Design Codes And Practical Applications of Concrete-Filled

1/35

Design Codes And Practical Applications of

Concrete-Filled Steel Tube (CFT) Structures

in Japanin Japan

22th/Jan./2015

Akihiko KAWANO

Kyushu UniversityKyushu University

2/35

Contents

Japanese laws and regulations, overview of the design guidelinesg

Concrete-filled steel tube structure design Guidelines of AIJ AIJ

Construction Statistics of CFT Buildings according to ANUHT-collected data ANUHT collected data

Recent CFT buildings in Japan

Summary

3/35

Japanese laws and regulations,p g ,overview of the design guidelines

4/35

Japanese laws and regulations, overview of the design guidelines

Structural design corresponds to laws and regulations in Japan

Figure 1 Flow of Japanese seismic design

5/35

Japanese laws and regulations, overview of the design guidelines

Overview of the design guidelines in Japan

MLIT (Ministry of Land Infrastructure and Transport) NotificationMLIT (Ministry of Land, Infrastructure and Transport) Notification

By the MLIT Notification No. 464 2002), CFT structure was observed as one of general structures in the building standards law. From then, CFT

structures were spread rapidly.

ANUHT (Association of new urban housing technology)guidelinesguidelines

ANUHT published "CFT structure technology standards and commentary with construction execution and design calculation

examples, etc." to supplement the MLIT Notification. The Chapter 2 is

the ANUHT Guidelines essentially.

AIJ (Architectural Institute of Japan ) guidelinesAIJ (Architectural Institute of Japan ) guidelines

The current Guidelines for Design and Construction of Concrete FilledSteel Tubular Structures was published at 2008. AIJ Guidelines are

revised approximately every 10 years since 1976.

6/35

Concrete-filled steel tube structure design Guidelines of AIJ

Comparison among AIJ guidelines, MLIT notification and

ANUHT guidelinesANUHT guidelines

Notification by MLIT is conservative enough. However, theexception is recognized.

Since ANUHT Guidelines are developed for high-rise buildings, it islimited to short columns and small width-to-thickness ratio.

AIJ Guidelines include slender columns and the larger width-to-AIJ Guidelines include slender columns and the larger width tothickness ratio, as long as the deformability is ensured

Table 2 Limitations and Regulations

Concrete

strength

Steel tube

yield strength

(N/mm2) (N/mm

2)

Confining effectD/t of

circular tube

D/t of

square tube

Length of

beam-column

g

(N/mm ) (N/mm )

Notification by

MLIT>=24

Circular &

Rectangular tubes<=50 <=34 l k /D <=12

AIJ< 90 < 440 Circ lar t be onl < 100* < 59* l /D < 30

Recommendations<=90 <=440 Circular tube only <=100* <=59* l k /D <=30

ANUHT

Recommendations<=90 <=440

Circular &

Rectangular tubes<=67 <=44 h 0/D <=6

7/35


Ultimate axial strength of column

Ultimate M-N strength of columng

Ultimate strength of beam-to-column connection

8/35


Ultimate axial strength of column

In AIJ guidelines as shown in Figure 2 lk/D less than 4 is classified as In AIJ guidelines, as shown in Figure 2, lk/D less than 4 is classified as short column. Compressive strength of the member is the yield strength of the cross-section.

G�l /D over 12 is classified as slender column Elastic-plastic flexural lk/D over 12 is classified as slender column. Elastic-plastic flexural buckling load is the compressive strength of the member.

G�lk/D between 4 and 12 is classified as intermediate column.

short columnyscccu FAFAN )1(1

slender columncrscrccu NNN 3

intermediate column4125.0 3112 DlNNNN kcucucucu

lk is buckling length k g g

Figure 2 Classification of ultimate compressive yield strength due to lk/D

9/35


Ultimate axial strength of column (2)

(a) Ultimate compressive strength of short column N(a) Ultimate compressive strength of short column Ncu1

Calculation formula of Ncu1 (lk/D less than 4) is the following equation.

FAFAN )1(

is a factor to represent the confinement effect.

