No. 39 August 2013

STEEL CONSTRUCTIONTODAY & TOMORROW

http://www.jisf.or.jp/en/activity/sctt/index.html【 m i n a t o 】“港(minato)” in Japanese, or port in English

Planned maintenance of port facilities and improvements tolifecycle cost assessment technology and to the reliabilityof port steel structures are becoming urgent tasks.
This issue features methods to deal with these tasks.

In this issue.....
1 Maintenance of Harbor Facilities
4 Life-Cycle Management of Portand Harbor Steel Structures

7 Influence of Defects and Exposure

Conditions on Coating Degradation
due to the Corrosion of Steel Piles
and Plates in Marine Environments

10 Evaluation of the Remaining Load-carrying Capacity
Published Jointly by

The Japan Iron and Steel Federation
Japanese Society of Steel Constructionof Corrosion-damaged Steel Structures and the Predictionof Future Performance

13 Lifecycle Performance Assessment Technology

for Port Steel Structures with a Focus on Post-repair Performance

16 Assessment Method to Determine the Remaining Strength ofCorrosion-deteriorated Port Steel Structures and Its Necessary
On-site Measurement of Corrosion Profile

From Posterior Maintenance to Preventive Maintenance

Maintenance of Harbor Facilities

by Naoki Endo, Port Management Office, Engineering Planning Division, Ports and Harbors Bureau,
Ministry of Land, Infrastructure, Transport and Tourism
Preface
Most of Japan’s port and harbor facilities
were constructed or underwent improvements in the 1970s and 1980s and are therefore expected to simultaneously enter superannuation in the near future. Like other social
infrastructure, these port and harbor facilities need to receive appropriate measures tocounter the effects of aging.
Japan, however, faces many other pressing concerns: severe fiscal limitations confronting both national and local governments,a declining population, a falling birthrate andan aging society. In light of these circumstances, it will be difficult to effectively deploy conventional countermeasures against
the superannuation of the nation’s social infrastructure. To cope with this, the Ministryof Land, Infrastructure, Transport and Tour-ism (MLIT) has established the Strategic
Committee on Social Infrastructure Maintenance and numerous other committees
mandated to study needed countermeasuresagainst obsolescence. The following text introduces one of these countermeasures, a preventive maintenance plan for ports and harbor facilities.
From Posterior Maintenance toPreventive MaintenancePublic wharves serve a key role among
port and harbor facilities. Of all the public
wharves in service at the end of March 2013,
about 8% had been in service for 50 or more
years since they were constructed. However,this rate is forecasted to grow to about 58%
after another 20 years at the end of March
2033 (Fig. 1). Because a growing number ofthese facilities are showing deterioration ordamage caused by the aging process (Fig. 2),
concern is rising with regard not only to functional deterioration but to the occurrence ofaccidents as well.
On-going superannuation poses twopressing problems: increasing lifecycle costs(the expense of future maintenance and improvements) and faltering public serviceability due to accidents and other adverse factors
attributable to aging. To meet this situation,
we consider it necessary to develop a newconceptual approach to maintenance: i.e., totransition from posterior maintenance, which
does not implement needed countermeasures
until drastic renewal work is judged necessary, to preventive maintenance that places
primary importance on prolonging service
life and minimizing lifecycle costs (refer toFig. 1 Construction of Public Wharves in Japan
(No.)
2500

No. of public wharves in use 50 or more years since construction
2000
No. of wharves constructed
1500

Accumulated No. of public wharves in use 50 or more years since construction

1000

500

0
1946

1951

1956

1961

1966

1971

1976

1981

1986

1991

1996

2001

2006

2011

2016

2021

2026

Ratio of public wharves in use 50 or more years since construction to the total of all public wharves
March
2013

About

8%

March
2023

10 years later

About

32%

March
2033

10 years later

About

58%

Total public wharves: about 5,000**No. of public wharfs with water depth of 4.5 m or more (Source: MLIT)
1 Steel Construction Today & Tomorrow August 2013

Fig. 2 Examples of Superannuated Wharves• Port and harbor facilities are exposed to salt damage and other severe application environments and they have many submerged sections that do not
permit visual observation of deterioration and damage.
• Because of the above, the deterioration and damage that might occur to submerged steel sheet and pipe piles and at the rear of wharf floor slabs areoverlooked, and this can lead to large accidents. Therefore, it is important to secure structural safety by means of appropriate maintenance.

Sinking of apron due to sucking out ofearth and sand at wharf rear

Peeling of concrete due to corrosion ofreinforcing bar

Fracture of steel pipe pile due tocorrosion

Pitting on steel sheet pile due to corrosion
and sucking out of earth and sand at wharf rear

Function/PerformanceFig. 3 Image of Preventive and Posterior MaintenanceImprovement
work (low cost)
Preventive
maintenance
Condition in which routine, appropriate
maintenance is provided

Drastic renewal
work (high cost)
Posterior
maintenanceStandard serviceable limit
Prolongation ofservice life of facility

Initial lifecycle (design service period)
Service period

Fig. 3).
We also consider it indispensable thatthoroughgoing maintenance should be put
into effect by port and harbor administratingorganizations, and that mechanisms should
be worked out to prevent potential accidents
and functional deterioration attributable tosuperannuation.

Specific Measures Promoted by thePorts and Harbors Bureau
In order to promote appropriately planned
maintenance as a countermeasure to superannuation, the Ports and Harbors Bureau has
striven to prepare laws and regulations andhas implemented various measures related totechnology and budgets aimed at preparing amaintenance plan and implementing appropriate maintenance based on that plan.

While the maintenance plan thus worked
out has content suitable for maintaining individual port and harbor facilities, studies have
yet to be made regarding project expense reductions in terms of all port and harbor facilities or regarding the leveling of annual
project expenses. Given such a situation, theBureau has introduced a “preventive maintenance plan” that allows comprehensive study
on a port-by-port basis.
Preventive Maintenance Plans
The preventive maintenance plan targets various facilities within a port, and specifies
countermeasures to the superannuation of facilities and it offers a nearly five-year project outline based on the countermeasuresthus specified. The plan was basically developed on a port-by-port basis. The main entities involved in preparation of the plan were
the national government (government organizations in charge of direct administrationof ports and harbors) and port and harboradministrating organizations. The plan was
worked out basically through necessary accommodations agreed to by both types of entities. The plan specifies in the “action guidelines” its basic policy determining whether orAugust 2013 Steel Construction Today & Tomorrow 2

Table 1 Preventive Maintenance Plan (Concept)–Preventive Maintenance Plan for Port A

Discontinuedusesinking

Hinode No. 4 wharf at Hinode area, Port of Shimizu (pier type, water depth of 12 m, completed
in 2011)

not countermeasures against superannuation
are to be implemented (see Table 1).
The determinations made using the “action guidelines” are based on a comprehensive overview that takes into account thesocial conditions surrounding a target facility (current application conditions, examination of application conversion plan or no
examination of alternative conversion plan,
3 Steel Construction Today & Tomorrow August 2013

assumption of emergency use or no assumption, requests from port users) and thephysical conditions (level of superannuation,
structural characteristics).
Further, in the decisions suggested by the“action guidelines,” it is necessary to examine not only facilities in active implementation of superannuation countermeasures but
also facilities that should be converted to other purposes or for which application should
be discontinued. For example, preventive
maintenance is not performed on facilities
standing on sites planned for reclamation or
on facilities to be converted to other uses because they can no longer serve as a mooring
facility. In this way, it is important to pay due
attention in planning preventive maintenanceso that a rational plan can be developed thattakes into account the minimization of lifecycle costs for all the facilities of the target port.
In addition, the plan must be able to appropriately maintain the port facilities as a stock
while at the same time securing all necessaryfunctions, and it must have planned and stra-tegic content.
Conclusion
The preventive maintenance plan is to be initiated in 2013. In order to better prepare theplan, we intend to reexamine the current planby taking into account emerging changes insocial trends and the various tasks involved
in implementing the preventive maintenanceprojects. We at the Ports and Harbors Bureau are striving to promote effective countermeasures against the superannuation of
port and harbor facilities. These efforts include: implementation of the current preventive maintenance plan that takes into accountthe operations of the examination council as
it continues deliberations on the plan and themaintenance measures based on the new legal system; and cooperation with port administration organizations and other related entities. Our goal is to maintain good-quality
public service.
￭

Life-Cycle Management

Life-Cycle Management of Port andHarbor Steel Structures
by Hiroshi Yokota, Professor, Lifetime Engineering Laboratory, Hokkaido University
Introduction
A port and harbor structure has a long lifetime and must be expected to meet demands
during its lifetime that cannot be foreseen.
Steel and concrete as principle structural materials tend to deteriorate due to physical andchemical agents under harsh marine environments and loss in structural performanceor even structural collapse may be consequences. At the initial design stage, designers
make several assumptions, in which probably
worst conditions are considered with certain
safety margins, so that the structure can keep
its structural performance over respective required levels. However, serious deterioration of structural members may be caused byinsufficient durability design with optimistic
assumptions and/or by lack of proper maintenance work.
To meet these facts, it is extremely important to pursue coordination between design and maintenance. The life-cycle management is an organized system to support
engineering-based decision making for ensuring sufficient structural performance andlong life of a structure at the design, maintenance, and all related work during the lifetime of a structure.

