No. 55 December 2018

STEEL CONSTRUCTIONTODAY & TOMORROW

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

Feature Articles

Steel-Concrete Composite
Structures
1 Current State of Studies of Steel-Concrete Composite Structures
5 Current State of Studies and Research on CFT Structures
9 Potential of Exterior Diaphragm-type Column to Beam
Connections

13 Steel Tubes for Building and CFT Structures

Serial Article: Latest Design of Steel Buildings in Japan (3)HIRAKATA T-SITE
15 Protruding Box

Photo: Atsushi Nakamichi

Structures Form
Expressive Façade
and Improve
Seismic Resistance

Back cover JISF Operations

Published Jointly by

The Japan Iron and Steel Federation
Japanese Society of Steel Construction

Feature Articles: Steel-Concrete Composite Structures (1)Current State of Studies of SteelConcrete Composite Structures

by Junichi Sakai
Professor, Fukuoka University

In the following article, the recent
trend in studies of steel-concrete composite structures is briefly introduced.
In addition, a study is also introducedof a new steel-concrete structure, forwhich we are promoting the development of studies.
Current State of Studies of
Steel-Concrete Composite
Structures
The typical steel-concrete composite
structures in common use in Japan areof three structures: steel and reinforced
concrete (SRC) structures, concretefilled steel tube (CFT) structures andreinforced concrete column-steel beam
(RC+S) mixed structures (Fig. 1). CFT
structures are structures that can easily utilize the structural features offered by the composite structure, and
CFT structures produced by the use ofhigh-strength steel members have been
widely applied in the construction ofhigh-rise buildings. RC+S structures
are mixed structures composed of reinforced-concrete columns that offer
both high rigidity and economic advantages and steel beams with which
the structural span can be made longer,
and thus they are extensively appliedin the construction of long-span officebuildings, commercial facilities and logistics warehouses.
In order to survey the recent trendof studies of steel-concrete composite structures in Japan, an analysis wasmade of 102 study reports in the fieldof steel-concrete composite structures
published in the Summaries of Technical Papers of the Annual Meeting for
FY2018 of the Architectural Instituteof Japan (AIJ)2). Fig. 2 shows a breakdown of study reports in the field ofsteel-concrete composite structures. As
shown in the figure, the mainstream in
1 Steel Construction Today & Tomorrow December 2018

Junichi Sakai: After receiving the master’s degree
at the Graduate School of Engineering, Kyushu University in 1989, he became associate professor at the
Kyushu University in 2001. He assumed his current
position as professor, Department of Architecture,
School of Engineering, Fukuoka University in 2007.
His specialized field covers structural engineering andsteel-concrete composite structures.

Fig. 1 Typical Steel-Concrete Composite Structures in Use in Japan1)
Encased steel
Steel tube

Steel beam

RC column(a) SRC(b) CFT

recent studies of steel-concrete composite structures has been on CFT and
RC+S structures.
While the content of studies of CFT
structure is wide-ranging, the main targets in studies have been placed on
the application of super high-strength
steel, rectangular-shaped CFT columns, long-period seismic motion,
slender columns and built-in steel reinforcement.
In the study of RC+S mixed structures, extensive studies have been
made of the effect of grade differences(height direction) in right and left steel
beams attached to RC columns and thedifferences in eccentricities (horizontal direction) of the beam core to thecolumn core that affect the behaviorsof connections. Further, studies havebeen reported on the mixed structuresthat consist of RC sections in the beam
ends and H-shaped steel frame in the
middle of the span. In addition, a lotof studies of the attachment of braces
have also been reported.
Very few studies have recently been
made in the field of SRC structures,and instead of this, the study of steelconcrete (SC) composite structures is

Cover plate(c) RC column-Steel beam

Fig. 2 Breakdown of 102 Study Reports
on Steel-Concrete Composite
Structures2)

FRP
5
M.S.C
6

Others18

SC Composite
Member
18

CFT
28

RC+S
27

CFT: Concrete-filled steel tube
RC+S: Mixed frame of RC column and steel
beam
M.S.C.: Mechanical shear connector
FRP: Fiber-reinforced plastics
Total: 102 study reports(Summaries of Technical Papers of AIJ
Annual Meeting for FY2018)

increasingly being promoted.
In the field of the study of SC structures, most studies target structural members in which steel reinforcing bars are eliminated from the SRC
structure, and studies are actively being promoted on structural members,
column-beam connections and seismic-resistant walls composed of concrete encased steel (CES) structures

that employ carbon fiber-mixed fiber
concrete. In addition, studies are also
being promoted on various kinds of SC
beams including SC foundation beams
and octagonal-section SC columns. Regarding octagonal-section SC columns,
an explanation will be made later.
In terms of the number of contributions at the AIJ Annual Meeting for
FY2008, while the total number has
decreased, it is noted that studies ofmechanical shear connectors and fiber-reinforced plastics have tended toincrease. In building construction in
Japan, the headed stud has been widely applied as the device to transfer
the stress between steel and concrete,
which however brings about concerns
about the increase in the number ofheaded studs to be applied. To copewith such a situation, studies of theperfobond connectors used in the fieldof civil engineering have recently beenpromoted for the field of building construction.
Fig. 3 shows an example of the results of a pressing test conducted byembedding three kinds of mechanicalshear connectors into concrete-headed studs, perfobond connectors andnew burring connectors3). Even for thetest specimen prepared by setting the
maximum strength of both the headed stud and perfobond connector to an
identical level, it can be understoodfrom the test results that the stiffnessof the headed stud was low but thatof the perfobond connector was high.
Further, as can be seen in the figure,both the stiffness and strength of the
new burring shear connector employing the burring steel plate are high, andas a result it is expected that the newconnector will be put into practical use.
In the field of civil engineering,

structures employing fiber-reinforced
plastics (FRP) have been constructed,
but there are concerns about increasing
construction costs attributable to its application. In the field of building construction, its application has been limited only to parts of building structures.
However, FRP offers high structural
performance such as being lightweightand has high strength and stiffness,and thus its application is considered
to grow in the future. Recently, studies
and exposure tests have been made forthe compression strength of carbon-fiber reinforced plastics (CFRP) members and the application of CFRP in the
splice plates of high-strength bolt friction joints.
Among the “others” pertinent study
reports shown in Fig. 2 are studies onbuckling-restraint braces, composite
slabs, and composition with woodenmaterials and steel pipe pile head joints.
Development Study of Octagonal-section SC Column
Steel and reinforced concrete (SRC)
structures are structures that were originally developed in Japan and offer
high seismic resistance. However, theyrequire reinforcing bar arrangement
and concrete placement in addition tosteel-frame fabrication, and as a result,the construction process becomes complex and construction costs tend to rise.
Accordingly, while SRC structures areapplied to parts of building structures,construction of all SRC-layer building
has decreased.
Aiming at further improving seismic resistance and enhancing manpower and labor savings involved in SRC
construction, we are promoting thedevelopment studies into octagonalsection steel-concrete (SC) columns

Fig. 3 Relationship between Load and Slip of Mechanical Shear Connector3)

Load per connector Q (kN)250

shown in Fig. 4. A dynamic feature ofoctagonal-section SC columns lies inthat, because concrete surrounded by
cruciform steel frame can effectively been confined by the use of steelframe flanges and webs, the bending
resistance and deformation capacity
can be enhanced. Specifically, the webof cruciform steel frames is located in
the center of the column section, andthus the octagonal section column can
resist high compressive axial load andsuppress axial contractions. As a result, octagonal-section SC columns
show stabilized large deformation behavior. Further, both bending strengthand stiffness can easily be adjusted byadjusting the thickness and width ofsteel-frame flanges.
Fig. 5 shows the conditions of concrete-confined effects obtained by thetest in which a uniform compressive
load is applied to the octagonal-section
concrete. As can be seen in the figure,the compressive strength and deformation capacity of octagonal-section column concrete are improved comparedto those of plain concrete (no reinforcement). Because of the limited space forthis study report, the method of analysis cannot be mentioned, but it canbe understood from the figure that thecompressive behavior of concrete canbe traced by means of analysis thattakes the concrete-confined effect into
account4).
Fig. 6 shows the results of a test inwhich the constant axial load and cyclic lateral load were applied to octagonal SC columns. It can be seen in the
figure that even when the steel-frame
dimensions differ one by one, the octagonal column possesses high seismic
resistance. The mechanism line in the
figure indicates the shear strength ofFig. 4 Cross Section of Octagonalsection SC Column

