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Steels, steel products and steel structures sustaining growth of society (infrastructure field)

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The performance of steel materials, on the other hand, has been improved to help promote the development of infrastructure. Out of the global steel consumption of about 1,300 million tons, 45% is for construction. The use of steel materials for construction is estimated to exceed 50% in China and top 60% in India, Mexico and Indonesia, respectively. In the future, it is expected that demand for steel materials in the field of infrastructure will continue to increase and that uses for steel materials will become increasingly diverse. Fire-resistant steels, unbonded braces and steel-framed houses are among typical examples. The development of fire-resistant steel overturned the established theory that structural steel offered poor fire resistance. The advent of fireresistant steel led to the birth of a market for steel building frames without fire-resistant covering. The practical application of unbonded braces has made it possible to spread the damage-controlled structure, in which the damage caused during an earthquake is confined to certain structural members, and the development of steel-framed houses has dramatically expanded the use of steel sheets around 1mm in thickness.
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* General Manager, Ph.D., Steel Structure R&D Center, Steel Research Laboratories
20-1, Shintomi, Futtsu, Chiba 293-8511
UDC 669 . 14 : 624 : 691 . 7
Steels, Steel Products and Steel Structures Sustaining
Growth of Society (Infrastructure Field)
Ryoichi KANNO* Masato TSUJII
Tomonori TOMINAGA Fuminobu OZAKI
1. Introduction
In this technical review, public facilities that support the safety,
security and progress of society and private facilities, including
buildings, are collectively called “infrastructure.” There are many
types of infrastructure—roads, railways, rivers, ports, flood control
afforestation, erosion control, architecture, housing, and electric
power. Specific structures (hardware) that constitute infrastructure
include bridges, foundations, revetments, embankments, tunnels,
buildings, houses, and works, etc. Because of its diversity,
infrastructure is required to have various functions and performances.
As exemplified by the Great East Japan Earthquake that caused
unprecedented property damage and loss of life, it is of paramount
importance that infrastructure incorporates a function for shelter from
such natural disasters as earthquakes and typhoons; that is, a function
to maintain the safety and security of society. On the other hand,
infrastructure, which is a result of economic activity, is also a fixed
asset accounting for part of the social expenditure. Therefore, it is
constantly exposed to severe demands for cost cutting. In view of
the rapidly changing society and economy, there may well be demands
that such infrastructure be completed in a comparatively short time.
Nevertheless, once completed, the infrastructure is expected to
function for a long time. Demands to meet complicated conditions
are a prerequisite for infrastructure. That is why energetic R&D into
infrastructure has been carried out for many years.
As demonstrated by, for example, the world’s first iron bridge
constructed in 1779, or the obsolete foghorn post of the signal cabin
(constructed in 1910)1) at Inubozaki, made from steel manufactured
at the former Yawata Steel works, iron and steel have long been among
the fundamental materials used for infrastructure. It is no exaggeration
to say that much of the progress in infrastructure that has been made
so far is attributable to steel materials. The performance of steel
materials, on the other hand, has been improved to help promote the
development of infrastructure. Out of the global steel consumption
of about 1,300 million tons, 45% is for construction. The use of steel
materials for construction is estimated to exceed 50% in China and
top 60% in India, Mexico and Indonesia, respectively. In the future,
it is expected that demand for steel materials in the field of
infrastructure will continue to increase and that uses for steel materials
will become increasingly diverse.
In this technical review, with the focus on steel products and building
materials for infrastructure and on technology for their application,
we review the change in market needs over the past forty to fifty years,
including the changes in market climate and conditions, and describe
activities to develop new technologies at Nippon Steel Corporation. In
addition, on the basis of the ongoing changes in the infrastructural
environment, we look to the future of technology in this particular field.
2. Changes in Environment and Needs in the Field
of Infrastructure
2.1 Changes in the field of infrastructure and Nippon Steel’s
products and technologies
Fig. 1 shows examples of major events, structures, natural
disasters and accidents, codes/standards and Nippon Steel’s new
products and new technologies, all having had a significant influence
on Japanese society and the economy in the past. In infrastructure
expansion and improvement, the National Comprehensive
Development Project, the Tokyo Olympics, the Osaka International
Exposition, etc. were major driving forces. As shown, huge
infrastructures, including the Shinkansen (bullet train), expressways,
long bridges and tunnels, have been constructed since the 1960s. In
that process, improvements have been made to conventional design
methodologies, such as the application of plastic design in place of
elastic design. On the other hand, the newly enacted environmental
laws, including the Noise Regulation Law and the Vibration
Regulation Law, strongly called for giving due consideration to the
environment during construction of infrastructures. By around 1970,
Nippon Steel established an organization to supply sheet piles, steel
pipe piles, light rolled sections, wide flange beams, and cold-rolled
box columns, etc. to meet the brisk demand for steel materials for
the development of infrastructure. Since the 1980s, the company has
developed and introduced to the market diverse building materials
and related technologies in a timely response to the enactment of
new laws or changes in design methods (Fig. 1).
2.2 Changes that influenced infrastructure and activities of
Nippon Steel
The changes in environmental conditions and technological needs
in the field of infrastructure can be analyzed from the following three
(1) Changes in environmental conditions accompanying social
growth (germination growth maturity)
The development process of Japanese society can roughly be
Technical Review
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Fig. 1 History of events, codes and standards, and steel products related to infrastructure
divided into a period of germination until around 1973, a period of
growth until around 1990, and a period of maturity up until the present.
During the process of growth, not only did the environmental
conditions change, but so too did the infrastructural requirements. In
the germination period, large-scale infrastructures need to be
developed within a short time; in the growth period, with the progress
of urbanization, infrastructure needs to be developed in harmony with
the city environment (e.g., use of lighter building materials and low-
noise, low-vibration work executed in confined spaces); and in the
mature period, with the ripening of the economy, reductions in
construction costs are called for, and demands to minimize life cycle
costs, and save energy, etc. become more conspicuous, and
accordingly, new materials that are less expensive and more durable
and that help save labor are sought.
(2) Changes in required performance induced by earthquakes,
typhoons and other natural disasters/accidents
Some changes have nothing to do with the growth of society.
Upgrading performance requirements to a more exacting standard in
the wake of a large-scale disaster is an example. When the safety/
security target changes markedly, the codes/standards applied to
determine the infrastructure specifications are revised, calling for
changes in seismic performance, fire-resistance performance,
resistance to landslides, etc. which are required of infrastructure. There
are cases in which the performance requirements of infrastructure
change remarkably as a result of improved accuracy in risk assessment
thanks to progress in science and technology or as a result of a change
in the framework for design methods on a global basis. For example,
in the new performance-based design method in which more than
one performance target is set for each level of damage to a structure,
technology to control damage is required.