(Ci l CFT 0 27 S CFT 0)

yscccu FAFAN )1(1

(Circular CFT: =0.27, Square CFT: =0)

cA is the cross-sectional area of concrete

sA is the cross-sectional area of steel pipesA is the cross sectional area of steel pipe

Fc is the design strength of concrete

Fy is the yield strength of steel pipe

10/35


Figure 3 The relationship of Ultimate compressive yield strength of circular CFT and Axial force share of steel pipeFigure 3 The relationship of Ultimate compressive yield strength of circular CFT and Axial force share of steel pipeFigure 3 The relationship of Ultimate compressive yield strength of circular CFT and Axial force share of steel pipe

Ultimate axial strength of column (3)

(a) Ultimate compressive strength of short column N (2)(a) Ultimate compressive strength of short column Ncu1 (2)

was determined to 0.27 by regression of the experimental data as shown in Figure 3.

When is 0.27, from Richart’s equation and von Mises yield criterion, the pipe hoop stress corresponds to -0.19ssy as shown in Figure 4.

compressivecompressive

tensile

Figure 3 Ultimate compressive strength

and Axial force component of steel pipe

Figure 4 Stress state of

yield condition of von Mises

11/35


Ultimate axial strength of member (4)

(b)Ultimate tensile strength of member N(b)Ultimate tensile strength of member Ntu

Tensile strength Ntu is not related to the length of the column.Infill concrete has no resistance in tension.

By assuming the pipe hoop stress in circular CFT = -0.19s y, the pipe longitudinal tensile yield stress is 2 s y ( 2 =1.08)

In case of square CFT the Confinement effect is not In case of square CFT, the Confinement effect is not considered

FAN

From the above, the following formula is derived.

ystu FAN 2

2=-1.08 circular CFT =0 square CFT

12/35


Ultimate axial strength of member (5)(c) Compressive strength of slender column N 3(c) Compressive strength of slender column Ncu3

NNN

Ncu3 is the superposed strength of cNcr (strength of concrete slender column) and sNcr (strength of steel pipe slender column) as follows:

crscrccu NNN 3

The cNcr and the sNcr are determined by the column curves in Fig 5 and 6, respectively.

AN ccrccrc

Recommendations for

the Plastic Design

and 6, respectively.

AN scrscrs

Allowable compressive stress for

sustained loading

Allowable compressive stress for

t l di

the Plastic Design

temporary loading

Figure 5 Column curve of concrete column Figure 6 column curve of steel pipe column

13/35


Ultimate axial strength of member (6)(d) Compressive strength of intermediate column Ncu2(d) Co p ess e s e g o e ed a e co u cu2

The Ncu2 is linearly-interpolated between short column andslender column (When lk/DH�12) .

4125.0 3112 DlNNNN kcucucucu

short column

slender column

intermediate column

Figure 2

14/35


Ultimate M-N strength of columnFollowing Equations indicate the superposed strength It corresponds Following Equations indicate the superposed strength. It corresponds to the static allowable state in plastic analysis.

In other words, the superposed strength need not satisfy compatibility in strains among steel and concrete However to compatibility in strains among steel and concrete. However, to satisfy the compatibility, the strength is maximized, and it is called as the generalized superposed strength.

usucu NNN

usucu

usucu

MMMN M are the bending moment and a ial force at the time of Nu, Mu are the bending moment and axial force at the time of

ultimate limit.

cNu, cMu are the axial force and bending moment will be resisted by

the concrete at the time of force ultimate limit the concrete at the time of force ultimate limit.

sNu, sMu are the axial force and bending moment will be resisted by

the steel pipe at the time of force ultimate limit.

15/35


Ultimate M-N strength of column (2)

Ultimate M-N strength of short columngFigure 7 shows M-N strength of Steel pipe (S) and filling concrete (C),

generalized superposed strength (blue line) and simple superposed

strength (red line). strength (red line).