Fig. 1 Life Cycle of A StructureLife-Cycle Management
The service life of structure is made up of all
the activities that go into planning, basic anddetailed designs, execution including material selection, production and construction,
maintenance including assessment and intervention, and decommissioning, as shown in
Fig. 1. The life-cycle management is an integrated concept to assist all activities managing the total life-cycle of structures to realize sustainability. Sustainability is one of thevery important keywords for port and harbor
structures, not only them but for all civil infrastructure.
In the life-cycle management, as shownin Fig. 2, the most important work is to formulate and to update the life-cycle management scenario (LCM scenario). The scenario
should be formulated in consideration of thefollowing items:• Environmental characterization;• Assumption in designs;• Result of verification;• Specification;• Initial cost estimation;• Maintenance scenario and methodologies ofthe life-cycle management;• Performance requirements;• Service life estimation;• Life-cycle cost;• Environmental cost; and• Obsolescence, demolition and reuse.
During the initial design stage, the service
life design will be applied to predict the durability and performance degradation. As schematically shown in Fig. 3(a), while lots of alternatives can exist, the fundamental concept
on how the structural performance should
be ensured must be well considered basedon conditions, design service life, structural characteristics, material properties, difficulties in assessment and intervention, social and economical importance, etc. For port
and harbor steel structures, corrosion of steel

Plan

DesignExecution

MaintenanceReplace

Ensuring function and performance
Ensuring quality and reliability
Reducing financial cost/Increasing benefit
Reducing environmental cost (burden)

Fig. 2 Life-Cycle Management System
Plan
Design• Conceptual design• Service life determination• Performance verification

LCM scenario
Execution
Maintenance• Functional obsolescence• Service life and future use• Performance assessment• Prediction

Scenario update

RecordDemolition/Re-use
Intervention

Fig. 3 LCM Scenarios(a) At the initial design stage(b) At the maintenance stage
August 2013 Steel Construction Today & Tomorrow 4

LCM Scenario
An example of the LCM scenario formulation will be presented1). An open-piled marginal wharf shown in Fig. 4 is taken up fora case study. The substructure of the wharf
is made of steel pipe piles, of which diameter and thickness are 1500 mm and 19 mm
Fig. 4 Open-Piled Wharf for the Case
Study
20 m
DL+4.7DL±0.0DL-12.0

DL- 5.0
D1500, t19(SKK490)

DL-18.0
D1500, t15(SKK400)
DL-35.5

5 Steel Construction Today & Tomorrow August 2013

Fig. 5 Variation in Corrosion Rate0

Corrosion rate (mm/year)
0.1
0.2
0.3

0.4

2
0
-2
-4

-6
-8
-10

Fig. 6 Increase in the Probability of
Failure due to Corrosion of
Steel Piles
Failure probability (×10-3)

4

Elevation (m)

Max
Ave
Min

-14

for the part above DL−18 m and 1500 mm
and 15 mm below it. According to the corrosion rate of steel, the profile shown in Fig. 5
is used which had been measured in a neighboring wharf for 26 years. The progress ofcorrosion generally differs location by location. Thus, as shown in the figure, the maximum, the average, and the minimum values
have to be considered to make probabilistic
approach.
To counter such the corrosion risk, four
LCM scenarios are formulated:• S1: No corrosion prevention• S2: Coating (DL+2.5∼−1.0 m)• S3: S2+S4• S4: Cathodic protection (DL−1.0∼−12 m)
The design life of the coating and cathodic protection systems is set at 50 years. In
fact, many scenarios can be considered depending on the design life of the corrosion
protection system. The corrosion protection
efficiency of the cathodic protection is set at90%2).
The structural performance is verified byusing the push-over analysis3) and dynamic response analyses for level-1 and level-2
seismic ground motions4). The probability of
failure of the wharf is increased due to corrosion of steel piles. Fig. 6 shows the failure probability over time against (a) level-1
ground motion and (b) level-2 ground motion. The allowable maximum values of the
failure probability are set at 0.00382) and 0.01
for level-1 and level-2, respectively. Therefore, before reaching the values, strengthening is needed to recover the performance.
Under those scenarios, S1 needs strengthening 3 times (16th and 30th years for level-1
and 44th year for level-2) during the design
service life of 50 years. S2 needs strengthening 2 times at 36th year for level-1 and45th year for level-2. While no strengthen-

4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0

0

S1

S2

S3

10

20
30
Time (years)

S4

40

50

40

50

(a) Level-1 ground motion-12
Failure probability (×10 -2)

is a principal cause of performance degradation to be considered at the initial design. Accordingly, corrosion of steel itself and/or deterioration of a corrosion protection systemshould be fully taken into account. In general, we do not have to worry about fatigue ofsteel for port and harbor structures.
Maintenance is the major strategy tocounter the degradation, which is carried out
to assess the present conditions of structure
and to quantify the level of structural performance. In addition, by predicting future
progress of structural performance degradation, the most appropriate method of intervention should be chosen for minimizing thelife-cycle cost or maximizing structural performance recovery under budget capping, asshown in Fig. 3(b). During the maintenancestage, maintenance engineers will initiallyfollow the scenario that had been assumed at
the design stage. For realizing strategic maintenance work, as mentioned earlier, a maintenance strategy should be properly formulated as the LCM scenario. The service life
design or durability design has been carriedout based on lots of assumptions at the initial design. Accordingly the output of the design has to be verified with the maintenancework because progress of deterioration including corrosion would not follow the design assumptions. This is related to the LCM
scenario update. The scenario should be updated with reflecting the actual situation of
the structure and changes in conditions.

1.0

S1

S2

S3

10

20
30
Time (years)

S4

0.8
0.6
0.4
0.2
0

0

(b) Level-2 ground motion

ing is needed, S4 needs 2 times only for level-1 ground motion at 16th and 33rd years.
For this calculation, steel plate welding is adopted for the strengthening. By the strengthening technique, load-carrying capacity canbe perfectly recovered, but the ductility canbe reduced by about 40% of the initial value due to the application of underwater wet
welding5).
Designers should select the best scenario
among its alternatives. For the selection, themost appropriate indicator should be determined for objective judgment. The life-cycle
cost will be one of the indicators, which will
be mentioned later.
Assessment and Evaluation
Since performance degradation of a port andharbor steel structure is mainly caused by corrosion of steel, corrosion progress should bemonitored during the service life. The progress of corrosion differs widely by its location
because of inhomogeneous characteristics ofmaterials and diversity of environmental conditions. By using the real corrosion data, theLCM scenario has to be updated.
Detection of age-related deterioration
should be very important to understand thecondition of a structure. The deterioration of
coating and other corrosion protection systems can be found at first as damages on theirsurfaces. The level of inspection and investigation has an influence on the method of

by their consequences. To reduce the risk offailure occurring within the design life when
the consequences of failure are judged to be
critical, it may be necessary to require particularly long design lives for specific members
or to strengthen the requirements for inspection and maintenance. To determine the LCM
scenario including the appropriate timing andmethod of intervention, estimation of life-cycle cost is one of the best indicators8).
The life-cycle cost is calculated basedon various assumptions, but it provides important information needed for making decisions about the future direction of maintenance. In the calculation, the initial cost,
maintenance cost including inspection cost,
and the cost of planned intervention are totalled.
Life-cycle cost estimation enables comparative cost assessments to be made over a
specified period of time. Being able to compare the costs of alternative LCM scenarios
allows selection of the most economic overall strategy.
The life-cycle cost calculations of thefour LCM scenarios are shown in Fig. 7.
Since strengthening needs cost, just before
reaching the allowable maximum value of
failure probability, corresponding costs are
increased. The figure indicates that preventive maintenance strategy is the least costly,
which is about one-third of the most costly
scenario. For 50 years, the most economical
scenario is S3 followed by scenarios S4, S2,
and S1. It means that the efficiency of corrosion prevention (preventive measure) shouldbe the best scenario in terms of cost. However, if the intended service life is shorter than
50 years, the best solution might be varied
depending on the service life.

Scenario Update
Some theoretical rules, simulation models,verification formulae, etc. are used for theprediction of deterioration progress. However, the trend that is observed through regular
maintenance work, for example the measured
corrosion rate, may have potentials for use in
the future progress of deterioration and/or
degradation during the maintenance stage.
Based on the data and assessment results, therule and process of deterioration and/or performance degradation have to be modified
and the scenario be updated for further prediction.