(3) Changes in the market brought about by innovative steel
Not all needs are driven by the market. Sometimes innovative
techniques and new business models, or innovations, can bring about
a change in the market, thereby giving birth to new needs. Although
this is considered rather unlikely to happen in the field of
infrastructure, innovations in steel materials or structures have brought
about a new market or a new need. Fire-resistant steels, unbonded
braces and steel-framed houses are among typical examples. The
development of fire-resistant steel overturned the established theory
that structural steel offered poor fire resistance. The advent of fire-
resistant steel led to the birth of a market for steel building frames
without fire-resistant covering. The practical application of unbonded
braces has made it possible to spread the damage-controlled structure,
in which the damage caused during an earthquake is confined to
certain structural members, and the development of steel-framed
houses has dramatically expanded the use of steel sheets around 1
mm in thickness. Nippon Steel has continued to develop new products
and new technologies adapted to the changes in environmental
conditions and market needs. The company’s activities in the field
of infrastructure can be summarized as follows.
I. Activities to realize a large-scale infrastructure that supports the
growth of society
II. Activities to enhance the seismic performance of infrastructure
in Japan—an earthquake-ridden country
III. Activities adapted to the progress of urbanization and the need
for environmental conservation
IV. Activities to check the deterioration of infrastructure and prolong
the life of infrastructure
V. Activities to set new trends through innovations.
We describe Activities I through IV in Section 3, and Activity V in
Section 4.
3. Activities Adapted to Changes in Market Conditions
and Needs
3.1 Activities to realize large-scale infrastructure in support of
society’s growth
Constructing a long-span bridge is a typical example of a huge
project. In the construction of long-span bridges, therefore, most
advanced steel materials and technologies have been employed. Fig.
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Fig. 2 History of maximum bridge span and related steels
Fig. 3 Tokyo Sky Tree® (Owner: Tobu Railway Co. and Tobu Tower Sky
Tree Co.)
2 shows the change in maximum span of suspension bridges, cable-
stayed bridges and truss bridges in Japan. As shown, the maximum
spans of suspension, cable-stayed and truss bridges have continually
been expanded. At present, the maximum span is roughly 2,000 m
for suspension bridges, 900 m for cable-stayed bridges and 500 m
for truss bridges.2, 3) It is steel materials that have allowed for such
long spans. Nippon Steel has developed and marketed high-
performance steel materials for long-span bridges (see the bottom
column in Fig. 2).
Looking at cables for suspension bridges, steel in the 1,550-MPa
class was employed for the George Washington Bridge in the 1930s.
For the Akashikaikyo Ohashi Bridge, steel cabling in the 1,800-MPa
class was developed. A cable of this type was also applied to the
Kurushimakaikyo Ohashi Bridge that was built later. For cable-stayed
bridges, spiral ropes of stranded wires (for the Katsuse Bridge) and
locked coil ropes were used in the 1960s. For the Toyota Ohashi
Bridge and other long-span bridges constructed later, cables of parallel
wire strands having higher tensile strength and larger elasticity
modulus were developed.3, 4)
Concerning steel plates, a tempered steel plate of 600-MPa class
was applied to the Tenmon Bridge, Japan’s largest truss bridge at the
time of completion. After that, large quantities of steel plates of 700/
800-MPa class were adopted for the Minato Ohashi Bridge. However,
the fabrication of those steel plates proved problematic, such as the
high preheating temperature. For the Akashikaikyo Ohashi Bridge,
therefore, a steel plate of 800-MPa class preheated at a lower
temperature was developed.5) Thereafter, attempts were made to cut
overall costs by further enhancing the fabrication of the above high-
strength steel plate. As a result, a high-performance steel, SBHS, for
bridges was developed.6, 7) The strength of steel in a plate-girder bridge
is determined by its fatigue and deflection. There are two grades of
SBHS—one has a yield strength of 500 MPa, the marginal strength
free from the above limitation, and the other is of 700-MPa class
suitable for suspension and cable-stayed bridges.
In order to impart both high strength and good weldability to
SBHS, the thermo-mechanical control process (TMCP) was applied
to restrain the addition of alloys and lower the preheating temperature
or eliminate the need to preheat for welding. It has been reported
that the cost of constructing the Tokyo Gate Bridge,6) in which 500-
MPa SBHS steel was used in large quantities for the first time, could
be reduced by as much as twelve percent. SBHS has been specified
in JIS and is being posted in design standards for road bridges.
In the field of architecture too, with the increase in building height
and span, more and more high-strength steels have been applied. For
Tokyo Sky Tree® (Fig. 3), which is the world’s tallest freestanding
radio tower (634 m) scheduled to be completed in 2012, the 780-
MPa steel and other high-performance steels that have lesser amounts
of alloying elements added to cut costs are abundantly used.8) In
addition, a seamless flux-cored wire without caulked parts (SF-55 of
Nippon Steel & Sumikin Welding Co., Ltd.) has been adopted as a
welding material. Through its high deposition efficiency, low
preheating temperature (low hydrogen concentration), etc., SF-55
helps enhance the efficiency of welding of high-performance steels
and ensure the prescribed quality of welds. On the other hand, the
super-high tension bolt SHTB® (1,400-MPa class)9) for jointing large-
section members, mainly those of high-rise buildings, has been put
to practical use, contributing to the strengthening of steel joints.
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Fig. 4 Relationship between frame collapse modes and in elastic
deformation capability
3.2 Activities to enhance the seismic performance of structures
in Japan—an earthquake-ridden country
In the past, the performance required of steel materials has been
revised each time that significant damage was caused by an
earthquake or major improvements in seismic technology were made.
The most important change was brought by the New Seismic Design
Code for Buildings introduced in 1981. In this method, the concept
of plastic design was added to conventional elastic design. As a result,
it became necessary for structures and their members to have not
only the prescribed strength, but also the prescribed deformability
after plasticization. Following the report that brittle factures of welds
had occurred in the Great Hanshin-Awaji Earthquake of 1995, even
more rigorous performance requirements relating to fracture
resistance were added. Thus, the performance requirements of steel
materials have changed in emphasis from strength to deformability
to fracture resistance. Described below are Nippon Steel’s pioneering
activities in response to the above changes.
