No. 54 August 2018

STEEL CONSTRUCTIONTODAY & TOMORROW

http://www.jisf.or.jp/en/activity/sctt/index.html

Feature Articles

Towards Highly Resilient andLonger-lasting Steel Bridges
1 Specifications for Highway Bridges-Revised in 2017 by Ministry of Land, Infrastructure,
Transport and Tourism-

4 Research Committee on Steel Bridges with Higher Resilience andLonger Service Life

6 Rationalized Design ofSteel Bridges and Load
Rating for Maintenance

9 Improvement of the Fatigue Strength of Steel Bridges andAssessment of the Effect of Repair and Reinforcement

12 Applicability and

Maintenance ofWeathering Steel Bridges
and Corrosion Repair
Methods for Steel Bridges

Special Topic

15 Possibility for Technological Innovation in Construction Employing
Statistical Mathematics Approaches

Back cover JISF Operations

Published Jointly by

The Japan Iron and Steel Federation
Japanese Society of Steel Construction

Feature articles: Towards Highly Resilient and Longer-lasting Steel Bridges (1)Specifications for Highway Bridges-Revised in 2017 by Ministry of Land, Infrastructure, Transport and Tourismby Masahiro Shirato
National Institute for Land and Infrastructure Management

Introduction
The Japanese Specifications for Highway Bridges (referred to as SHB hereafter) was revised in July 2017 by the Ministry of Land, Infrastructure, Transport
and Tourism (MLIT) and issued to roadadministrators. SHB is the legally-binding design code for national highways
and expressways and the de-facto standard for other roads.
The background of the revision thistime arises from MLIT’s recent policiesof:✓ Increasing productivity in the construction and preservation of infrastructure✓ Ensuring the long-term functionalityof bridges with lower life-cycle costs
and higher reliability
It is key to taking up developmentsin the industry and academic sectors in atimely manner to achieve these policies,
while reliability and quality are assured.
Accordingly, SHB has fully restructured
its code structure and verification process such that it is capable of providing
principles on how to make decisions on
the sufficiency of a bridge to the code requirements even when employing various new developments.
Performance-based Specifications
In consideration of diversifying materials and structural types, it is necessary
to have a code structure that is capableof verifying the performance in a directway, not only by means of conformity with the standards. Accordingly, theperformance-based code structure in the2017 revision is comprised of the following five main aspects:#1. Functional requirements for bridge
systems are divided into strength performance, durability performance,and supplemental performance.
#2. The standard bridge service life has
been clarified as 100 years.
#3. Both the strength and durability per1 Steel Construction Today & Tomorrow August 2018

Masahiro Shirato: Head of
Bridge and Structures Division,
National Institute for Land andInfrastructure Management(NILIM), Ministry of Land, Infrastructure, Transport and Tourism(MLIT), Japan

formance requirements are structured in a hierarchical manner fromthe bridge system level, the subsystem level (superstructure, substructure, and connection between superstructure and substructure), to theelement level.
#4. For every single provision, both performance requirements and corresponding standards/deemed-to-satisfy are simultaneously set out as a
package.
#5. The bridge strength performance requirement is given using a so-called
performance matrix, comprising design situations and bridge state/function requirements, including the required levels of reliability for eachcombination of design situation andbridge state/function requirement.
Performance Structure
Figure 1 shows the relationship between
the performance requirements and Table
1 compares the definitions of strength

performance and durability performance.
Bridge strength performance is theprimary performance requirement outof the three basic performance requirements and the requirement for the loadcarrying functions as a bridge system. A
bridge system maintains a state that has asafety margin to the critical state such as
collapse and also offers the service level
for time-variant load combinations during a design service period, where thesafety margin and service level are simultaneously fulfilled with desirable reliability, respectively.
Bridge durability performance is defined as the prerequisite requirement tobridge strength performance. The bridge
system needs to continue to mobilize thedesigned strength performance with adesirable certainty during the given design service period, considering aging
and deterioration. SHB requires ensuring
reliability for the period for which thephysical assumptions that are employedin the verification calculation for bridge

Fig. 1 Performance Requirements
Functional and safety objectives for thedesign service period(= Bridge performance)
Structural safety to be ensured at
any time by bridge strength
performance requirement

Bridge condition to be ensured up to
the end of the design service period bybridge durability performancerequirement

Supplemental performance to fulfill functional or safety objectives
e.g. Live load displacement limits, failsafe devices etc.

Prerequisites
Certainty and easiness in inspection, maintenance and repair/replacement ofstructural elements
Assurance of construction quality

Table 1 Definitions of Performance Requirements Including Reliability
Bridge strength performance

Bridge durability performance

Action/load
requirements

Instantaneous simultaneous
actions and loads at any time
during the design service life(=100 years)

Accumulation of persistentactions/effects and long-lasting
cyclic actions/effects up to theend of design service life(=100 years)

Resistance/durability
requirements

The bridge and its components(elements) shall maintain therelevant strength margins forrequired safety andload-carrying functions,
respectively.

It shall be ensured that material
deterioration or distress to
structural elements will not
violate design assumptions tohold the bridge strength
performance by the end of thegiven design service life.

Typical verification index

Strength or displacement on
load-displacement curves

Period on the time axis interms of maintaining strength
design assumptions

strength performance will not be violated by material deterioration or distress,
where the physical assumptions include
the effective cross-sectional area or material strengths of the considered structural elements.
In other words, SHB does not require
the prediction of the residual strengthof a bridge at the end of the design service period in consideration of aging
and deterioration with time, because it
is not practical to measure the time-variant reliability in strength or functionality against time-variant load combinations, while simultaneously considering
the degradation of element strengths andrigidity with time-dependent deterioration and aging.
The durability performance requirement of a bridge over the design service
period is equivalent to examining service
life issues and conducting so-called service life design, because it needs to consider the durability period of its elements,
components, or subsystems, the probableand worst-case mode and extent of failures, and the associated needs for maintenance, repair, or element replacement.
Namely, SHB practically considers thatthe reliability of bridge durability performance is equivalent to the feasibilityof a balance of durability, inspectability,
maintainability, and repair or element replacement workability under restrictions
over the design bridge service period.
Design Service Period for Bridge
Systems
The design bridge service period is newly
defined as the period in which the bridge
system is expected to provide design
function with relevant maintenance. The
standard design service period for bridge
systems is set at 100 years. In practice,engineers need to refer to the design service period when examining the feasibility levels of planned and worst-casemaintenance and remedial work with restrictions in individual projects.
It is worth noting that, in SHB, thestandard design service period also considers the reference period to determine
a set of load combinations for the verification of bridge strength performance.
Systematic Performance Verification Process
Practically, it is difficult to prove the extent of the achievement of bridge system
performance, because a bridge is a very
complex system. In the same way, it isalso premature to make a universal rule
to measure bridge strength performance
as a system in a direct way because too
many combinations of materials and elements and element arrangements areavailable as bridge systems to set numerical criteria for verification.
Accordingly, SHB allows that the performance verification of a bridge system
can be dissolved into the accumulationof performance verification for all elements for both bridge strength performance and durability performance. In
terms of bridge strength performanceverification, bridge system performancecan be represented by the strength performance of its critical subsystem or element.
The three-tier classifications in theload-carrying state of bridge systems aredefined, and this can be translated into
a combination of the load-carrying statesof superstructures, substructures, andgirder-to-column connections, respectively. The three-tier classifications in
the load-carrying state are also definedfor superstructures, substructures, andgirder-to-column connections, respectively. The stability of subsystems withplastic hinges can be theoretically dealt
with at this level if needed. In a similar way, the three-tier load-carrying stateclassifications for structural elements
are also defined, so that one can represent each of the three-tier classificationsin the load-carrying state of superstructures, substructures, and girder-to-column connections using a relevant combination of element load-carrying states.
In terms of bridge durability performance, a design element durability period is allowed for individual elements,
where the design element durability period is the period the mechanical characteristics of materials and the effective
cross-section area in the element remain
the presumed conditions in evaluating
bridge strength performance.
The design element durability period is not necessarily 100 years. Clarifying that not all elements shall function
as expected at the design stage for 100
years straight encourages innovations tomake durability design more reasonable.
A given bridge element can be replaced,allowing the bridge as a system to continue providing bridge strength performance. For example, replaceable decks,
bearings, bracing systems and so on may
be used or new developments for preserving structural elements may be employed with special cautions for inspectability and repairability even if it still has
limited proof data or little experience. Inversely, all elements may be given a design element durability period as long as
possible in some cases especially when
any preserving work is unfavorable during the design service period of a bridge
system due to other limitations or service
requirements.
In addition, all provisions package aseries of fundamental and mandate performance requirements and corresponding widely-accepted standards/deemedto-satisfy. Actually this concept was
originally introduced in the previous revision held in 2003. This kind of packaging clarifies that given design equations,factored strength or other limit values,
structural details etc. are not mandatory and alternatives are allowed to be employed if they meet the mandate performance requirements. In this context, thestandards are also expected to work as
an exemplification of target performancelevels including reliability, such that theperformance of an alternative solution
can be ascertained by whether the alterAugust 2018 Steel Construction Today & Tomorrow 2

