critical factors in displacement ductility assessment of high … · 2017. 11. 23. · ductility...

TECHNICAL NOTE

Critical factors in displacement ductility assessment of high-strength concrete columns

Ali Taheri1 • Abdolreza S. Moghadam1 • Abass Ali Tasnimi2

Received: 31 December 2016 / Accepted: 5 September 2017 / Published online: 25 September 2017

� The Author(s) 2017. This article is an open access publication

Abstract Ductility of high-strength concrete (HSC) columns

with rectangular sections was assessed in this study by

reviewing experimental data from the available literature. Up

to 112 normal weights concrete columns with strength in the

range of 50–130 MPa were considered and presented as a

database. The data included the results of column testes under

axial and reversed lateral loading. Displacement ductility of

HSC columns was evaluated in terms of their concrete and

reinforcement strengths, bar arrangement, volumetric ratio of

transverse reinforcement, and axial loading. The results

indicated that the confinement requirements and displacement

ductility in HSC columns are more sensitive than those in

normal strength concrete columns. Moreover, ductility is

descended by increasing concrete strength. However, it was

possible to obtain ductile behavior in HSC columns through

proper confinement. Furthermore, this study casts doubt about

capability of P/Agfc0 ratio that being inversely proportional to

displacement ductility of HSC columns.

Keywords High-strength concrete � HSC � Columndatabase � Confined concrete � Ductility � Displacementductility

List of symbols

Ag Gross cross-sectional area of column

As Total area of longitudinal steel

b Width of reinforced concrete section

dbl Bar diameter of longitudinal reinforcement

dbs Bar diameter of confinement reinforcement

fc0 Concrete compressive strength based on standard

cylinder test

fyl Yield strength of longitudinal reinforcement

fyt Yield strength of transverse reinforcement

h Height of reinforced concrete section

L0 Free length of ColumnP Axial force

Po Nominal axial column strength at zero eccentricity

(Eq. 22.4.2.2-ACI318-14)

s center-to-center spacing of tie reinforcement along

column height

s1 Center-to-center spacing of laterally supported

longitudinal reinforcement

V Shear force

lD Displacement ductility factorql Longitudinal reinforcement ratio determined as ratio

of total area of longitudinal reinforcement to gross

cross-sectional area

qs Volumetric ratio of transverse reinforcementdetermined as total volume of transverse

reinforcement divided by volume of concrete

D1 Identical to yield displacementD2 Identical to ultimate displacement

Introduction

Ductility and inelastic deformability of reinforced con-

crete columns are essential for overall strength and

stability of structures during a strong earthquake. Duc-

tility of columns can be achieved through proper con-

finement of core concrete. In the current design of

& Ali [email protected]

1 Structural Engineering Research Center, International

Institute of Earthquake Engineering and Seismology (IIEES),

Tehran, Iran

2 Department of Structural Engineering, Department of Civil

and Environmental Engineering, Tarbiat Modares University,

Tehran, Iran

123

Int J Adv Struct Eng (2017) 9:325–340

https://doi.org/10.1007/s40091-017-0169-6

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building codes, the requirements for confinement steel

have been outlined, but most of these requirements are

intended for columns with normal strength concrete,

where specified compressive strength does not usually

exceed 40 MPa.

In the last decades, strengths of concrete much higher

than 50 MPa have gained acceptance in the construction

industry. Strengths of concrete up to 130 MPa have been

used successfully in building and bridge construction,

where according to the publication of ACI-363 (2010), they

have economic advantages. Furthermore Ramezanianpour

(2014) explains using high-performance concrete (HPC)

and high-strength concrete (HSC) have more beneficial

effects for sustainable development.

Although HSC has gained acceptance in practice and

some special publication and reports like ACI-SP293

(2013), ACI-363 (2010) and fib bulletin 42 (2008) have

been supported this technology, the application of HSC in

high seismic regions has lagged behind its application in

the low seismicity region. For instance, before the publi-

cation of ACI318-2014, the issues related to HSC columns

including their strength and ductility were not addressed

appropriately, whereas state of the art of HSC was reported

by joint ACI-ASCE Committee 441 in 1996. Anyway,

strength and ductility of HSC columns is one area where

little design information is available for practicing

engineers.

Before the current century, ductility of HSC column

with steel reinforcement had been examined by some

researchers such as; Chung et al. (1980), Watanabe et al.

(1987), Muguruma et al. (1990), Mugurumu (1991),

Sugano et al. (1990), Sakai (1990), Kabeyasawa et al.

(1990, 1991), Thomsen and Wallace (1992), Azizinamini

et al. (1994), Ghosh et al. (1998) and Kato et al.(1998).

Furthermore, contemporary investigators have continued

this topic such as; Sharma and Bhargava (2005), Ishikawa

et al. (2008), Elwood et al. (2009a, b), Murthy et al. (2013),

Kimura et al. (2013), Zhu et al. (2016), Jin et al. (2016),

Ding et al. (2017), and Gaitan (2017).

This paper evaluates the displacement ductility of HSC

columns based on existing experimental data in terms of

concrete strength, confinement steel strength, longitudinal

bar arrangement, volumetric ratio of transverse reinforce-

ment, and axial loading. Furthermore, it presents critical

factors in the displacement ductility assessment of HSC

columns based on the outcomes of a research project in

which a literature review was conducted on experimental

data due to lateral load reversal loading for concrete with

compressive strengths approximately more than 50 MPa

and up to 130 MPa. The correlation between confinement

parameters and column displacement ductility are illus-

trated as well.

Column tests considered

Although ACI-318 (2014) has some special requirements

for concrete columns with specified compressive strength

exceeding 70 MPa, normal weight concrete with strength

higher than 50 MPa is generally referred to as HSC. ACI-

363 (2010) and CSA-A23.3 (2014) consider HSC as

concrete with 28-day cylinder strength higher than 55 and

50 MPa, respectively. It is defensible, because to produce

and test of this kind of concrete special care is required.

Furthermore, since the strength of most ready-mix con-

crete supplied, and strength of most concrete used in

experimental researches were limited to 40 MPa, which

provided the source for the majority of the building code

provisions, the strength exceed more than 50 MPa is the

adequate bound for HSC. Therefore, the experiments

evaluated in this paper include reinforced concrete col-

umns with normal weight aggregate having specified

compressive strength of concrete with the range of

50–130 MPa.

There are not many experiments of HSC columns under

lateral reversed cyclic loading in the literature. Up to 112

HSC column tests with square sections under combined

axial force and lateral loading reversals have been evalu-

ated in this study. The columns were tested under axial

force along with unidirectional bending and shear force

reversals. As illustrated in Fig. 1, mainly four types of

column specimens were tested in the experimental inves-

tigations, commonly a vertical ram was used to apply a

constant axial compression load, and one or two horizontal

jacks or actuators were used to apply the lateral reversed

cyclic load or displacement. Sezen (2002) presented four

kind of setup that we adopt them and introduce in Fig. 1,

but in this investigation only three of them were found in

literature, so the type D is not used in this paper.