(1) Pursuit of higher material strength and higher member strength
(large section)
Amid the trends toward taller buildings and higher seismic
performance, Nippon Steel has been pursuing steel materials of
greater strength and steel members with higher yield strength (for
larger sections). Representative high-strength steel materials include
BT-HT440,10) whose tensile strength is 590 MPa, and BT-HT630,11)
which has a higher tensile strength of 780 MPa. These steel materials
were adopted for the Yokohama Landmark Tower and Kokura Station
Building. Recently, the company has developed H-SA700,12) which
has 700-MPa class yield strength, and a high-strength yield ratio (YR)
relaxation-type steel that features high productivity and low cost.13)
As examples of steel members having large sections, there are the
extra-thick H-Shape (HSGH®)14) and large Hyper-Beam®.15) HSGH®
has mainly been used in foreign countries. It was adopted for Taipei
101 (China, 2004) and Burj Khalifa (UAE, 2007), amongst others.
The company’s advanced molding technology has made it possible
to manufacture extra-thick H shapes having outer dimensions up to
580 mm × 471 mm, with the maximum web thickness and maximum
flange thickness being 95 mm and 130 mm, respectively. The wide-
flange beam (H beam) having fixed outer dimensions (Hyper-Beam®)
that was developed as an alternative to a welded H-beam is also now
available in larger sizes. It is now possible to manufacture Hyper-
Beams with a beam depth up to 1,000 mm. The Hyper-Beam has a
large beam depth and permits reducing the web thickness and
increasing the flange thickness and width and hence, it helps bring
about an economical design.
(2) Pursuit of higher plastic deformability of steel members and
Nippon Steel has carried out two pioneering activities to enhance
the plastic deformability of its steel products. One was research on
enhancing the deformability of a steel member by lowering the yield
ratio of the steel material. Yield ratio (YR) is the ratio of yield strength
to tensile strength. After introduction of the New Seismic Design
Code for Buildings in 1981, the company was quick to begin research
on the yield ratio of steel materials and the deformability of steel
members. As a result, it showed that lowering the yield ratio of the
steel material improved the plastic deformability of the steel member
markedly.16) Thanks to the above pioneering research, the yield ratio
has come to be positioned as one of the performance indicators for
steel materials for seismic structures. The other was an activity to
enhance the deformability of the entire framework of a steel structure.
This was research focused on the variance of the yield point (YP) of
steel materials.17) As a means of enhancing the deformability of a
steel framework, there is a design technique that engenders a total
collapse mechanism of the beam yield type. The underlying concept
is that the beams are made to yield before the columns so as to increase
the number of plastic hinges in the framework and thereby disperse
the damage over the entire framework (Fig. 4). With the aid of a
probabilistic method, the company demonstrated that the
deformability of the entire framework could be improved by reducing
the variance of the yield point (narrowing down the margin of YP)17).
That was the finding that reducing the variance of the yield strength
would increase the possibility of the beams yielding before the
The above research results into the yield ratio and the variance of
the yield point were reflected on rolled steels for building frames
(SN Steels; JIS G 3136-1994) that were subsequently standardized.
The standard provides for upper limits of yield ratio, and upper and
lower limits of yield points, etc. as matters relating to the mechanical
properties of steel materials, which contribute to the improved seismic
performance of building frames. It should be noted that the provisions
concerning yield ratios have been introduced in the United States,
Europe and China, providing an example of Nippon Steel’s activities
being globalized.
(3) Pursuit of fracture resistance to prevent brittle fractures
In the wake of the brittle fractures that affected steel structures
during the Great Hanshin-Awaji Earthquake, Nippon Steel played a
leading role in carrying out a national project to investigate the causes
of brittle fractures and establish technology to prevent them. In that
project, the company clarified that the brittle fractures of welds at
the beam ends were influenced by the fracture toughness and yield
ratio of the steel material and by details of the joints. At the same
time, the company presented specific conditions and a design flow
to prevent brittle fractures, taking into consideration the details of
the column-beam joints, the presence of welding defects, and the
fracture toughness of materials and welds, etc.18, 19) The results of the
national project have been incorporated into the “Guidelines on
Prevention of Brittle Fractures of Welded Joints at Beam Ends of
Steel Frames,”20) which have been contributing to the improved
reliability of steel-frame structures. In addition, the company has
developed HTUFF® Steel,21) which permits securing a high HAZ
(Heat-Affected Zone) toughness even when welding with a large heat
input (e.g., electro-slag welding) which tends to cause the material
to deteriorate, through refinement of the HAZ structure by effective
utilization of precipitates.
Although this is an entirely different approach, Nippon Steel has
also developed and commercialized all-bolted building frames
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(a) GANTETSU pile®(b) NS-Eco pile®
Fig. 5 Example of environmentally-conscious steel pipe pile
Fig. 6 Enlarged pile tip reinforcement of TN-X pile (2,400mm φφ
(Hyper-Frame®)22) that have dispelled concern about fractures. This
structure uses high strength bolts for all the connections and joints
that are subject to stress concentration and thereby eliminates the
need to weld those connections and joints. It obtained general approval
from the construction minister in 1997 (for buildings up to five
3.3 Activity to respond to progress of urbanization and demand
for environmental protection
3.3.1 Progress in civil engineering structures accompanying
The advances in civil engineering structures in urban areas can
roughly be divided into: progress with pile foundations with an
increase in scale and height of structures; progress with retaining
walls that serve to separate specific structures from ports and rivers
in horizontal expansions of urban areas; and progress with tunnels,
shafts and other underground structures in vertical expansions of
urban areas. Nippon Steel has supplied steel products and technologies
adapted to the progress of those structures.
Early pile foundations were mostly pinewood piles and cast-in-
place concrete piles.23) With the increase in the size of structures,
steel pipe piles which provide a larger bearing capacity and better
work quality were developed. In 1963, JIS standards for steel pipe
piles were established, and in 1971, the Japanese Association for
Steel Pipe Piles (the present Japanese Association for Steel Pipe Pile/
Steel Sheet Pile Technology) was inaugurated. Nippon Steel has
contributed much to the development, practical application and spread
of steel pipe piles.
Steel sheet piles have long been used. According to a report, steel
sheet piles were used in the construction of the main building for
Mitsui as far back as 1903. At first, sheet pile technology was
introduced from the United States and Europe. In order to meet the
growing need for sheet piles with a higher yield strength, Nippon
Steel developed new type of sheet pile known as the “Z-sheet pile”
(in 1959). Around 1960, the company created a steel pipe sheet pile
with a new construction, allowing for dramatic improvement in cross-
sectional characteristics. Thereafter, the company has continually
developed new products adapted to increasingly diverse needs.