As for the simple superposed strength, concrete portion mainly supports the axial load and steel portion supports bending moment,

except that axial load is in tension or axial load is over the concrete except that axial load is in tension or axial load is over the concrete

compressive strength.

Figure 7 Superposed strength

16/35



Ultimate M-N strength of short columnUltimate M N strength of short column

Stress blocks for the generalized superposed strength are shown in Figure 8, where the neutral axes of concrete and steel pipe match.

A f i l CFT th i ld t f th t d th t l i

5 ð’ö � ¥ � å�¡�Ü�î�” 5 ð’ö� ¥ � å � ¡�Ü 5 ð’ö � ¥ � å�¡�Ü�î�” 5 ð’öConcrete steel pipe Concrete steel pipe

G�As for circular CFT, the yield stress of the concrete and the steel pipe is changed by confinement effect.

� ¥ � å � ¡�Ü 5 ð’ö

cBc

� ¥ � å �¡� 5 ð’ö

s ycF0.89 s y

� ¥ � å � ¡�Ü 5 ð’ö

cBc

� ¥ � å �¡� 5 ð’ö

s ycF0.89 s y

Concrete steel pipe Concrete steel pipe

1 08 s y1 08 s y

yccBc FtD

tF

2

278.0

Circular CFT Square CFT

Figure 8 Calculation of generalized superposed strength

1.08 s y s y1.08 s y s y

17/35



Ultimate M-N strength of slender columnUltimate M-N strength of slender column

The strength is obtained by the simple superposed strength by the equations below.

In the case of slender CFT, the concrete column bending strength cMu and the steel pipe column bending strength sMu

consider the additional moment due to the deflection and axial consider the additional moment due to the deflection and axial

force.

Confinement effect is not considered due to low stress level.

usucu NNN

usucu MMM

18/35



Ultimate M-N strength of the slender concrete columnUltimate M N strength of the slender concrete column

The strength makes a parabolic approximation with respect to the theoretical solution which assumes the full plastic strength at the critical portion (interpretation)critical portion (interpretation).

The maximum axial force of the parabola is set 0.9 times of buckling strength cNcr. However, when only the axial force acts and no bending force acts it is possible to use the N

Strength of cross section

14

MNN

M ucuc

When, crcuc NN 9.0

bending force acts, it is possible to use the cNcr.

interpretation

max9.0

19.0

MNN

M c

crccrc

uc

When, crcuccrc NNN 9.0

0M 0uc M

0max2

1

max MC

CM c

cb

bc cb FC 0045.0923.0

Parabola

cNu is the axial force of concrete column

cMmax0 is the maximum bending strength of

concrete section

1cb

Figure 9-1 M-N strength of slender concrete column

19/35



Ultimate M-N strength of the slender pipe columng p p

As shown in Fig. 9-2, the ultimate strength of steel pipe column sMu is taking the moment magnification factor into account. It is given by the following equation.the following equation.

sN

u

011 us

Es

us

crs

us

us MN

N

N

NM

sN

cr

Steel tube (S)

s cr

Moment magnification factor

MM

0

sNu is the Axial force of the steel column

sNE is the Euler buckling load of steel column

sMu0 is the bending strength of steel column

h i l f i 0

Figure 9-2 M-N strength of slender steel pipe column

Mu

sM

u0when axial force is 0

20/35



Superposed strength of slender CFT columnp p gThe strength is determined as simple superposed strength (S + C) of

concrete (C) and steel(S), as shown in Figure 10.

Steel resists primarily bending moment and concrete resists axial

N

Steel resists primarily bending moment, and concrete resists axial force. Both steel and concrete columns must meet the deflection

compatibility, so that bending strength of steel column is reduced by

additional moment

uNMMM 1

When crcu NN 9.0

Nu

Superposed strength(S+C)

Ncu3

additional moment.

k

uusucu

NMMM 10

When>*crcucrc NNN9.0

N

Strength of slender CFT

sNcr

N

When>*

k

uusu

N

NMM 10

crcucu NNN 3

Steel tube (S)cNcr

0.9cNcr

>* crcucu3

k

crcusu

N

NMM 1 Mu

Concrete (C)

sMu00

Figure 10 M-N strength of slender CFT column

21/35



Ultimate M-N strength of intermediate column g

When the Nu is below 0.9cNcr , the strength is same as the slender column. While Nu exceeds 0.9cNcr, the strength is interpolated between Ncu2 and the point of M-N interaction corresponding to

Nu

between Ncu2 and the point of M N interaction corresponding to 0.9cNcr.