According to loading protocol of each experiment,

firstly, it was attempted to apply a constant axial load, then

lateral loading/displacement sequence were applied. This

Lateral loading/displacement sequence was repeated cycles

of stepwise increasing amplitudes, so it had several steps.

Each step included a number of cycles. The oscillation

amplitude in the first step was chosen since the specimen

remains in the elastic range and it was incrementally

increased to a certain extent, leading to the deterioration or

failure of the specimen. See Fig. 2.

The geometry of column sections includes square and

rectangular shapes with different types of confinement

steel, including circular and square spirals, and a large

number of different arrangements of ties. Figure 3 shows

the types of reinforcement arrangements.

Cross-sectional dimensions for square columns ranged

between 150 and 600 mm. The rectangular columns had a

326 Int J Adv Struct Eng (2017) 9:325–340

123

200 by 150 mm cross section. Concrete strengths with up

to 130 MPa were used. The main variables considered

were concrete strength, level of axial load, reinforcement

arrangement, volumetric ratio and strength of tie rein-

forcement. Table 1 shows the highlights of research pro-

grams on the HSC column experiments under lateral load

reversals and their main parameters. Table 2 shows a

summary of the variables.

Analysis of test data

Ductility of columns subjected to lateral deformation

cycles was evaluated in terms of displacement ductility and

drift ratios. As Park (1989) has described, there are

alternative definitions for ductility ratio. The displacement

ductility ratio is defined as the ratio of maximum dis-

placement recorded prior to exceeding 20% strength decay

under cyclic loading, to the yield displacement. Figure 4

depicts the definition of the displacement ductility ratio and

equation number one may derive it. This definition is the

same as the one used previously by Saatcioglu (1991) in

Fig. 1 Column TestConfiguration—Adapted from

Sezen (2002). a Doublecurvature specimen (Setup Type

A), b Cantilever specimen(Setup Type B), c Specimenwith single stub (Setup Type C),

d Specimen with Double stub(Setup Type D)

Fig. 2 Lateral loading/displacement sequence

Fig. 3 Steel confinement configurations

Int J Adv Struct Eng (2017) 9:325–340 327

123

Table

1H

igh

lig

hts

of

rese

arch

pro

gra

ms

on

HS

Cco

lum

ns

Ref

.in

dex

Ref

eren

ceN

um

ber

so

f

use

dd

ata

Set

up

typ

eC

on

fin

emen

t

con

fig

ura

tio

n

Str

eng

th(M

Pa)

Dim

ensi

on

s1

L09

h9

b(m

m)

Var

iab

les

IC

hu

ng

etal

.(1

98

0)

2B

25

95

009

15

09

20

0f yt,

s

IIW

atan

abe

etal

.(1

98

7)

2C

14

HO

58

54

59

22

59

22

5–

III

Mu

gu

rum

aet

al.

(19

90

)4

B7

W8

6,1

16

50

09

20

09

20

0f c0 ,f y

t,P

IVS

ug

ano

etal

.(1

99

0)

7B

7W

,8

PS

67

,85

50

09

25

09

25

0R

A2,f c0 ,f y

t,s,P

VS

akai

(19

90)

7C

1W

,6

W,

7W

10

01

00

09

25

09

25

0R

A2,f y

t,s

VI

Kab

eyas

awa

etal

.(1

99

0)

3B

4P

S,

8P

S9

15

009

25

09

25

0R

A2,P

VII

Mu

gu

rum

u(1

99

1)

4B

7W

13

05

009

20

09

20

0f y

t,P

VII

IK

abey

asaw

aet

al.

(19

91)

1C

8P

S6

41

00

09

25

09

25

0–

IXT

ho

mse

nan

dW

alla

ce(1

99

2)

11

B4

CT

,5

71

–1

03

48

59

15

29

15

2R

A2,f c0 ,f y

t,P

XA

zizi

nam

ini

etal

.(1

99

4)

7C

3,

45

1–

10

49

659

30

59

30

5R

A2,f c0 ,f y

t,s,dbs,P

XI

Hw

ang

etal

.(2

00

5)

8B

3–

56

98

009

20

09

20

0R

A2,f y

t,s

XII

Hw

ang

etal

.(2

01

3)

5A

10

,1

1,

15

83

–1

12

18

009

60

09

60

0f c0 ,

s,d

bs,

P

XII

IB

ayra

kan

dS

hei

kh

(19

97)

5B

3,

55

5,7

22

01

09

30

59

30

5R

A2,f c0 ,f y

t,s,dbs,P

XIV

Par

ket

al.

(19

98

)5

C5

93

,98

16

009

35

09

35

0f c0 ,f y

t,s,d

bs,P

XV

Bay

rak

and

Sh

eik

h(2

00

4)

4B

57

42

01

09

30

59

30

5f y

t,s,d

bs,P

XV

IM

arti

ross

yan

and

Xia

o(2

00

1)

6A

47

6,8

61

01

69

25

49

25

4d

bl,d

bs,P

XV

IIW

oo

ds

etal

.(2

00

7)

8C

56

96

259

20

39

20

3s,d

bs,P

XV

III

Ham

mad

(20

10

)1

4C

15

1–

10

08

009

20

09

20

0f c0 ,f y

t,P

XIX

Seo

ng

etal

.(2

01

1)

1B

95

83

50

09

45

09

45

0–

XX

Ou

etal

.(2

01

3)

8A

99

2–

12

51

80

09

60

09

60

0f c0 ,

s,P

aC

olu

mn

free

len

gth

(L0 )

,d

epen

ds

on

test

con

fig

ura

tio

nty

pes

iseq

ual

to2L

inA

and

Dca

ses,

and

iseq

ual

toL

inca

ses

Ban

dC

,se

eF

ig.

1bR

ein

forc

emen

tar

ran

gem

ent


123

Table 2 Parameters and variables

# Ref.

index

Setup

type

Section type fc0

(MPa)

fyl(Mpa)

fyt(Mpa)

L0

(mm)

b

(mm)

h

(mm)

s1(mm)

s

(mm)

dbl(mm)

dbs(mm)

P (N)