B6-6
Burring connector (new)

200
P12-0
Perfobond connector

150
100

S13
Stud

50
0

0

5

10
Slip δ (mm)1520December 2018 Steel Construction Today & Tomorrow 2

SC columns in the case when the full
plastic moment of the column section,
calculated using the yield strength ofsteel and the compressive strength of
concrete, is to be demonstrated on thecolumn head and base. The figure also shows the result of an analysis thattakes into account the concrete-con-fined effect, and it can be said that thetest results are precisely evaluated bythis analysis.
Fig. 7 shows the column-beam connection of a mixed-framing structurecomposed of octagonal-section SC columns and steel-frame beams. As shownin the figure, the detail of weld-join-

ing of an exterior diaphragm and vertical stiffener is proposed to confirm thetransfer of stress occurring in columnbeam connections5). Further, two cruciform frame test specimens composedof octagonal-section SC columns andsteel-frame beams were prepared, anda test was conducted in which a constant axial load was applied for mixed
structures to handle the stress occurring
during an earthquake, and then an anti-symmetrical positive/negative alternating cyclic shear load was applied toboth ends of the beam. Fig. 8 shows thetest results obtained so far.
In the test, the design was made sothat attainment to the ultimate strength
by column-beam connection precedesthat by column and beam in each ofthese two specimens. One difference
between these two specimens is whether
or not the vertical stiffener is arrangedon the column-beam connection. Whileboth specimens show excellent hysteresis loop in seismic resistance, the diagonal-direction concrete compression

Fig. 5 Concrete-confined Effect of Octagonal-section
SC Column Member 4)
CH-200x80x4.5x4.5

N (kN)

1000

c

Test

800
600

Analysis(Confined effect)

400
Plain
concrete20000δ (mm)

2

4

6

8

10

Fig. 6 Relationship between Shear Strength and Rotation Angle of Octagonal-section SC Column Member4)
Compressive strengthof concrete 30 N/mm2

CH-190x60x4.5x6n

300 Q (kN)
200

0.3

AnalysisCH-190x100x2.3x2.3

Mechanism line

Q (kN)

300

Mechanism line

300 Q (kN)

Analysis

200

200

100

100

100

0

0

0

-100

-100

-100

-200
-300
-6

300
200
100
0.6

CH-190x100x4.5x6

Test
-4

-2

0

Q (kN)

2

R (%)
4

6

-200
-300

200

Analysis

100
0

-100

-100

-200

Test
-4

-2

-6

0

2

R (%)
4

3 Steel Construction Today & Tomorrow December 2018

-4

-2

0

300 Q (kN)

Mechanism line

0

-300
-6

Test R (%)

6

4

6

Test

-200
-300
-6

-4

-2

0

Q

Mechanism line

Analysis

R

-200
-300
-6

2

Mechanism line

Analysis

Test
-4

-2

0

2

R (%)
4

6

Q

2

R (%)
4

6

strut is likely to form in the connection
panel due to the arrangement of the vertical stiffener, and as a result the shear
strength of the connection slightly increases. Further, it has become possible
to confirm the effect of vertical stiffener arrangement on the suppression ofshear deformation in connections6).
In the installation of octagonal-section SC columns, reinforcing bar arrangement is not required in terms of
construction, and steel-frame flanges
can be used as the concrete form, whichis considered to lead to simplified construction work. For octagonal-section
SC columns, plain concrete is planned
to be applied, and the high-level quality
control required for the concrete used
for CFT structures is not required. To
that end, we are examining the appli-

cation of octagonal-section SC columns
in the construction of low- and medium-rise buildings.
High Expectations for Octagonal-section SC Columns
The trend in studies of steel-concrete
composite structures in Japan has been
analyzed based on the reference literature2), the results of which are introduced above. The development ofstudies is proceeding for new octagonal-section SC columns and octagonal
column-steel frame mixed structuresthat are expected to not only allow for
both manpower and labor savings but
also offer enhanced structural performance. Their structural behavior is also introduced above. ￭Fig. 7 Column-Beam Connection of Mixed Structure Composed of
Octagonal-section SC Column and Steel-frame BeamSC column
Vertical stiffener

Vertical stiffener
Steel beam

External diaphragm

References
1) AIJ: Teaching materials for structure, 2014.3
2) AIJ: Summaries of Technical Papersof Annual Meeting, Vol. Structure
III, pp. 1345-1548，2018.08. (inJapanese)3) Teruhisa Tanaka and Junichi Sakai:
Development of a new shear connector using burring steel plate, Research, Development, and Practicein Structural Engineering and Construction, ASEA-SEC-1, Perth, November 28–December 2, 2012．
4) Yo Kuratomi, Junichi Sakai, Teruhisa Tanaka and Kensuke Kawahara:
An analytical study on elastic-plastic behavior of steel and concrete
composite columns with cruciform
steel sections，Proceedings of the Japan Concrete Institute, pp.1039-1044,
2014.7. (in Japanese)5) Yo Kuratomi, Junichi Sakai, Teruhisa Tanaka and Daiki Fuchigami: Structural performance of steel
beam to steel and concrete composite column joints with band
plates，Proceedings of the Japan
Concrete Institute, pp. 1057-1062,
2017.7. (in Japanese)
6) Yo Kuratomi, Junichi Sakai, Teruhisa Tanaka and Daiki Fuchigami:
An experimental study on elasticplastic behavior of mixed structures
composed of SC columns and steel
beams, Proceedings of the Japan
Concrete Institute, pp. 1117-1122,
2018.7. (in Japanese)

Fig. 8 Relationship between Load and Deformation of Column-Beam Connection
Composed of Octagonal-section SC Column and Steel-frame Beam6)

Beam end load
P (kN)
100

Beam end load
P (kN)
100

P

75

b u

P
j u

50

P'

25
0

0
-25

-75
-100

Rotaition angle R (%)
-6

-4

-2

0

2

(a) With vertical stiffener

4

6

-j Pu

-50

-bPu

-75
-100

P

j u

50

-25

-j Pu'

b u

P'

25

j u

-50

P

75

j u

-j Pu'

Rotaition angle R (%)
-6

-4

-2

0

2

4

-j Pu

-bPu

6

(b) No vertival stiffener
December 2018 Steel Construction Today & Tomorrow 4

Feature Articles: Steel-Concrete Composite Structures (2)Current State of Studies and Research
on CFT Structures

by Keigo Tsuda, Emeritus Professor, and Masae Kido, Associate Professor
The University of Kitakyushu
Keigo Tsuda: After finishing the mastercourse at the Graduate School of Kyushu University, he served as research
assistant of Kyushu University in 1977
and then as associate professor of Kyushu University. He became professorof the University of Kitakyushu in 2001
and emeritus professor in 2018.