native method offers an equivalent or
better performance than the standard interms of reliability.
Bridge Strength Performance andReliability Concept
Table 2 shows an example of the performance matrices.
Design situations are classified into permanent situations, variable situations, and rare situations, when considering the design service period, modeledwith load combinations that account fora given target occurrence probability ofload combination for 100 years.
Secondly, for each design situation,
the state of the bridge shall maintain the
structural safety margin to avoid any fatal failure/collapse as well as achieve theload-carrying function requirement simultaneously, where the required reliabilities differ for the structural safetymargin and the functional requirement
for a particular design situation.
In this context, the term “performancerequirement” in SHB includes accountability for reliability in the given load
combinations and resistances, respectively. From the viewpoint of accountability to the public, this description of
the performance matrix exemplifies concerns of road users such as “What kindsof situations are considered in design?”,“Does the bridge work in the case of anearthquake or hazard?”, “How reliable isit?” and so forth.
The present revision has employed apartial factor format for design equationsin terms of the verification of strength
performance, instead of a single safe-ty factor format (or an allowable stressformat). Design load combinations are
regarded as the representatives of stochastic simultaneous loading processes
to bridges over the bridge service period and are given to meet a target occurrence level.
Load factors and load combination
factors are used to define load combinations, and they are to be determined inreference to an intensive probabilistic
study, various analyses on the relationship between earlier design load combinations and design results, and trial design examples with new partial factors.
For example, although this is one of thereferences to set out load combinations,an intensive Monte Carlo simulation has
been conducted on simultaneous stochastic loading processes for 100 years foras many as 60 bridges at different sites,
employing the Ferry-Borges Castanheta probabilistic load combination model of different loads, i.e., live loads, thermal effects, wind loads, seismic effects,
and snow loads. The result has indicatedthat the load combinations for the variable design situation in the revised SHB
basically account for 95% non-exceedance probability in the 100-year maximum values of combined loads.
The limit states in resistance are defined as boundaries between two statesin Table 2. Resistance factors and several other partial factors are applied to thenominal resistance corresponding to thelimit state. Resistance factors are basically estimated to make the factored value of the resistance as a lower 5% fractile value, while other partial factors arefurther applied to this factored resistancedepending on the code requirements.
Remarks
The performance-based specifications
are crucial to accept various types andlevels of developments from material orelement levels to bridge structural systems.
This revision is expected to promote
the proactive acceptance of innovative
design and construction technology tomeet the diverse public demands in acost and time saving manner, while assuring the reliability and quality of structures. In this context, for example, the2017 revision of SHB has newly incorporated the characteristic values and partial factors for high-performance steels
such as a series of SBHS (steel for bridge
high-performance structure) and superhigh-tension bolts of S14T.
The concept of performance-based
specifications is also crucial to developing retrofit or refurbishment designcodes for existing structures, because design codes for existing structures haveto deal with more diversifying load environments and element condition states
than new structures.
We are seeking the enhancement of
SHB for the retrofit, repair, and maintenance design, taking advantage of theconcept of performance-based specification. ￭Table 2 Performance Matrix for National Expressways and Highways and Other Related Arterial Roads
StatesStates from the viewpoint of load-carrying function

State from the viewpoint ofstructural safety

Function State 1: The bridge is
intact to carry loads.

Function State 2: While the loadcarrying function degrades at partsof elements, the bridge still holds theload-carrying function prescribed
for the corresponding situation.

Safety State: The bridge has a
relevant safety margin to avoid acritical state.

Prevailing a permanent
or variable load

The fulfillment of the state isrequired with a given reliability
which is supposed to be different
from that for structural safety.

(Not required)

The fulfillment of the state isrequired with a given reliability.

Prevailing rare kind or
scale of load(Not required)

The fulfillment of the state isrequired with a given reliability
which is supposed to be different
from that for structural safety.

The fulfillment of the state isrequired with a given reliability.

Design situations

LS1

LS2

LS3

LS1, LS2, and LS3 = Limit State 1, Limit State 2, and Limit State 3, respectively
3 Steel Construction Today & Tomorrow August 2018

Feature articles: Towards Highly Resilient and Longer-lasting Steel Bridges (2)Research Committee on Steel Bridges with
Higher Resilience and Longer Service Lifeby Kazuo Tateishi
Chairman of the Research Committee on Steel
Bridges with Higher Resilience and Longer Service
Life (Professor, Nagoya University)

Kazuo Tateishi: After finishing the master course
at the Tokyo Institute of Technology, he entered
East Japan Railway Company in 1988. Then,he served as associate professor at the Tokyo
Institute of Technology and The University of Tokyo in 1997. He assumed his current position as
professor of the Graduate School of Engineering,
Nagoya University in 2003.

Currently in Japan, there is a need to prepare for great earthquakes that are forecasted to occur in the near future like theTokyo inland earthquake and the Nankai/Tonankai earthquakes. There has also been a call for the provision of structural performance that ensures safety
against such great earthquakes, not only for structures to be built in the future
but also for the vast number of structuresthat have already been constructed. At
the same time, it has become important
to appropriately renew and repair a vast
amount of existing social infrastructure
under finite financial conditions.
In order to meet these requirements, it

er resilience” and “longer service life,”
which plainly express these emerging
tasks, have been applied in naming the
Research Committee.

will be necessary to promote technological developments that provide greater reductions in terms of the time and cost required to renew and repair infrastructure,
while securing its safety. In this regard, in
terms of steel structures, it will be necessary to refine the technology that can accurately estimate the performance of various
structures. In addition, it will be necessary
to promote technological developments
conducive to not only the rationalized design of steel structures and the reductionof construction costs but also the efficientmaintenance of existing steel structures
and their prolonged service life.
To these ends, the two terms “high-Outline of the Research Committee
The Research Committee on Steel Bridges with Higher Resilience and Longer
Service Life was established in 2015
within the Japanese Society of Steel
Construction (JSSC) as a research project commissioned by the Japan Iron andSteel Federation (JISF). Its road map
to attain its respective research tasks isshown in Fig. 1.

Fig. 1 Road Map to Attain Respective Research Tasks of the Committee on
Steel Bridges with Higher Resilience and Longer Service Life
Tasks

① Subtask 1
Working Group on
Rationalized Design② Subtask 2
Working Group on Fatigue
Strength of Steel Bridges③ Subtask 3
Working Group on
Corrosion and Durabilityof Steel Bridges

Interdisciplinary tasks inabove-mentioned threesubtasks
Steering Conference〜 FY2014

Verification ofload-carrying
capacity ofcolumn andun-stiffened plate

FY2015FY2016FY2017FY2018FY2019

Revision of Specifications for Highway
Bridges: Introduction of load andresistance factor design method
Presentation of load and resistance factor forcolumn and stiffened plate and presentation of
constitutive law for seismic analysis that candeal with cyclic loading
Collection of load rating data andits trial analysis

Presentation of example ofapplication of SBHS (steel for
bridge high-performance structure)member in seismic design

Preparation of
Structuring of design, inspection andload rating manual rating systems; Organization of(draft)manual for bridge assessment

Expansion ofdesign fatigue
class

Effect on fatigue life improvement including that by theuse of high-strength steel (experiment, analysis anddesign method)Standardization of effect on fatigue
life improvement

Trial for andarrangement of
fatigue life
improvement

Collection of information on detective method for fatigue
crack, proving of repairing and reinforcing methods forfatigue crack

Preparation of guideline for crack
repair and service life prolongation
methods

Surveys of task
submitted by
Ministry of Land,
Infrastructure,
Transport andTourism

Guideline for maintenance andcorrosion diagnosis data
Assessment of practical bridge dataand examination of reliability
improvement measure

Maintenance andcorrosion
diagnosis

Preparation of handbook on design
and maintenance and its reflection
in standard

Examination about steel bridge
Preparation ofTechnical data on steel bridge
Survey andcorrosion diagnosis technology
corrosion map and having high corrosion resistanceassessment ofcorrosionpractical example
protection manualof corrosion ofbridge① Interdisciplinary assessment of attainments of each working group→Proposal of
attainments to society ② Tackling with the research task that supplements the niche between
fields (between subtasks and different fields) ③ Creation of research theme for future

