile, trial calculations for the approximate cost of these projects have been made:¥380 billion for the 8-km section and ¥250
billion for the 55-km section, for a total of¥630 billion.
Under its basic guiding principle of pursuing safety and driving ease and of supplying high-quality services for its users, Metropolitan Expressway Co., Ltd. is committed tocarrying out maintenance work in the future.
(Refer to Photo 9)￭co.jp/english/technology/mm-maintenance/
References
1) Website of Metropolitan Expressway Co.,
Ltd. (Japanese)2) M. Okada, T. Mizoguchi and T. Aikawa: Metropolitan Expressway Reaching 50-year Anniversary since Opening, Bridge and Foundation Engineering, pp 11-16, Dec. 2012
(Japanese)

About Metropolitan Expressway Co.,Ltd.
Further information about expressway maintenance and other operations of the company
is available at:• Corporate information: http://www.shutoko.
co.jp/english/• Maintenance operations: http://www.shutoko.
Photo courtesy: Metropolitan Expressway Co., Ltd.

Photo 9 The Tsurumi Tsubasa Bridge (foreground) and the Yokohama Bay Bridge (background) at the Bay Shore Route of Metropolitan Expressway.
Safe traffic is assured capitalizing on advanced expressway maintenance technologies.

15 Steel Construction Today & Tomorrow August 2014

From RC Slab Bridge to Steel Deck Bridge

Replacement of RC Slabs with Steel
Decks on Mikawaohashi Bridgeby Tomoo Mito
Eight-Japan Engineering Consultants Inc.
The Mikawaohashi Bridge is a non-composite
steel girder bridge having a length of 398 m anda continuous 2+3+2 span composition. It is installed where the Kanazawa-Mikawa-Komatsu
Route, a major local highway, crosses the Tedori River in Ishikawa Prefecture. The bridge wasin need of retrofitting due to the following con-cerns: increasing traffic volume, progressive deterioration of the RC slab caused by airborne
salt, the need for another sidewalk to be installedon the bridge’s upriver side (bridge widening)and measures to treat the B-type live load required by the Japanese Highway Bridge Design
Specifications.

Fig. 1 Section of Mikawaohashi Bridge (before and after replacement of slabs)
Original section(Downriver side)

Asphalt
pavement(Upriver side)

Asphalt
pavement
RC slabSection after replacement of slabs(Downriver side)
Sidewalk(Upriver side)

Vehicle lane Vehicle lane
Asphalt
pavement
RC slabSidewalk

Fig. 2 General Drawing of Mikawaohashi Bridge
To Komatsu

Bridge length
Steel 2-span continuous non-composite plate girder
Steel 3-span continuous non-composite plate girder

To Kanazawa
Steel 2-span continuous non-composite plate girder

To improve the above situation which thebridge was suffered, the previously adopted,
conventional RC slab for the bridge was replaced with a steel deck (Fig. 1). The replacement project that was conducted on the Mikawaohashi Bridge is outlined below.
Bridge Outline and Need for Replacement
The Mikawaohashi Bridge is installed 200 m
from the mouth of the Tedori River in Mikawa-Minami, Hakusan City, Ishikawa Prefecture.
The bridge has a length of 398 m (span divisions:
51.0+58.6, 58.6+59.0+58.6, 58.6+51.0 m). The
superstructure is composed of two 2-span continuous non-composite steel plate girders andone 3-span continuous non-composite steel plate
girder; and the substructure is an RC wall-typepier with an open caisson foundation (Fig. 2).
The Mikawa Bridge formerly located upriverfrom the Mikawaohashi Bridge was constructed in 1938. It was used for vehicle traffic until
1972 when the Mikawaohashi Bridge was put
into service, and was afterwards used for bicycle
and pedestrian traffic (Photo 1).
However, removal of the Mikawa Bridge became necessary because of an inadequate condition in terms of the river section. This thengenerated concerns about the form of the new
replacement sidewalk that would be installed on
the upriver side of the Mikawaohashi Bridge. In
addition, B-type live load reinforcement was implemented for the main girders of the Mikawaohashi Bridge from 1997 to 1998. But as deterioration of the concrete slabs (corrosion of the steel
reinforcing bars, peeling-off of the surface concrete) progressed, diverse countermeasures wererequired, including: widening of the bridge to accommodate the new sidewalk, measures to treat
Mikawaohashi Bridge(completed in 1972)

Mikawa Bridge(completed in 1938)