Concrete-filled steel tube (CFT) structures are a kind of steel-concrete composite structure. They feature highstructural performance such as highload-carrying capacity and high deformation capacity. In Japan, their application started in the latter part of the
1950s, and CTT structures have widely
been used in the construction of a number of high-rise office buildings.
The first study report of CFT structures submitted in Japan was the “Experiment and analytical study onbuckling loads of CFT compressive
members” prepared by Prof. Shizuo
Ban and others in 1956. Then in 1961,
a similar report was submitted: “Experiment and analytical study on the centrically loaded CFT slender columns” by
Prof. Takeo Naka, Prof. Ben Kato andothers. In 1981, Prof. Kenji Sakino reported a doctoral dissertation on CFT
structures, a first of its kind in Japan.
In the “Project to Develop New Urban-type Multiple Dwelling Housing
System” promoted for five years startingfrom 1985 by the Ministry of Construction, the CFT structure was adopted asa structural system for high-rise apart-

ment housing. In this regard, an experimental study on beam-column members
was conducted to evaluate the performance of the structural system thus
adopted. Further, in “Composite andHybrid Structures,” a U.S.-Japan Cooperative Earthquake Engineering Research promoted over five years startingfrom 1993, the CFT working group wasestablished, and experimental researchon the column members and beam-tocolumn connections of CFT structures
was promoted by widely changing thestrength of materials and the widththickness ratio and diameter-thickness
ratio of steel tubes.
The recent trends in research andstudies on CFT structures are introduced in the following:
Design Guidelines and Application Ranges
Two latest versions of the design guidelines for CFT structures have been published in Japan-Recommendations for
Design and Construction of Concrete
Filled Steel Tubular Structures (2008)by the Architectural Institute of Japan (AIJ) and Technical Standards andCompressive strength of concrete*

18〜90 N/mm

Tensile strength of steel*

Smaller than 590 N/mm2

Yield stress of steel*235〜440 N/mm2

Ratio of limiting value of width (diameter) to thickness

1.5 times of AIJ steel standard* AIJ Recommendations

5 Steel Construction Today & Tomorrow December 2018

Commentaries for Concrete Filled Steel
Tubular Structures (2012) by the Association of New Urban Housing Technology. In addition, the Guidebook on Design of Concrete Filled Steel Tubular
Structures for use for young designers
and university students has also been
published by the Architectural Instituteof Japan.
The application range of material
strengths for CFT structures specified
in the AIJ’s Recommendations for Design and Construction is set at 18~90
N/mm2 for the compressive strength of
concrete, 590 N/mm2 or lower for thetensile strength of steel, and 235~440
N/mm2 for the yield stress of steel tubes(Table 1). The standard section of CFT
columns is set to be square and circular (Fig. 1). In addition, experimental
studies are being promoted on the application of rectangular CFT columns
and the strength and deformation capacity of reinforced-type CFT columns inwhich steel reinforcing bars are built-in
into the steel tube.

Fig. 1 Cross Sections of CFT Columns

Table 1 Requirements for CFT Structures

Ratio of buckling length to section depth

Masae Kido: After finishing thedoctoral program at the Graduate
School of the University of Kitakyushu, she became lecturer of the
University of Kitakyushu in 2007.
She assumed her current positionas associate professor of the University of Kitakyushu in 2012.

2

Not longer than 50 for columns
Not longer than 30 for beam-columns

SquareCircular

RectangularFig. 2 Range of Short, Intermediate
and Slender Columns
Short

Nu

Intermediate
Buckling strength

Slender column

0

4
12
lk/D
Buckling length - section depth ratio

Fig. 3 Column Strength Curves

Buckling strength

AIJ CFT Recommendations2c B =150 N/mm

10000

120

8000

90
60
36

6000
4000
2000
0
0

lk/D=30

0.5

1• Ultimate Strength of Columns
Subjected to Axial Load andFlexural Shear Stress
For columns subjected to both compressive strength and flexural shear stress, thecurrent AIJ’s Recommendations shows
design equations for each of three different types of columns-short, intermediate and slender, as in the case of the design of compressive members. Presently,
as with compressive members, the range
in which the full plastic moment of column sections can be expected to display
in terms of the relation with the normalized slenderness ratio of steel tube column λc, the axial load ratio of column ny
and the member end bending moment ratioκis being examined using Fig. 4 as ananalytical model.
That is, in the relational equation ofFig. 4 Loading Conditions andMoment Diagrams

Proposed column strength

12000 Ncr (kN)

dicator and is based on strength cumulatively added with the buckling strengthof both steel and concrete columns withno distinction as short, intermediate andslender columns.
Fig. 3 shows a comparison between
the column strength thus proposed andthe compressive strength calculated using the AIJ’s Recommendations. In the
figure, sσy is the yield stress of the steel
tube and cσB the compressive strength of
concrete. As shown in Fig. 3, the proposed strength cumulatively added withthe buckling strength of both steel andconcrete columns well agrees with thebuckling strength calculated using AIJ’s
Recommendations in all ranges of normalized slenderness ratios even when the
distinction as short, intermediate or slender columns is not applied1).

M2
= M1

c

Fig. 5 Column Strength Curves
1.2

Normalized slenderness ratio of steel column

ny

=0

1

FP

D

N

M1

Mm
(Mmax)

M1(M1max)2s y =325 N/mm

=0.05
0.1

0.8

Column section

2• Studies on Long-period Seismic
Motions
There are concerns about the effect of agreat earthquake occurring with the Nankai Trough as an epicentral region on
high-rise buildings with a long natural
period. Studies on CFT columns to treat
long-period seismic motions are currently being promoted. In the Building Standard Maintenance Promotion Projectof the Ministry of Land, Infrastructure,
Transport and Tourism, examinations
were made of the method to verify thesafety of CFT columns against long-period seismic motions in 20132), in whichtests were made pertaining to the casewhere CFT columns are subjected toconstant displacement amplitude cyclic

M2 = M 1tlk/D=50

0.05 or lower, it can be understood fromthe correlation between the bending moment and the axial load vis-à-vis the
maximum strength of columns shown in
Fig. 5 that the full plastic moment of the
CFT column section can be expected tocome into play. Currently, the method toevaluate the column strength in the range
in which the full plastic moment of thecolumn section cannot be expected is being examined.
As regards the square CFT columns
causing shear fracture, there are cases in which fractures occur in the caseof a shear span ratio=1 or lower, but it
has been known that the square CFT column’s hysteresis characteristic for shear
fracture is not inferior to the performancein the case of bending fracture. Currently, study is underway on the shear fracture of circular CFT columns.

N

D =250 mm
t =12 mm
D/t =20.8
2s y =325 N/mm

1.5ny・λc2=α(1+κ), when the value of α is

Axial load

Recent Trends in Studies on CFTColumn Members• Ultimate Strength of Columns
Subjected to Axial Loads
In the currently-prevailing AIJ’s Recommendations for Design and Constructionof Concrete Filled Steel Tubular Structures, as shown in Fig. 2, the slenderness
parameter of columns subjected to compressive force is examined by selecting
the ratio lk/D of the effective length lk tothe section depth D, and where the ratio
is lk/D=4 or lower, columns within thisratio are defined as short columns, where
the ratio is lk/D=more than 4~12 or lower as intermediate columns, and where
the ratio is lk/D=more than 12 as slender columns, and the design equation ischanged depending on the ratio lk/D selected.
As of now, as the compressive
strength evaluation equation for CFT
columns, the design equation is proposedthat takes the normalized slenderness ratio of steel columns as the slenderness in-c B =90 N/mm

2

0.15
0.2

0.6
0.3

0.4

0.25

0.2
0

0

0.2

0.4

0.6

0.8

1

Flexural strength

1.2

1.4

M1max/Mp

December 2018 Steel Construction Today & Tomorrow 6

loading under constant or variable axial
loads. In addition, based on the capacity obtained from member tests, a procedure has been proposed that evaluates
CFT column damage employing seismic
response analysis.
Meanwhile, there is high demand toaccumulate test data. To meet such a demand, in 2015 the Building Committee of the Japan Iron and Steel Federation entrusted to the Japanese Societyof Steel Construction the study on longterm seismic motion, in which the Working Group on Survey and Study on Retained Performance of Column Members
against Long-period Seismic Motions
was established to promote a three-year
study from 2015 to 2017.
As a link with the three-year study, we
conducted a number of tests on CFT columns subjected to constant displacement

amplitude cyclic loading under constantaxial loads by setting as the experimental variable the ratio of effective length tosection depth lk/D, the axial load ratio ny,
the displacement amplitude (rotation angle) R0, and the sectional shape (square,
circular)3). Examples of test results thus
far obtained are introduced below:
Tests were carried out under the load-

Fig. 6 Loading Conditions

NL

ing condition shown in Fig. 6. Photo 1
shows the CFT column loading apparatus. Fig. 7 shows the relationship between the lateral load and the rotation
angle in the following three cases at lk/
D=14: axial load ratio =0.15 and rotation
angle=1.5%; axial load ratio =0.3 and rotation angle=1.5%; and axial load ratio=0.6 and rotation angle=1%. The figure