1 I B 2 58.6 370 344.0 500 150 200 132 70 NIa NI 351,600

2 I B 2 59.7 370 361.0 500 150 200 132 58 NI NI 358,200

3 II C 14HO 58.3 420 1300.0 545 225 225 54 50 NI NI 590,288

4 II C 14HO 58.3 420 1300.0 545 225 225 54 50 NI NI 590,288

5 III B 7 W 85.7 400 328.0 500 200 200 52 34 NI NI 2,159,640

6 III B 7 W 85.7 400 792.0 500 200 200 52 34 NI NI 2,159,640

7 III B 7 W 115.8 400 328.0 500 200 200 52 34 NI NI 1,945,440

8 III B 7 W 115.8 400 792.0 500 200 200 52 34 NI NI 1,945,440

9 IV B 7 W 66.7 404 833.0 500 250 250 62 45 NI NI 1,292,313

10 IV B 7 W 84.5 404 833.0 500 250 250 62 35 NI NI 1,478,750

11 IV B 7 W 66.7 404 315.0 500 250 250 62 50 NI NI 2,376,188

12 IV B 7 W 66.7 404 833.0 500 250 250 62 40 NI NI 2,376,188

13 IV B 8PS 66.7 404 1362.0 500 250 250 62 45 NI NI 2,376,188

14 IV B 7 W 84.5 404 833.0 500 250 250 62 35 NI NI 2,693,438

15 IV B 8PS 84.5 404 1362.0 500 250 250 62 35 NI NI 2,693,438

16 V C 7 W 100.0 380 774.0 1000 250 250 62.5 40 NI NI 2,187,500

17 V C 7 W 100.0 380 774.0 1000 250 250 62.5 40 NI NI 2,187,500

18 V C 7 W 100.0 380 344.0 1000 250 250 62.5 60 NI NI 2,187,500

19 V C 7 W 100.0 380 1126.0 1000 250 250 62.5 60 NI NI 2,187,500

20 V C 6 W 100.0 380 774.0 1000 250 250 187.5 60 NI NI 2,187,500

21 V C 6 W 100.0 380 857.0 1000 250 250 182.5 60 NI NI 2,187,500

22 V C 1 W 100.0 340 774.0 1000 250 250 180 30 NI NI 2,187,500

23 VI B 4PS 91.0 871 1334.0 500 250 250 95 40 NI NI 1,990,625

24 VI B 8PS 91.0 871 1334.0 500 250 250 95 40 NI NI 1,990,625

25 VI B 4PS 91.0 871 1334.0 500 250 250 95 40 NI NI 2,957,500

26 VII B 7 W 130.0 400 408.0 500 200 200 52 34 NI NI 1,783,600

27 VII B 7 W 130.0 400 873.0 500 200 200 52 34 NI NI 1,783,600

28 VII B 7 W 130.0 400 408.0 500 200 200 52 34 NI NI 2,459,600

29 VII B 7 W 130.0 400 873.0 500 200 200 52 34 NI NI 2,459,600

30 VIII C 8PS 64.0 612 968.0 1000 250 250 65 40 NI NI 1,480,000

31 IX B 4CT 103.0 517 792.0 485 152 152 26 56 NI NI 0

32 IX B 4CT 86.0 517 792.0 485 152 152 26 56 NI NI 397,389

33 IX B 5 87.0 455 792.0 485 152 152 26 56 NI NI 0

34 IX B 5 83.0 455 792.0 485 152 152 26 56 NI NI 191,763

35 IX B 5 90.0 455 792.0 485 152 152 26 56 NI NI 415,872

36 IX B 5 67.0 475 1261.0 485 152 152 26 56 NI NI 0

37 IX B 5 75.0 475 1261.0 485 152 152 26 56 NI NI 173,280

38 IX B 5 82.0 475 1261.0 485 152 152 26 56 NI NI 378,906

39 IX B 5 76.0 475 1261.0 485 152 152 32 56 NI NI 351,181

40 IX B 5 87.0 475 1261.0 485 152 152 38 56 NI NI 402010

41 IX B 5 71.0 475 1261.0 485 152 152 44 56 NI NI 328,077

42 X C 3 53.8 473.34 454.0 965 305 305 130 67 19.05 12.70 850034

43 X C 4 50.9 473.34 495.4 965 305 305 130 41 19.05 9.53 804,204

44 X C 3 100.9 473.34 454.0 965 305 305 130 67 19.05 12.70 1,595,312

45 X C 4 100.3 473.34 495.4 965 305 305 130 41 19.05 9.53 1,586,582

46 X C 4 101.6 473.34 752.8 965 305 305 130 67 19.05 9.53 1,607,315

47 X C 4 101.8 473.34 752.8 965 305 305 130 41 19.05 9.53 1,609,497

48 X C 4 103.8 473.34 495.4 965 305 305 130 41 19.05 9.53 2,463,349


123

Table 2 continued

# Ref.

index

Setup

type

Section type fc0

(MPa)

fyl(Mpa)

fyt(Mpa)

L0

(mm)

b

(mm)

h

(mm)

s1(mm)

s

(mm)

dbl(mm)

dbs(mm)

P (N)