Fig. 7 Life-Cycle Cost Calculation

Life-Cycle Cost
If member failures might cause hazards tosafety, possible failures should be categorized

LCC (×10 8 JPY)

structural performance assessment. Assessment can be made by the condition-based
concept and the performance-based concept6).
The performance-based concept should beapplied for performance assessment, but generally needs costs, advanced techniques, etc.
Thus, the condition-based assessment is reluctantly accepted because of its feasibility.
The grading system has been often applied,
in which the state of deterioration is evaluated and judged using the deterioration grade.
Visual inspection has been most often applied to grade the condition of structure andmake judgment whether further, detailed investigation is needed or not. For proper grading, inspection should be carried at with regular intervals. If the deterioration grade isassociated with structural performance, theperformance can be indirectly assessed. The
visual inspection is only able to provide thechange in appearance of structural member,but structural performance has to be evaluated as precisely as possible. If the relationship between structural performance (structural capacity) and the grade of deterioration
could be found even tolerant margins of errors, the intervention could be discussed withusing the deterioration grade7).
When the visual inspection is insufficient
to provide proper data for assessment, the detailed inspection is recommended to carryout. The detailed inspection or investigation
includes quantification of the degree of deterioration with non-destructive or destructive
techniques, etc. In case that the data of quality and amount is satisfactory to do numericalanalysis, direct assessment can be made. As
mentioned earlier, deterioration has considerable variation; thus, such variation is necessary to be precisely quantified.

4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0

S1

0

10

S2

S3

20
30
Time (years)

S4

40

50

so that the life-cycle cost reduction and performance maximization can be attained. Thismay make it possible to realize sustainabilityof port and harbor structures. To further develop the system, research is necessary on accurate structural performance verification ofexisting structures including the methodology of inspection and investigation and precise prediction on future progress of deterioration and performance degradation.
￭
References
1) Ozaki R, Yokota H, Hashimoto K and Furuya K (2013): Evaluation of life cycle scenarios for open-type wharf based on change
in failure probability by corrosion of steel
pipe piles, Journal of Japan Society of Civil
Engineers, B3, 69(2), (in Japanese, in press).
2) Ministry of Land, Infrastructure, Transport
and Tourism (2007). Technical Standards andCommentaries for Port and Harbour Facilities in Japan.
3) Yokota H, Kawasaki S, El-Bakry H, Sugawara R, Takegahana N and Kawabata N(1999). Seismic performance and ultimate
load-carrying capacity of an open piled marginal wharf, Proceedings of the 9th International Offshore and Polar Engineering Conference (ISOPE), Brest, 520- 527.
4) PIANC/MarCom/WG34 (2000). Seismic design guidelines for port structures, Balkema Publishers.
5) Chen X, Kitane Y, and Itoh Y (2010). Mechanical properties of fillet weld joints byunderwater wet welding in repairing corrosion damaged offshore steel structures, Journal of Structural Engineering, 56A.
6) International Standardization Organization(2010). ISO 13822 Bases for design of structures - Assessment of existing structures.
7) Yokota H, Iwanami M, Yamaji T and Kato E (2008). Maintenance Strategy of Harbor Structures in Japan Based on Life-Cycle Management, Lifetime Engineering ofCivil Infrastructure, 2, 229-238.
8) Sato W, Yokota H, Hashimoto K, Furuya K
and Kato H (2011). Influencing factors onlife-cycle cost of mooring facilities, Journal of Japan Society of Civil Engineers, F4,
67(4), I_181-I_190, (in Japanese).

Concluding Remarks
The life-cycle management system including
evaluation of structural performance and prediction of the progress of deterioration would
be one of the best tools for building and maintaining structures. The author expects that rational and effective maintenance is realized
August 2013 Steel Construction Today & Tomorrow 6

Coating Degradation due to Corrosion

Influence of Defects and Exposure
Conditions on Coating Degradation
due to the Corrosion of Steel Piles andPlates in Marine Environments

by Nobuaki Otsuki, Professor, and Takahiro Nishida, Assistant Professor, Department of International
Development Engineering, Graduate School of Engineering, Tokyo Institute of Technology
Corrosion of Offshore Steel Structures in Marine Environments
Because offshore steel structures are exposed to severe corrosion environments,
it is important to understand how structural deterioration progresses due to corrosion
in paint coated steel and to establish a method for forecasting declines in structural performance. Meanwhile, in order to assess the
progress of long-term deterioration in a relatively short period of time, an acceleration
test has been proposed1).
However, the influence that exposure andacceleration conditions exert on the progression of quality deterioration has not yet beenclarified. Accordingly, there is as yet no clarification of the “acceleration magnification,”
i.e. the correlation between the period of acceleration test and the exposure period in an
actual corrosive environment. In particular,

Many pinholes

Many pinholes at edge
Many pinholes

Many pinholes at edge

Many pinholes at edge

Many pinholes at center

Many pinholes at edge

Depth

the LWL. In this way, the corrosion of unpainted steel products applied in marine environments progresses due to macrocell corrosion, which occurs mainly in (1) anodic
areas where the corrosion rate increases and(2) cathodic areas where the corrosion rate
decreases. In order to prevent such corrosion
from occurring, it has become general practice to apply the corrosion-protection measures such as paint coating to offshore steel
structures.
Among the major corrosion-protection
Corrosion of Steel Products in Marine
mechanisms offered by painted coatings are:Environments
Many examples exist of studies pertaining cutting off of corrosive substances such as
to the corrosion of unpainted steel products Cl−, O2 and H2O and suppressing the forin marine environments. For example, the mation of reaction sites for corrosion prodstudy results shown in Fig. 1 (a)2) are ob- ucts. It is conventionally thought that, whentained, through which it is known that the proper coatings are applied, coating degracorrosion rate increases in the upper HWL dation occurs with difficulty, and when a desection (splash zone) and in the zone below fect is created by collision by a ship or otherstructure with offshore steel
structures, corrosion (mainFig. 1 Distribution of Corrosion in Steel Plates in Marine Environments
ly microcell corrosion) will
Splash zone
occur in the area of the deAtmospheric About
East South
North
West
zone
0.1 mm/y
fect. However, it has been
confirmed by the results of
exposure tests conducted
Splash zone About
0.3 mm/yin an actual application en(Subtropicalzone: 0.5~0.6
vironment (Bay of Suruga,
Tidal zone
mm/y)Mean high water
20-year exposure), shownlevel (HWL)in Fig. 1 (b)1), that blistering, ripping and other types
Tidal zone
Macrocell corrosion
Beneath averageof coating degradation octidal zone:
Mean low
Localized corrosion
cur in actual application enwaterlevel (LWL)
vironments and that the area
Submerged Aboutof corrosion expands.
0.1~0.2 mm/yzone
Submerged zone
We judged that the causeof such corrosion phenomena was attributable to macAbout
Mud zonerocell corrosion, and con0.03~0.05 mm/y
ducted a study using special
test specimens that enable
Corrosion rate
the measurement of macro○:Peeling off of top coating ●:Red rusting ×:Pinhole detection(a) Without paint-coating2)(b) With paint coating1)
cell corrosion current using
there are many examples in existing researchthat have noted the uniform corrosion (microcell corrosion) that occurs in steel products, but there are fewer examples of researchthat have examined the progress of deterioration targeting the localized corrosion (macrocell corrosion).
We have examined these issues from theperspective of coating degradation, the results of which are introduced below.

7 Steel Construction Today & Tomorrow August 2013

divided steel products, as introduced in thefollowing chapter.
Influence of the Corrosion of Steel
Products on Coating Degradation and
the Progress Mechanism
Fig. 2 shows a conceptual drawing of microcell and macrocell corrosion.
As shown in the figure, in the microcell
corrosion, both anodic and cathodic reactions uniformly occur: the anodic reactions
in which iron dissolution occurs and the cathodic reactions in which oxygen and water
are consumed to form hydroxide ions. As ameans to assess microcell corrosion in suchcases, the commonly adopted method relies

anode, which was used to assess the macrocell corrosion.
Fig. 4 shows the time-dependent change
in the macrocell current density of specimen (a) and in the microcell current densityof specimen (b), both of which were painted
with a phthalic acid-type coating (thickness:
150 μm) and provided with defects. It has
been confirmed from the figure that, while
the macrocell current density in the defectsection was pronounced at the initial stage of
exposure, the negative current density (cathode current density) in the coated section
steadily increased; and as the exposure period increased, the macrocell current density inthe defect section continued to rise. Further,

Fig. 3 Outline of Divided Steel Plate Specimens

125mm

Fig. 2 Outline of Microcell and Macrocell Corrosion

on the polarization resistance obtained using
AC impedance and other methods. In this regard, the commonly used method is that proposed by M. Stern and A.L. Geary3) to convert from polarization resistance to microcell
current density.
In macrocell corrosion, locally occurring
anodic reactions cause corrosion. In order toassess such macrocell corrosion, it is necessary to measure the current that flows from
cathode to anode. However, it is difficult to
directly measure current flowing through asteel product. To solve this problem, we prepared the divided test specimens shown in
Fig. 3, and proposed a method to directly assess the current that flows from cathode to(a) Front side
(Exposure surface)
Paint(b) Back sidewith lead wire
Defect part

Paint coated part

Lead
wire

(c) Specimen arranged
by epoxy resin
Paint coated part

Steel plate
Epoxy
resin

Ring No.