Specimen

Axial force

Q

Lateral force

R=( /L)

Photo 1 CFT column loading apparatus

Dimensionless lateral force Q /Q pc

Dimensionless lateral force Q /Q pc

Fig. 7 Relationship between Lateral Load and Rotation Angle
1.5
1
0.5

CFT ny=0.15
R0=1.5% Initialstiffness
l k/D=14

0

Plastic collapse
Mechanism line

-1.5
-3

Steel tube yield
LD14n15R15
Maximum strength

200 cycles

-2
-1
0
1
2
3
Dimensionless rotation angle R/Rpc
ny=0.15, R0=1.5%

CFT ny=0.3
R0=1.5%lk/D=141

0.5

LD14n30R15

-0.5

-0.5

-2
-1
0
1
2
3
Dimensionless rotation angle R/Rpc
ny=0.15, R0=1.5%

7 Steel Construction Today & Tomorrow December 2018

-1

0

1

2

ny=0.3, R0=1.5%

0.5

145 cycles

-2

3
R/Rpc

Q/Qpc

1

S-LD14n15R15

60 cycles

-1.5
-3

0

CFT ny=0.6
R0=1%
lk/D=14

0

-1

0

Q/Qpc

1

0

1.5

Steel ny=0.15
R1
0=1.5%
lk/D=14
0.5

-1.5
-3

1.5

-0.5

1.5

-1

Q/Qpc

0.5

-0.5
-1

1.5

LD14n60R1

-1
-1.5
-3

11 cycles
-2

-1

0

1

2

ny=0.6, R0=1%

3
R/Rpc

1.5 Q/Qpc

Steel ny=0.3
R0=1.5%lk/D=141
0.5

Steel ny=0.6
R0=1%
lk/D=140-0.5

LD14n30R15

-1
-1.5
-3

-0.5

28 cycles
-2

-1

0

1

ny=0.3, R0=1.5%

2

3
R/Rpc

S-LD14n60R1

-1
-1.5
-3

10 cycles
-2

-1

0

1

ny=0.6, R0=1%

2

3
R/Rpc

also shows the case of tests made for hollow steel tube columns. Fig. 8 shows thetrend of lateral loads (Q0i/Qmax) at the rotation turning point and the trend of axial strain (εv%). Photo 2 shows the column base after testing. As the axial load
ratio and the displacement amplitude become large, the reduction of the load becomes large. The future plan calls for the
proposition of a method to evaluate thestrength deterioration performance of
CFT columns.

pected to demonstrate high impact resistance, a method to quantitatively
evaluate impact resistance has been developed4).
• CFT Columns Employing Super
High-strength Steel
Tests for CFT column members produced employing super high-strength
steel products with tensile strength ratings of 800~1,000 N/mm2 are underway.
In the manufacture of weld built-up box
column members, because strict welding
conditions are imposed on over-matching welding, studies of CFT members
built up by means of under-matchingwelding are currently being promoted.

• Studies on Impact ResistanceIn the Great East Japan Earthquakethat occurred in 2011, building damage
caused by tsunamis posed a lot of concern. Because CFT columns can be ex-

CFT

n=0.15, R0=1.5%

Steel

n=0.3, R0=1.5%
n=0.6, R0=1%

Axial strain v (%)

lk/D=14 positive side
3
2.5

0.8

2
1.5
1

n=0.3, R=1.5%
n=0.6, R=1%

Steel

0.5

0.2

0

0.7
0.6

0.5
0

1

CFT n=0.15, R=1.5% 0.9

50

100

0.4
150
CyclesLateral load Q0i /Qmax

Fig. 8 Relationship between the Axial Strain,
Lateral Load and the Number of Cycles

Development of CFT Structures with Higher Structural Performance
It is expected that a structural
performance evaluation methodwith high precision will be established for CFT columns that
not only are produced employing high-strength steel members
beyond the application range ofcurrently-prevailing design standards but also include slendercolumns having diverse sectional configurations. We expect further development of CFT struc-tures that will offer higher structural
performance. ￭References
1) Masae Kido, Keigo Tsuda, Masayuki
Haraguchi: Evaluation of strength of
concrete filled steel tubular columns
with flexural buckling, J. Struct. Constr. Eng., AIJ. Vol. 82 No. 735, pp.753763, 2017.5 (in Japanese)2) Narihara Hiroyuki et. al: Study on safety assessment methods for super-highrise steel buildings against long-period
earthquake ground motions, Part 2733, Summaries of Technical Paper ofAnnual Meeting, Architectural Instituteof Japan C-III, pp.1251-1264，2014.9(in Japanese)
3) Masae Kido, Toshiyuki Fukumoto, Keigo Tsuda, Yasuo Ichinohe, Koji Morita:
Study on the Strength and cyclic rotation
capacity of CFT beam-columns against
long duration earthquake, Steel Construction Engineering, Vol. 24 No.94,
pp.49-64, 2017.6 (in Japanese)
4) Akihiko Kawano, Hiromitsu Kawaguchi:
Development of an evaluation method
for impact resistant capacity of concrete
filled tubular members against tsunami flotsam collision, J. Struct. Constr.
Eng., AIJ. Vol. 80 No. 715, pp,14971503, 2015.9 (in Japanese)CFT

ny=0.15, R0=1.5%

ny=0.3, R0=1.5%

ny=0.6, R0=1%

Steel

ny=0.15, R0=1.5%

ny=0.3, R0=1.5%

ny=0.6, R0=1%

Photo 2 Column bases after testing
December 2018 Steel Construction Today & Tomorrow 8

Feature Articles: Steel-Concrete Composite Structures (3)Potential of Exterior Diaphragm-type
Column to Beam Connections

by Tsuyoshi Tanaka
Professor, Kobe University

Exterior Diaphragm-type Column
to Beam Connections
Among the methods to connect square or
circular steel tube columns and H-shapebeams is the exterior diaphragm connection method, which is shown in Fig. 1.
In the exterior diaphragm-type column
to beam connection, the diaphragm is
not arranged inside the closed-section
column, but it is arranged as it protrudes
over the outer periphery of the column

Tsuyoshi Tanaka: After receiving master’s degree at
the Graduate School of Engineering, Kobe University,
he entered Asanuma Corporation in 1985. He became
associate professor at the Kobe University in 1999. Heassumed his current position as professor at the Architecture, Faculty of Engineering of Kobe University in2010. His specialized field covers structural engineering and steel structures.

so as to function to transfer the bending
stress of the beam to the column.
In a through diaphragm-type connection, it is necessary to cut the column at
the connecting position and weld-join
it. On the other hand, in an exterior diaphragm-type connection, because it is acolumn penetration type, an application
advantage is brought about in which column fabrication is not required.
Meanwhile, in exterior diaphragm-

Fig. 1 Column to Beam Connection Stiffened by Exterior Diaphragms(a) Circular hollow section (CHS) column(b) Concrete-filled steel tube (CFT ) column

Fig. 2 Local Deformation at Column to Beam Connection(a) CHS column

9 Steel Construction Today & Tomorrow December 2018(b) CFT column

type connections, local deformation(out-of-plane deformation of steel tubewall) occurs at the connections as shownin Fig. 2, and accordingly, in order to secure stiffness and strength of connection,
it is necessary to design the details of the
shape and dimensions of diaphragms.
Further, in through diaphragm-typeconnections, it is possible to perform
all full penetration welding operations
for connections by means of flat position welding, but in exterior diaphragmtype connections, because the welding is
performed under conditions in which thecolumn is aligned horizontally in common practice, it is necessary to performweld-joining of not only column and diaphragm but also diaphragm and beamflange by means of horizontal position
welding. Furthermore, as the depth ofdiaphragm increases, there are cases inwhich the attachment of exterior members and the securing of piping space arehindered.
Due to these demerits, through diaphragm-type connections have been adopted extensively in Japan, and currently
the application of exterior diaphragmtype connections to practical projects has
been limited.
Higher Strength of Columns andWelding Operations
Recently, high-strength steel products
are increasingly been adopted in largescale building construction projects. In
addition, super high-strength steel products with a tensile strength rating of 780
N/mm2 (H-SA700) have been developed
and their practical application has started.
Higher-strength steel products not only keep up with the trend towards theconstruction of higher-rise and longerspan buildings but also enhance free-Structural Tests• Test Specimens