49 XI B 4 68.6 430.71 779.1 800 200 200 75 57 12.70 6.00 813,228

50 XI B 5 68.6 430.71 779.1 800 200 200 75 65 12.70 6.00 813,228

51 XI B 3 68.6 430.71 779.1 800 200 200 75 38 12.70 6.00 813,228

52 XI B 4 68.6 430.71 779.1 800 200 200 75 40 12.70 6.00 813,228

53 XI B 5 68.6 430.71 779.1 800 200 200 75 46 12.70 6.00 813,228

54 XI B 3 68.6 430.71 779.1 800 200 200 75 27 12.70 6.00 813,228

55 XI B 4 68.6 430.71 548.8 800 200 200 75 40 12.70 6.00 813,228

56 XI B 5 68.6 430.71 548.8 800 200 200 75 46 12.70 6.00 813,228

57 XII A 10 83.4 744 817.3 1800 600 600 117 140 25.00 13.00 17,119,000

58 XII A 10 88.5 735 820.0 1800 600 600 117 100 25.00 16.00 14,515,000

59 XII A 11 95.1 735 820.0 1800 600 600 117 100 25.00 16.00 14,515,000

60 XII A 15 83.1 739 820.0 1800 600 600 153 45 25.00 16.00 20,117,000

61 XII A 15 112.1 739 820.0 1800 600 600 153 45 25.00 16.00 20,117,000

62 XIII B 3 72.1 454 463.0 2010 305 305 133.5 95 19.50 16.00 3,321,785

63 XIII B 5 71.7 454 542.0 2010 305 305 133.5 90 19.50 11.30 2,380,593

64 XIII B 5 71.8 454 542.0 2010 305 305 133.5 90 19.50 11.30 3,310,231

65 XIII B 5 71.9 454 463.0 2010 305 305 133.5 100 19.50 16.00 3,314,082

66 XIII B 5 54.7 454 464.0 2010 305 305 133.5 108 19.50 12.70 3,234,969

67 XIV B 5 74.1 521 1360.0 2010 250 350 170 75 19.50 8.00 3,053,487

68 XIV B 5 74.1 521 1360.0 2010 250 350 170 75 19.50 8.00 4,533,965

69 XIV B 5 74.2 521 1402.0 2010 250 350 170 75 19.50 11.10 4,816,821

70 XIV B 5 74.2 521 1402.0 2010 250 350 170 140 19.50 11.10 3,056,829

71 XV C 5 98.0 446 1317.0 1600 350 350 135 62 24.00 9.20 3,602,000

72 XV C 5 98.0 446 453.0 1600 350 350 135 64 24.00 12.00 3,602,000

73 XV C 5 93.0 446 1317.0 1600 350 350 135 43 24.00 9.20 6,835,000

74 XV C 5 93.0 446 453.0 1600 350 350 135 45 24.00 12.00 6,835,000

75 XV C 5 93.0 446 1317.0 1600 350 350 135 62 24.00 9.20 6835000

76 XVI A 4 76.0 530 503.0 1016 254 254 80 50 19.00 9.00 489,000

77 XVI A 4 76.0 530 503.0 1016 254 254 80 50 19.00 9.00 979,000

78 XVI A 4 76.0 530 503.0 1016 254 254 80 50 19.00 9.00 534,000

79 XVI A 4 86.0 530 503.0 1016 254 254 80 50 16.00 6.00 1,068,000

80 XVI A 4 86.0 530 503.0 1016 254 254 80 50 16.00 6.00 534,000

81 XVI A 4 86.0 530 503.0 1016 254 254 80 50 16.00 6.00 1,068,000

82 XVII C 5 69.0 402 280.0 625 203 203 88 76 13.00 3.20 415,872

83 XVII C 5 69.0 402 280.0 625 203 203 88 76 13.00 4.80 415,872

84 XVII C 5 69.0 402 280.0 625 203 203 88 76 13.00 6.40 415,872

85 XVII C 5 69.0 402 280.0 625 203 203 88 76 13.00 8.00 415,872

86 XVII C 5 69.0 402 280.0 625 203 203 88 66 13.00 5.50 415,872

87 XVII C 5 69.0 402 280.0 625 203 203 88 86 13.00 6.40 415,872

88 XVII C 5 69.0 402 280.0 625 203 203 88 135 13.00 8.00 415,872

89 XVII C 5 69.0 402 280.0 625 203 203 88 193 13.00 9.50 415,872

90 XVIII C 1 51.3 400 298.0 800 200 200 150 40 16.00 8.00 507,707

91 XVIII C 1 53.8 400 298.0 800 200 200 150 40 16.00 8.00 528,530

92 XVIII C 1 54.5 400 298.0 800 200 200 150 40 16.00 8.00 534,361

93 XVIII C 1 73.0 400 274.0 800 200 200 150 40 16.00 10.00 688,449

94 XVIII C 1 76.4 400 274.0 800 200 200 150 40 16.00 10.00 716,768

95 XVIII C 1 77.0 400 274.0 800 200 200 150 40 16.00 10.00 721,765

96 XVIII C 1 94.7 400 516.0 800 200 200 150 40 16.00 10.00 869,190


123

evaluating ductility of normal strength concrete columns or

by Razvi and Saatcioglu (1994) in measuring ductility of

HSC columns.

lD ¼DuDy

ð1Þ

To achieve the points of equivalent yield displacement,

first, two horizontal lines Hu and 0.75Hu, are drawn, see

Fig. 3. Then, a continuous line from origin to meet point of

the 0.75Hu line and curve up to the Hu line is drawn.

Projection of the last meet point on horizontal axis is an

equivalent point of yield displacement that is shown by Dy.Finally, project the meet point of 0.8Hu line and original

curve on horizontal axis to get ultimate displacement.

Consequently, the drift ratio is found by dividing the

same maximum recorded displacement by the free length

column, (Du,/L0). The displacements are caused by cyclic

loading where at least two cycles of deformation are

imposed on the member at each deformation level. The

deformations are increased incrementally, where each

increment is less than twice the yield displacement, which

is a standard loading protocol as described by Park (1989)

and recommended by FEMA-461 (2007). Table 3 presents

ductility and drift ratios obtained from the evaluation of

112 column specimens, as well as equivalent yield and

ultimate displacement.

Investigation of experiment data indicates that HSC

column ductility is a function of three groups of parame-

ters, as ACI-ASCE Committee 441 (ACI-ASCE 2010) and

Razvi and Saatcioglu (1994) described: (1) Those related to

applied loading, (2) Those related to confinement rein-

forcement, and (3) Those related to concrete type. The

significance of each of these groups of parameters is

assessed separately in these pair reviews. Approach of this

paper is similar to the mentioned ones, but it maintains its

own attitude and uses more new data and records.

Effect of concrete compressive strength and axialload on ductility

Figure 5 displays variation of displacement ductility (lD)versus concrete strength for three kinds of column test

setup that Fig. 1 depicts their configurations. This Fig-

ure indicates an increase in concrete compressive strength,

tending to lower ductility in all kinds of column test con-

figurations. This effect casts doubt about capability of P/

Table 2 continued

# Ref.

index

Setup

type

Section type fc0

(MPa)

fyl(Mpa)

fyt(Mpa)

L0

(mm)

b

(mm)

h

(mm)

s1(mm)

s

(mm)

dbl(mm)

dbs(mm)

P (N)