R-0

R-1

R-2

R-3

R-4

R-5

Area (cm2)

2.4

8.6

14.6

20.7

26.7

32.8

(d) Cross section of specimen

Positive value (Anode)

90

70

Negative value (Cathode)

80

50
40

Blister

30
20
10

Paint

(a) Macrocell

R-5

ct

R-4

R-3

Defe

R-2

-10

R-1

0

Du

on
rati

ys)

(da

70
60
50
40

Blister

Ripping

30
20
10
0

Defe

ct

Paint

R-5

60

R-3

Ripping

R-0

Microcell current density (μA/cm2)

80

R-0

Macrocell current density (μA/cm2)

Fig. 4 Time-dependent Changes of Macrocell and Microcell Corrosion of Paint-coated Steel Specimens with Defects

rat

Du

)

ys

da

(
ion

(b) Microcell

August 2013 Steel Construction Today & Tomorrow 8

when the pH within the blisters was measured, it was confirmed that a high alkaline
environment of pH 10~13 was generated,suggesting the possibility that OH is generated and accumulated under the painted-coated part due to cathodic reaction. Taking theseresults into account, it is believed that blistering, ripping and other types of coating degradation are strongly affected by the cathodic
reaction of macrocell corrosion.
An examination of this behavior suggested that the deterioration of paint-coated steel
products progresses as shown in Table 1. In
particular, because the period when blistering
occurs is largely related to further expansionof the area of corrosion, it is extremely important to specify the period when blistering
occurs. Then, we tried to calculate the acceleration magnification from the acceleration
test to the actual exposure environment bycomparing the acceleration test results withactual exposure test results.
Verification of Validity in Convertingfrom Acceleration Test Results to Actual Exposure Period
Table 2 summarizes the period up to the occurrence of blistering in the acceleration tests
conducted on paint-coated steel productswith defects (50°C, salt immersion) and inmembers exposed to the actual environment.
As shown in the table, the values forecasted
by the acceleration test results are consistent
with the values obtained from the actual exposure test results. Therefore, our proposed
approach as introduced above is consideredvalid for converting from acceleration test results to actual exposure test results.
Promotion of Research on the Corrosion Protection of Offshore Steel
Structures
In this text we have introduced the results ofour most current examination of steel product corrosion in a marine environment, specifically the influence of steel product defects
and exposure conditions on coating degradation. But, as many of the other factors involved in corrosion remain unclear, the promotion of research into the corrosion of steel
structures exposed to actual application environments is a pressing issue for engineers.
We will be gratified if the results of our study
and the proposal introduced prove helpful instructuring of future maintenance systems
and the prolongation of social infrastructureservice life.
￭

9 Steel Construction Today & Tomorrow August 2013

References
1) Committee of Structural Engineering, “Guidelines for Evaluation of Durability and LoadCarrying Capacity for Steel Structures under
Marine Environment,” Structural Engineering Series 19, (2009) JSCE
2) Coastal Development Institute of Technology, “Corrosion Prevention of Port and Har-bor Steel Structures: Improvement Manual(Revised Edition),” 1997
3) M. Stern and A. L. Geary, “Electrochemical
Polarization: I. A Theoretical Analysis of the
Shape of Polarization Curves”, Journals of
the Electrochemical Society, Vol. 104, No.
1, pp. 6-63 (1957)

Table 1 Corrosion Progress around Defect of Paint-coated SteelSteps

Corrosion progress

Schematic figure

Step 1: Incubation(Before blistering)

Before the generation of blister ofpaint, the macrocell corrosion
between defect part and paint coatedpart occurs and hydroxide ion is
accumulated between paint and steel
due to cathodic reaction. In this term,
the microcell and macrocell corrosion
progress at defect part.

H2O and O2

Macrocell current

The blister of paint is generated by
the osmotic pressure of water due tothe high concentration of hydroxide
ion and increase of diffusivity ofpaint. After that, the blister
progresses to the ripping of paintand the paint coating is damaged.

Step 2: Propagation(Before ripping)

Step 3: Acceleration(After ripping)Corrosion

H2O and O2

Corrosion

Generation of blister

The corrosion reaction around defectis accelerated by ripping of paint.
Especially ripping part changes from
cathode to anode of macrocell
corrosion and more serious corrosion
is generated.

Corrosion

Corrosion

Generation of ripping

Table 2 Magnification of Each and Total Factors and Comparison between
Estimated and Actual Values of Duration of Incubation Periods for
Paint-coated Steel with Defect
Factors

Temperature
Solution
Paint
thickness

Conditions for setting eachmagnification or duration
V1
V2

= exp

Ea 1

1

R

T1

T2

3%NaCl: ×1.0;
Seawater: ×2.3
Y1 8.16ln(X1)-34.77=
Y2 8.16ln(X2)-34.77
Y:Duration;X:Thickness

Paint typePhthalic: ×1.0;
Tar epoxy: ×4.6

Dissolved
oxygenY=0.28X + 0.24
Y:Duration;
X: Dissolved oxygen

Total
magnification

Multiply all magnification

Laboratory

Lab data Site data

From observation

MagnifiSite data
cationMagnification

21.8˚C
(T1)

×5.1

16.2˚C(T1)

×7.4

NaCl3% Seawater×2.3

Seawater

×2.3

150 µm
(X2)

150 µm(X1)

×1.0

675 µm(X1)

×5.3

Phthalic

Phthalic

×1.0

Tar epoxy×4.6

5.1 mg/L 5.0 mg/L

×1.0

7.0 mg/L

×0.7

50˚C
(T2)

×1

Estimated
duration
Actualduration

FuttsuMiyako1)(Outside exposure) (In-situ exposure)

2~5 days

×11.7

×290.523.4~58.3 days

1.6~4.0 years

37 days

1~5 years

Load-carrying Capacity of Corroded Steel Structures

Evaluation of the Remaining
Load-carrying Capacity of Corrosiondamaged Steel Structures and thePrediction of Future Performanceby Katashi Fujii, Professor, Department of Civil and Environmental Engineering, Graduate School ofEngineering, Hiroshima University

Investigation of Corrosion Conditions
In order to accurately evaluate or predict theremaining load-carrying capacity of a structure, it is necessary to know its current corrosion conditions such as wall thickness andthree-dimensional coordinates on the unevensurface caused by corrosion. In rating the remaining strength of a member, the statistical values of the corroded plate thicknesses,
such as average thickness and standard deviation, are used as the representative indices, and as the measurement of the corrosion
condition has become more minute and precise, these statistical values thus obtained become more accurate. For example, although
the coordinates of uneven surface of the wall
can be measured minutely and with high precision by means of three-dimensional laser
measurements (Photo 1), the current practicefrequently used to measure the wall thickness
is the adoption of ultrasonic thickness gauges. However, the use of ultrasonic thickness
gauges makes it difficult to perform multipoint measurements.

Photo 1 Surface coordinates obtained using a three-dimensional laser instrument
The photo on the left shows measuring conditions, and the photo on the right shows athree-dimensional image obtained from the measured results. (Courtesy: Keisoku Research Consultant Co.)

Fig. 1 Wall Thickness Measurement Points at Cross Section of Steel Tubular Pile

About 10 cm

About 10 cm

Wall thickness measurement point at section

In the case of evaluating the average thickness at a cross section of steel tube, when individual measurements are made at a total of
20 points (4 sites × 5 points; see Fig. 1) per
section, the average thickness tr of the crosssection can be rated by tr = tavg − S, which canbe safe1). Here, tavg and S are the average value and the standard deviation at each of the
20 points of wall thickness respectively.
Evaluation of Remaining Loadcarrying Capacity
It can be said that the finite element method
is the most effective and reliable means currently available for evaluating the remaining
strength of corroded steel structures or members. Figs. 2 and 3 compare the analytical results and the experimental results pertaining
to the remaining axial compressive strengthof 6 steel tubular piles exposed to offshore
conditions for 19 years. The analytical results
were obtained using the elasto-plastic large
deformation finite element analysis2). In thisanalysis, the thicknesses at the nodal pointsof each shell element were given by the daFig. 2 Comparison of Remaining Axial
Compressive Strength of Corroded Steel Tubular Piles between Finite Element Analysis
and Experimental Results

Maximum load (FEM)

Because coastal and offshore steel structuresin particular are exposed to severe corrosive
environments, the loss of strength due to reduced wall thickness caused by corrosion
poses problems in terms of structural safety. The following discusses how to secure thestructural safety of corroded steel structuresin marine environment through our research
on an evaluation of the load-carrying capacity of corroded steel tubular piles and the prediction of their future performance.