When crcu NN 9.0

N1

Ncu2

straight line

k

uusucu

N

NMMM 10

When NNN 900.9 NEq.15

When>* crcucu NNN 9.02

crccrcuusu

N

N

NN

NNMM

9.01

10

9.010

0.9cN

cr

k

uusucu

N

NMMM 10

kcrccrs NNN 1.0M

usM

u00

Figure 11 M-N strength of intermediate

column

22/35



Common details of beam-to-column connections in Japan Common details of beam to column connections in Japan

Three types of standard beam-column joints are used in Japan.

Through diaphragm type is the most popular. Inner diaphragm type is used for super high-rise buildings External diaphragm type is used for super high-rise buildings. External diaphragm type is

becoming popular, so that it is the safest and is easy to fill steel pipe

with concrete.

They are all designed as a rigid moment connection External They are all designed as a rigid moment connection. External diaphragm type is better to be checked in terms of the rigidity and

strength of the diaphragm.

Figure 12 Beam to CFT-column connections

23/35

Ultimate Strength of beam-to-column connections

Ultimate Strength of connection panel

Shear strength of the panel pQu is calculated in Pipe

psQu

Shear strength of the panel pQu is calculated in the superposed strength.

G�Shear Strength of steel pipe is evaluated by the shear strength of pipe web portion.

Pipe

flange

cD

shear strength of pipe web portion.

G�Arch mechanism of concrete in Fig14, there are a main arch and sub arches which are restraint

by steel pipe flanges The plastic hinges are Main arch f t

Sub arch of concrete

Qby steel pipe flanges. The plastic hinges are

formed in steel pipe flanges. of concrete

Sub arch of

pcQu

upcupsup QQQ Sub a c o concrete

Pipe flange

Bd

upcupsup QQQ

32

22

yysups

FnFAQ

s

g

Plastic hinges

Q

32ups Q

ccs

cc

sf

sc

upc FDFD

MDQ sin4tan

2

Figure 14 Plastic collapse mechanism of

arch for concrete part of the joint panel

cD pcQucc

ysf FDt

M4

2

24/35

Construction Statistics of CFT Buildingsgaccording to ANUHT-collected data

25/35

Construction Statistics of CFT Buildings according to

ANUHT-collected dataANUHT-collected data

>Ü>Ü>Ü>Þ

The frequency of total floor area

>ä>Ý

>â>à

>Ý>ß

>Ý>Ø>Ü>Ü>ÜHZ>ß>Ø>Ü>Ü>Ü?�>Þ

HZ>Ý>Ø>Ü>Ü>Ü?�>Þ

>ä>Ü

>Ý>â>à

>Þ>å>Ý

>Þ>à>Æ

>Þ>Ü>Ø>Ü>Ü>ÜHZ>ß>Ü>Ø>Ü>Ü>Ü?�>Þ

>Æ>Ø>Ü>Ü>ÜHZ>Ý>Ü>Ø>Ü>Ü>Ü?�>Þ

? ?�?�

>ß>ß

>Æ>å

>ª>Ü

>ä>Ü

>â>Ü>Ø>Ü>Ü>ÜHZ>ª>Ü>Ø>Ü>Ü>Ü?�>Þ

>à>Ü>Ø>Ü>Ü>ÜHZ>Æ>Ü>Ø>Ü>Ü>Ü?�>Þ

? ? ?�>Ì?�?�?�?�?�>Ì?�?�?