August 2018 Steel Construction Today & Tomorrow 4

Many research committees were established based on the commission by JISF
and had already started research activities earlier in 1997 (see Table 1). Capitalizing on the long years of research activities, these committees have contributed
to solving many emerging issues faced bysteel bridge, and these research achievements have been reflected in the preparation of design standards and guidelines.
The working groups of the research committees have summarized their researchachievements, which are published in the
JSSC Technical Reports (Japanese).
One primary objective of the current
research committee lies in the promotionof research conducive to constructing
highly resilient and longer-lasting steel
bridges at low cost in order to further expand the application of steel bridges. To
achieve this goal, it is necessary to establish a system with the participation ofmultiple related organizations that support steel bridge development and to reflect research results in future design
standards and guidelines.
At the request of JSSC, I assumed thepost of committee chairman, and Prof.
Yoshiaki Okui of Saitama University andProf. Jun Murakoshi of Tokyo Metropolitan University assumed the posts of vicecommittee chairmen respectively. Then, 25
experts working in a wide range of fields
from industry, government and academia
participated in the research committee.
Three Working Groups to Promote Specific Research
The following three working groups
have been set up in the research committee to implement specific surveys and research:• Working Group on Rationalized Design:
Aim to rationalize design methods pertaining to load-carrying capacity and seismic
resistance of steel bridges (Chief: Prof.
Yoshiaki Okui of Saitama University)• Working Group on Fatigue Strength of
Steel Bridges: Aim to refine fatigue design for steel bridges and technologies
to deal with fatigue (Chief: Prof. Kengo Anami of Shibaura Institute of Technology)• Working Group on Corrosion and Durability of Steel Bridges: Aim to establish
corrosion-protection methods for weathering steel and ordinary steel (Chief: Prof.
Eiji Iwasaki of Nagaoka University ofTechnology)
In order to improve the resilience andservice life of steel bridges, it is necessary
to improve the performance of each of the
5 Steel Construction Today & Tomorrow August 2018

Table 1 Chronology of Research Committees on Steel Bridges
FY

Research Committee

Working Group

1997- Research Committee
1999 on Next-generation
Civil Engineering
Steel Structures• Working Group on Design of Rationalized Steel Bridge Girders• Working Group on Seismic Design Method for Steel Bridges• Working Group on Application of High-performance Steel
Products for Steel Bridges

2000- Research Committee
2002 on the Performancebased Design ofSteel Bridges• Working Group on Safety and Applicability of Steel Bridges• Working Group on Corrosion Protection and LCC for Steel
Bridges• Working Group on Seismic Resistance of Steel Bridges• Working Group on Higher Performance of Steel Bridges

2003- Research Committee
2005 to Improve Steel
Bridge Performance• Working Group on Rationalized Design Methods• Working Group on Improvement of Steel Bridge Durability• Working Group on Seismic Design Guidelines for Steel Bridges• Working Group on Weathering Steel Bridges

2006- Research Committee
2008 to Improve
Performance andReliability of Steel
Bridges• Working Group on Rationalized Structure and Design for Steel
Bridges• Working Group on Fatigue Strength of Steel Bridges• Working Group on Seismic Design Guidelines for Steel Bridges• Working Group on Weathering Steel Bridges

2009- Research Committee
2012 on Improvement ofStructures andDesign Method for
Steel Bridges• Working Group on Rationalized Structure and Design for Steel
Bridges• Working Group on Fatigue Strength of Steel Bridges• Working Group on Seismic Design Method for Steel Bridges• Working Group on Weathering Steel Bridges

2013- Research Committee
2014 on Improvement ofStructures andDurability of Steel
Bridges• Working Group on Rationalized Structure and Design for Steel
Bridges• Working Group on Fatigue Strength of Steel Bridges• Working Group on Maintenance for Weathering Steel Bridges

2015- Research Committee • Working Group on Rationalized Design2017 on Steel Bridges with • Working Group on Fatigue Strength of Steel Bridges
Higher Resilience and • Working Group on Corrosion and Durability
Longer Service Lifeof Steel Bridges

three areas of structural members: loadcarrying capacity, seismic resistance anddurability. For that purpose, it is necessary to conduct further studies on the fracture mechanisms and deterioration mechanisms peculiar to steel members. Further,prolonged service life for steel bridges
can only be attained assuming that appropriate maintenance is implemented, andthus technologies for inspection, repair
and reinforcement in the maintenance ofsteel bridges are important issues for technological development.
Three working groups have promoted
R&D activities based on the wide-ranging
issues mentioned above. Taking the opportunity of this three-year milestone fromthe start of survey and research at the respective working groups in 2015, the results of their surveys and research havebeen summarized. The three articles thatappear on the following pages 6~14 givean outline of these research attainments.
Towards Higher Resilience andLonger Service Life
The performance level required for steel
bridges has changed over time, and design methods have also undergone changes in line with this. One typical example
is a new design requirement triggered by
the Kumamoto Earthquake of 2016. Thatis, it is now required for bridge structures
to withstand multiple large-scale seismic
motions. Further, a major revision, the introduction of the load and resistance factor design method, was made in the Specifications for Highway Bridges publishedin 2017, and as a result it is now requiredthat further enhancements be made to thereliability of damage control and the easeof maintenance. Other new issues haveemerged: the issue of how to implement
effective inspection and countermeasuresagainst damage that is not yet evident alongwith the start of full bridge inspections.
Given such circumstances, two demands have emerged in the field of steel
bridges-the handling of the emerging
issues mentioned above and the continued contribution required for the revisionof technical standards planned for the future. The contribution towards the revision of technical standards and specifications by accumulating research results
will serve as an effective means of realizing enhanced resilience and longer service life for steel bridges. To that end, theCommittee on Steel Bridges with Higher
Resilience and Longer Service Life wasre-established in 2018, and will continue to promote research activities conducive to enhancing resilience and longer
service life for steel bridges. ￭Feature articles: Towards Highly Resilient and Longer-lasting Steel Bridges (3)Rationalized Design of Steel Bridges andLoad Rating for Maintenanceby Yoshiaki Okui
Chief of the Working Group on Rationalized
Design, Research Committee on Steel Bridges
with Higher Resilience and Longer Service Life
(Professor, Saitama University)

Further attempts are being directed towards the development of the technology
not only conducive to building national
resilience and regenerating obsolete social infrastructure but also to design steel
structures with international competitiveness. In accordance with these attempts, the Working Group on Rationalized Design of the Research Committee
on Steel Bridges with Higher Resilienceand Longer Service Life has promoted
research on steel bridges since 2015 focusing on the following themes:• Examination of statistical information on
the ultimate limit strength and serviceability limit strength of stiffening plates• Assessment of local-global interaction
buckling of columns• Investigation of rationalized design ofcomposite girders• Study on rationalized high-tension bolt
joints• Application of advanced analytical approaches in design• Examination of rationalized seismic design• Load rating of existing bridges
Outlines of the achievements from research on three themes-first, fourth andseventh-are introduced respectively inthe following article.
Examination of Statistical Information on Ultimate Limit Strengthand Serviceability Limit Strengthof Stiffening Plates
Steel for bridge high-performance structures (SBHS) was standardized in theJapanese Industrial Standards (JIS) in
2008, and its application was approvedin the Specifications for Highway Bridges1) in 2017. While reports of many material test results have already been available for SBHS, there are few reports on
the load-carrying capacity of structuralmembers manufactured employing SBHS.
To cope with such a situation, we
have conducted a compressive loading

Yoshiaki Okui: After graduating from the Graduate Schoolof Science and Engineering, Saitama University, he joined
Kawasaki Heavy Industries, Ltd. in 1985. Then he served
as associate professor at Saitama University in 1993 andvisiting researcher at Delft University of Technology in Netherlands in 1996. He assumed his current position as professor at Saitama University in 2009. His profession covers
structural engineering and bridge engineering.

test for stiffening plates using SBHS500(yield strength: 500 N/mm2) to compare
the load-carrying capacities between
mild steel SM490Y (yield strength: 355
N/mm2) and high-performance steel SBHS500. Each of two specimens (slenderness parameter: RR=0.5, 1.2) were prepared using SBHS500 and SM490Y. The
slenderness parameter is defined as:

where,
b and t: Entire width and thickness ofstiffened plate
σy: Yield strength
μ: Poisson’s ration: No. of panels to be divided by stiffening plate
As seen in Photo 1 showing a test
specimen, a square steel tube column
was manufactured that is structured using four stiffening plates, for which anaxial compressive loading test was conducted.