For urban tunnels, concrete segments had long been the
mainstream. With the development of traffic networks in urban areas,
branches and sections that are subject to a larger load have increased
in number. Accordingly, composite segments of steel and concrete,
such as NM and CP Segments,24, 25) have been developed. In addition,
through the development of a continuous underground steel wall made
of special structural steel (NS-BOX)26), etc., the company has
responded to the continued increase in size and depth of tunnel shafts.
3.3.2 Response to market needs relating to the environment
In light of growing consciousness about the environment
surrounding construction, the government enacted the Noise
Regulation Law in 1966 and the Vibration Regulation Law in 1976.
Under those conditions, the “low-noise, low-vibration pile embedding
method,” in which piles are built in a previously excavated hole, was
developed to take the place of the conventional method of pile-driving
by hammer. At the same time, a new method that does not produce
much waste soil was called for. These were the “Gantetsu Pile® 27)
and “NS Eco-Pile® 28) that were developed to meet the above
demands. The Gantetsu Pile® is a composite of a steel pipe pile and
soil and cement developed by applying the existing soil improvement
technology. It uses a special finned steel pipe to obtain a solid
composite unit (Fig. 5 (a)). The NS Eco-Pile® is a steel pipe pile that
has a large-diameter cutter blade at the front end so that it can be
rotated and pressed into the ground (Fig. 5 (b)). In order to develop
this new pile, the penetrability by rotation and the bearing capacity
of various steel pipes were studied in earnest.28) The NS Eco-Pile®
has become widespread as the representative method of building a
pile foundation. Producing virtually no waste soil, it is highly
evaluated as an environment-friendly method.
3.3.3 Response to demand for piles of higher yield strength and
reduced cost
Examples of steel pipe piles and steel sheet piles developed in
response to the progress of urbanization are described below.
(1) Long, large-section steel pipe pile method to meet need for higher
yield strength
In the field of building foundations, the 2001 Revision of the
Building Standards Law made it possible for civil engineers to adopt
their own bearing capacity equation based on the prescribed loading
test, thereby paving the way for practical use of piles with a larger
bearing capacity.29) The “TN-X”30) method was developed under such
conditions. In this method, a large protective foot is formed by
injecting cement milk into the ground through a steel pipe while
rotating a spreading blade head inserted into it and mixing the cement
milk with the soil (Fig. 6). The maximum diameter is 1,400 mm for
the pile and 2,400 mm for the protective foot. In a bearing stratum
whose N-value is 60 or more, a system of steel pipe piles can manifest
a pile-end bearing capacity of up to 17,900 kN. This method can be
applied even to long steel pipe piles driven 70 to 75 m deep into the
ground. It is also applicable to high-strength steel pipes (NSPP 520).
(2) New steel sheet piles enabled cost reductions
Formerly, steel sheet piles were mostly 400 mm in width. Since
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Fig. 9 U-shaped rib stiffening pole
1997, when an action plan concerning measures to cut the cost of
public works was formulated, it has become an urgent necessity to
cut construction costs. Under that condition, Nippon Steel developed
a 600-mm-wide steel sheet pile,31) as well as a 900-mm-wide hat-
type sectioned steel sheet pile.32) The development of such wider
sheet piles has made it possible to reduce the number of sheet piles
required and shorten the construction period.
At present, two hat-type sectioned sheet piles are available: 10H
and 25H. As a single unit, Type 25H is among the world’s largest
steel sheet piles. In addition to the large width, the salient
characteristics of the hat-type sectioned sheet piles are that the shape
has been optimized from the standpoint of cross-sectional
performance and impact resistance and that the joints have been
shifted to the outermost edges (Fig. 7) so as to prevent shear
displacement at joints found with conventional sheet piles, and to
further enhance the cross-sectional performance. As a result,
compared with conventional steel sheet piles (IIw, IIIw), the hat-type
sectioned steel sheet pile (10H, 25H) has higher cross-section
performance while ensuring good drivability.31)
Nippon Steel has also been developing steel sheet piles for new
uses. Ordinary steel sheet piles are resistant to horizontal forces from
soil and water pressure, etc. The company has developed a new steel
sheet pile that is resistant to vertical forces as well. Thus, it has
proposed a steel sheet pile foundation that serves not only as a
retaining wall but also as a foundation.33) Namely, a pair of hat-type
sectioned sheet piles are fitted together at the end to form a closed
section (Fig. 8), thereby making it possible to use steel sheet piles
for foundations as well. The closed section at the end of the newly
developed steel sheet pile has an end-bearing capacity comparable
to that of a steel pipe pile.
3.4 Activities to check the deterioration of infrastructure and
prolong the life of infrastructure
3.4.1 Improving fatigue resistance by controlling residual stress
The problem of fatigue in steel structures has become especially
conspicuous with heavily operated railways and heavy-duty road
bridges. Accordingly, stringent maintenance and management,
Fig. 8 Hat-shaped steel sheet pile with pile tip enclosure
Fig. 7 Configuration of hat-shaped steel sheet pile
including periodic inspections and checking for cracks, are required
of those steel structures. A number of bridge collapses and suchlike
caused by fatigue cracking have been reported abroad. In Japan, too,
fatigue failures in road signposts and lampposts, etc. have made the
news. Fatigue cracking is caused by welding defects or high stress
concentration at the surface of a weld or tensile residual stress
comparable to the yield strength of the weld. Here, we describe
Nippon Steel’s activities to improve the fatigue resistance of steel
structures with a focus on reducing the tensile residual stress of the
It is the “U-ribbed structure”34) that offers good fatigue
performance thanks to a low stress concentration and a small tensile
residual stress achieved by improving the details of the joints (Fig.
9). This structure was proposed by Nippon Steel as an alternative to
the triangular rib enforcement for the bases of lampposts and road
signposts, etc. The salient characteristic of this structure is that in
addition to a reduction in stress concentration by the U-ribbed
reinforcement, the tensile residual stress of the weld is significantly
reduced as the steel pipe thermal deformation after rib welding
introduces a compressive stress around the part subject to stress
concentration. It has been reported that thanks to the combined effect
of relieving stress concentration and reducing tensile residual stress,
the U-ribbed structure is a very effective way to improve the fatigue
life of a steel structure. It has already been employed on many
lampposts along expressways.
There is a technology to enhance the fatigue performance of welds
by peening — that is hammering the welds using a special tool. This
is “
sonix® UIT” (Ultrasonic Impact Technology) developed by an
engineer of the former Soviet Union in 1970. The UIT is mounted
with a striker pin at the front end that impacts the weld as it vibrates
at high speed. Nippon Steel conducted basic research into UIT,
including an attempt to clarify the mechanisms of UIT, and research
on the application of UIT to actual steel structures. As a result, it has
been clarified that the effect of UIT owes to multiple factors, such as
the introduction of a compressive residual stress by the impact of the
striker pin, the relieving of stress concentration by improving the
shape of the weld, and refinement of the weld’s surface structure.35)
With out-of-plane gusset joints, etc., the application of UIT has
promoted their JSSC fatigue grade up about two ranks, from D to B.