97 XVIII C 1 98.6 400 516.0 800 200 200 150 40 16.00 10.00 901,674

98 XVIII C 1 99.8 400 516.0 800 200 200 150 40 16.00 10.00 911,669

99 XVIII C 1 99.6 400 516.0 800 200 200 150 40 16.00 10.00 364,001

100 XVIII C 1 77.6 400 613.0 800 200 200 150 40 16.00 12.00 726,763

101 XVIII C 1 77.1 400 274.0 800 200 200 150 40 16.00 10.00 289,039

102 XVIII C 1 77.3 400 516.0 800 200 200 150 40 16.00 10.00 724,264

103 XVIII C 1 77.9 400 274.0 800 200 200 150 40 16.00 10.00 1,312,671

104 XIX B 9 57.5 608 500.0 3500 450 450 90 50 12.70 9.53 1,164,375

105 XX A 9 92.5 735 862.0 1800 600 600 115.6 450 32.00 13.00 3,330,000

106 XX A 9 99.9 735 862.0 1800 600 600 115.6 450 32.00 13.00 3,596,400

107 XX A 9 96.9 735 862.0 1800 600 600 115.6 260 32.00 13.00 3,488,400

108 XX A 9 107.1 735 862.0 1800 600 600 115.6 260 32.00 13.00 3,855,600

109 XX A 9 108.3 735 862.0 1800 600 600 115.6 450 32.00 13.00 5,848,200

110 XX A 9 125.0 735 862.0 1800 600 600 115.6 450 32.00 13.00 8,100,000

111 XX A 9 112.9 735 862.0 1800 600 600 115.6 260 32.00 13.00 8,128,800

112 XX A 9 121.0 735 862.0 1800 600 600 115.6 260 32.00 13.00 8,712,000

aNI no information is available

Fig. 4 Schematic representation of equivalent yield and ultimatedisplacement


123

Table 3 Other test parameters

# ql qs s1/h s/h Po (KN) P/Po qsfyt/fc0 P/Agfc0 M/Vh Dy (mm) Du (mm) lD Drift (%)

1 1.42% 3.00% 0.66 0.35 2174.3 0.16 0.18 0.20 2.50 2.5 27.0 10.8 5.4%

2 1.42% 3.00% 0.66 0.29 2211.1 0.16 0.18 0.20 2.50 2.5 18.0 7.2 3.6%

3 2.13% 2.33% 0.24 0.22 2908.2 0.20 0.52 0.20 1.20 2.5 12.0 4.8 2.2%

4 2.13% 2.33% 0.24 0.22 2908.2 0.20 0.52 0.20 1.20 2.5 24.0 9.6 4.4%

5 3.81% 4.37% 0.26 0.17 3412.4 0.63 0.17 0.63 2.50 3.0 6.0 2.0 1.2%

6 3.81% 4.37% 0.26 0.17 3412.4 0.63 0.40 0.63 2.50 3.0 22.0 7.3 4.4%

7 3.81% 4.37% 0.26 0.17 4396.8 0.44 0.12 0.42 2.50 3.0 10.0 3.3 2.0%

8 3.81% 4.37% 0.26 0.17 4396.8 0.44 0.30 0.42 2.50 3.0 24.0 8.0 4.8%

9 2.40% 2.00% 0.25 0.18 4064.4 0.32 0.25 0.31 2.00 3.0 20.0 6.7 4.0%

10 2.40% 2.57% 0.25 0.14 4987.3 0.30 0.25 0.28 2.00 3.0 19.0 6.3 3.8%

11 2.40% 2.60% 0.25 0.20 4064.4 0.58 0.12 0.57 2.00 2.0 5.0 2.5 1.0%

12 2.40% 2.25% 0.25 0.16 4064.4 0.58 0.28 0.57 2.00 2.0 7.0 3.5 1.4%

13 2.40% 2.08% 0.25 0.18 4064.4 0.58 0.42 0.57 2.00 2.0 10.0 5.0 2.0%

14 2.40% 2.57% 0.25 0.14 4987.3 0.54 0.25 0.51 2.00 2.0 10.0 5.0 2.0%

15 2.40% 2.67% 0.25 0.14 4987.3 0.54 0.43 0.51 2.00 2.0 15.0 7.5 3.0%

16 2.44% 1.28% 0.25 0.16 5762.4 0.38 0.10 0.35 2.00 5.0 10.0 2.0 1.0%

17 2.44% 1.92% 0.25 0.16 5762.4 0.38 0.15 0.35 2.00 6.0 20.0 3.3 2.0%

18 2.44% 1.55% 0.25 0.24 5762.4 0.38 0.05 0.35 2.00 6.0 10.0 1.7 1.0%

19 2.44% 1.28% 0.25 0.24 5762.4 0.38 0.14 0.35 2.00 6.0 20.0 3.3 2.0%

20 2.44% 1.28% 0.75 0.24 5762.4 0.38 0.10 0.35 2.00 5.0 10.0 2.0 1.0%

21 2.44% 1.26% 0.73 0.24 5762.4 0.38 0.11 0.35 2.00 5.0 10.0 2.0 1.0%

22 1.81% 1.28% 0.72 0.12 5601.0 0.39 0.10 0.35 2.00 4.0 5.0 1.2 0.5%

23 1.63% 1.41% 0.38 0.16 5642.9 0.35 0.21 0.35 2.00 3.0 15.0 5.0 3.0%

24 2.44% 1.41% 0.38 0.16 6044.7 0.33 0.21 0.35 2.00 3.0 15.0 5.0 3.0%

25 1.63% 1.41% 0.38 0.16 5642.9 0.52 0.21 0.52 2.00 3.0 7.8 2.6 1.6%

26 3.81% 4.40% 0.26 0.17 4861.2 0.37 0.14 0.34 2.50 3.5 22.0 6.3 4.4%

27 3.81% 4.40% 0.26 0.17 4861.2 0.37 0.30 0.34 2.50 3.2 20.0 6.3 4.0%

28 3.81% 4.40% 0.26 0.17 4861.2 0.51 0.14 0.47 2.50 3.5 11.0 3.1 2.2%

29 3.81% 4.40% 0.26 0.17 4861.2 0.51 0.30 0.47 2.50 3.5 15.0 4.3 3.0%

30 2.44% 1.87% 0.26 0.16 4250.3 0.35 0.28 0.37 2.00 5.0 28.0 5.6 2.8%

31 2.47% 2.06% 0.17 0.37 2267.8 0.00 0.16 0.00 3.20 6.0 15.0 2.5 3.1%

32 2.47% 2.06% 0.17 0.37 1942.2 0.20 0.19 0.20 3.20 4.0 15.0 3.7 3.1%

33 2.47% 2.74% 0.17 0.37 1926.0 0.00 0.25 0.00 3.20 5.0 12.0 2.4 2.5%

34 2.47% 2.74% 0.17 0.37 1849.4 0.10 0.26 0.10 3.20 5.0 15.0 3.0 3.1%

35 2.47% 2.74% 0.17 0.37 1983.5 0.21 0.24 0.20 3.20 4.0 13.0 3.2 2.7%

36 2.47% 2.74% 0.17 0.37 1554.3 0.00 0.52 0.00 3.20 5.7 18.0 3.2 3.7%

37 2.47% 2.74% 0.17 0.37 1707.6 0.10 0.46 0.10 3.20 5.0 18.0 3.6 3.7%

38 2.47% 2.74% 0.17 0.37 1841.6 0.21 0.42 0.20 3.20 4.0 18.0 4.5 3.7%

39 2.47% 2.19% 0.21 0.37 1726.7 0.20 0.36 0.20 3.20 4.0 15.0 3.7 3.1%

40 2.47% 1.83% 0.25 0.37 1937.4 0.21 0.27 0.20 3.20 5.0 12.0 2.4 2.5%

41 2.47% 1.57% 0.29 0.37 1631.0 0.20 0.28 0.20 3.20 4.0 11.0 2.7 2.3%

42 2.44% 2.73% 0.43 0.22 5220.8 0.16 0.23 0.17 1.58 5.4 37.6 7.0 3.9%

43 2.44% 3.82% 0.43 0.13 4997.3 0.16 0.37 0.17 1.58 6.2 49.2 8.0 5.1%