>Ý>å

>Ý>ä

>Þ>Ý

>ä>Ü>Ø>Ü>Ü>ÜHZ>å>Ü>Ø>Ü>Ü>Ü?�>Þ

>â>Ü>Ø>Ü>Ü>Ü >ª>Ü>Ø>Ü>Ü>Ü?�

?�?�?

>â

>Ý>Ý

>â>Æ

>ß>Ü>Ü>Ø>Ü>Ü>Ü?�>ÞHZ

>Ý>Ü>Ü>Ø>Ü>Ü>ÜHZ>Þ>Ü>Ü>Ø>Ü>Ü>Ü?�>Þ

>Ü >Æ>Ü >Ý>Ü>Ü >Ý>Æ>Ü >Þ>Ü>Ü >Þ>Æ>Ü >ß>Ü>Ü >ß>Æ>Ü

>œ?!?�?�?�?�>Ì?�?�>Ì?�? ?�?�?�

Figure 15 The frequency of total floor area

26/35



The eaves height of the building

>Æ>ÜHZ>Þ>Ü>Ü?�

>Þ>Ü>ÜHIHZ

>â>Ü >Ý>Ü>Ü

>Ý>Ü>ÜHZ>Ý>Æ>Ü?�

?�?

>à>ÆHZ>â>Ü?�

>â>ÜHZ>Ý>Ü>Ü?�

>æ? ?"?�?�>Ì?�?�?�?�?�

>Þ>ÜHZ>ß>Ü?�

>ß>ÜHZ>à>Æ?�

>æ

HZ>Þ>Ü?�

>Ü >Æ>Ü >Ý>Ü>Ü >Ý>Æ>Ü >Þ>Ü>Ü >Þ>Æ>Ü >ß>Ü>Ü >ß>Æ>Ü >à>Ü>Ü >à>Æ>Ü

>œ?!?�?�?�?�>Ì?�?�>Ì?�? ?�?�?�

Figure 16 The eaves height of the building

27/35



Application of CFT buildings

? ?�

>ß?�?�?�?�?�

>ÿ?�?�?�?�?�

>í?�? ?�? ?�?�?�?

>ò? ?�? ?�?�?%

>ÿ?�?�?�?�?�

>ß?�?�?�?�?�>×>þ?�? ? ?�?�?�?�>ß?�?�?�?�?�>×>í?�? ?�? ?�?�?�?

>þ?�? ? ?�?�?�?�

>ß?�?�?�?�?�>Ì>×>Ì>þ?�? ? ?�?�?�?�

>ß?�?�?�?�?�>Ì>×>Ì>ô?�? ?�?�

>ß?�?�?�?�?�>Ì>Ì>í?�? ?�? ?�?�?�?

Figure 17 Application of CFT buildings

28/35



Concrete Strength N/mm2

13.1H�2.9H�

36N/mm2

60N/mm2~

23 7H�

~36N/mm2

24.0H�

23.7H�60N/mm2

36N/mm236N/mm2

17.7H�15.4H�

3 2H�42N/mm242~60N/mm2

3.2H�36~42N/mm2

Figure 18 Strength of concrete

29/35



The shape of cross section

19.4 17.7

62.9

Figure 19 The shape of the cross section

35/35

Summary

Structure design method of Japan (Primarily seismic design) can be selected from several.

The research of CFT began from 1960 in Japan, but it did not spread until it is recognized as the general structure by p g g ybuilding standard in 2002.

In Japan, structural design of CFT has been done in ANUHT In Japan, structural design of CFT has been done in ANUHT guidelines and AIJ guidelines.

AIJ guidelines applicable range is wide AIJ guideline shows AIJ guidelines applicable range is wide. AIJ guideline shows the design method of slender column and beam-to-column connection. For all of them, superposed strength is applied.

CFT is mainly used in the office building and it is also used in relatively small buildings by ANUHT statistics.

A couple of recent CFT buildings are introduced.

36/35

Thank you for your attentionThank you for your attention

“Ito” new campus plan “Ito” new campus plan

of Kyushu University of Kyushu University of Kyushu University of Kyushu University

Documents

Design Codes And Practical Applications of Concrete-Filled