The technology has been increasingly applied to crane runway girders
and bridges.36)
3.4.2 Activities to prevent corrosion of offshore structures by using
high-performance steels
In recent years, large projects in marine locations need to remain
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Fig. 10 Stainless steel cladding protection (Haneda Airport D-runway)
remained strong and techniques to predict the long-term durability
of weathering steels taking into account the local environment have
been called for. Under those conditions, Nippon Steel has developed
new weathering steels and new techniques to evaluate their durability.
In the case of JIS weathering steels (containing Cu, Ni and Cr),
the reaction (at the steel surface) of chlorine ions (Cl
) in the rust
layer impairs their durability. The “Ni-based weathering steel”40) was
developed based on the knowledge that the above reaction of Cl
ions is restrained in weathering steel whose Ni concentration exceeds
a certain level. In a simulated exposure test carried out in a coastal
area exceeding 0.05 mdd too, the developed steel proved to have
good resistance to salt damage. Two types of Ni-based weathering
steel have been developed—1%Ni and 3%Ni—so that the better type
can be selected according to the actual environment.
Macroscopically, the applicability of weathering steels has been
judged based on the concentration of airborne salt and the distance
from the nearest coast. However, judging the applicability of specific
weathering steel has become increasingly difficult, calling for
microscopic and quantitative information. The technology that
Nippon Steel developed to meet this need is software (“YOSOKU®”)
to predict the decrease in steel plate thickness by corrosion that takes
into account all the environmental factors, such as the temperature,
humidity, sulfur oxide concentration, and wind velocity.41, 42) This
has enabled more rational judgment on the applicability of weathering
steels. In addition, the company has developed a “patch test method,”
which permits quantifying the durability of steel easily, and various
application techniques,42) including a rust-stabilizing paint that
restrains the initial rust from dropping.
4. Setting New Trends through Innovation
4.1 Challenging the common belief that structural steels have
poor resistance to fires
Until the advent of fire-resistant steels (around the 1980s), the
great majority of steel-framed buildings were required, almost without
exception, to meet the specifications for fire-resistant structures (mean
steel temperature not higher than 350 and maximum steel
temperature not higher than 450) provided for by the Building
Standards Law of Japan. In those days, it was considered common
sense to cover a steel frame with a fireproofing material with good
heat insulation. Therefore, the image of “steel-framed buildings
having poor resistance to fires” was quite prevalent. On the other
hand, a number of problems involved in applying a fireproofing
material had already been pointed out, including the poor working
environment, extended period of construction, and reduced freedom
of architectural design. Under those conditions, technology to
dispense with the need for a fireproofing material was much sought
after. In 1988, Nippon Steel came up with a “fire-resistant steel”
having excellent high-temperature properties,43) and succeeded in
putting it to practical use for the first time in the world. The salient
characteristic of the fire-resistant steel was that it was the world’s
first structural steel that guaranteed a yield strength equivalent to
two thirds or more of the normal-temperature F-value (design material
strength) at the prescribed high temperature, in this case 600.
Fig. 11 shows the high-temperature strength properties of the fire-
resistant steel, SM50A-NFR (present NSFR490A)44). It can be seen
from Fig. 11 that the fire-resistant SM50A-NFR steel has greater
high-temperature strength than the steel material for ordinary welded
structures, SM50A (present SM490A), and that its yield point (YP)
at 600 is equivalent to at least two thirds of the design material
strength (22 kgf/mm2, 216 MPa) at ambient temperatures. By
corrosion-free for 100 years or more. Under that condition, Nippon
Steel has developed long-term anticorrosion technology using
titanium, stainless steel and other high-performance materials.37, 38)
Titanium has excellent corrosion resistance. However, since
titanium is expensive and cannot be welded with iron, the application
of this material for corrosion prevention had been limited. Around
1990, Nippon Steel developed an inexpensive titanium-clad steel
product and an economical titanium welding method, which were
applied for the first time in the world to the steel bridge piers of the
Tokyo Wan Aqualine Expressway (Trans-Tokyo bay bridges and
tunnel) in the splash and tidal zones. After that, the titanium-clad
steel was also employed for the lower part of the Monbetsu Ryukai
Observation Tower, and the floating structure of the Yumemai Ohashi
Bridge, etc. The problem of welding the titanium-clad steel plate (1
mm titanium cladding on 4 mm steel plate) to the bridge pier was
solved by welding the steel part of the plate to the steel member of
the bridge pier.
“Stainless steels” are second only to titanium in corrosion
resistance. They had been considered as promising corrosion-resistant
materials applicable to steel structures. However, conventional
stainless steels, such as SUS 316L, were subject to pitting and crevice
corrosion in environments without cathodic protection against sea
corrosion. Therefore, new materials with better corrosion resistance
were required. With an eye on its NSSC270 (20Cr-18Ni-6Mo) steel
that had been put to practical use in seawater desalination plants,
etc., Nippon Steel proposed a new anticorrosive coating method for
the jackets in the splash and tidal zones in the Haneda Airport Re-
expansion Project. The proposal was accepted and the new method
was put into practice (Fig. 10). In order to implement the method, in
which the steel pipe is covered with a thin sheet of stainless steel
about 0.4 mm thick, the company developed a new indirect seam
welding method, which has helped cut the cost of covering
significantly. In addition, in the above project, the company proposed
a new anticorrosion method in which the steel girders of the runway
should be covered with a thin panel of titanium. This proposal was
also adopted.39)
3.4.3 Weathering steels in corrosive atmospheres and their application
As steel materials which do not require anticorrosion painting,
weathering steels have been widely used. However, the conventional
JIS weathering steels (SMA steels) can only be used effectively when
the airborne salt concentration is within a certain limit or in areas a
minimum distance away from the coast. On the other hand, in coastal
areas, the need to construct bridges using weathering steels has
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(a) Outdoor parking lot (b) Atrium building
Fig. 12 Applications of fire resistant steel
Fig. 11 Mechanical properties at elevated temperatures of fire-resistant
steel and ordinary steel (SM)41)
Fig. 13 Outline of unbonded brace
guaranteeing such high-temperature strength properties, Nippon Steel
succeeded in creating a new market for “steel-framed buildings
without fireproof covering,” including, for example, drive-in parking
facilities (Fig. 12 (a)) and atriums (Fig. 12 (b)) which are free from
flashover fires. In addition, the application of fire-resistant steel has
made it possible to omit the covering work, shorten the construction
period and design neat steel frames without fireproof covering (Fig.