The test specimens were prepared byjoining circular steel tube columns (○300×12) manufactured by press-forming 780 N/mm2-grade steel plates (HSA700) with 490 N/mm2-grade H-shapebeams (H-400×150×9×16, SN490B)
by the use of exterior diaphragms, on
which the tests were conducted. Examples of the tests conducted are introduced
below:
Fig. 3 shows the structure of column
to beam connection specimen. The depthof the diaphragm (SN490B) is hd =50mm, and the plate thickness td =16 mm.
Welding of diaphragms and steel tubes
adopted in the test is by grooved fillet welding with a bevel angle of 60°as

shown in the figure, and diaphragm andsteel tube were weld-joined by means of
CO2 gas shielded arc welding employing
welding wire (YGW18) for use for 490
N/mm2-grade steel.
The tests were conducted for two cases using two specimens: a circular hollow section (CHS) steel tube specimen(TD-16/H) and a concrete-filled steel
tube (CFT) specimen (TD-16/C). The
design standard strength of filling concrete was set at Fc24, and crushed stone
with a maximum size of 20 mm was used
for the coarse aggregate.

• Loading and Measurement

Methods
As shown in Fig. 4, one end of the circular column is joined to the pin jig, andFig. 3 Test Specimen (unit: mm)

16

400
50

12
300

12
300

dom in design. It is expected that higher-strength steel products will contributetowards the creation of affluent architectural spaces and structure that suffers
less damage during major earthquakes.
In particular, application of 780 N/
mm2-grade steel products for steel columns in building construction brings
about considerable merits. However,when examining the wider applicationof 780 N/mm2-grade steel products, weld
performance and welding operation are
obstacles to its wider application. Guaranteeing the preparation of over-matching weld joints for 780 N/mm2-gradesteel products poses problems such as
extreme difficulty in construction andleads directly to high construction costs.
When steel products with a tensile
strength of 780 N/mm2 are used for columns and those of 590 N/mm2 or lower
are used for beams and diaphragms, andfurther, when the connection is preparedby the use of exterior diaphragms, it becomes unnecessary to weld columns in
the preparation of column to beam connections.
Currently in Japan, triggered by ashortage of welders, development of various kinds of robotic welding methods is
actively being promoted for use for weldjoining of columns and diaphragms, andas a result, the horizontal position welding of columns and diaphragms by robotics welding is becoming available. To
that end, there is a fair possibility of effectively handling tasks involved in thetrend for higher strength of columns by
the optimum use of exterior diaphragmtype connections.

S=11

16
16

150

400

Fig. 4 Specimen and Test Setup

CFT Columns and Local Deformation
As explained above, because local deformation occurs in exterior diaphragmtype connections, there are cases inwhich column to beam connections prepared by the use of exterior diaphragms
are not accepted as a rigid connection.
While local strength is improved by theuse of super high-strength steel, local
stiffness is not improved. In exterior diaphragm-type connections, diaphragms
are not arranged inside the steel tube
column, and thus concrete can easily befilled inside the column. Accordingly,
suppression of local deformation in column to beam connections can be expected by the use of concrete-filled steel tube
(CFT) columns.

December 2018 Steel Construction Today & Tomorrow 10

another end to the pin roller jig, to which
positive/negative increment cyclic loading is applied using the hydraulic oil jackinstalled on the beam end.
The displacement transducers arearranged in the vicinity of the connection to measure local deformation Lθ,beam deformation Bθ and total deformation Tθ(=Lθ+Bθ) including both thelocal and beam deformations shown in
Fig. 5.
The loading cycle is set at ±Bθp,±2Bθp, ±4Bθp, ±6Bθp and ±8Bθp for Tθ
by setting as the standard the elastic
deformation angle Bθp that corresponds
to the beam’s full plastic strength B Pp,
and the cyclic loading mentioned
above is twice applied to the specimen
respectively.

• Test Results
Fig. 6 shows the relationship between
the beam end load P of two specimens
and Tθ, Lθ and Bθ. The broken line in

the figure shows the calculated valueof the beam’s elastic stiffness and thefull plastic strength BPp. The progressof the test for each of two specimens is
as shown below:
In the specimen TD-16/H of the circular hollow section (CHS) steel tube
column, local yielding preceded, but
along with the increase in the load applied, plasticization of beam became
clear at the loading cycle of ±4Bθp.
At the cycle of ±2Bθp, ductile crack-

Fig. 5 Total Beam Deformation Tθ, Local Deformation Lθ andBeam Deformation Bθ

Fig. 6 Load-Deformation Curves(a) CHS column(b) CFT column(1) T θ11 Steel Construction Today & Tomorrow December 2018

(2)Lθ(3) Bθ

ing occurred at the internal corner section, and at the first cycle of ‒­6 Bθp, asshown in Fig. 7, this cracking developed diagonally to the diaphragm side
to cause a reduction in load-carrying
performance.
In the specimen TD-16/C of theconcrete-filled steel tube (CFT) column, local yielding and beam yielding
simultaneously occurred at the loading
cycle of ±2 Bθp, but since then the plastic deformation of beam steadily ex-celled. At the cycle of ±4 Bθp, ductile
cracking occurred at the internal corner section, and at the first cycle of ‒8
Bθp, after this cracking developed diagonally to the diaphragm side, diaphragm caused a fracture. Meanwhile,
local buckling of the beam was observed at the cycle of ±4Bθp.
When comparing deformation between TD-16/H and TD-16/C, local
stiffness of TD-16/C was increased byfilling concrete by 1.7 times, and it isFig. 7 Fracture of Diaphragmknown that plasticization of the beam
was promoted.
Fig. 8 shows the positive-side skeleton curve in the case in which the P－
Tθ relationship is made dimensionlessusing BPp and Bθp. The elastic stiffness in the P－Tθ relationship reaches a level that falls short of the case ofbeam end rigid connection by 12% due
to concrete filling, and as a result it is
known that elasto-plastic behavior andplastic deformation capacity nearly
similar to those of the beam-collapse
type can be obtained for rigid connection framing.
Potential Exterior Diaphragmtype CFT Column to Beam
Connections
Exterior diaphragm-type connections
are the traditional connection system.
This type of connection can offer effective solutions in the application ofsteel tube columns manufactured using
super high-strength steel products. In
cases when the development and diffusion of robotics flat-position welding
will be promoted in the future, I consider it rational to choose exterior diaphragms for column to beam connections. ￭Fig. 8 Skelton Curves
1.8

P/B PpTD-16/C

1.6
1.4
1.2
1

TD-16/H

0.8

:P
:P

0.6

e

0.4

p

max

0.2
T

0

0

2

4

6

8

/ p
10

December 2018 Steel Construction Today & Tomorrow 12

Feature Articles: Steel-Concrete Composite Structures (4)Steel Tubes for Building and CFT
Structures

Committee on Overseas Market Promotion, The Japan Iron and Steel Federation
BCR and BCP Standards for Coldformed Square Steel Tubes
Cold-formed square steel tubes are usedmainly as columns in steel-frame building structures in Japan and are one of themost popular steel products for building columns. The manufacturing process
takes either of two forms: roll forming(BCR) and press forming (BCP). Fig. 1
shows the manufacturing process.
Neither BCP nor BCR standards are
established in the JIS (Japanese Industrial Standards), but listed in MDCR (standards for steel products for construction)
established by the Japan Iron and SteelFederation. The steel products specified
in these standards are structural members
approved by the Ministry of Land, Infrastructure, Transport and Tourism of Japan.
The available size range is 200×6
mm~550×25 mm for BCR and 200×6

ly, and their mechanical properties suchas yield point are the same as those in the
JIS SN standard (rolled steels for building structures). Charpy absorption energy is specified at 27J or more at 0ºC for

mm~1,000×40 mm for BCP.
Chemical composition is shown in Table 1. Mechanical properties are shownin Table 2. BCP235 and BCP325 correspond to SN400 and SN490 respective-（%）

Table 1 Chemcal Composition of BCR and BCP Materials
SymbolThickness
mm
Min/Max

C
Max

Si
Mn
P
Max Min/Max Max

S
Max

N1)
Max

Ceq2)
Max

Pcm3)
Max

MDCR0002BCR295
2017

6/22

0.20

0.35

/1.40

0.030

0.015 0.0062)

0.36

0.26

6/40

0.20

0.35

0.60
/1.40

0.030

0.015 0.0062)

0.36

0.26

6/40

0.18

0.55

/1.60

0.030

0.015 0.0062)

0.44

0.29

6/40

0.18

0.55

/1.60

0.020

0.005 0.0062)

0.44

0.29

Type
Material
designation standard

400 N/mm
BCP235
grade MDCR00032017
BCP3252490 N/mm MDCR0012BCP325T
grade
2014
2

Notes:1) In case when elements to fix N, such as Al, are added and inclusion of solid-solution type N is
0.006% or below, total inclusion of N can be increased up to 0.009%.
2) Ceq = C+Mn/6+Si/24+Ni/40+Cr/5+Mo/4+V/14
3) Pcm = C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B; Applied in place of Ceq
according to the agreement between supplier and purchaser.