Photo 1 Stiffening plate compressive test specimen prepared using SBHS500 (steel
for bridge high-performance structures)
August 2018 Steel Construction Today & Tomorrow 6

Study on Rationalized High-tension Bolt Joints
The ultimate bending capacity of steel
girders with compact sections reaches its
full plastic bending moment. Accordingly,
in order to design bolt joints for compact
sections, it is necessary to define the critical condition that can assure the bending
capacity of the bolt joint up to the full plastic bending moment and to examine the design method that can be applied under sucha critical condition. In order to develop adesign method that can meet these needs,
the flexural loading test has been conducted on the I-girder bolt joint (Photo 2).
Fig. 3 shows the relationship between
the applied load P divided by the load Py
at the yield bending moment, and the bolt
hole deformation δb made dimensionlessusing the bolt axial diameter d. If 5% of
a normalized bolt hole deformation δb/d
is defined as an ultimate strength limit, it
7 Steel Construction Today & Tomorrow August 2018

Fig. 1 Comparison of Load-Displacement Curve
between SBHS500 and SM490Y in Axial
Compressive Loading Test
1.0

R R= 0 . 5

Axial compressive load P/Py

0.8

0.6

R R= 1 . 2

0.4

SBHS500

0.2

SM490Y
0

0

1

2

3

4

5

6

Axial compressive displacement U/Uy

7

Fig. 2 Ultimate Limit Strength and Serviceability Limit
Strength of Stiffening Plates Examined by Meansof Monte Carlo Simulations
1.0

Cr

/

y

1.2

Normalized strength

Fig. 1 shows the relationship between
axial compressive load P and axial compressive displacement U. In the figure,the vertical and horizontal axes are normalized using the yield axial force Py andthe yield displacement Uy, respectively.
The test results showed that SBHS steel
tube columns has a compressive loadcarrying capacity similar or superior tothat of mild steel columns.
In order to standardize designs employing SBHS, it is necessary to acquire
probabilistic information that shows
variations in the load-carrying capacity of structural members. In this regard,
examinations have been made employing the Monte Carlo simulations with thenonlinear finite element analysis and response surface method.
Fig. 2 shows an example of examination results- the relationship between the slenderness parameter andthe normalized strength of stiffening
plates2). In this figure, the ultimate limit strength (ULS) and the serviceability
limit strength (SLS) obtained from theMonte Carlo simulations are shown, andthe round mark indicates the average value of strength, and the error bar aboveand below the round mark shows 5% and
95% fractile values, respectively.
Fig. 2 also shows the load-carrying capacity of SBHS500 and SM490Y(Exp. SBHS500, Exp. SM490Y) obtained in the axial compressive loading
tests mentioned above and the curve ofstandard load-carrying capacity (JSHB)
prescribed in the Specifications for Highway Bridges1) currently in use.

0.8
0.6
ULS (ultimate limit strength)

0.4

SLS (serviceability limit strength)

0.2
0

0.0

Exp.SBHS500
JSHB (standard loadcarrying capacity in
Exp.SM490Y
Specifications for Highway Bridges1))

0.2

0.4

0.6

0.8

1.0

Slenderness parameter RR

Photo 2 Flexural bending test for I-girder bolt joint

1.2

1.4

is understood from the figure that a loadcarrying capacity 1.3 times or more thatof the yield bending moment can be assured for the bolt joint.
Generally, the full plastic bending moment is about 1.3 times the yield bending moment, and thus in cases when thedefinition of ultimate limit strength mentioned above is applied, it is possible todesign a bolt joint for compact section.
The Working Group on Rationalized Design will promote research aimed at clarifying the behavior of bolt joints after
sliding by means of experiments and analyses. The final goal is to standardize a rational ultimate limit state design method
for high-strength friction-joining bolts.

sen. The bridge was constructed in theearly part of the 1970s and was designed
based on the allowable stress design method by the use of the design live load (L20)of the old design specicfications3).
Load rating was conducted using as
the design load the B live load prescribedin the current Specification for Highway
Bridges, and the rating factor RF was
calculated using the following equation:

where,
C: Strength
D and L: Dead and live load effects
IM: Dynamic allowance factor
γd and γl: Dead and live load factors
Fig. 5 shows the result of calculating
the RF values for the bending capacity ofI-girder. The RF values were calculated
in conformity with four different specifications (old SHB: Specifications for
Highway Bridges3); current SHB: Specifications for Highway Bridges1); JSCESSSCS: Standard Specifications for Steeland Composite Structures4); and AASHTO: AASHTO MBE5)).
The target bridge was designed inconformity with the old SHB, in which
the allowable stress design method with

Load Rating of Existing Bridges
for Their MaintenanceIn many countries, it has become an urgent
task to assess the performance of bridges
that have been constructed based on old design standards and shown any performance
deterioration and damage. Japan is not an
exception. In the current research, we haveexamined load ratings that aim to assessing
the performance of existing bridges.
As a target bridge to be adopted forcase study, a simply-supported composite
I-girder bridge shown in Fig. 4 was cho-

Fig. 3 Relationship between Applied Load P/Py and Bolt
Hole Displacement Amount δb /d in Flexural
Bending Test for I-girder Bolt Joint
1.6

Applied load P/Py

1.5
1.4
1.3

a safety factor of 1.7 was employed.
Then, the design live load was changed
from TL-20 to B live load, and therefore
the RF value currently in use for load rating falls short of 1.0.
However, because the substantial safety factor has been reduced due to the revision to the partial safety factor methodin the current SHB, the RF value reaches nearly 1.0. In JSCE SSSCS and AASHTO MBE, because the full plastic bending moment is adopted as the bending
capacity, the RF value becomes larger.
As future research subjects, it is important to grasp real site-specific trafficload level and to investigate the safetylevel of existing bridges taking into account their periodic inspection results.
The Working Group on Rationalized Design will strive to tackle these emerging
tasks in and after fiscal 2019. ￭References
1) Japan Road Association: Specificationsfor Highway Bridges, Maruzen, 2017
(in Japanese).
2) Rahman, Md., Okui, Y., Shoji, T., Komuro, M.: Probabilistic ultimate bucklingstrength of stiffened plates, considering
thick and high-performance steel, J. ofConstructional Steel Research, Vol.138,
pp.184-195, 2017.
3) Japan Road Association: Specificationsfor Highway Bridges, Maruzen, 1956
(in Japanese).
4) Japan Society of Civil Engineers (JSCE):
Standard Specifications for Steel andComposite Structures, 2007.
5) AASHTO: Manual for Bridge Evaluation, 2018.

1.2
1.1
1.0
0.9
0.8

L1

L2

L3

W1

W1 W2

Fig. 5 Results of Calculation of RF Values
pertaining to Bending Capacity

W2

0

1

2

3

4

5

6

7 8

Bolt hole displacement δR/d (%)

2.0

L1 L2 L3

Fig. 4 Sectional Drawing of the Bridge Targeted in Case Study(Simply-supported Composite I-girder; Span: 34.4 m)
7300

7300

1.5

450
RF

450

16500
1000

Bending capacity

1.0

0.5
G1
1250

G2

G3

4 @ 3500 = 14000

G4

G5
1250

0.0

Old JSHB

JSHB

JSCE

AASHTO

August 2018 Steel Construction Today & Tomorrow 8

Feature articles: Towards Highly Resilient and Longer-lasting Steel Bridges (4)Improvement of the Fatigue Strength of
Steel Bridges and Assessment of the Effectof Repair and Reinforcement

by Kengo Anami
Chief of the Working Group on Fatigue
Strength of Steel Bridges, Research Committee
on Steel Bridges with Higher Resilience andLonger Service Life (Professor, Shibaura
Institute of Technology)

reinforcement on fatigue cracks
An outline of the examination and research on the first and third tasks is introduced below:

40

Fig. 1 Test Specimens and Fatigue Tests
Loading

340

100
12

12
240
B
700

A

C

F
D
50
E
50

Crack

75

105

106
Loading cycle, N10

G (50)H (40)
107

R=0.5
200

Grid blasting

9 Steel Construction Today & Tomorrow August 2018

PPP

JSSC
A (190)B (155)C (125)100

D (100)

80
60
40

HP

108

400

200

UIT

UIT (R=0, B) SBHS500
PPP (R=0) SBHS500
PPP (R=0, B) SBHS500
HP (R=0) SBHS500
B: Blast
HP (R=0, B) SBHS500

Spring for controlling（mm） stress ratio

Strain gauge

As-welded

20
104

Stress range (MPa)12painting, and influences of stress fluctuations in the large stress ratio forecasted
to occur due to dead load stress.
Fig. 1 shows the out-of-plane gusset
fatigue test specimens. The steel products applied to the test were SM490(rolled steel for welded structures) andSBHS500 (steel for bridge high-performance structures). The peening treatment applied for these examinations covered ultrasonic impact treatment (UIT),
hammer peening on base metal (HP) andExamination of Methods for Fatigue Strength Improvement by
Means of Weld Toe Treatment
Peening treatment is one of the methods
for improving the fatigue strength of weld
joints, and its application to steel bridges in Japan, particularly to existing steel
bridges, has shown
Fig. 2 Fatigue Test Results (SBHS500 Specimen)
a steady increase. In
400
the current research,
R=0experimental examiJSSC
nations pertaining to
A
(190)
200
the effect obtained
B (155)by means of peening
C (125)treatment have beenmade-influences of100
D (100)blast treatment made80
AW (R=0) SBHS500
E (80)AW (R=0, B) SBHS500
after peening treat60
UIT
(R=0)
SBHS500
ment and prior toF (65)
Stress range (MPa)Recently in Japan, various kinds of fatigue problems have become apparent insteel bridges. In order to prolong theirservice life, it will be more necessary in
the future to upgrade approaches for the
improvement of fatigue strength and for
effective maintenance including repair
and reinforcement.
For that purpose, the Working Groupon Fatigue Strength of Steel Bridges, theResearch Committee on Steel Bridges
with Higher Resilience and Longer Service Life, was established in the JapaneseSociety of Steel Construction. Aiming at
accumulating information conducive tothe longer service life of steel bridge fromthe aspect of fatigue issues, the Working
Group has promoted examinations relating to the following three tasks:• Method to improve fatigue strength bymeans of weld toe treatment
Methodto enhance fatigue crack inspec•tion efficiency• Method to assess the effect of repair andKengo Anami: After graduating from the School of Engineering, Tokyo Institute of Technology in 1993, he served
as research associate at Lehigh University in the US in
2001 and as associate professor at Shibaura Institute ofTechnology in 2008. He assumed his current position as
professor at the Department of Civil Engineering, Shibaura
Institute of Technology in 2014. His profession covers steel
structures and their maintenance.