In 1989, Nippon Steel issued guidelines on the fire-resistant design
of buildings using fire-resistant steels and established a new method
of verifying fire resistance beyond the criteria of the Building
Standards Law of Japan. The above guidelines were the forerunner
of performance-based design methods in the field of fire engineering.
In 1990, Nippon Steel disclosed its fire-resistance technology to the
other integrated iron and steel manufacturers, paving the way for the
spread of fire-resistant steels. The development of fire-resistant steels
is an example of pioneering, innovative and foresighted development
of building materials that not only allowed for steel-framed buildings
without fireproof covering, but also created a new trend toward the
development of performance-based fire-resistant methodology. It also
leads the current trends in the development of building materials—
reduction of CO2 emissions and improved recyclability of steel frame
members by minimizing the application of fireproof covering.
4.2 Development of buckle-free braces and damage-controlled
Braced structures are one type of rational construction. However,
a brace is subject to buckling under a compressive force. If the brace
buckles, its yield strength and energy-absorbing capacity decline
markedly. When a cyclic force (e.g., a seismic force) is applied to
the brace, plasticization under tension and buckling under
compression occur alternately. As a result, the hysteretic behavior of
the brace becomes extremely complex. Therefore, it was common
sense in structural design that “compression resistance is not expected
of braces.” But the unbonded brace challenged that notion.45) Nippon
Steel worked out a mechanism for restraining the buckling—a
drawback—of braces. The mechanism was first put to practical use
in 1986. The unbonded brace consists of a plane or cruciform section
steel plate constrained by a steel tube and concrete via unbonded
material (e.g., asphalt) (Fig. 13). This forms a bracing member whose
buckling is effectively restrained.
The unbonded brace was applied as a damage-controlling member
of a damage-controlled structure that was proposed at the same time
that the unbonded brace was developed. This set a major trend toward
seismic-resistant buildings. The damage-controlled structure allows
for improved seismic performance and continued use of the building
by replacing the damage-controlling member that absorbs the seismic
energy in a concentrated manner. In view of the spread of damage-
controlled structures, Nippon Steel developed a new low-yield-point
steel, “BT-LYP®,” to enhance the performance of unbonded braces.46-48)
It has been demonstrated that unbonded braces using the LYP steel
have a stable hysteretic characteristic and a good low-cycle fatigue
characteristic. They have been widely used in Japan and abroad. In
the United States, they are specified in the Standards of the American
Institute of Steel Construction (AISC) and the number of hospitals
and other public buildings that are applying them is increasing.
4.3 Steel houses that can even be built by carpenters, and
proposals on “shapes”
The history of steel houses in Japan dates back more than half a
century. Steel houses are typically light-gauge, steel-framed
constructions which now account for 10% to 20% of all new houses.
A light-gauge, steel-framed house is built by connecting 2.3-mm or
thicker steel sections together by means of welding or bolting.
Ordinarily, it is subjected to the electro-deposition process to ensure
the required durability. Since building light-gauge, steel-framed
houses requires large-scale equipment and high levels of skills,
they are generally built at an integrated plant. The above restriction
has prevented them from becoming more popular, and accounts,
at least in part, for their modest share of the market despite their
long history.
Our “Steel House” activity was started with the aim of breaking
out of such a situation.49) Under the Urban Steel Society (sponsored
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(a) Skelton (b) Self-drilling connection
Fig. 14 Outline of steel-framed house
Fig. 15 Light-gauge steel shapes as substitutes to wooden member
by the present Ministry of Economy, Trade and Industry), Nippon
Steel took the initiative in launching research on steel houses in 1994.
Steel house (Fig. 14) constructions were popular in the United States
and Australia in those days. They were so-called two-by-four steel
houses fabricated by joining together galvanized steel shapes about
1.0 mm thick using self-drilling tapping screws. The steel shapes
used are so thin that they can be cut with a circular saw and screw-
jointed with an impact screwdriver. Unlike conventional steel-framed
houses, the two-by-four steel house requires no special skills, and
can even be built by carpenters.
Although the two-by-four steel house was expected to open a
new market, there were a number of legal and technical problems
and limitations that had to be cleared before it could be put to practical
use in Japan. Nippon Steel played the leading role in promoting the
establishment of standards and criteria relating to design, construction
and durability of steel houses. In 2001, the company succeeded in
having an official design code of steel houses. As a result, it became
possible to use galvanized shapes 0.4 to 2.3 mm thick as structural
materials, and two-by-four steel houses came to be recognized as
comparable to wooden houses and traditional light-gauge steel-
framed houses. Today, steel houses that have secured official
fireproof certification are applied to company houses and bachelor
dormitories, etc. of up to three stories.50)
The two-by-four steel house also prompted the utilization of steel
sheet members in Japan. As the thickness of the steel material is
reduced, it becomes easier to obtain steel members of various cross-
sectional shapes by cold roll forming. On the other hand, this can
lead to a complex form of buckling of the member accompanied by
twisting or local deformation. Therefore, Nippon Steel has conducted
research on design methodology paying special attention to the
buckling of thin steel members and optimization of cross-sectional
shapes by taking advantage of the freedom of form.51) Fig. 15 shows
an example of replacing a wooden member with a steel sheet member.
As shown, it has become possible for the company to propose various
cross-sectional “shapes,” starting from C-shaped through Σ-, Ω-
and J-shaped, and so on.52) Incidentally, the technology developed
here is utilized as “Katachi Solution®” to reduce weight and increase
rigidity in home appliance cabinets, etc. (see Chapter 1, 1-3).
5. Outlook for Future Technologies
5.1 Steel materials to secure greater safety against disasters/
One of the lessons many have learned from the recent Great East
Japan Earthquake is probably the most rudimentary question as to
the possibility of accurately estimating the scale of a natural disaster.
After all, any prediction technique that depends on a limited amount
of data accumulated over decades or so has its own limits. Thus, it is
necessary that the infrastructure should be equipped with as much
resistance to external forces as possible and that it should be easily
repairable if damaged. The direction of technological development
for that purpose is considered to utilize the “redundancy” of structures
and implement “stratification”53) of structures, whereby the structures
are classified according to their role as in skeleton infill.