Maximum load (experiment)
August 2013 Steel Construction Today & Tomorrow 10

Height (mm)Fig. 3 Buckling Collapse Condition of Corroded Steel
Tubular Piles (Splash zone)

Position of minimum
sectional area

Sectional area (mm2)Experiment

Analysis

Experiment

AnalysisHeight-direction distributionof average wall thicknessof cross section

Fig. 4 Simple Prediction of Remaining Axial Compressive Strength Using Buckling Curve without Corrosion
1.4(Underwater)(Underwater)
NO. 3 , NO. 4 , NO. 6

1.2

σ u/σ y

1.0
0.8
0.6

(Tidal zone)
NO. 2(Splash zone)
NO. 1 , NO. 5

Plantema(1946)
ave-0.8s**
t **

0.4
0.2
0.0

0.2

0.4

0.6

Rt=1.65∗(2R/t R)∗(σ y/E)

Fig. 5 Modeling of Corrosion Depth Forms
Corrosion factor

Corrosion depth
at grid point i

Falling spot

Corrosion
depth (mm)Affected zone
(the shaded area is dug by a corrosion factor)
Corroded grid point

Falling spot

11 Steel Construction Today & Tomorrow August 2013

Affected zone

0.8

1.0

ta measured with 1-mm intervals. It can beseen from these figures that both the remaining strength and the collapse mode can be
precisely evaluated in cases when the analysis is made using accurate corroded surface
measurements.
Further, the remaining axial compressive
strength can be evaluated easily by using thebuckling strength curve in the case of no corrosion. In this case, the remaining strength
can be obtained by substituting the statisticalindex (representative thickness) to the widththickness parameter in the case of corrosion,in which the representative thickness can beobtained using the average thickness and thestandard deviation obtained from measured
thicknesses. Fig. 4 shows the remaining axial compressive strength of corroded tubularpiles, obtained by means of above method, inwhich the representative thickness to be evaluated is set as (average value − 0.8 × standard
deviation of measured thicknesses) and this issubstituted to the width-to-thickness ratio parameter Rt, then the axial compressive stress
σu can be obtained from the non-corroded
buckling strength curve.
However, due attention should be paid tothe following: The finite element analysis allows for the evaluation of remaining strength
taking into account every buckling mode in
the collapse, but when using a simple evaluation equation, the remaining strength only
for the specified buckling mode can be evaluated. That is, in Fig. 4, only the local buckling strength of steel tubular piles is given,and the global buckling strength cannot be
evaluated.
Prediction of Remaining Loadcarrying Capacity
In order to realize minimum lifecycle costs
for steel structures, it is necessary to predict secular changes in remaining load-carrying capacity and to draw up future maintenance plans. If simple models can be used
to express secular changes in the surface unevenness shape of steel plate that have beencaused by a deterioration in corrosion-protection function and subsequent corrosion, it
will be possible to predict future declines instrength3).
In the corroded surface generation model (Fig. 5), the surface of the steel plate is divided into a grid, and the corroded surface isexpressed using the corrosion depth at eachintersection in the grid. In this model, thefollowing four factors are assumed: 1) two
kinds of factors, deterioration factor and corrosion factor that have a certain strength andFig. 6 Examples of Analysis of Coating
Deterioration Conditions (Dark
areas: Exposed base metal)

Fig. 7 Recoating Period and Simulation Results for Residual Wall
Thickness after 100 Years (Submerged zone)(a) Lapse of 50 years(a) Recoating every 50 years(b) Lapse of 100 years

a certain affected region respectively, will
randomly fall on the surface; 2) the deterioration factor decreases the corrosion protection function; 3) when the corrosion protection function become lower than a thresholdof corrosion prevention, the corrosion starts
on the steel surface; and 4) consequently thesurface is dug by corrosion factor, as shownin Fig. 5. The parameters for deterioration
factor and corrosion factor (strength, affected radius, number of annual falls) can be decided from measurements of the actual corrosion conditions. It is now possible by useof this model to predict the corroded surface,
and when the strength of the structure can beevaluated by means of finite element analysis
considering the corroded surface shape thus
predicted, it becomes possible to predict future remaining load-carrying capacity of thestructure. Meanwhile, in cases when repaint-(b) Recoating every 30 years(c) Recoating every 10 years

Remaining strength (%)

ing is carried out, the values for corrosionprotection functions are to be renewed.
Fig. 6 shows the surface condition inwhich certain years passed since the initialstage coating and the base metal was exposed, and Fig. 7 shows the contour lines depicting remaining wall thickness obtained
from simulations. Fig. 8 shows the resultsof axial compressive strength analysis conducted on steel tubular piles using the resultsof corroded surface prediction. As shown in
Fig. 8, it is now possible to provide convincing prediction ofremaining loadFig. 8 Predicted Results for Strength Loss Affected by Recarrying capacicoating Period (Submerged zone)
ty of steel structures by adopting
the approach described above.
At the time ofinitial design ofstructure, the reliability of thesepredictions may
be lowest beWithout coating
Experimental result
cause the predicWith coating (no recoating)tions of corroWith coating (recoating every 50 years)
sion progression
With coating (recoating every 30 years)
are based entireWith coating (recoating every 10 years)
ly on assumed parameters. HowLapse of years (years)
ever, in cases

when parameters of the model will be revisedin accordance with the actual corrosion conditions measured at each stage of periodic inspection, more accurate and reliable updated strength of the structure will consequently
be able to be predicted. We consider that, incases when a maintenance plan is worked out
based on the predictive approach describedabove, it will finally be possible to reduce thelifecycle costs of steel structures to a minimum.
Acknowledgement
The current research was conducted with a
specified research subsidy granted by the Japan Iron and Steel Federation and as a link in
the activities of the Task Committee on Evaluation of Corrosion Protection and Durability for Steel and Composite Structures under
Offshore Environments (chaired by E. Watanabe)4), the Committee on Steel Structuresof the Japan Society of Civil Engineers. We
wish to thank the committee members and related organizations for their generous support
and cooperation.
￭
References
1) Fujii, K., Kaita, T., Satake, R. and Tokinori,
Y. (2012) “Reliability of thicknesses measured by in-situ ultrasonic measurement andremaining strength evaluation based on themeasured thicknesses for a corroded circular
steel tube in marine environment” Journalof Structural Engineering, JSCE, Vol. 58A,
pp. 692-700. (in Japanese)2) Fujii, K., Kondo, T., Tamura, I., Watanabe,E., Itoh, Y., Sugiura, K., Nogami, K. and Nagata, K. (2006) “Ultimate Strength of Corroded Circular Steel Tube in Marine Environment” Journal of Structural Engineering,
JSCE, Vol. 52A, pp. 721-730. (in Japanese)3) Fujii, K., Hashimoto, K., Watanabe, E., Itoh,Y., Sugiura, K., Nogami, K., Nagata, K. andNakamura, H. (2010) “A Prediction Methodof Strength Deterioration in Aging of Circular Steel Tube Corroded in Marine Environment”, Journal of JSCE, Ser.A, Vol. 66,
No. 1, pp. 92-105. (in Japanese)
4) Task Committee on Evaluation of Corrosion
Protection and Durability for Steel and Composite Structures under Offshore Environment(ed. by Watanabe, E.) (2009) “Guidelines for
Evaluation of Durability and Load-Carrying
Capacity for Steel Structures under Marine
Environment” Committee of Structural Engineering JSCE. (in Japanese)

August 2013 Steel Construction Today & Tomorrow 12

Lifecycle Performance Assessment

Lifecycle Performance Assessment
Technology for Port Steel Structureswith a Focus on Post-repair
Performanceby Yoshito Itoh, Professor, Yasuo Kitane, Associate Professor, and Mikihito Hirohata, AssistantProfessor; Civil Engineering, Graduate School of Engineering, Nagoya University

Load Carrying Capacity of Steel Pipe
Piles after Steel Plate Welding Repair
Fig. 1 shows the steel plate welding repair
method1)—a typical method used to repair
and strengthen corroded steel pipe and sheet
piles. In this method, the corrosion-damaged
section is covered with steel patch plate,which is welded to the existing steel member using fillet welding. In cases when the
corroded section is located in seawater, underwater wet welding is frequently adopted.
Welding environments, dry or wet, can affectcharacteristic weld properties. It is reported
that many weld defects occur during underwater welding and that whereas the hardnessof welds in underwater welding increases
when compared to that of open-air welding,Fig. 1 Repaired Steel Pipe Pile

Patch plate

Longitudinalfillet weld

13 Steel Construction Today & Tomorrow August 2013

Fig. 2 Relative Changes of Strength and Ductility from Open-air Welds toUnderwater Welds
60%

SY295

Strengthincrease

40%

Ductility
decrease

Prolongation of the Service Life ofAging Port/Harbor Steel Structures
In order to prolong the service life of aging
port/harbor steel structures by means of rationalized maintenance, it is important to precisely gauge performance before and after repair, to assess lifecycle performance during
the designed service life, and to provide appropriate inspection and maintenance. Targeting steel pipe piles with deteriorating performance due to corrosion, we have studied
the post-repair load carrying capacity and durability of these piles repaired by steel plate
welding. An outline of our study follows.