44 2.44% 2.73% 0.43 0.22 8856.3 0.18 0.12 0.17 1.58 7.0 28.0 4.0 2.9%

45 2.44% 3.82% 0.43 0.13 8813.7 0.18 0.19 0.17 1.58 6.4 38.6 6.0 4.0%

46 2.44% 2.36% 0.43 0.22 8914.9 0.18 0.17 0.17 1.58 6.8 27.0 4.0 2.8%

47 2.44% 3.82% 0.43 0.13 8925.5 0.18 0.28 0.17 1.58 7.5 37.6 5.0 3.9%

48 2.44% 3.82% 0.43 0.13 9085.2 0.27 0.18 0.26 1.58 6.4 31.8 5.0 3.3%


123

Table 3 continued


49 2.54% 1.38% 0.38 0.29 2710.8 0.30 0.16 0.30 4.00 2.4 8.7 3.3 1.4%

50 2.54% 0.86% 0.38 0.33 2710.8 0.30 0.10 0.30 4.00 1.8 8.5 3.2 1.4%

51 2.54% 1.38% 0.38 0.19 2710.8 0.30 0.16 0.30 4.00 2.4 8.9 3.6 1.5%

52 2.54% 1.96% 0.38 0.20 2710.8 0.30 0.22 0.30 4.00 2.3 9.9 3.7 1.6%

53 2.54% 1.22% 0.38 0.23 2710.8 0.30 0.14 0.30 4.00 3.1 12.1 4.4 2.0%

54 2.54% 1.95% 0.38 0.14 2710.8 0.30 0.22 0.30 4.00 2.6 13.0 4.9 2.2%

55 2.54% 1.96% 0.38 0.20 2710.8 0.30 0.16 0.30 4.00 2.3 9.7 3.6 1.6%

56 2.54% 1.22% 0.38 0.23 2710.8 0.30 0.10 0.30 4.00 2.4 10.1 3.7 1.7%

57 2.25% 0.87% 0.20 0.23 30,972.6 0.55 0.09 0.57 1.50 5.8 18.0 3.1 1.0%

58 2.25% 1.91% 0.20 0.17 32,425.2 0.45 0.18 0.46 1.50 12.4 50.4 4.1 2.8%

59 2.25% 1.91% 0.20 0.17 34,399.3 0.42 0.16 0.42 1.50 11.7 68.4 5.8 3.8%

60 2.25% 0.89% 0.26 0.08 30,842.4 0.65 0.09 0.67 1.50 12.6 68.9 5.5 3.8%

61 2.25% 0.89% 0.26 0.08 39,516.7 0.51 0.07 0.50 1.50 10.4 23.8 2.3 1.3%

62 2.58% 3.15% 0.44 0.31 6643.6 0.50 0.20 0.50 6.59 4.6 21.2 4.6 1.1%

63 2.58% 2.84% 0.44 0.30 6612.8 0.36 0.21 0.36 6.59 3.6 22.3 6.2 1.1%

64 2.58% 2.84% 0.44 0.30 6620.5 0.50 0.21 0.50 6.59 3.8 19.0 5.0 0.9%

65 2.58% 5.62% 0.44 0.33 6628.2 0.50 0.36 0.50 6.59 4.0 28.0 7.0 1.4%

66 2.58% 3.06% 0.44 0.35 5303.2 0.61 0.26 0.64 6.59 6.2 24.2 3.9 1.2%

67 2.74% 1.83% 0.49 0.21 9253.0 0.33 0.34 0.34 5.74 15.1 57.4 3.8 2.9%

68 2.74% 1.83% 0.49 0.21 9253.0 0.49 0.34 0.50 5.74 9.8 27.3 2.8 1.4%

69 2.74% 3.54% 0.49 0.21 9263.1 0.52 0.67 0.53 5.74 7.1 44.7 6.3 2.2%

70 2.74% 1.90% 0.49 0.40 9263.1 0.33 0.36 0.34 5.74 9.4 35.8 3.8 1.8%

71 2.95% 2.27% 0.18 0.18 11,516.7 0.31 0.31 0.30 2.29 14.0 56.0 4.0 3.5%

72 2.95% 3.75% 0.18 0.18 11516.7 0.31 0.17 0.30 2.29 12.0 48.0 4.0 3.0%

73 2.95% 3.28% 0.12 0.12 11,011.5 0.62 0.46 0.60 2.29 10.7 16.0 1.5 1.0%

74 2.95% 5.33% 0.13 0.13 11,011.5 0.62 0.26 0.60 2.29 12.8 19.2 1.5 1.2%

75 2.95% 2.27% 0.18 0.18 11011.5 0.62 0.32 0.60 2.29 12.8 12.8 1.0 0.8%

76 3.52% 3.67% 0.31 0.20 5224.6 0.09 0.24 0.10 2.00 11.4 91.2 8.0 9.0%

77 3.52% 3.67% 0.31 0.20 5224.6 0.19 0.24 0.20 2.00 9.9 79.2 8.0 7.8%

78 3.52% 3.67% 0.31 0.20 5224.6 0.10 0.24 0.11 2.00 9.4 75.2 8.0 7.4%

79 2.48% 1.63% 0.31 0.20 5447.2 0.20 0.10 0.19 2.00 11.7 81.9 7.0 8.1%

80 2.48% 1.63% 0.31 0.20 5447.2 0.10 0.10 0.10 2.00 10.2 61.2 6.0 6.0%

81 2.48% 1.63% 0.31 0.20 5447.2 0.20 0.10 0.19 2.00 10.7 37.5 3.5 3.7%

82 1.29% 0.30% 0.43 0.37 2599.2 0.16 0.01 0.15 1.54 4.4 15.3 3.5 2.4%

83 1.29% 0.67% 0.43 0.37 2599.2 0.16 0.03 0.15 1.54 3.7 14.5 3.9 2.3%

84 1.29% 1.20% 0.43 0.37 2599.2 0.16 0.05 0.15 1.54 4.5 18.6 4.1 3.0%

85 1.29% 1.87% 0.43 0.37 2599.2 0.16 0.08 0.15 1.54 3.6 11.4 3.2 1.8%

86 1.29% 1.09% 0.43 0.33 2599.2 0.16 0.04 0.15 1.54 3.7 21.3 5.8 3.4%

87 1.29% 1.10% 0.43 0.42 2599.2 0.16 0.04 0.15 1.54 4.2 15.3 3.6 2.4%

88 1.29% 1.08% 0.43 0.67 2599.2 0.16 0.04 0.15 1.54 2.6 14.3 5.4 2.3%

89 1.29% 1.14% 0.43 0.95 2599.2 0.16 0.05 0.15 1.54 2.6 12.7 4.8 2.0%

90 2.01% 2.13% 0.75 0.20 2030.8 0.25 0.12 0.25 2.00 5.0 31.0 6.2 3.9%

91 2.01% 2.13% 0.75 0.20 2114.1 0.25 0.12 0.25 2.00 7.0 28.0 4.0 3.5%

92 2.01% 2.13% 0.75 0.20 2137.4 0.25 0.12 0.25 2.00 7.0 30.0 4.3 3.8%

93 2.01% 3.34% 0.75 0.20 2753.8 0.25 0.13 0.24 2.00 5.5 19.7 3.6 2.5%

94 2.01% 3.34% 0.75 0.20 2867.1 0.25 0.12 0.23 2.00 5.2 21.5 4.1 2.7%

95 2.01% 3.34% 0.75 0.20 2887.1 0.25 0.12 0.23 2.00 5.5 24.0 4.4 3.0%

96 2.01% 3.34% 0.75 0.20 3476.8 0.25 0.18 0.23 2.00 4.8 12.0 2.5 1.5%


123

Agfc0 ratio being inversely proportional to HSC columns

ductility ratio. Indeed, increasing fc0 will reduce the value

of this ratio, where according to other studies like Sheikh

and Yeh (1990) or Shiekh and Khoury (1993), ductility of

column will decrease by increasing P/Agfc0 ratio and it is

absolutely conflicting with the result depicted in Fig. 5,

which shows reduction in HSC column ductility by

increasing the concrete strength. This concern becomes

more challenging in the ASCE 41 (2013), where a larger

range of modeling parameters for the nonlinear structural

analysis of columns for smaller P/Agfc0 ratios is observed.