20104

E (80)F (65)AW (R=0) SBHS500
AW (R=0.5) SBHS500
UIT (R=0.5) SBHS500
PPP (R=0.5) SBHS500
HP (R=0.5) SBHS500
105

106
Loading cycle, N10

G (50)H (40)
107

108

Examination of Methods to Assess the Effect of Repair and Reinforcement on Fatigue Cracks
The stop-hole method and splice plate
reinforcement have been applied as representative repair and reinforcement
methods for fatigue cracks in steel bridges. In the current research, taking noticeof these two methods, we have examined
the method to assess the effects obtainedby their use.

• Examination of Method to As-

sess the Effect of the Stop-hole
MethodIn the stop-hole (SH) method, further
propagation of cracks is prevented byproviding a round hole to the crack tip.
In this regard, few examinations havebeen made of cracking along the weld
toe. In the current research, experiments
and analyses have been carried out targeting cracks occurring along the weld
toe to examine the applicability of the
SH method and the assessment method
for fatigue strength after application of
the SH method.
Fig. 3 shows fatigue test specimens(non-load-carrying cruciform weld joint
specimen: H-type specimen provided
only with hole; and SH-type specimen
provided with slit and stop hole).
In the current research, because astop hole is provided for the weld toe,
two specimens were prepared in order toavoid the superposition of stress concentrations occurring due to weld geometries
and stop hole -specimens in which thestop hole center is located 1 mm and 5mm respectively apart from the weld toe.
The fatigue crack initiation point was at
the cross point of the stop hole and the toein the former specimen, and the stop hole
tip or in the toe on the reverse side of thestop hole tip in the latter specimen, andthe position in the current research agreed
with the maximum stress occurrence position obtained in the FEM analysis in
103

40 60
100

Fig. 3 Tension Test Specimens with Stop Holes
R40

9

1 mm

Center

Weld

50

150

50

50

60 40
100
H-TypeSH-Type

5 mm
Center
H5-A.SH5-S50C
H5-A-3R.
SH5-S50C-3R

50 50 50

Stress ratio
R=0• Examination of Method to As-

sess the Application Effects of
Splice Plate Reinforcement
Splice plate reinforcement has widely been applied as a method of reinforcing fatigue cracks. In order to further improve splice plate reinforcement, it has
been required to establish a design method for splice plates and an approach toconfirm the application effect after reinforcement. In the current research, noting that the stress concentration factor (αSH) of the stop hole located undersplice plates has a direct relationship withreinforcement effects, we have examined
an estimation equation forαSH and an ap-

Existing results (Mori et. al.)(Stop hole on flat plate)

Weld

HI-A. SHI-S50C
Slit along
weld toe
50

which these two specimens are modeled.
Fig. 4 shows the fatigue test results arranged in terms of the local stress range
in the fatigue crack initiation point mentioned above. There are no wide differences in the fatigue test results for respective specimens. Further, these fatigue test
results basically agree with those of existing stop-hole specimens in which thecrack is assumed to occur from the weld
toe and to propagate to the flat plate.
These test results were then evaluated within the local stress range thattakes into account the stress concentration on welds and the stress concentration caused by the use of the SH method.
As a result, even in the case where theSH method was applied to cracks along
the toe, we could show the possibilityof assessing the repair effect of the SH
method in the same way as in the case of
adopting the SH method when the crack
tip exists in a conventional flat plate.

Fig. 4 Fatigue Test Results

Load stress range (MPa)

air-type needle peening (PPP). Grit blasting was adopted for blasting treatment,
which was conducted at the bridge member fabrication plant under commonly applied conditions. A fatigue test was
conducted under the conditions of twostress ratios, R=0 and R=0.5, by meansof plate bending fatigue testing.
Fig. 2 shows examples of the fatigue
test results. Under all testing conditions,no difference in fatigue strength was observed regardless of the type of peening
treatments applied.
In the fatigue test conducted at thestress ratio of R=0, both of as-welded andpeening-treated test specimens showed nodifference in fatigue strength before andafter blasting, and considerable effects on
fatigue strength improvement were observed from peening treatments. On theother hand, in the test conducted at thestress ratio of R=0.5, while the fatigue
limit of the peening-treated specimen was
improved over that of the as-welded specimen, the effect of peening treatment on
fatigue strength improvement was greatly
reduced compared to the case of the test
conducted at the stress ratio of R=0.
Currently, the data obtained in thetests and the results of existing fatigue
tests are being collected to examine thedesign S-N curve after peening treatment.

As-welded-A
H1-A

JSSC-A

H5-A
H5-A-3R

3R: Grinder-treatment
was applied to theweld toe (radius: 3 mm).

SH1-S50C-A
SH5-S50C-A
102
105

SH5-S50C-A-3R
106
Loading cycle

107

August 2018 Steel Construction Today & Tomorrow 10

proach that estimates the stop-hole stressfrom strains occurring on the splice plate.
At first, axial tension tests (Fig. 5 (c))
and FEM analyses (Fig. 5 (d)) were conducted employing the test specimen (Fig.
5 (a) and (b)) prepared using as the parameter the dimension of splice plate
structure. Fig. 5 (e) showsαSH before theoccurrence of slipping of the splice plate.
As can be seen in the figure, while thestress concentration factorαSH is greatly
reduced by the use of splice plates in every case of specimen parameters, the level of reduction is affected by the splice
plate dimensions.
Next, analyses were made of more cases of stress concentrations on stop holesby means of an analytical approach sim-

ilar to that mentioned above. Based on
the analytical results, we have noted thestress reduction effect f1 brought about by
providing the splice plate to the cracked
section to increase the effective section
and the crack opening suppression effect (bridging effect) f2 brought about by
the use of splice plates, which has led totwo proposals: an equation to estimate
the relationship between the splice plate
dimensions and the stress concentration
factorαSH (Fig. 6) and a rationalized design approach for splice plates.
Further we have organized the relationship of stresses between stop holes
and splice plates, which has also led toa proposal: a method that estimates thestrain occurring in a stop hole from themeasured strain values just above the stophole (Fig. 7). Fig. 6 shows the comparison of stress concentrations on the stophole and Fig. 7 the comparison of strainsat the stop hole respectively in the caseof no fastening of bolts on the stop hole.
In the current research, it has become
possible to propose a highly accurateαSH
estimation equation and an approach toconfirm the effect of splice plates on
crack reinforcement with the use of thestrain at the reference point. It is expected in the future that these proposals will
be applied widely to assess the effect ofsplice plate reinforcement in more complex stress conditions and conditions
close to those in practical bridges. ￭Fig. 5 Tension Tests
No. 1: Without splice plate
Surface conditions:
The splice andbase plates of all specimens were
coated with inorganic zinc-rich
paint (thickness: 75 μm), except for
specimen No. 3 in which the baseplate was grinder-finished.
o: Application of high-strength bolt to stop hole; ×: No application of high-strength bolt to stop hole(b) Geometrical parameters of specimens
Stress concentration
on stop hole, αSH(a) Tension test specimens

Stop hole

Strain gauge

Specimen(d) FEM analytical models

Stress concentration on stop hole, αSH (FEM)

Fig. 6 Comparison of Stress Concentrations on Stop
Holes (Eq. 1 and FEM)
Stress concentration
factor in the case of
no fastening of bolton stop holeStress concentration on stop hole, αSH(estimated using Eq. 1)(e) Stress concentration on stop holes

Fig. 7 Comparison of Strains Occurring in Stop Holes(Eq. 2, FEM)