24%

SYW295

SY295
STK40041%30%Corroded
SYW29530%

STK400
21%

20%

SY295
22%

7%

0%
20%
28%
40%
45%

43%

60%

49%
61%

67%

80%

83%

Transverse
100%
Longitudinal

ductility of underwater welds decreases2).
Similar results were obtained from strength
tests of fillet welds using steel pipe and steel
sheet piles as the base metal3). As shown in
Fig. 2, underwater fillet weld joints havelarger static strength but much smaller ductility than open-air welds, and it was learned
that these effects are more significant in sheet
pile steel than in pipe pile steel.
Further, tests were conducted whereby steel plate welding repairs based on thecurrent design method were applied to steel
pipes whose wall thicknesses had been artificially reduced by cutting and whereby postrepair structural performance of the pipe wasthen examined by applying compression or
flexural loading4). These tests clearly showed
that, while stiffness and load carrying capacity of the repaired pipe against compression or
flexural loading were recovered to nearly thesame levels as before corrosion damage oc-

curred, the corresponding ductility decreased
from pre-corrosion levels. Fig. 3 shows theload-displacement curve obtained from theflexural loading tests.
As discussed above, the static strength ofsteel pipe after repair can be recovered to precorrosion levels, but the repaired steel pipe
will then be subjected to cyclic loading during earthquakes, and thus an important question arises as to whether or not the repaired
steel pipe will be able to show appropriate
energy absorbing capacity.
Fig. 4 shows the load-displacement curveof four kinds of steel pipes that were subjected to cyclic flexural loading in the nonlinear
finite element analysis: (a) intact pipe (216.3
mm in outside diameter, 12.7 mm in wall
thickness); (b) steel pipe having a wall thickness that was uniformly reduced by 6 mm in
a 150 mm-long section; (c) steel pipe having
a wall thickness that was uniformly reduced

Fig. 3 Load-Displacement Relationships of Steel Pipes under Flexural Loading
1.8
Intact1.6
1.4

Repaired byopen-air welding

Applied load (P/Py0)

1.2
Repaired byunderwater welding

1.0
0.8

Photo 1 Steel pipe pile repaired by patch plateswith petrolatum coating and FRP coverThickness-reduced

0.6
0.4
0.2
0.0

0

5

10

15

20

Midspan displacement (δ/δy0)

Fig. 4 Load-Displacement Curves of Steel Pipes under Cyclic Flexural Loading(a) Intact pipe(b) Thickness-reduced pipe(c) Repaired pipe with a 6 mm thickpatch plate(d) Repaired pipe with a 9 mm thickpatch plateby 6 mm and was then weld-repaired using 6
mm-thick patch plate; and (d) steel pipe having a wall thickness that was uniformly reduced by 6 mm and was weld-repaired using
9 mm-thick patch plate.
It is found from the figure that, in orderto recover the energy-absorption capacity ofcorrosion damaged steel pipe to that of intact pipe, it is necessary to employ steel patch

plate with a thickness greater than the reduction in wall thickness caused by corrosion5).

Examination of the Corrosion Characteristics of Welds Using a Seawater
Bubbling Test
In order to show lifecycle performance, it isnecessary to understand post-repair corrosion resistance. In the current practice, corrosion-protection coatings are applied to steel
pipe piles that have been repaired by meansof steel patch plate welding. Photo 1 shows
an example of such steel pipe piles to which
petrolatum coating was applied and an FRP
cover over the coating had been attached. It
is accepted that such a corrosion protection iseffective for about 20 years; however, in cases when an FRP cover has been damaged byfloating objects and a part of petrolatum coating has been gouged away, the repaired section is once again exposed to the corrosive
environment. While many research results
are available that pertain to the corrosion
characteristics of steel members in seawater,
less research has been conducted that compares general sections of steel members withwelded joints in order to demonstrate differences in corrosion characteristics.
Given this lack of data, we used a bubbling corrosion acceleration test (3% NaCl solution, 50°C, 28 days)6) to examine thecorrosion characteristics of steel weld joints.
Fig. 5 shows an outline of the testing apparatus used in the test. Two kinds of base plate
were used for the test specimens, SY295 andSYW295, while SM490 steel plate was used
for the patch plates. The patch plates andbase plates were weld-joined by means of fillet welding using E4319 welding electrodes.
In the test, pre-test and post-test surface
profiles were measured and compared usinga laser displacement sensor to determine corrosion loss in the welds. Fig. 6 shows the corrosion loss in the weld of one specimen. As
seen in the figure, the fillet weld joint shows
uniform corrosion, and lacks any locally severe corrosion generated by uneven sectionsin the weld bead surface or by welding toes.
August 2013 Steel Construction Today & Tomorrow 14

Fig. 5 Accelerated Exposure Test System for Underwater Corrosion
Flow meter

760
Air : 2.0ℓ/min (per one air-hose)

Air: 2.0ℓ/min (per one air-hose)
3% NaCl 120, 50℃
Bubble350

710

Specimens

Specimens(a) Plan view(b) Side viewFig. 6 Change of Surface Profile of Weld due to Corrosion
Base plate

Welds

Patch plate

Base plate

Welds

Patch plate

Before experimentCorroded region
experiment
AfterAfter
experiment

Further, no significant difference was observed in the corrosion loss attributable tothe direction of the welding (longitudinal ortransverse fillet welding), the steel type ofthe base plates or the welding environment(open-air or underwater). Furthermore, it isfound that corrosion loss in the weld joints issimilar to that in the steel plate.
Lifecycle Performance Assessmentof Port Steel Structures
With the goal of improving the lifecycle
management of port/harbor steel structures,
we examined the load carrying capacity ofcorrosion damaged steel pipe piles that had
been repaired by means of steel plate welding in order to better understand the lifecycle
performance of steel pipe piles. Our future
goal is to assess the post-repair load carrying
capacity of entire pier/quay structures in addition to single steel pipe piles.
￭
References
1) Coastal Development Institute of Technology (2009): Port Steel Structure CorrosionPrevention and Repair Manual, version 2009
15 Steel Construction Today & Tomorrow August 2013

(in Japanese).
2) Brown, R.T. and Masubuchi, K. (1975): Fundamental research on underwater welding,Welding Journal, Vol. 54, No. 6, pp. 178188.
3) Chen, X., Kitane, Y., and Itoh, Y. (2010): Mechanical properties of fillet weld joints byunderwater wet welding in repairing corrosion-damaged offshore steel structures, Journal of Structural Engineering, JSCE, Vol.
56A, pp. 742-755.
4) Kitane, Y., Itoh, Y., Watanabe, N. and Matsuoka, K. (2009): Compressive and flexural tests of thickness-reduced steel pipes repaired with patch plates using underwater

wet welding, Journal of Structural Engineering, JSCE, Vol. 55A, pp. 889-902 (in Japanese).
5) Furunishi, K., Kitane, Y., Watanabe, N. and
Itoh, Y. (2011): Cyclic flexural behavior of
thickness-reduced steel pipe repaired bywelded patch plate, Steel Construction Engineering, JSSC, Vol. 18, No. 72, pp. 1-16
(in Japanese).
6) Takemi, J., Hirohata, M., Kitane, Y. and Itoh,Y. (2013): Corrosion deterioration characteristics of welded parts of steel by accelerated
exposure test simulating environments in theseawater, Journal of Structural Engineering,
JSCE, Vol. 59A, pp. 747-757 (in Japanese).