Table 2 Mechanical Properties of BCR and BCP Materials
Typedesignation

Material
standard

SymbolThickness
mm
Min/Max

Yield point or strength
N/mm2) Min/Max
t<12 mm12≤t

Tensilestrength
Min/Max

Yield ratio %Max

Elongation %Min

t<12 mm12≤tt≤16 mm16<tCharpy impact
test; Absorbed
energyJ Min (0℃)

MDCR0002BCR295
2017

6/22

295/

295/445400/550

-

90

231)

271)

272)

BCP2356/40

235/

235/355

400/510

-

80

18

22

272)

BCP3256/40

325/

335/445490/610

-

80

17

21

272)

490 N/mm2 MDCR0012BCP325T
grade
2014

6/40

325/

335/445490/610

-

80

17

21

702), 3)400 N/mm2
grade

MDCR00032017

Notes:1) JIS No.5 test piece (tube axial direction): No.1A test piece for others2) Applied for wall thicknesses of over 12 mm and average value of 3 test pieces
3) Applied for both plain/corner parts

Fig. 1 Manufacturing Process for BCR and BCP Materials
Leveler
Slit coil

Shear Coil-to-coil Looper
weld-joining

FormingHigh-frequency
Non-destructive
welderinspection
OilingCutting
Flyingcutting-off

Bundling
Roll-forming method (BCR)

13 Steel Construction Today & Tomorrow December 2018

Beveling

FusingRemoval of Sizing
Marking
weld beadCutting/End
facing

Temporary assembly
Inner welding

Pressing

Outer welding

Inspection

Straightening
Press-forming method (BCP)

wall thicknesses exceeding 12 mm, thesame as in the SN standard.
BCP325T, which secures toughness inthe bent corners of steel tubes in the BCP
standard and allows the same treatment asthat in the SN standard, has recently been
approved by the Ministry of Land, Infrastructure, Transport and Tourism of Japan.
Steel Plates for Weld Built-up Box
Columns
Built-up box columns weld-assembled
from steel plates have been used for concrete-filled steel tube (CFT) structures(Fig. 2) in Japan, which are applied in
the construction of high-rise buildings
because the sectional size of columns islarge and exceeds the production rangeof BCP or BCR. Table 3 shows the mechanical properties of steel plates forbuilding structures.

High-strength steel plates in steel
grades, 780 N/mm2 (H-SA700) and 590
N/mm2 (SA440), were jointly developed
by JISF member companies. The material standards for these products were
established by the Japan Iron and SteelFederation and enlisted in the standards
H-SA700 and SA440 respectively. Table
4 shows chemical composition of thesesteel plates. The carbon equivalent (Ceq)
is suppressed to a low level to ensure favorable weldability even for the maximum plate thickness of 100 mm.
Especially for SA440, its upper andlower limits for yield strength and tensile strength are specified within a narrow range, and further its yield ratio is
specified at max. 80%. Thus, SA440 satisfies a higher level of performance requirements that are essential in securing
the seismic resistance of buildings. On

Fig. 2 Concrete-filled Steel Tube (CFT)Square Column Structure

the other hand, rather higher yield ratiois specified for H-SA700, and thus it isincorporated in the special design guideline that requires for H-SA700 to be fully in an elastic state even subjected to severe seismic thrusts. ￭Table 3 Mechanical Properties of Steel Plates for CFTs
Designation

Yield point or
proof stress

Thickness(mm)
Min/Max

Thickness(mm)(N/mm2)
Min/Max

Tensilestrength(N/mm2)
Min/Max

Yield ratio(%)
Max

Tensile test
Thickness(mm)
6≤t≤20

H-SA700A

6/50-

700/900

780/100098

H-SA700B

6/50-

700/900

780/1000

98

SA440-B
Grade 60

19/100-440/540590/740

80

SA440-C
Grade 60

19/100-440/540590/74080

SN490B(Grade 50)

6/100

t<12
12≤t≤4040<t325/
325/455
295/415490/61080SN490C(Grade 50)

16/100-325/455

490/61080Impact test
CharpyTestabsorbedtemp.
Test
energy (J)specimen (°C)
Min
No.5
0
No.4
471)
No.5
No.5
471)
-20
No.4
No.5

Elongation

20≤t≤506≤t≤2020≤t≤50

(%)
16
16
24
16
16
24

t≤50
40<t

20
26

No.4
No.5

6≤t≤1616<t≤50
40<t

17
21
23

No.1A
No.1A
No.4

Through-thickness
tensile test (%) min
Ave. of3 tests

Each
value

-

-

-

-

0

471)

-

-

0

471)

25

15

0

271)

-

-

0

271)

25

15

Note:1) Applied for wall thicknesses of over 12 mm and average value of 3 test pieces

Table 4 Chemical Composition of Steel Plates for CFTs
Thickness
Designation(mm)
Min/MaxC(unit: wt%)

Si

Mn

P

S

Thickness
(mm)

Max

Min/
Max

Max

Max

Max

Ceq1) Maxt≤40

40<t≤50Pcm2) Max
50<t

t≤40

H-SA700A
H-SA700B

6/50
6/50

-

0.25
0.25

/0.55
/0.55

2.00
2.00

0.030
0.025

0.015
0.015

SA440-B
Grade 60

19/100

-

0.18

/0.55

1.60

0.030

0.008

0.44

0.47

0.28

0.30

SA440-C
Grade 60

19/100

-

0.18

/0.55

1.60

0.020

0.008

0.44

0.47

0.28

0.30

SN490B(Grade 50)

6/100

t≤50
50<t

0.18
0.20

/0.55

1.60

0.030

0.015

0.44

0.46

0.29

/0.55

1.60

0.020

0.008

0.44

0.46

0.29

SN490C
16/100(Grade 50)

0.65
0.60

40<t≤50

50<t

0.32
0.30

Notes:1) Ceq = C+Mn/6+Si/24+Ni/40+Cr/5+Mo/4+V/14
2) Pcm = C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B; Applied in place of Ceq according to the agreement between supplier and purchaser.
December 2018 Steel Construction Today & Tomorrow 14

Serial Article: Latest Design of Steel Buildings in Japan (3)HIRAKATA T-SITE-Protruding Box Structures Form
Expressive Façade and Improve
Seismic ResistanceTakenaka Corporation
The HIRAKATA T-SITE is a proposal-type commercial facility with a combination of floors with diverse kindsof themes, centering on books. It was
opened in 2017 in front of the Hirakata
Station in Osaka. Its outstanding structural feature is a glass curtainwall thatwidely opens to the streets and a building appearance that is composed of protruding box construction. A comfortableatrium spreads within the building. (Photo 1)
A variety of advanced devices havebeen incorporated in order to realize thisopen space and to enhance the structural
strength, among which are the corrugat-

ed steel plate seismic-resistant walls andthe seismic-resistant box structure. The
structural outline of the HIRAKATA TSITE is introduced in the following:
Towards the Creation of a Relaxing Community Living Room
The HIRAKATA T-SITE was constructed on a site that is located adjacent toa railway station, and is a typical “railway station neighborhood project.” In
the commercial facilities provided in thebuilding of conventional “railway stationneighborhood redevelopment projects,”
these facilities are behind the commercial facilities in urban centers in terms of
PHOTO: ATSUSHI NAKAMICHI