Strain on stop hole, εSH (FEM, μ)(c) Tension tests

Reference point

εSH =｛0.487(P/D) +1.63｝
・εref
・・(2)
P: Bolt pitch; D: Bolt diameter
εref: Strain at reference point
Strain on stop hole, εSH (estimated using Eq. 2, μ)

11 Steel Construction Today & Tomorrow August 2018

Feature articles: Towards Highly Resilient and Longer-lasting Steel Bridges (5)Applicability and Maintenance ofWeathering Steel Bridges and Corrosion
Repair Methods for Steel Bridges

For steel bridges, in addition to a proposal for an effective means of combating corrosion that takes into account
minimized LCC (lifecycle cost) and other economic rationalities, there is strong
demand for a proposal for maintenancetechnology that effectively prevents theperformance deterioration caused bycorrosion.
To cope with such a situation, taking
notice of the reduction of corrosion-protection costs and the technology to prevent corrosion-induced deterioration anddamage, it is urgently required to examine the following tasks: the application tobridge construction of weathering steel
that allows the reduction of LCC underappropriate corrosion environments andthe technology that maintains weathering steel bridges; and a measure that improves corrosion resistance and durability of steel bridge, a method that applies
corrosion-resistant materials, and a measure that retains and recovers the corrosion-protection performance of steel

bridges.
Given such a situation, the Working
Group on Corrosion and Durability of
Steel Bridges of the Research Committee
on Steel Bridges with Higher Resilienceand Longer Service Life, established in
the Japanese Society of Steel Construction, has promoted research on the applicability of weathering steel bridges
and technology for their maintenance, as
well as countermeasures against the corrosion of steel bridges. Some of the attainments obtained in this research are
introduced below:

salt from the road surface have been reported.
Thus, targeting steel bridges constructed in areas where the amount of
airborne salt from the sea is lower, wehave surveyed the amount of deicing salt
sprayed, the amount of salt flying to thesteel bridge girder, and the corrosion lossof plate thickness of steel. For that purpose, the device that accumulates the flying deicing salt and the steel product test
pieces subjected to exposure were arranged as seen in Photo 1.
Fig. 1 shows the relationship between

Application and Maintenance ofWeathering Steel Bridges• Applicability of Weathering Steel
Bridges in Deicing Salt-sprayedAreas
In snowfall and cold areas, corrosion
damage caused by the leakage of rainwater containing deicing salt is found inmany steel bridges. Further, examples ofcorrosion due to the scattering of deicing

Photo 1 Arrangement of flying salt accumulator
and exposed steel product test pieces

Fig. 1 Amount of Deicing Salt Sprayed andAmount Flying onto Girders

Fig. 2 Amount of Flying Deicing Salts andCorrosion Loss of Plate Thickness

Corrosion loss of plate thickness
by one-year exposure A (μm)

Eiji Iwasaki: After finishing the doctoral course at
the Graduate School, Nagaoka University of Technology in 1990, he served as associate professorof Nagaoka University of Technology. He assumed
his current position as professor, Graduate Schoolof Nagaoka University of Technology in 2012. His
profession covers structural engineering, steel
structure engineering and structural analysis.

Monthly flying amount of deicing salton the lower flange upper surface C (mdd)by Eiji Iwasaki
Chief of the Working Group on Corrosion and
Durability of Steel Bridges, Research Committee
on Steel Bridges with Higher Resilience andLonger Service Life (Professor, Nagaoka
University of Technology)

10

1

0.1

0.01

Bridge on the north bound road
Regression line C=0.74S
Bridge on the south bound road
Regression line C=1.30S
0.001
0.001
0.01
0.1
1
10
Monthly spray amount of deicing salt including residualon the road surface S (kg/m/day)

300
100

30

10

1
0.001

Central area of Honshu
Shikoku Island
Previous research (Protective rust)Previous research (Detached rust)
0.01
0.05 0.1
1Annual flying amount of deicing salt C (mdd)August 2018 Steel Construction Today & Tomorrow 12the amount of deicing salt sprayed on
the road surface and the amount of salt
flying on the upper surface of the girder
lower flange. The approximate salt flying amount on the bridge girder can beassumed from the relational equation in
the figure. Fig. 2 shows the relationshipbetween the amount of flying deicing
salt and the corrosion loss of steel plate
thickness caused by 1 year of exposure.
The figure also includes the relationshipbetween the amount of airborne salt fromthe sea and the above-mentioned corrosion loss1). While there is a difference interms of flying substances, that is, theflying salt from the sea (airborne salt)
and the flying deicing salt, it is known
that an identical relationship pertaining
to the amount of flying salt and the corrosion loss can be observed in the figure.

become clear that special-type bridges
account for about 9% of all weathering
steel bridges.
Further, surveys have been made of
the structural details and corrosion-protection performance of 27 weathering
steel bridges constructed in the Pacific coastal area. According to the survey
results, while no damage problems were
found in bridges constructed in the environmentally sound sites distant from thesea, detachable rust was found in bridges
constructed near the sea. In this regard,
it will be necessary to confirm the corrosion conditions of the node, anchorage and embedded section of bridges by
expanding the survey target to those located near the sea and in deicing saltsprayed areas.

• Case Studies of Surveys of Truss,

termine the Corrosion Conditionsof Weathering Steel by Means of
Image Processing
While weathering steel demonstrates
corrosion-protection performance that
capitalizes on its protective rust, there
are cases where the protective rust is
not generated depending on the corrosion environment. Therefore, it is necessary to assess the corrosion conditions bymeans of inspection. Whether or not theprotective rust is generated is judged bymeans of visual inspection of the rust appearance. In the case of applying visualinspections, however, variations occur inArch and Other Special-type Bridges Employing Weathering Steel
Examples of damage and countermeasures for I-girder and box-girder bridges
employing weathering steel have alreadybeen accumulated. However, information on damage examples for truss andarch bridges as shown in Photo 2 is basically limited. Literature surveys showthat highway bridges account for 92%
of all weathering steel bridges, railway
bridges account for 4% and other bridges 4%, thus indicating a high share forhighway bridges. In this regards, it has• Examination of Approaches to De-

Photo 2 Special-type bridges constructed using weathering steel

Fig. 3 Overlapped Rust Particles

13 Steel Construction Today & Tomorrow August 2018

Fig. 4 Three-dimensional Corrosion Map

the judgement depending on the engineer
who undertakes the inspection.
To mitigate such uneven results, wehave examined a method that assesses
the corrosion conditions by means of image processing of rust extracted using thecellophane tape test. With this method,
the corrosion conditions can be judged
from the size of the rust particles, butwhen the numbers of multiple rust particles overlap as seen in Fig. 3, it is impossible to implement accurate judgement.
To solve this problem, we have examined the cutting method for overlappedrust particles, and as a result it has become possible to show the diameter ofrust particles in which nearly no detachable rust occurs.
Countermeasures against theCorrosion of Steel Bridges• Preparation and Application ofCorrosion Maps by the Use ofThree-dimensional Models
Most of the recording and judgement ofcorrosion conditions at the stage of inspection are entrusted to the skill of theengineer who undertakes the inspection.
Further, because the corrosion map currently in use is prepared using two-dimensional models and photo images, apractical approach has not yet been established that specifically correlates the
corrosion conditions with the cause of
the corrosion. In order to implement the
future maintenance of steel bridges, itwill be necessary to examine an effective
method to record corrosion conditions
during inspection and to control related
information.
As one solution to deal with these concerns, we have prepared a three-dimensional corrosion map (Fig. 4). Specifically, we prepared the three-dimensional
corrosion map by the use of three-dimensional images to make a corrosion confirmation tool that visually expresses thecorroded section, which was proposed as
an approach that integrates maintenanceinformation and an item that trains inspection engineers.
The three-dimensional mapping of
corrosion levels and ranges can serve asa means for specifying the cause of corrosion and can be applied for the examination of the cares required to takein maintenance. Further, this approach
can serve as an effective tool for educating inspection engineers who explain
cares to be taken by corrosion inspection
method and methods of how to apply thethree-dimensional corrosion map media.

plate thickness measurement method that
employs eddy current with no need forsurface treatments such as rust removal.
(Refer to Fig. 5) Further, employing thefinite element method based on elastoplastic finite displacement analysis, wehave examined the shear strength assessment method for girder ends where local
corrosion occurred. In addition, taking
notice of the carbon fiber-applied repair
method as an approach that reinforces
the reduced strength caused by corrosion
loss in girder edges, we have examined
the strength improvement mechanism
for corroded girder ends.