Strength of Corrosion-deteriorated Steel Structures

Assessment Method to Determine
the Remaining Strength of Corrosiondeteriorated Port Steel Structures and
Its Necessary On-site Measurement ofCorrosion Profile
by Kunitomo Sugiura, Professor, Department of Civil and Earth Resources Engineering, Graduate
School of Engineering, Kyoto University
financial burden and that, accordingly, it will
be necessary to immediately establish lifecycle design/management technology that will
effectively utilize existing facilities and prolong the service life by means of proper repairs.
To this end, it is important not only to design, construct and manage new facilities thatare easy to inspect and observe, but also to
implement “preventive maintenance” thatwill prolong the service life of entire facili-ties by means of early damage detection andminor repair of existing facilities. It will also be necessary to utilize materials and structures that offer high durability, to work out
and implement longer service life measuresand to prolong the service life of entire infrastructure systems. The final goal is to reduce
the total cost. (Refer to Fig. 1)
In Japan, the application of steel sheet
piles in the construction of wharves and otherport facilities started in 1926 and that of steel

Fig. 1 Measures Taken to Prolong Service Life of Facilities
Promotion of longer service life of facilities

Survey on advanced example/
Human resources development

Diagnosis of structural
Understanding of structural
integrity by means of inspection integrity level of infrastructure by means ofinspection; Working out ofWorking out of service life
service life prolongation
prolongation plan
plan based on inspection
result; Implementation of
Implementation of project
preventive repair based on
based on the prolongation plan
the plan

Development of service life
prolongation and LCC reduction
technologies, and training oftechnical staff and developmentof human resource

Promotion of technological development●Technological development for inspection and observation
In order to promote preventive maintenance of infrastructure, new technology is developed for inspecting thestructural section difficult for visual inspection, and inspection efficiency and inspection effectiveness are enhanced.

Conventional chipping
Ultrasonic non-destructive
inspection
inspection
Example of inspection and diagnosis technology
for steel section embedded into concrete

Diagnosis of deterioration
by means of analysis of
lubrication oil used fordrainage machinery

Identification of leakage
section by use of infrared
ray●Technological development for repair
BridgeFlood gate
Beforepainting

After provision ofcountermeasure

Toward Longer Service Life of
Infrastructure
Surrounded by seas in every direction, Japanrelies on port and harbor facilities to play a
key role in promoting smooth economic andsocial development. As logistics facilities,
these ports and harbors generally consist of
wharves and other mooring facilities, of waterways and basins, such as fairways and anchorages, and of breakwaters and other protective facilities for securing safe harbor
areas. While they have performed admirably
through the individual and collective execution of their various functions, 30~50 years
have passed since they were constructed.
Given this situation, it is certain that maintenance costs will increase in the future, and itis therefore important to appropriately maintain these port and harbor facilities.
In Japan, the nation’s social infrastructure,such as highways and river and harbor facilities, were intensively constructed during
a period of high economic growth. In lightof this, the Ministry of Infrastructure, Land,
Transport and Tourism (MILT) has drawn up
an estimate of required future maintenanceand renewal costs based on past investment
returns for infrastructure under MILT control (highways, ports/harbors, airports, public rental housing, sewage, urban parks, rivercontrol facilities, coastlines and coastal facilities). Trial calculations show that costs forthe required maintenance/renewal will surpass the allocated funding in 2037, and that,of the approximately ¥190 trillion required
for renewal over the 50 year period from
FY2011 to 2060, about ¥30 trillion worth ofrenewals (16% of the total expense) will be
impossible to implement1). This fact suggeststhat it is necessary to implement planned andstrategic maintenance with the least possible

RC deck cracking
Source: MILT

Repair using carbon
fiber sheet

SewerageAfterpainting

Highly durable painting

Culvert renewal method

August 2013 Steel Construction Today & Tomorrow 16

Fig. 2 Example of Straight Pile-type Shore Bridge
SlabFig. 4 Composition of Elements of Plane Frame Structureof Pier
0.6 m (section 9)
1.2 m (section 8)

Back-fillingstoneFoundation rubble mound

Lining

1.0 m (section 7)
1.2 m (section 6)
2.0 m (section 5)
1.2 m (section 4)

Coveredstone

0.8 m (section 3)
1.2 m (section 2)

Pipe pile

1.0 m (section 1)

Fig. 3 Trend in Vertical-direction Corrosion of Offshore Structure2)
Atmospheric
zone

Depth

Splash zone

Tidal zone
Submergedzone

Sea bottom
mud zone
Corrosion rate

pipe piles in the latter part of the 1950s. Because of their applicability in rapid shoreline
construction, these steel products have seen
extensive use. Steel port facilities come incontact with seawater and are exposed to severe environmental conditions such as deviations in water level and direct tidal splashing,
thereby showing corrosion behaviors thatare different from those of land-based steel
structures. Along with the increase in applications of steel products in port and harbor
facilities, studies have been made to clarify
corrosion mechanisms, develop diverse corrosion-protection methods and improve repair and strengthening methods. Prior to theestablishment of corrosion-protection technologies, it was most common to build unprotected structures that in place of corrosion protection were designed with corrosion
allowances that increased wall thicknesses
rather than suppress corrosion. Today, newly
constructed steel structures increasingly employ corrosion-protection systems such as ca17 Steel Construction Today & Tomorrow August 2013

thodic protection or surface coating/painting.
While these newly-constructed structures
have a specified period of durability during
which their corrosion-protection functions
should remain viable, it is still necessary to
implement periodic inspections and constantly monitor remaining performance so that thestructure’s required performance is not impaired by the corrosion of its steel members.
Meanwhile, it is well known that corrosion reduces the plate thickness of steel
members applied in port steel structures andcauses a decline in the load-carrying capacity of not only each structural member but of
the entire structure as well. Accordingly, it isextremely important in terms of maintenanceto appropriately evaluate the remaining structural performance of corrosion-deteriorated
steel structures. In evaluating the remaining
load-carrying capacity of port steel structures, various parameters have been proposedby means of analytical and experimental approaches to evaluate the load-carrying capacity of steel members subjected to various
sectional forces2). However, most of theseexperimental and analytical approaches target only some of the structural members, andthus evaluations are not very frequently madeof an entire structure.
Then, in the following, an examination
was conducted targeting a pier composed ofsteel pipe piles and RC slabs (a model having three piles for a plane frame, Fig. 2). The
results of this assessment summarize the effect of corrosion-induced performance deterioration (Fig. 3) on the horizontal load-carrying capacity of the piles. In the assessment,
the steel pipe specimens were extracted fromcorroded piles exposed to a marine environment for about 19 years. The corrosion profiles of the specimens were measured using alaser displacement transducer, and the corro-sion profiles thus obtained were used as the
typical corrosion characteristics of the steel
pipe piles in the marine environment3)4).
FEM Analysis of a Straight Pile-type
Pier with Pipe Piles Subjected to Corrosion-induced Performance Deterioration
A plane frame structure (height: 10.2 m; pileintervals: 6.5 m), in which 3 pipe piles (outside diameter: 800 mm; wall thickness: 16mm) are arranged parallel to each other at
identical intervals, was adopted as a model of an entire pier having steel pipe piles
whose performance had deteriorated due tocorrosion, and the effect of the plane framewith corroded steel pipe piles on the horizontal load-carrying capacity was analyzed
by changing the corrosion deterioration patterns. Meanwhile, analysis was made using
the finite element analysis code ABAQUS(Ver. 6.10)5). Fig. 4 shows the plane frame
model that was structured as a pier model
having corroded pipe piles and used in the
FEM analysis. The pipe pile bases having
a length 2.75 times the outside diameter ofpipe and the pipe pile tops having a length2.25 times the outside diameter were modeled using shell elements (4 node reduced
integration shell elements), and the intermediate sections were modeled using beam
elements. Meanwhile, the shell elements andthe beam elements were to be rigidly joinedat the nodes, the number of the shell elementsin the steel pipe circumferential direction was
set at 150, and meshing in the axial directionof the members was conducted using similardimensions. The RC slab was to be elastic,
and to be rigidly joined with the shell area ofthe pipe pile tops. The base edges of the pipe
piles were completely fixed as the boundary conditions, and a maximum horizontal

Fig. 5 Example of Load-Displacement
Relation
2,500
Load (kN)

2,000
1,500
1,000
500
0
0

B-a-a-aB-b-b-bB-c-c-cB-d-d-d

200

400

600

800

Displacement (mm)1,000

Performance Evaluation of Corrosion-deteriorated Piers Based on Onsite Measurements
The representative wall thickness of the corroded steel pipe piles used in the pier models
targeted by the current study was determinedassuming that on-site measurements of wall
thickness were based on the currently-prevailing “Corrosion Prevention of Port andHarbor Steel Structures: Improvement Manual6).” In the procedure for determining thickness, the cross-section having the least thickness was selected from among pile section in
the splash, tidal and submerged zones, and
4- or 8-direction measurement center points
were selected within the same cross-section
with the point of minimum thickness as thestarting point (Fig. 6). Further, within a 10cm square patch around selected center point,
5 points including 4 points each separated byabout 3.2 cm in longitudinal and circumferential directions from the starting point wereextracted, and the average thickness thus obtained was set as the on-site measured thickness of piles for evaluation (Fig. 7).
The analysis targeted 1 pile (outside diameter: 406.4 mm; length: 10.5 m; original thickness: 9 mm; steel grade SKK490).
Of the analytical models, Ave-[ ] in Fig. 8
denotes the model that adopts the average
thickness in each section shown in the figure;4d denotes the model for which 4 points ofthickness measurement were selected in thecircumferential direction at the time of selecting the center measurement point with theFig. 6 Example of Measurement Position in Height and Circumferential Direction6)
Offshoresteel structure
H.W.L

a

Mean tidal
level

C

b
c

L.W.L

d

B

Sea bottom

DA
Sea sideFig. 7 Wall Thickness Measurement
Points within 10 cm-square
Area6)
About 10 cm