Photo 1 HIRAKATA T-SITE featuring protruding box structures
15 Steel Construction Today & Tomorrow December 2018

product line-up, and further in terms ofdaily life, their convenience is far inferior to that of mass merchandise outlets
and family restaurants operating along
major roads. In spite of good access offered by the “railway station neighborhood project” in which many persons
pass by as they travel to offices andschools, the attractiveness as a commercial area had been fading.
Under these circumstances, it was required to realize a commercial facility
with living value in front of Hirakata Station in which the book street of Tsutaya
Books that attracts attention in the DAIKANYAMA T-SITE in Tokyo is posiProject Outline of HIRAKATA T-SITE
Location: Okahigashicho, Hirakata, Osaka
Project owner: SO-TWO Inc. (representative
land owner)
Main applications: Shops, restaurants, banks,
parking lots
Area: Site area 2,723.59 m2; Building area
2,494.07 m2; Total floor area 17,533.44 m2
Structure: Steel, partly SRC
No. of story: 1 basement, 9 stories aboveground
Maximum height: 39,830 mm
Architecture, interior: Takenaka Corporation
Interior of TSUTAYA BOOKS: CCC Design
Company, Takenaka Corporation
Lighting: Uchihara Creative Lighting DesignInc.
Sign: Nippon Design Center, Inc.
Graphic Art: Hiromura Design Office
Fabric: Studio Akane Moriyama
Construction: JV of Takenaka Corporation and
Maeda-gumi
Design term: June 2013~December 2014
Construction term: January 2015~February
2016Mechanical bicycle parking lot
Outdoor equipment▽RFL

Rooftop planting

TerraceFinance lounge

4,500

Finance lounge

4,500

▽7FL

Terrace

Bank

Bank

▽6FL

▽5FL

PHOTO: ATSUSHI NAKAMICHI

Kids room

Kids floor

4,500

Beauty and life salon

▽4FL

4,500

Living/event space
Café

▽3FL

Restaurant

3,900

Café

Pilotis260

Rest space

4,600

▽1FL

TerraceApple store▽2FL

Food market▽B1FL

Photo 3 Looking down the first-floor atrium entrance from the third floor

Terrace“Community living room”

3,800

Photo 2 Bustling inside the HIRAKATA T-SITE
overflowing into the plaza in front of thestationTerrace

Restaurant

▽8FL

4,500

PHOTO: TAIZO FURUKAWA

Concept of Building Appearance
Generally in the construction of commercial facilities on high-price land, becauseof the necessity to secure large floor
plates that fully occupy the construction
site, buildings with flat and wide wall areas tend to be constructed. In the current
project, several rooftop terraces appear
on the side facing the front of the station
due to the alternate piling of the voluminous box structures.
Then, capitalizing on rooftop terraces
to be used as play areas for children anda site for restaurants and cafes, we attempted to produce in the front of the station a landscape where people can gather together. In this landscape of gathering
together, it is important that the terrace
can be seen from the neighboring terrace,that the eyes of people visiting for different purposes can intertwine each other,and that those who are present can feelthe presence of each other. If the terraces
were arranged in a linear manner along
the plaza, such a condition couldn’t bebrought about. Important here is thatclusters of people with identical sympathies in terms of lifestyle can be seen byeach other.

Fig. 1 Sectional Drawing
4,270 600

Building Composition
Tsutaya Books has conventionally
opened its bookshops in a low-rise building or as a building tenant. The current HIRAKATA T-SITE is a nine-story
building-type shop, a first of its kind for
Tsutaya Books. As a result, a key pointin the plan was how to arrange the bookstreet that connects the upper and lower floors of the building and how to link
the book street with other streets. The façade facing the station plaza is finishedentirely with a glass wall so that the bustling atmosphere inside the building canbe presented to the outside. (Photo 2)
In the HIRAKATA T-SITE building,each living proposal is treated as a volume, which is not piled up straight andvertically but is piled in a shifted form
like Jenga. In doing so, a comfortable
two-layer atrium space is produced.

On the station front side, seven box
structures protrude. Three box structures
arranged on the fourth to fifth floors arecomposed of a two-layer atrium and theexterior walls are finished entirely with aglass curtainwall. The box structure protrudes into the front of the station by up
to about 5 m. Its height is about 8.5 m
and its width about 7.5 m, and the bookshelf arranged on the wall surface and toa full ceiling height plays a role in connecting the upper and lower floors. (Photo 3)
When viewing a cross-sectional view,the two-layer atriums are arranged in theform of alternate pilings to the side of thestation and to the reverse side of the station in order to provide an image as if theinside space of all of the floors are connected. (Fig. 1)
Every atrium is small in scale, but
their linkage brings about a sense of integration in construction. The priority inthe structural plan of the HIRAKATA TSITE was for every visitor to feel as if
they were in their living room or homewherever they are in the HIRAKATA TSITE.

4,500

tioned as a core facility.
In order to regenerate the railway station neighboring area, we consideredthat it was not only important for the
HIRAKATA T-SITE project to offer attractive content with living value, witha book street as a core facility, but also
for the community to be steadily developed there, capitalizing on the living value thus created. In addition, we considered that what is required for producing
such values is the creation of the site likea “community living room” into which
local citizens freely gather together.

7,950
D

9,600
C

9,600
B

A

December 2018 Steel Construction Today & Tomorrow 16

The inside space of the protruding
box structures serve as a “community living room,” and the outside surfaceof the box structure plays a role as thewall surface of the plaza in front of thestation. That is, the HIRAKATA T-SITE
building itself forms part of the plaza infront of the station.
Inside of the Building
Because the main proposal in the project was to “create a relaxing community living room,” determining the scaleof each building element was important.
When the living space, visitor and book
are taken into account as the main players, the size of the structural members
would become excessively large, and as
a result it would be felt that somethingis wrong. For example, when the size ofcolumns at the book street reaches 600
mm in diameter, the building construction itself lacks structural balance. To
solve this problem, we considered that,
if the core on the east side and the box
structure on the west side were treated asseismic-resistant elements and if the design can be made so that the axial force
is borne only by the column, the column
diameter could be reduced to 300 mm or
less. Finally, a column diameter of 267.4
mm was determined due to the efforts ofthe structural designers.
Structural Plan
The design concept of the HIRAKATA
T-SITE lies in “creating a relaxing community living room.” The structural designer understood the concept to be the“creation of a safe space where a senseof security can be obtained.” While there
are buildings that demonstrate a senseof safety and security by adopting a mega-structure, we considered that such asystem was inappropriate for the HIRAKATA T-SITE. When examining theprovision of a space that is comfortable
and relaxing, it is better not to expose thebuilding structure to the outside. To that

end, we considered it desirable not to expose the structural members themselvesby adopting thin, slender members.
With regard to structural safety, theclient had a high interest in seismic resistance, and it was demanded that theseismic resistance of the HIRAKATA TSITE be set at 1.25 times that prescribedin the Building Standard Law of Japan.
In order to achieve the compatible performance of highly comfortable spaceand high seismic resistance, it was necessary to prepare a tenacious structuralplan that makes optimum use of the narrow space in which the structural members are arranged. An aggregate of devices are incorporated into the constructionof the building-for example, in the construction of the façade, in addition to theadoption of slender structural members,some devices are used so that the slender
members can demonstrate seismic resistance even in their use as they are.
A main seismic-resistance element
adopted was the corrugated steel plate
seismic-resistant wall, which was arranged on the core side. While the wallcauses plastic deformation during major
earthquakes, it is high in fatigue strength,
and thus it has a structure to function asa response-control member that absorbs
seismic energy.
Seismic-resistant Elements
The corrugated steel plate seismic-resistant wall is arranged on the core side.
Meanwhile, in the façade on the station
plaza side that widely opens to the out-

Fig. 2 Arrangement of
Steel Frame Membersside, nearly no seismic-resistant elements are arranged, which creates therisk of the whole building structure toundergo torsional behavior during earthquakes. To remedy this, we examined
whether this eccentricity could be suppressed by making the most of the protruding box structure as a seismic-resistant element. In order for the protruding
box structure to demonstrate even a little
bit of high rigidity to a seismic force that
deforms the box structure to a rhombus
shape, the column and beam were inserted into the outer frame panel of the box
structure. (Photo 4)
Further, some devices were incorporated to improve the rigidity of the box
structure-including the adoption of
concrete-filled steel tubes (CFT) for thecolumns that support the box structure,
and an increase in the size of the periphery beams. (Fig. 2)
As a result, the eccentricity of thewhole building structure was successfully suppressed with no arrangement ofbraces or other diagonal members in the
open surface on the station plaza side but
by making optimum use of the box structures.
The aspect width of the outer-frame
finishing panel is 400 mm. In order to fit
the columns and beams into this width,
it was required to suppress the external
width of the columns and beams to 300
mm or less for the wall surface and to
330 mm or less for the floor surface. This
was an extremely high hurdle in terms ofstructural design.