• Approaches to Assessing the• Examination of Multi-function

Residual Strength of Corroded
Girder Ends and Recovering
Their Function
The frequency of the occurrence of corrosion damage is high in girder ends, andpractically about 40% of total corrosion
damage occurs there. For these corrosion-damaged sections, the residual plate
thickness is measured, and the residual
strength is assessed based on these measurement results, and then methods forrepairing and reinforcing these corroded
sections can be examined.
However, there remain some concerns
in each of the above-mentioned steps.
Then, we have examined the residualCorrosion-protection Decks asa Means to Improve Corrosive
Environments
Multi-function corrosion-protection
decks have been developed by several
teams. These decks not only play a roleas scaffolding but also shut out corrosion factors to improve the corrosive environment around bridge girders. (Refer
to Fig. 6 and Photo 3)
We have examined the performancerequired for multi-function corrosionprotection decks. We have also examined the economic advantages in theirapplication by comparing LCCs between
two bridges in which the deck was ap-

plied and not applied. Further, we haveintroduced the results of performanceverification tests conducted to confirm
the corrosion-protection performance ofthe deck.
As a result of the performance verification tests, many effects brought about
by the use of the multi-function corrosion-protection deck have become
clear-the shutting out of airborne salt
and reduction of wetting time inside thedeck. In addition, the result of steel product exposure tests showed high corrosion-protection performance of the deck.
However, decks have not been applied in actual bridges for very long time,
and this is a technology that still has few
examples of performance verification inpractical applications. Accordingly, there
remain some tasks in the use of multifunction corrosion-protection decks, andthus it will be necessary to continue toexamine their practical applications. ￭Reference
1) Public Works Research Institute of the
Ministry of Construction, Kozai Cluband Japan Bridge Association: Joint Research Report on Application of Weathering Steel to Bridges XVIII, 2003 (inJapanese)

Fig. 5 Distribution of Residual Plate Thickness in Girder Web Ends

Uniform corrosion

Lower corrosion

Central corrosion

Upper corrosion

Thickness(mm)

Fig. 6 Multi-function Corrosion-protection Deck
Full-cover typeInter-girder type

Airborne salt
RainwaterAir, water vapor

Airborne salt
RainwaterAir, water vapor

Photo 3 Interior of multi-function corrosion-protection deck

August 2018 Steel Construction Today & Tomorrow 14

Sp ecial Topic

Possibility for TechnologicalInnovation in Construction
Employing Statistical
Mathematics Approaches
by Tomoyuki Higuchi
The Institute of Statistical
Mathematics, Research
Organization ofInformation and Systems

The terms “mathematical statistics”
and “statistical mathematics” are closely similar, often causing confusion. But
they differ completely in content and academic orientation. While mathematicalstatistics is a branch of theoretical statistics, statistical mathematics is the termcoined by the persons concerned whenthe Institute of Statistical Mathematics
was established in 1944.
Statistical mathematics is regarded as a system of rational and empiricalmethodology. It discerns what is crucial
among practical issues, formulates it anddevises plans for experiment and examination, through which data is obtained,
and the analysis of this data and prediction lead to the establishment of action
guidelines. Thus, the fields that statistical mathematics covers are substantially vast.
Data Science and Artificial Intelligence
Data science is regarded as an integral
system that implies diverse scientific fields involved in statistics, including
machine leaning, data mining and data
optimization. Fig. 1 shows the conceptof data science showing the arrangementof diverse scientific fields from the perspective of mathematics and shows theoverlapping of diverse scientific fields.
The domain covered by artificial intelligence (AI), the term currently applied, is
15 Steel Construction Today & Tomorrow August 2018

Tomoyuki Higuchi: After finishing the doctoral course at the School of Science,
The University of Tokyo, he entered The Institute of Statistical Mathematics in
1989. He is currently engaged in a position as Director of the Research Organization of Information and Systems (Inter-University Research Institute Corporation) and Director-General of The Institute of Statistical Mathematics since 2011.
His profession covers Bayesian modeling. He is focusing his research efforts
on data assimilation and emulation (simple alternative method for simulation bymeans of machine learning).

wider than that of data science. But, theconceptual figure shows rapid changes
with time.
When examining AI from the perspective of mathematics, it is the computational technology that combines machine learning, statistics, data mining,
optimization and other fields. Machinelearning can be defined as a learning sys-

tem composed of a combination of threeelements: an objective, a mathematicalmodel and a learning algorithm.
The objective corresponds to what
you want to do by means of the data—theregression, discrimination and classification of data. There are many and diverse
mathematical models. In deep learning,
an artificial neural network (ANN) is ad-

Fig. 1 Overview of Mathematical Fields Relating to Data
Simulation science(first-principle deduction science)

AI: Anything and everything

Data science
Statistics

Optimization
Deep learning
Data mining(narrow sense)

Signal processing
Image processing
Machine learning

ControltheoryData engineering
Database engineeringopted as one of these mathematical models. ANN is a nonlinear function that realizes the input-output performance inwhich links of physiological nerves havegreatly been simplified. That is, deeplearning is one machine learning approach. Unknown parameters are included in the mathematical model. The method to determine the unknown parameteris called the learning algorithm.
When a combination of these threeelements is fixed, the machine learning
method makes it possible to program.

efficients that connect node with eachother becomes enormous. Because theweight coefficient is a parameter, thecase frequently occurs in which the unknown numbers reach nearly 1 billion.
An issue of over-fitting that certainly occurs when the number of parameter isless than that of the data has been steadily mitigated in the age of big data.
The number of nodes included in the
middle layer and how each node connects with each other, that is, the structure of the middle layer should be appropriately selected for the application.
As the application target for which deeplearning has attained many successful results, the voice, natural language and image are cited as the three main targets.
Diverse types of deep learning structures have been classified according to
the type of structures and the application
domain, which is schematically shown in
Fig. 2.

Deep Learning
Deep learning is a nonlinear functionthat is basically identical to the neuralnetworks that were popular in the 1980s(the second AI boom period). The interval between input and output is called
the middle (hidden) layer, in which many nodes are included. While the number of middle layers was one or two in
the 1980s, the current number properly reaches dozens. There are even cases where the number reaches 100, andin the case of an application example fornatural language, it reaches nearly 1,000.
As a result, the number of weight co-

Weaknesses of Artificial Intelligence
Machine learning is an inductive inference in which a rule is established, anddecision-making is attained based on thedata. In inductive inference, there areseveral original weaknesses. Accordingly, in order to appropriately apply AI, it
is indispensable to correctly understandthese weaknesses.
First of all, inductive inference isstrong in terms of interpolation but weakin terms of extrapolation. When considering an estimation using inductive inference of an extremely rare phenomenon
that has never occurred, this weakness
will become obvious. On the other hand,so-called numerical simulations that numerically solve a fundamental formula are strong in extrapolation, but in thecase of adopting numerical simulations
for interpolation, it is disadvantageous interms of calculation costs.
Further, it is important to correctly
understand the difference between correlation and cause/effect. When machinelearning is applied, it is easy to find correlations from among big data. Regarding the difference between correlationand cause/effect, a recommendation on
the electronic commerce site says: “Ifnecessary actions are promoted and thenif sales increase as a result, that will do.”In other words, the goal in the field ofFig. 2 Classification of Deep Neural Networks (DNN) in Deep Leaning
Sequentially-aligned (serial) data: Voice, text
Correlating witheach other
Data point
SampleLong short-term
memory (LSTM)

Recurrent neuralnetwork (RNN)
Long-range correlationand sudden obvious
effects are incorporated

Deterministic
Independent each otherYes
Supervised
learning

Output form

Boltzmann machine
Bayesian networ

Image

Is there any certain
pattern in thelocal structure?

Learning form
Probabilistic

Convolutional neuralnetwork (CNN)

Particularly no pattern

Unsupervised
learning

Adoption ofFeedforward neural network
reinforced
Basic neural network
learning element
Generative adversarial
nets (GAN)

Auto encoder
Toward generative model
Variational autoencoder(VAE)

August 2018 Steel Construction Today & Tomorrow 16

commerce is only attained in terms ofcorrelation.
On the other hand, for a problem that
directly links with human life, such as
the management of the safety of infrastructure, it is essential to identify thecause and the effect, or to understandthe relationship between the cause andthe effect. Also, on occasions where legal accountability is required as in thesale of financial instruments, it becomes
important to adapt the instrument to theconsumer’s needs and application conditions.
In this way, in the promotion of scientific research and the operation of the
manufacturing industry, it is essential toclearly identify the route that connects
the cause with the result (in other words,
the casual relationship), but there is alimit in identifying the casual relationship only by means of machine learning.
In particular, because the artificial neuralnetwork (ANN) obtained from machinelearning is a black-box, efforts are needed to make its input/output relationshipinto a “white box.”
Further, in the inductive method, serious examinations should be made of how
to handle, depending on the specified
problem, false-positives or false-negatives that cannot essentially be treated aszero. In cancer diagnosis, for example, inorder to avoid false-negatives (where thepatient has no problem in a cancer diagnosis, but actually does suffer from cancer), false-positives are accepted. Meanwhile in self-diving of cars, because
swift steering operation is very dangerous, false alarms generated by the sensor
are not incorporated one by one into theoperating (control) plan. In other words,
a design concept that avoids false-positives is adopted.
In this way, there is a limit in inductive methods in which the rule is established only by the use of data, and thus
how to adjust the balance between falsepositive and false-negative has become adifficult task in the application of AI in
business operations.
Digital Twins
There is no conceptual difference between digital twins and cyber physicalsystems, and in explaining them, the following three elements—1) measured data, 2) numerical simulations, and 3) experience and intuition—serve as theimportant players. Noticing to the relationship among these three elements, theleading-edge technologies in the industrial field are outlined below:
17 Steel Construction Today & Tomorrow August 2018