Mikawaohashi Bridge Tedori River
Mikawa Bridge
Planned for removal

Photo 1 Mikawaohashi Bridge and Mikawa
Bridge (taken from left coast side)
August 2014 Steel Construction Today & Tomorrow 16

the B-type live load on the slabs, and reductionof bridge weight that was also effective for seismic retrofit.
Tasks and Approaches Aimed at
Increasing the Service Life of the
Mikawaohashi Bridge
Three major issues faced the Mikawaohashi
Bridge:• Progressive Deterioration of the RC
SlabA previous investigation of the RC slab made in
1996 showed that many cracks had developed
and that the surface concrete was sloughing, andsubsequent periodic bridge inspections showedthat the deterioration was progressing. In a 2006
investigation of the chloride ion content, it was
confirmed that the presence of chloride ions inthe steel reinforcement would soon reach a critical level where corrosion would occur (Photo2). Accordingly, it was assumed that deterioration of the RC slab would progress quickly due
to corrosion of the steel reinforcement caused bydamage from salt water.
• Necessity of Installing Another Sidewalk
It was determined that the Mikawa Bridge (pedestrian bridge) located just upriver from the
Mikawaohashi Bridge had to be removed without delay because of an inadequate condition interms of the river section as mentioned above.
In response, the citizenry of nearby Hakusan
City demanded that after removal of the Mikawa Bridge a replacement sidewalk be installedon the upriver side of the Mikawaohashi Bridge
so as to secure safety and convenience.
• Lighter Weight for Improvement ofBridge Seismic Performance
It was made clear through separate examinations
that to widen the bridge while utilizing the RC
slab as it was would increase the weight of thesuperstructure, thereby impairing the bridge’s
seismic retrofit. Therefore, reducing the weightof the superstructure was an indispensable requirement for improving the seismic perfor-

mance of the entire bridge structure.
In order to find an approach that would accomplish these three tasks, extensive examinations had to be made with regard to widening thebridge and, further, to replacing the RC slab andthe effect that would have on structural performance, work efficiency and the existing bridgepiers. As a result of these studies, steel decking
was adopted as the method to replace the RC
slab because of the following reasons: wideningof the bridge and reduction of the dead weight
could be made compatible, without any adverse
effect on the work to reinforce the B-type live
load already underway, and the weight of thesuperstructure could be reduced sufficiently toachieve improved seismic performance within
the required range of design.
Replacing Slab with Minimum Effect on
Traffic
In replacing the RC slab with a steel deck, thefollowing two aspects were taken into consideration when determining the optimum bridge
width.
• Determination of Final Width—Basedon the Stress of the Main Girders
Trial calculations to determine the total width of
the bridge upon completion considered four cases with respect to the stress of the main girders:
B=12.6 m, 13.6 m, 14.6 m and 15.6 m. As a result, it became clear that the total width must be
13.6 m or less in order to remain within an allowable stress of the main girders that were currently undergoing reinforcement for the B-type
Fig. 3 Determination of Final Width—
Based on Replacement Work(In the case of securing twolanes: Total breadth of 13.6 m
or more is required)First-stage work
Upriverside work(Vehicle lane) (Vehicle lane)

Floor slab

live load.

• Determination of Final Width—Basedon Replacement Work
Because traffic in both morning time and evening
time is heavy and, further, because a crossing islocated at the end of the bridge, it was feared that
traffic congestion would occur while the RC slab
was being replaced by a steel deck. Therefore,
an important premise was that two lanes (one ineach direction) had to remain open during the
replacement work. The narrowest width thatwould allow two lanes to remain open during thework was 0.4+6.0×2+0.3×2+0.2+0.4=13.6 m.
As a result of the above examinations, awidth of 13.6 m was adopted as the optimum
width of the bridge. (See Fig. 3)
Design Concepts of Slab Replacement• Stress Verification in Main Girders
While the Mikawaohashi Bridge is a non-composite girder structure, in its replacement of RC
slabs with steel decks, stress verification was implemented by taking into account the composite
effect produced by combined use of steel deckand main girders and based on the following
concepts:
1) The dead load before installation of the steel
deck would be borne only by the sections of
the existing main girders.
2) The dead load after installation of the steel deckand the live load would be borne by the composite sections including the steel deck. (Fig.
4)3) Stress verification would be made at each stepin the replacement work and by putting together the stress occurring in the above two.
4) Because of reduced thickness due to corrosionin the sections of the main girders, the section
calculations would be made by decreasing the
thickness of the webs and lower flanges basedon the survey results. Meanwhile, the calculations would be made by taking into accountthe sections where the existing girders are reinforced using stiffening plates.
Calculationof Stress at Each Step of•
the Work Process
Because the stress verification is made by takFig. 4 Section of Composite Girder

Second-stage work

Main girder

Downriverside work(Vehicle lane) (Vehicle lane)

Replaced steel deck

Existing main girder

Photo 2 Exposure of steel reinforcement of RC
slab (photo taken in 2006)

17 Steel Construction Today & Tomorrow August 2014

ing into account the composite effect of the steel
deck and the existing main girders as mentioned
above, and because the replacement work is done in progressive steps that take traffic management into account, the structural system differs
at each step in the process.
To cope with such a situation, the steps in thereplacement process were worked out as shownin Fig. 5. In order to prevent bridge collapse, thestress conditions were checked at each step toconfirm that both the allowable values and thedesign loads lay within specified levels pertaining to safety during the replacement work, to theFig. 5 Replacement Work by Step
Step-1
Current condition(Downriver side)(Upriver side)
Asphalt pavement
RC slabAsphalt pavement