Corrugated steel plate
seismic-resistant wall
Main seismic-resistant element ataboveground floors
Seismic-resistantbox structure
Suppression of torsion due tomaldistribution of seismic-resistantelement in long-side direction

PHOTO: TAKENAKA CORPORATION

Concrete-filled steel
tube (CFT) box columndrgroung unde ottom plate
n
ti
is
x
b
E
r wall,exterio

Photo 4 Steel structure construction
17 Steel Construction Today & Tomorrow December 2018

Improvement of rigidity ofseismic-resistant box structure

The aspect width of the panel was important for the box-shaped space of the
two-layer box atrium surrounded withbooks. When the aspect width surpasses
400 mm, this wider size does not fit withthe atrium design purpose thereby losing
a sense of living. Accordingly, we asked
for the structural team to by no means
surpass 400 mm.
When only 300 mm was available as
the width for arranging the columns, thebest that could be done normally was toarrange only the columns that support
the box-shaped atrium space. However, in order to improve the safety evenslightly, every available device including the column fitting method was incorporated.
Adoption of Seamless SteelTubes for Columns
It was decided to adopt corner-less roundsteel tubes as the columns to be arrangedin the center of the building because their
PHOTO: TAKENAKA CORPORATION

application not only offers a sense ofstructural scale but allows for the wider
use of available space and brings about
no danger to passing visitors. Then, inorder to make the size of the tube as thinas possible, heavy-wall seamless steel
tubes were selected. The outside diameter was unified to 267.4 mm for use inevery floor, and the wall thickness of thesteel tube column that support the heaviest weight at the lowest floor was set at
55 mm. Because of its seamless finish,
the tubes have no weld beads and thus
are structurally fine for use as columns.
In common practice in round steel
tube making, steel plates are rounded
and weld-joined. When using excessively heavy-wall steel plates to manufacture
heavy-wall tubes, it is difficult to bend
and weld them together, and thus it is noteasy to manufacture steel tube columns
with a heavy wall thickness but a slender
diameter. On the other hand, the seamlesssteel tube is manufactured by piecing thecenter of a defect-free round billet, andthus it can be said that the seamless tube
is most suitable for use for columns requiring heavy wall thickness but slender
diameter.
The seamless steel tubes with the outside diameter and wall thickness that we
wanted to adopt was not available in thenormal size range of steelmakers. However, it was confirmed through negotiations with the manufacturer that the specified size could be made available andfurther advance adjustments were madewith a fabricator concerning to the fittingof on-site weld joints of the heavy-walltubes, which led to successful adoption.
(Photos 5~6, Fig. 3)

Among other devices incorporated into the construction of the building was
the attachment of commonly-applied Hshapes to commonly-applied square steel
tube columns.
Requests for Future Steel
Structures
It is considered that the round columns
with an outside diameter of 267.4 mm
used in the construction of the HIRAKATA T-SITE cannot easily be produced
employing reinforced concrete. In other words, it is the steel’s attractivenessthat can realize the structural section requiring high strength, even by the useof comparatively small-section members. On the other hand, even when applying slender steel members, there arecases in which a slender member prepared so finely may become unexpectedly thick due to fire protection coveringand this would be a disappointment for
us. To that end, we strongly desire that an
application method be found that makes
the most of the slenderness offered by
the steel.
In steel products, wide-width or narrow-width H-shapes and I-shapes arefreely available, and further specified
sizes can be selected from ready-madeproduct line-up. It is possible to produce
a weld built-up box steel column used in
the current project and also to make thesteel members slender. It is another attractiveness of the steel that it can wrestle with applications in the structural sections that allow for the exposed use of
the steel itself and are important in termsof design. ￭Fig. 3 Arrangement of Steel Structural Members at Fourth Floor
Photo 5 Heavy-wall seamless steel tube used
as column
PHOTO: TAKENAKA CORPORATION

Corrugated steel plate
seismic-resistant wall
Arrangement of main abovegroundseismic-resistant element in the periphery of core
Simple reinforcementof connection
Development of reinforcement
detail for connection between
box column and H-shape beam

Heavy-wall seamlesssteel tube

Photo 6 Building structure employing heavy-wallseamless steel tube

Adoption of slender, heavy-wall round steel tubes
to lessen danger of passing visitors by making
slender the column at the building center spacemeele
ant force
t
s
i
ic
es
ic-r ismsm on seieti
fsn o irecutio side-db
irtldis ong
Ma reat lt
tont

December 2018 Steel Construction Today & Tomorrow 18

JISF Operations

Support of Workshop on Steel Structures in Jakarta

The Workshop on Steel Structures in Jakarta was held on July 19, 2018. This
workshop was hosted by the Ministry of
Public Works and Housing (PUPR) of
Indonesia, into which the Japan Iron andSteel Federation (JISF) and Japanese Society of Steel Construction (JSSC) participated as supporters.
Total participants amounted to morethan 60-those working in related government agencies and industries, and university professors. Subsequent to an opening address each by the Minister Economic

Affairs of the Embassy of Japan in Indonesia and Director General Syarif of Construction Development of PUPR, several lectures pertaining to steel construction
were delivered by lecturers from both Japanand Indonesia. On this occasion, PUPR expressed its intention to establish the Indonesian Society of Steel Construction (ISSC)
by assembling those involved in iron andsteel in both the public and private sectors
in Indonesia. In this regard, JSSC is expected to play a role in driving the dissemination of steel construction in Indonesia.

Japan’s Ministry of Economy, Tradeand Industry promoted the “Project on Human Resources Nurturing Support for the
Introduction and Dissemination of Japan’s
Disaster-prevention Steel Technologies inIndonesia” for three years from 2014. Following this, JISF and JSSC have jointly
promoted diverse projects to disseminate
steel construction in Indonesia. As a linkwith this project, JISF and JSSC have extended advice and cooperation to PUPR
and other related organizations concerning
the establishment of the ISSC.

Lecture Delivery at the SEAISI Annual Conference

The Conference and Exhibition of SEAISI (South East Asia Iron and Steel Institute) were held on June 25~28, 2018 at
the Ritz-Carlton Jakarta in Indonesia, towhich the Japan Iron and Steel Federation(JISF) dispatched Chairman Kenichiro
Fujimoto of JISF’s International Environment Strategic Committee (Environment
Div., Nippon Steel & Sumitomo Metal
Corporation) to deliver a lecture.
In the Session 10B Environmental
Management on the third day of Conference sessions, he delivered a presentation titled “Steel’s Competitiveness fromthe Environmental Perspective.” Specifically, he introduced the Japanese steel industry’s initiatives to preserve the glob-

al environment-highly-efficient CO2
emissions reduction technology and
COURSE50 (CO2 Ultimate Reduction
System for Cool Earth 50) and at thesame time explained that steel is a very

STEEL CONSTRUCTION TODAY & TOMORROW
Published jointly by

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

high-performance material from the perspective of lifecycle assessment. His presentation at the SEAISI Conference wastaken up in major Japanese steel press
and created a lot of attention.

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