Fig. 3 Detection of Abnormal Values such as Outliers,
Abnormal Sections and Change Points
Measureddata

Machine learning

Discrimination
model

Numerical
simulation

Experienceandintuition

Restriction conditioned To apply for preparationof supervised data
by fundamental
formula (conservation law)

When a fundamental formula is unavailable in examining the target phenomena, generative models have
conventionally and empirically been prepared using the measured data to control
the target phenomena. The scale of themathematical model to be applied has
undergone changes from simple models like multivariable auto-regression
models previously applied to large-scalemodels with deep learning currently applied.
The detection of abnormal values is amost important issue for the entire industry. In the case of examining the detection of abnormal values occurring in industrial operations employing the threemajor elements mentioned above, discrimination models to detect abnormal
values are prepared using numerical simulations and experience/intuition as supervised data and from the measured data obtained through machine learning.
Fig. 3 shows the process and structureof the discrimination model employing
these three major elements in detectionof abnormal values. The opposite is theemulation approach—a technique thatuses the measured data as supervised data and prepares a regenerative model forthe measured data by means of machinelearning, based on the results of numerical simulation.
The numerical simulation usually requires a great deal of calculation time.

But in the case of emulation, the structured generative model is an extremely simple model like a linear regression
model, and therefore the computation
carried out in a design parameter spacecan be attained at a high speed. Fig. 4
shows the role played in emulation by
the three important elements—measured
data, numerical simulations, and experience and intuition.
It is the data assimilation that integrates the three sources of informationfrom the measured data, numerical simulation and experience/intuition using
Bayes’ theorem. Fig. 5 shows the relationship among the three elements in adigital twin. Research on data assimilation has been actively promoted since
the mid-1990s, and currently data assimilation is indispensable for forecasting
weather conditions. That is, data assimilation is regarded as a technology that isroutinely applied.
Utilization of Databases and Linkage Technologies
Research that expresses the experienceand intuition using numerical formulas is
being promoted at an accelerated pace byconstructing generative models for interested targets employing enormous accumulated databases and by means of machine learning. While radically different
from the field of civil engineering, thisresearch can be explained with the exam-

Fig. 4 Emulation and Virtual Measurement
Application for the
preparation ofsupervised data

Measureddata

Machine learning

Emulation

Constructing of
measurement
model using
statistical model
Experienceandintuition

Numerical
simulation
Production of big data using thegenerative model based on thefundamental formulaFig. 5 Relationship among Three Elements in Digital Twins

Measureddata
How to makeintegrated useof threeinformation
sources is
crucialGenerative model
equipped withlearning function

Digital twin

Numerical
simulation

Experienceandintuition

Normally, the generativemodel based on
fundamental formulaple of new medicine development.
When information about the structures of a vast amount of organic compounds accumulated in a database isexpressed in graphs, the pattern is completely different from that of the graphthat expresses human-to-human links as
seen in social network services (SNS).
In other words, while there are certain

patterns in graphs pertaining to organic
compounds, it is difficult for humans tofind patterns from the vast amount of databases thus far accumulated. Machinelearning has demonstrated high performance in handling such emerging tasks.
Information about molecular structures can be transformed by the use ofcertain transformation formulas to astring that expresses the chemical formula (that is to say, a chemical structure formula). While the string does not conformto the three-dimensional structure of theoriginal compound on a one-to-one basis, it can fully express the characteristicfeatures of organic compounds. Once theinformation about molecular structures istransformed to the form of a string as explained above, it becomes possible to apply diverse natural language processing
technologies that have recently shown
rapid progress.
For example, if a certain chemical
formula is given, the subsequent formula can probabilistically be formedby the use of the word predictive function found in a smart phone or other advanced devices. When this function is repeatedly applied, it is possible to produce
many virtual molecules that reflect diverse patterns existing in compounds inthe database. To these ends, employing
the machine learning approach, the tacit knowledge hidden in databases should
be positively mathematized as a generative model corresponding to prior information.
It is urgently needed to make evident
information hidden in databases and at
the same time to introduce linkage technologies that handle related informationin an integrated manner. In the case of
applying the Internet of Things (IoT) for
monitoring social infrastructure, a single
data setting is insufficient, and it is inevitably required to integrate diverse kindsof information (data that cannot be obtained on the spot and data stored by other related organizations). In data integration, it becomes necessary to provide
diverse devices such as for loss treatment(imputation) and quality guarantee.
For example, in analyzing the data obtained from many position/acceleration
sensors arranged on a bridge, video information of passing vehicles using a fixedcamera is very useful. In addition to theinformation thus obtained, meteorological information pertaining to the amountof local solar radiation and the wind velocity should be analyzed. The mathematical foundation of information linkage
technology is mainly entrusted to Bayesian’ statistics, and thus a considerable
amount of calculation time is required
to realize rational inferences. To remedy
this, many devices to make simple inferences have been put into effect. ￭August 2018 Steel Construction Today & Tomorrow 18

JISF Operations

SEAISI Training Program Held in JapanThe Japan Iron and Steel Federation
held the SEAISI Training Programin Japan on 23rd to 27th of October
2017. The program, sponsored by theSouth East Asia Iron and Steel Institute (SEAISI), is annually held aiming
at improving diverse kinds of skills ofsteel-related persons in the six “ordinary regular member countries” of
SEAISI. Japan and the three “supporting regular member countries”
of SEAISI-Korea, Taiwan and Australia-have extended cooperation inholding the program on an alternating basis among these four countries.
The program was held in Japan for the
first time in four years since 2013. It
accepted 17 persons working at steelmakers in six ordinary regular member
countries.
The 2017 program in Japan washeld with the theme of “Japan’s High

Performance Steel Products (Feature,
Key Performance Indicator in Production Process and R&D),” in which
three lectures were delivered:• Application of High-performance Steel
Products in Bridge Construction in Japan• Application of High-performance Steel
Products in Building Construction inJapan• Application and Operation of JapaneseIndustrial Standards (JIS) in the Fieldof Iron and Steel Products
The program covered site visits to
the Kimitsu Works of Nippon Steel &Sumitomo Metal Corporation, the East
Japan Works of JFE Steel Corporation and the Kakogawa Works of Kobe Steel Ltd., where lectures were alsodelivered explaining key performanceindicators in production processes conducive to the management of entire
steelworks operations, new ironmak-ing technologies and methods to reduce CO2 emissions from mediumand long-term perspectives.
In addition, program participants
visited the National Institute for Material Science, where lectures were alsodelivered pertaining to research being
promoted on structural material technologies, material strength and seismic
technologies.

Lecture Delivery at the SEAISI ForumThe Japan Iron and Steel Federation(JISF) dispatched Masamichi Sasaki, amember of JISF’s Committee on Overseas Market Promotion, to the 2017
ASEAN Iron and Steel Sustainability Forum held by the South East Asia Iron andSteel Institute in Manila, the Philippines,on November 27, 2017. He delivered alecture titled “Market Development of
Steel Structures in Japan-Standard-

ization, Building Codes and Steel Products.” The lecture was delivered at therequest of the Sub-Committee on SteelApplications in Construction Sector of
SEAISI. It was one of lectures deliveredby committee members and other related persons. Japan participates in the SubCommittee as an observer.
In the lecture from Japan, diverse
initiatives exerted for the promotion

STEEL CONSTRUCTION TODAY & TOMORROW
Published jointly by

The Japan Iron and Steel Federation
3-2-10, Nihonbashi Kayabacho, Chuo-ku, Tokyo 103-0025, Japan
Phone: 81-3-3669-4815 Fax: 81-3-3667-0245
URL http://www.jisf.or.jp/en/index.html
Japanese Society of Steel Construction
3F Aminosan Kaikan Building, 3-15-8 Nihonbashi, Chuo-ku, Tokyo 103-0027, Japan
Phone: 81-3-3516-2151 Fax: 81-3-3516-2152
URL http://www.jssc.or.jp/english/index.html

of market development for steel structures in Japan were introduced with aremark-why steel structures have attained remarkable development in Japan is greatly attributable to the systematic preparation of steel structure-related
laws and design approaches, technological development, and framing for efficient construction and logistics.

© 2018 The Japan Iron and Steel Federation
Edited byCommittee on Overseas Market Promotion, The Japan Iron and Steel Federation
Chairman (Editor): Kei Teshima
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