Utilizing redundancy means making a structure that does not
collapse even if a member or a part of it is lost. In the wake of the
Great East Japan Earthquake, a concept similar to structural
redundancy was proposed for breakwaters to protect against
tsunamis.54) Developing new rational structures and design methods
is a task to be tackled in the future. It calls for new steel materials
with superior deformability and fracture resistance to conventional
ones. Concerning the stratification of structures, on the other hand,
as proposed in the national project “New Structural Systems,”55) it is
expected that “functional distribution” to distribute horizontal and
vertical forces among different members of a structure will progress,
and that the use of the most appropriate steel material for each place
will be promoted. Regardless of which direction —redundancy or
stratification—technology takes in the future, the performance
required of steel materials, such as strength, deformability and fire
resistance, will become more diverse and structures and their members
that support safety will be expected to perform better.
5.2 Globalization and value of Japanese safety/security
In view of the brisk activity in infrastructural development in the
newly industrialized economies (NIEs), the demand for steel materials
will be sure to expand rapidly in the future. Fig. 16 lists the countries
in order of consumption of structural steels, based on data made
available by the World Steel Association (WSA) and the Japan Iron
and Steel Federation (JISF) (some countries have been excluded due
to a lack of official data). China is preeminent in steel consumption.
India has already surpassed Japan and the United States. Mexico,
Thailand, Brazil, Egypt, and Turkey, etc. are catching up with
Fig. 16 Steel consumption in construction market by country (2010, WSA
and other sources)
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Table 1 Comparison of environmental design rating systems
Japan United States Europe
Steel advantages (BREEAM,
Strength Considered No No
Ductile Considered No No
Durable Considered No Considered
Noncombustible No No No
Recyclable No Considered Considered
Dismantling Considered No No
CO2 emission Considered No Considered
Germany, Italy and other industrialized countries. In terms of the
per-capita consumption of structural steel and nominal GDP, India
and Indonesia, etc. are far lower than the industrialized nations.
Bearing that in mind, the growth potential for infrastructure in the
world is great.
China and some other NIEs have developed their own design
standards. Many of the NIEs, however, employ advanced design/
construction techniques from the United States, Europe or some other
industrialized country. The susceptibility to natural disasters, such
as earthquakes, differs from country to country. Therefore, in
designing and constructing a steel structure in a locality, it is necessary
to give due consideration to the specific conditions of that locality.
In particular, concern about earthquakes and tsunamis is growing
around the world. In addition, with the improvement in living
standards, the interest in protection of the environment of densely
populated cities is mounting. Japan has the most advanced
technologies for coping with earthquakes and landslides coupled with
environment-friendly construction technologies. All in all, there is a
good possibility that Japanese safety/security technology and
environment-friendly technologies based mainly on steels will be
able to play an important role in the global market.
5.3 Growing attention to sustainability
While the sustainable growth of society is discussed in earnest,
the sustainability of infrastructure is rapidly attracting increasing
attention. In the United States, Europe and Japan, environmental
performance evaluation systems for buildings have already been
proposed and put into practice (CASBEE in Japan)56). Those
evaluation systems quantitatively evaluate the environmental
performances of buildings in terms of environmental friendliness,
running costs, and comfort for users, etc. In the future, infrastructural
specifications, mainly for buildings, will be strongly influenced by
those evaluation systems.
Steel materials are comparatively light in weight and have good
seismic resistance, durability, recyclability, and can be easily
dismantled, etc. Thus, they can be evaluated as highly sustainable
materials. However, none of the existing environmental performance
evaluation systems fully take those properties into consideration.
Table 1 compares the evaluation systems of Japan, the United States
and Europe in terms of how much consideration is given to the
advantageous characteristics of steel materials. It can be seen that
they differ noticeably. In view of the expected growth of infrastructure
on a global basis, the demand for its sustainability will increase and
opportunities to fully utilize the properties of steel materials are
expected to expand.
6. Conclusion
We have so far reviewed past changes in market conditions and
market needs and the company’s responses to those changes. We
have also discussed the outlook for future technologies. In the first
half of the text, we described how the change in the infrastructural
environment has been brought about not only by the growth of society,
but also by the changes in performance required of infrastructure as
a result of disasters and accidents, and the development of innovative
new technologies in steels. In addition, we have introduced the
company’s five characteristic activities (building large-scale
infrastructure; improving seismic resistance; responding to
urbanization; preventing deterioration/prolonging the life of
infrastructure; and creating new trends). In the second half, as an
outlook for future technologies, we discussed the possibilities of steel
materials from these three standpoints: steel’s role in ensuring safety;
growth potential of steel in the world market; and response to the
demand for sustainable infrastructure. In this technical review, we
have seen that steels and their application technologies have
progressed hand in hand with the development of infrastructure and
have met the diversified needs of our ever-growing society, and that
our company has been among the world leaders in technological
development while creating new trends in steel technology. There is
no doubt that steels will continue to be an important element in the
support of infrastructure. Nippon Steel intends to continue developing
advanced new technologies adapted to ever more diverse market
needs and supply them to the world market on a timely basis.
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Chief Researcher, Ph.D.
Steel Structure R&D Center
Steel Research Laboratories
Senior Researcher, Dr.Eng.
Steel Structure R&D Center
Steel Research Laboratories
Ryoichi KANNO
General Manager, Ph.D.
Steel Structure R&D Center
Steel Research Laboratories
20-1, Shintomi, Futtsu, Chiba 293-8511
Chief Researcher, Dr.Eng.
Steel Structure R&D Center
Steel Research Laboratories
Fuminobu OZAKI
Senior Researcher, Dr.Eng.
Steel Structure R&D Center
Steel Research Laboratories
Senior Researcher, Dr.Eng.
Steel Structure R&D Center
Steel Research Laboratories
Senior Researcher
Steel Structure R&D Center
Steel Research Laboratories
Senior Researcher
Steel Structure R&D Center
Steel Research Laboratories
Tetsuro NOSE
General Manager, Dr.Eng.
Welding & Joining Research Center
Steel Research Laboratories
General Manager, WELTECH Center
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... A significant reduction of using steel was observed during the economic recession in Brazil in the 1980s, while steel became common from the 1990s during which national economic stability achieved (De Nardin and Debs, 2013). The rapid growth of steel construction was beneficial from the growing economy in many marketplaces such as the UK (Moore and Tordoff, 2007) and Japan (Kanno et al., 2012). Urbanization and demographic changes can support the growth of steel-intensive construction projects because of the increasing demand for public areas, playground facilities and other urban furniture, reflecting the rapid economic growths in many developing countries. ...
... The need for safe buildings to be constructed in the earthquake zones (e.g. Japan) has urged the adoption of structural steel regarding its strength and ductility against strong seismic loading (Kanno et al., 2012). Sustainable construction is a critical concern because of its high economic significance and strong social and environmental impacts (Zhong and Wu, 2015). ...