About 3.2 cm

sion (B-b-b-b) caused by 19 years of exposure. Further, the load-carrying capacity fellby 18.3% and 25.7% respectively from intact level, which corresponded to increases
in corrosion loss of 1.2 times (B-c-c-c) and1.4 times (B-d-d-d). Also, displacement at
the time of maximum loading fell below intact level as the corrosion loss increased. In
addition, along with corrosion progress, various changes were observed in the axial force
bearing of each pile, and significant differences in local buckling behavior and loadcarrying capacity were found, from which it
is known that the structural performance ofentire structures must be evaluated.
Meanwhile, as a result of selecting corrosion-damaged pipe piles configured as Model B-2, we see that even in cases where oneof the piles shows remarkable corrosion,loading can be borne by the remaining piles,
thereby demonstrating that the load-carrying
capacity of an entire structure depends on the
total corrosion loss of the entire structure.

About 10 cm

displacement of 1,000 mm was assigned tothe entire slab in the in-plane horizontal direction. Steel grade SKK490 was adopted forthe steel pipe; the wall thickness was input at
every node in the shell elements; and in the
beam elements, the cross-sectional properties used for the hollow circular cross-section
with equal diameters were input for every element employing the average thickness.
Three cases were analyzed: Model A with
one pile; Frame Model B-1 with a corrosion
pattern in which three piles show same corrosion; and Frame Model B-2 in which only one pile shows large corrosion loss. As regards Model A, it was prepared using a pilesimilar to that used in the plane model, in
which the top edge of the pile was set as therigid surface, a rigid element was attachedto the top edge, rotation restriction was applied to the rigid element, and then analysis
was made until the maximum horizontal displacement reached 1,000 mm. In the analysis,
the level of corrosion loss in each model waschanged in increments of 0.0 (no corrosion),
1.0, 1.2, 1.4, 1.6 and 1.84 times the standard
corrosion loss obtained in actual measurements of wall thickness; these corrosion levels were classified as a, b, c, d, e and f; andthe analytical model cases are marked using
B-[○]-[△]-[□] (○: left pile; △: center pile; □:right pile, and corrosion patterns for thesethree piles are expressed using the symbolsa~f). By the way, because the corrosion conditions differ according to the circumferential
direction of the pile, the horizontal strengthof Model A was confirmed by changing thehorizontal loading direction by a 45° pitch,
and as a result the horizontal load-carrying
capacity averaged 548 kN (559 kN max., 537
kN min.), and the deviation range was within
about 4% of the average value.
Fig. 5 shows an example of the horizontal loading-horizontal displacement relation(B-1 Model). The load-carrying capacity was
reduced by about 14.2% from the intact level (B-a-a-a) due to the progression of corro-

About 3.2 cm

minimum thickness as the starting point; and8d shows the model in which 8 points wereselected. Further, B-[ ]-[ ]-[ ] (for example
B-4-4-4 in the figure) denotes the model forwhich an average thickness was not adopted for each separated section but, rather, thesection was separated in the longitudinal direction depending on the thickness measurement direction. The wall thickness calculated
as the measurement value in each separated
section was input in the analysis. [ ] shows
the number of thickness measurement points
in circumferential direction in the splash, tidal and submerged zones (from left to right).
Meanwhile, s-Det shows the model in which
the corrosion profile is reproduced in detail;and, while average thickness, linear interpolation and other assumptions are included in
the section for which thickness measurement
was not made, this analysis case is assumed
to offer the greatest detail regarding thickness measurements and the highest accuracy with regard to the horizontal load-carrying
August 2013 Steel Construction Today & Tomorrow 18

Fig. 8 Load-Displacement Relation of Pipe Pile Model Based on Virtual On-site
Measurement
0.6 m (section G)
0.81 m (section F)

1.0 m (section D)
0.2 m (section C)

Load (kN)

1.39 m (section E)

3.2 m (section B)

3.3 m (section A)
Displacement (mm)capacity of the pipe piles.
Fig. 8 shows the load-displacement relation of each analytical model. The marginof error in terms of horizontal load-carrying
capacity obtained in comparison with s-Det
amounted to 16.8% for Ave-4d and 13.1%
for B-4-4-4. While 4 points per cross-section are specified for on-site measurementin the currently prevailing manual, it canbe seen from the above that the load-carrying capacity of the model is given a comparatively low (safe-side) evaluation comparedto the actual load-carrying capacity. This isbecause the thickness of the sectional area
having the minimum thickness was input as
the wall thickness of the piles in the entire
splash zone, and thus the thickness appliedin all zones was less than actual thickness.
In order to precisely evaluate the load-carrying capacity, it is considered important to reproduce the local strength of the splash zone
where it is strongly subjected to the effect ofbending moment and in which the thickness
variation is large.
Further, when examining the results inwhich the number of measured cross-sectionsin the splash and tidal zones is increased to 2
or 3, and when the analytical results are compared with those of s-Det, a load-displacement curve closer to that in s-Det can be obtained by increasing the number of measured
cross-sections. This is considered to be so be-cause the average thickness per cross-section
can be calculated with a greater level of accuracy by increasing the number of measured
sectional areas. Towards this end, while onsite measurement involves some difficulty,
it is desirable to measure the thickness using
multiple cross-sections for each zone where
corrosion characteristics are judged to be
similar, and, also, it is considered sufficientin measuring thicknesses to adopt 4 points set
at 90° intervals within a cross-section.
Ideal Approach to On-site
Measurements
As a result of plane frame analysis of astraight steel pipe pile pier, it was learned
that the effect of the location of severely corrosion-damaged pipe piles on the load-carrying capacity is less, and that the load-carrying capacity of the entire structure depends
on the corrosion loss of the entire structure.
Also, as a result of evaluating the remaining load-carrying capacity by means of onsite pipe pile wall thickness measurements
based on the currently-prevailing manual, it
was learned that, while a margin of error of
13% or more is found in comparison with theload-carrying capacity in the case when corrosion is modeled in detail, a safe-side loadcarrying capacity can be found.
Further, while thickness measured at 4
points within one cross-section is sufficient,

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
Yotsuya Mitsubishi Bldg. 9th Fl., 3-2-1 Yotsuya, Shinjuku-ku, Tokyo 160-0004, Japan
Phone: 81-3-5919-1535 Fax: 81-3-5919-1536
URL http://www.jssc.or.jp/english/index.html

particularly in the splash zone where the remaining wall thickness deviates greatly, it ismore effective to modify the measured thickness using the standard deviation of measured thickness, and it is desirable to measure the thickness in multiple cross-sections.
Detailed studies are being promoted to findthe ideal approach to on-site measurements
by which the remaining load-carrying capacity of pier structures can be precisely evaluated in terms of engineering that employs limited on-site measurement results￭
References
1) Ministry of Infrastructure, Land, Transport
and Tourism: MILT White Paper 2012
2) Task Committee on Evaluation of Corrosion
Protection and Durability for Steel and Composite Structures under Offshore Environment(ed. by Watanabe, E.) (2009) “Guidelines for
Evaluation of Durability and Load-Carrying
Capacity for Steel Structures under Marine
Environment” Committee of Structural Engineering JSCE.
3) Tamura I., Watanabe E., Itoh Y., Fujii K., Sugiura K., Nogami K., Nagata K. and Oka T.:“Examination of Profile Measurement andRemaining Compression Strength of Corroded Steel Pipe in Marine Environment”,
Journal of Structural Engineering, JSCE,
Vol. 51A, pp. 1103-1110, March 2005.
4) Fujii K., Kondo T., Tamura I., Watanabe E.,
Itoh Y., Sugiura K., Nogami K. and Nagata K.: “Remaining Compression Strength ofCorroded Circular Tube in Marine Environment”, Journal of Structural Engineering,
JSCE, Vol. 52A, pp. 721-730, March 2006.
5) Dassault Systemes Simulia: ABAQUS Analysis User’s Manual, Version 6.10.
6) Coastal Development Institute of Technology, “Corrosion Prevention of Port and Harbor Steel Structures: Improvement Manual (Revised in 2009), CDIT Library No. 35,
2009.

© 2013 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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