In addition, when variation of ductility is displayed

versus P/Agfc0, a kind of scatter of data is found. Figures 6,

7 and 8 depict these variations for three column test

configurations (Setup Type) and 14 major steel confine-

ment configurations (Section Type) previously displayed in

Figs. 1 and 3. Although, in some instances the trends are

descending, for some other major instances are ascending,

Table 3 continued


97 2.01% 3.34% 0.75 0.20 3606.7 0.25 0.17 0.23 2.00 4.1 18.0 4.4 2.2%

98 2.01% 3.34% 0.75 0.20 3646.7 0.25 0.17 0.23 2.00 3.8 16.5 4.3 2.1%

99 2.01% 3.34% 0.75 0.20 3640.0 0.10 0.17 0.09 2.00 6.0 27.5 4.6 3.4%

100 2.01% 4.80% 0.75 0.20 2907.1 0.25 0.38 0.23 2.00 4.5 31.6 7.0 4.0%

101 2.01% 3.34% 0.75 0.20 2890.4 0.10 0.12 0.09 2.00 4.0 31.5 7.9 3.9%

102 2.01% 3.34% 0.75 0.20 2897.1 0.25 0.22 0.23 2.00 4.0 28.0 7.0 3.5%

103 2.01% 3.34% 0.75 0.20 2917.0 0.45 0.12 0.42 2.00 5.5 17.0 3.1 2.1%

104 1.00% 2.38% 0.20 0.11 11,029.4 0.11 0.21 0.10 7.78 36.7 207.9 5.7 5.9%

105 3.57% 0.24% 0.19 0.75 36,740.7 0.09 0.02 0.10 1.50 7.0 14.6 2.1 0.8%

106 3.57% 0.24% 0.19 0.75 38,924.3 0.09 0.02 0.10 1.50 7.0 15.0 2.1 0.8%

107 3.57% 0.42% 0.19 0.43 38,039.1 0.09 0.04 0.10 1.50 10.2 22.9 2.2 1.3%

108 3.57% 0.42% 0.19 0.43 41,048.8 0.09 0.03 0.10 1.50 8.3 22.9 2.8 1.3%

109 3.57% 0.24% 0.19 0.75 41,402.9 0.14 0.02 0.15 1.50 7.5 12.8 1.7 0.7%

110 3.57% 0.24% 0.19 0.75 46,330.7 0.17 0.02 0.18 1.50 6.9 14.0 2.0 0.8%

111 3.57% 0.42% 0.19 0.43 42,760.3 0.19 0.03 0.20 1.50 6.2 12.0 1.9 0.7%

112 3.57% 0.42% 0.19 0.43 45,150.4 0.19 0.03 0.20 1.50 8.0 13.9 1.7 0.8%

Fig. 5 Displacement ductility versus concrete compressive strength

Fig. 6 Displacement ductility versus axial load ratio, Setup Type A

Fig. 7 Displacement ductility versus axial load ratio, Setup Type B


123

like Section Type 3, 4, 5 and 8 in Setup Type B and

Section Type 3 and 7 in Setup Type C. Hence, it is not

possible to conclude when P/Agfc0 ratio increases, the dis-

placement ductility of HSC column decreases or not.

Parameters related to confinement

Passive confinement pressure is directly related to volu-

metric ratio of confinement steel that can be applied by

bars and ties. Increase in the volumetric ratio of a specific

grade of steel directly translates into a proportional

increase in the confinement pressure. Therefore, both

strength and ductility of confined concrete are increased.

According to Table 3, it is obvious that displacement

ductility increases by increasing volumetric ratio of con-

finement steel. However, some cases do not obey this rule;

these exceptions occurred due to change in other parame-

ters. Therefore, confinement steel was studied further along

with transverse reinforcement spacing, concrete compres-

sion strength, and strength of confinement reinforcement,

which is discussed in the following section.

Strength of confinement bars

Confinement pressure is generated from tensile forces

developed in confinement steel. It is, therefore, likely to

expect that the steel yield strength plays an important role

in concrete confinement. However, tensile stress in con-

finement steels is created as an outcome of lateral expan-

sion of concrete, which in turn is dependent on the

mechanical properties of concrete. If the lateral strain in

concrete is not high enough to impose higher stresses on

transverse reinforcement, a high capacity of steel may not

be utilized.

The previous research indicates conflicting views on the

use of high-strength steel as confinement reinforcement.

However, by referring to Mugurumu (1991) and Aziz-

inamini et al. (1994), it seems that high yield strength

transverse reinforcement (yield strength exceeding

750 MPa) has been shown to be advantageous when the

level of axial loads is high (above 40% of column axial

load capacity). When the level of axial load is relatively

low (less than or equal to 20% of axial load capacity), the

use of higher yield strength steel for transverse reinforce-

ment may not result in any improvement in the strength and

ductility of HSC columns.

Table 4 shows the results of four test columns that can

compare the effect of yield strength of transverse rein-

forcement on the ductility of HSC columns. All four

specimens were subjected to constant axial load levels

equivalent to 17% of the column capacity, and repeated

lateral loads and all of them had approximately the same

concrete strength. However, the steel yield strength of

lateral reinforcement is classified at two levels of normal

strength (#44 and #45 specimens) and high strength (#46

and #47 specimens). On the other hand, the volumetric

reinforcement ratio for specimen numbers 44 and 46 is 2.73

and 2.36%, respectively, and for specimen numbers 45 and

47 is 3.82%. As it is observed, although the steel yield

strength of lateral reinforcement increases approximately

50%, the displacement ductility and drift ratio of these

specimens do not change significantly and even for speci-

men number 47, displacement ductility is less than speci-

men number 45.

A justification of this condition is due to low limit of

axial compression loading, and the tension stress of lateral

reinforced does not reach the yield point and thus con-

finement stress for both couple specimens are the same so

that displacement ductility values are approximately near

to each other. This result indicates that increasing the yield

strength of the transverse reinforcement has no influence

on the ductility capacity of HSC columns at relatively low

axial load levels. However, on the other hand, when axial

loading is growing, some differences in comparing duc-

tility are exposed. As Table 5 shows, the displacement

ductility of columns increased by rising yield strength of

Fig. 8 Displacement ductility versus axial load ratio, Setup Type C

Table 4 Effect of yieldstrength of ties—adapted from

Azizinamini et al. (1994)

# P/Agfc0 fc

0 (MPa) fyt (MPa) s(mm) qs lD Drift index

44 0.17 100.9 454.0 67 2.73% 4.0 2.9%

45 0.17 100.3 495.4 41 3.82% 6.0 4.0%

46 0.17 101.6 752.8 67 2.36% 4.0 2.8%

47 0.17 101.8 752.8 41 3.82% 5.0 3.9%


123

the transverse reinforcement when ratio of axial compres-

sion loading was above 40% of column axial load capacity.

Confinement pressure is a passive pressure activated by

lateral expansion of concrete under axial compression. This

pressure is dependent on the ability of concrete to expand

laterally prior to failure. In addition, the strength of lateral

steel limits the confinement pressure. If the transverse

strain of HSC is not high enough to pull the confinement

steel to its capacity, then the full capacity of steel is not

utilized. On the other side, HSC is a brittle material and

may not develop transverse expansion high enough to pull

the steel to its yield level. However, it is expected when the

confinement steel develops its strength prior to concrete

strength decay, since in this case, the tensile force in the

confinement steel is directly related to the amount as well

as the yield strength of steel.