... It offers better retention of strength and stiffness than carbon steel at elevated temperatures; hence, enhanced fire resistance may reduce the need for protective fire coating in structural steel members (Gardner, 2005). The application of fire-resistant steel technology not only avoids a number of problems in fireproofing coating, but also changes the attitude regarding poor fire resistance function of steel-framed buildings (Kanno et al., 2012). While the high material prices of steel products hinder their applications in construction sector (Gardner, 2005), technological advances bring reducing cost on the other hand (Kanno et al., 2012;Robinson, 1998). ...
Purpose The steel construction market has undergone gradual development in the past decades given its profound impacts on environment, economy and society. The purpose of this paper is to facilitate a better understanding of the major drivers and issues behind the market development of the steel construction industries around the world. Design/methodology/approach A three-step desktop research was conducted to select relevant research outputs published in the past 20 years. The research methodology in conducting these studies and their research trends were analyzed. Then the potential influencing factors for the market development of steel construction were identified through a content analysis of the selected studies. Findings A total of 59 articles were identified accordingly. These influencing factors were divided into five main themes: contextual, institutional, industrial, project-related and individual factors. In terms of the frequencies of these factors appeared in previous studies, “continuous development of standards, codes, and specifications” and “advance in product and process technology” were the top two driving forces in the market development of steel construction, while “cost issues” was the most frequently reported obstacle. Originality/value The study takes an initiative to establish a practical classification framework that can be dedicated to illuminating the critical issues or success factors affecting the development of the steel construction market. This framework can help policymakers, industry practitioners and researchers achieve sustaining success in steel construction in the developed, emerging and inactive markets.
... Figure 3 shows the timelines of steel amount ordered for bridge constructions, 4 maximum spans of suspension, cable-stayed and truss bridges, and some of the newly developed materials. 5 Over a period of 30 years from the late 1960s, approximately 500 000 tons of steel continued to be used in bridge construction every year. With such an active bridge construction rate, the centre spans of all types of bridges-suspension, cable-stayed and truss-have continued to expand, and at present are at their maximum at approximately 2 000 m, 900 m and 500 m, respectively. ...
Full-text available
Over the course of the past 150 years, since the first iron- and steel-based bridge was constructed in 1868, Japan has become one of the most advanced countries in the construction of steel structures. Various innovative and elegant steel structures were constructed in the past such as the world's longest suspension bridge called the Akashi Kaikyo Bridge. The advances of steel structures were attributed to a significant extent to the development of high-performance steels. Such materials developed in Japan were characterized by three types of versatilities: strength, functional, and sectional. Some examples of such materials include fairly high and low strength steels, high-bridge performance steel, seismic-resistant steel, fire-resistant steel, and size-flexible H-shaped beam. In Japan, these steel material innovations enabled the progress in steel structures to leap forward and in turn challenging new structures gave birth to further advancements in steel materials. In this paper, the advancements of steel structures and materials were reviewed, focusing largely on the steel materials and their contributions to the construction of steel structures. In addition, in light of recently developed innovative steels and their strength-increasing potential, the further advancements of steel materials were suggested for the future innovations of steel structures.
Inhibition action of Syzygium jambos leaf extract on corrosion of mild steel in 1 M HCl was evaluated through mass loss measurements, potentiodynamic polarization and electrochemical impedance spectroscopic techniques. Temperature studies revealed a decrease in efficiency with rise in temperature and corrosion activation energies increased in the presence of the extract. Inhibition action of the inhibitor is explained by adsorption process, and it follows Langmuir adsorption isotherm. Thermodynamic data for inhibitor adsorption suggest the occurrence of physical and chemical adsorption of the extract on mild steel in 1 M HCl solution. The results were supplemented by FTIR and scanning electron microscopy.
The use of structural steelwork (SS) for buildings continues to grow worldwide, owing to its sustainability benefits. However, the market share of SS in the building sector of Hong Kong greatly lags behind other markets. This paper focuses on providing comprehensive understanding of the issues that greatly drive or inhibit the SS adoption in Hong Kong from a project lifecycle perspective. The methodology encompasses both qualitative and quantitative approaches. Semi-structured interviews were conducted with 28 professionals from developer, structural engineering consultant, main contractor, steel specialist contractor, and steel stockholder companies. The results identified 12 driving factors and 25 barriers affecting SS adoption in Hong Kong. A questionnaire survey with 118 practitioners was conducted to identify the most important driving factors and barriers. The results revealed that “increased speed of construction” and “must-have requirements” were the two most important driving factors; while “shortage of skilled labor”, “shortage of supervisors working directly under main contractors”, “high construction costs”, “shortage of experienced designers and draughts men”, and “lack of education, training, and design experience on SS” were the five most critical barriers. This may imply that education and training is needed to improve knowledge and skills of professionals and workers, and thus to ensure adequate supply of manpower. The findings of this study not only contribute to the existing body of knowledge on SS practices, but also provide valuable references for helping practitioners and policy makers to promote sustainable construction methods within the building sector.
Aluminium alloys are nowadays preferred as materials for bridge guiderails especially for bridges connecting oceanic islands or spanning inlets due to their inherent corrosion resistance. But because of the limited mechanical strength of aluminium alloy, fasteners of guiderail members are made from steel materials. It has been found that contact between bare steel fasteners and aluminium alloy members can cause galvanic corrosion in the aluminium alloy. Research was carried out to investigate the capability of different surface treatments on fasteners and aluminium alloy members to inhibit galvanic corrosion under atmospheric exposure for periods of one and three years. It was found, among other results, that stainless steel fasteners treated with zinc flake coating were the most effective inhibitors of galvanic corrosion on aluminium alloy members.
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Recently, studies on seismic energy isolation and damping structures abound and a number of attenuation mechanisms have been proposed. One of them proposes to utilize the elasto-plastic hysteresis of steel, using low yield strength steel as material. This study conducted low-cycle fatigue tests to clarify the low-cycle fatigue characteristics. Hysteresis characteristics and energy absorption characteristics of low yield strength steel will be discussed in the next report. As a result, the following conclusions were obtained concerning low-cycle fatigue characteristics of low yield strength steel. (1) The low-cycle fatigue characteristics (ε-N_f relationship) of low yield strength steel can be expressed by the Manson-Coffin equation. (2) Despite major differences in static ductility and other properties, low-cycle fatigue characteristics vary little by steel type. (3) The effect of strain rate on low-cycle fatigue characteristics is small. (4) The Monson-Coffin equation's coefficient C_1 and m_1 of low yield strength steel deviate from the values obtainable from the conventionally proposed equations. (5) A correlation of C_1=2.1/460^ exists in all types of steel.
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