Step-2At the time of upriver side work

(Vehicle lane) (Vehicle lane)

Work zone

stress of the main girders upon completion of thework, and to the bearing reaction force and design load.
The steps of the work process are shown in
Fig. 5.
Reinforcement of Existing RC Slab during Replacement
At the midway point of replacing the RC slab
with the steel deck while simultaneously keeping two lanes of traffic open, the middle slabs atthe center of the existing RC slab overhang the
support structure. Because the wheel loads workon the downriver side of the overhanging sectionof these slabs and because the slabs have a thinwall thickness (16 cm) and are designed for sidewalk use, they are reinforced using temporary
stringers and brackets. (See Fig. 6 and Photo 3)
Successful Replacement of RC Slabwith Steel Deck
The work of replacing the RC slab with a steel
deck on the Mikawaohashi Bridge started in2010 and was completed in 2014.
The service life of the bridge has been prolonged by removing the existing RC slab, which
was suffering progressive deterioration and declining structural strength, and by replacing itwith a steel deck. And, further, seismic performance has been improved by reducing the over-all structural weight. On top of this, because asidewalk was added to the upriver side of the
Mikawaohashi Bridge, the Mikawa Bridge wasremoved without impeding conventional traffic(Photo 4).
Further, because two lanes of traffic weremaintained without the installation of a temporary bridge during the replacement work, not only was the effect on traffic minimal, but both theconstruction term and the overall cost were reduced.
It will be glad if the current report serves asa useful reference when planning future bridge
slab replacements, which are forecasted to increase.
￭
References
1) S. Matsui: Highway Bridge:Design/Construction
and Maintenance, Morikita Publication (Oct.
2007)2) Guidelines for Fatigue Design of Highway
Bridges, Japan Road Association (Mar. 2002)
3) Manual for Design and Construction of Replacement Steel Decks, Japan Bridge Association (Sept. 1994)
4) Design Guidelines for Tension Joining Using
High-strength Bolts for Bridges, Japanese Society of Steel Construction (Aug. 2004)

Fig. 6 Reinforcement of DownriverSide RC SlabThickness of floor slab at walkway t=16 cm

Step-3At the time of downriver side work

Reinforcing
stringer
BracketPhoto 3 Bracket for use for RC slab reinforcement

Work zone(Vehicle lane) (Vehicle lane)

Step-4Completed form
(Sidewalk)(Vehicle lane)(Vehicle lane)(Sidewalk)

Photos 4 and 5 Mikawaohashi Bridge after replacement with steel deck
August 2014 Steel Construction Today & Tomorrow 18

JISF Activities

Second Steel Construction Conference in Cambodia Being
PlannedThe Japan Iron and Steel Federation (JISF) is planning a second
conference to be held in Cambodia. It is tentatively titled “Recent Technologies for Steel-structure Construction 2014” and willtake place in Phnom Penh, Cambodia in December 2014, under
expected joint sponsorship by JISF, the Ministry of Public Works
and Transport (MPWT) of Cambodia and the Institute of Technology of Cambodia (ITC). In early June of this year, a meeting topromote the conference was held between JISF and its two Cambodian counterparts.
The conference will consist of a number of sessions. In thesession for engineers, there will be five lectures given by experts
from both nations that will discuss steel-structure technologies in
the fields of ports/harbors, bridges and buildings. In another session that will feature participation by key persons from both nations, extensive discussions will focus on the promotion of steelstructure construction in Cambodia.
In December 2012, JISF joined with MPWT and ITC to holdthe first conference, titled “Conference on Advanced Technolo-

gies for Steel Construction 2012,” in Phnom Penh. The event wasa success with the participation of about 200 engineers from thegovernmental, academic and private sectors.
￭

Conference on Advanced Technologies
for Steel Construction 2012 held in 2012in Phnom Penh, Cambodia

Request for Participation in Survey of
Steel Construction Today & Tomorrow
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and Steel Federation (JISF) and the Japanese Society of Steel
Construction, is published three times a year. It is the only English
periodical that distributes technological information about steel constructionin Japan to the worldwide construction community.
We are conducting a survey of the periodical’s readership regarding
publication of the three issues planned for fiscal 2014. The survey’s major
aim is to gain an accurate understanding of reader needs so as to enhance
the usefulness of the publication. The survey forms are available as follows.
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Phone: 81-3-3669-4815 Fax: 81-3-3667-0245
URL http://www.jisf.or.jp/en/index.html
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© 2014 The Japan Iron and Steel Federation
Edited byCommittee on Overseas Market Promotion, The Japan Iron and Steel Federation
Chairman (Editor): Tetsuya Akahoshi
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