When the amount of confinement steels are too much,

the column’s ductility may decrease as presented in

Table 6. As it is seen, ductility of specimen number 85

significantly falls; however, it has the highest volumetric

ratio. It seems, when amount of steels are too much, the

cohesion and bonds of steel and concrete are not appro-

priate, and before confinement steel reach to its maximum

strength concrete column core would be crushed.

Transverse reinforcement spacing

The spacing of lateral reinforcement is a significant factor

affecting the distribution of confinement pressure as well as

stability of longitudinal reinforcement. Closer spacing of

transverse reinforcement raises uniformity of lateral pres-

sure and improves effectiveness of confinement reinforce-

ment, having optimistic effects on the ductility of HSC

columns. Cusson and Paultre (1994) observed that decrease

in tie spacing outcome in better strength and stiffness. Al-

Hussaini et al. (1993) observed that reducing the tie

spacing from 0.8 to 0.2 times the column dimension

increased strength (P/Agfc0) by only 6%. Sudo et al. (1993)

concluded that reduction in spiral pitch outcome in

increases in strength and the corresponding strain, and

improved the descending branch of the stress–strain cor-

relation of confined concrete.

The results point to improvement in ductility with

reduction in lateral spacing. However, the spacing alone

cannot affect the confinement mechanism, unless the other

positive confinement factors are available. For instance, the

volumetric ratio and/or yield strength of steel must be

sufficiently high for spacing to make a difference in the

confinement. Table 7 shows the effect of spacing of

transverse reinforcement on the displacement ductility ratio

adapted from studies conducted by Woods et al. (2007) and

Hwang et al. (2005), which indicated that with invariable

of other parameters, the higher ductility occurred by lower

spacing of lateral reinforcement.

The improvement associated with the use of high-

strength confinement steel is more pronounced in columns

with higher volumetric ratio of transverse steel and lower

strength of concrete. It is expected, since the tensile force

in confinement steel is directly proportional to the amount

and the yield strength of steel, a higher strength concrete

would require higher confinement pressure. Therefore, the

test data are also evaluated using a non-dimensional ratio.

Sugano et al. (1990) as well as Razvi and Saatcioglu

(1994), Saatcioglu and Razvi (1993) reported a correlation

between the non-dimensional parameter of confinement

ratio, qsfyt=f0c and axial deformability of HSC columns

subjected to concentric loads. Razvi and Saatcioglu (1994)

in their study concluded that in all cases, axial deforma-

bility under compression loading increases with increase of

qsfyt=f0c ratio. Furthermore, the study includes comparisons

Table 5 Effect of yieldstrength of ties and axial

loading—adapted from

Muguruma et al. (1990)

# P/

Agfc0

fc0 (MPa) fyt (MPa) s(mm) qs lD Drift index

5 0.63 85.7 328.0 34 4.37% 2 1.2%

6 0.63 85.7 792.0 34 4.37% 7.3 4.4%

7 0.42 115.8 328.0 34 4.37% 3.3 2.0%

8 0.42 115.8 792.0 34 4.37% 8 4.8%

Table 6 Effect of volumetric ratio—adapted from Woods et al.(2007)

# P/Agfc0 s(mm) qs qsfyt/fc0 lD Drift index

82 0.15 76 0.30% 0.01 3.5 2.4%

83 0.15 76 0.67% 0.03 3.9 2.3%

84 0.15 76 1.20% 0.05 4.1 3.0%

85 0.15 76 1.87% 0.08 3.2 1.8%

Table 7 Effect of lateral reinforcement spacing—adapted fromHwang et al. (2005)

# Section typ. s(mm) qs qsfyt/fc0 lD drift index

49 4 57 1.38% 0.16 3.3 1.4%

51 3 38 1.38% 0.16 3.6 1.5%

52 4 40 1.96% 0.22 3.7 1.6%

54 3 27 1.95% 0.22 4.9 2.2%


123

of columns made with distinctly different strength con-

cretes with approximately the same qsfyt/fc0 ratios. Thecomparison indicates that column deformability remains

essentially unchanged when the qsfyt=f0c ratio is maintained,

irrespective of concrete strength. However, it is important

to notice that for compared specimens, comparable rein-

forcement arrangements, tie spacing, and axial load levels

were employed.

Razvi and Saatcioglu (1994) reported the relationship

between concrete strength, confinement steel strengths and

the volumetric ratio of transverse reinforcement. Sugano

et al. (1990) stated that the product qsfyt be increased inproportion to concrete strength. They recommended that

the qsfyt/fc0 ratio should be at least 0.2 to obtain ductilebehavior. Nagashima et al. (1992) reported that 120 MPa

concrete columns showed a sudden drop in strength at a

strain of approximately 1% when qsfyt/fc0 was less than18 MPa (qsfyt/fc0 ratio less than 0.15), and developed strainsin excess of 2% when this product was higher than 18 MPa

(qsfyt/fc0 ratio greater than 0.15). The same research pro-gram reported that the minimum value of 9 MPa for qsfytproduced satisfactory performance for columns with

60 MPa concrete. Hatanaka and Tanigawa (1992) showed

that the qsfyt/fc0 ratio must be kept constant to maintain thesame ductility for normal strength and HSC columns.

Nishiyama et al. (1993) reported that a 4% volumetric ratio

of 800 MPa confinement steel was required to obtain

ductile columns when concrete strength was 110 MPa (i.e.

qsfyt/fc0 = 29%).Review of additional test data, where the volumetric

ratio of steel for HSC was lower or equal to that of the

companion lower strength concrete column, does not nec-

essarily show the same trend. This indicates that the

reduction in concrete deformability due to increased

strength may be offset by increasing the volumetric ratio,

qs, and steel yield strength, fyt, such that the product qsfyt isincreased in proportion to the increase in concrete strength.

Further research is needed to confirm this point.

It is highly important to notice in review of the literature

that only correlation between the non-dimensional param-

eter of confinement ratio,qsfyt=f0c and axial deformability of

HSC columns subjected to concentric loads has been found

and there is not a comprehensive investigation to develop a

correlation between qsfyt=f0c and displacement ductility, lD.

However, Razvi and Saatcioglu (1994) indicated a similar

result like what was explained concerning axial

deformability.

Table 3 illustrates variation of displacement ductil-

ity,lD, with the confinement ratio, qsfyt=f0c. In view of this

study, for all kinds of column test configurations (setup

types in Fig. 1), the general trend of displacement ductility

is ascending versus the confinement ratio. See Fig. 9.

Tie arrangement

Arrangement of reinforcement is another parameter

affecting the distribution of confinement pressure. If the

lateral force applied by transverse reinforcement on con-

crete is well distributed around the perimeter of the core

concrete, the distribution of lateral pressure becomes

almost uniform, improving the effectiveness of confine-

ment reinforcement. Some researches such as Mander et al.

(1988), and Saatcioglu and Razvi (1992) have shown that

the arrangement of transverse reinforcement has major

effects on strength and ductility of normal strength con-

crete columns. In addition, other researchers like Yong

et al. (1988), Sakai (1990), and Saatcioglu and Razvi

(1993) observed the same effect. The results indicate that

HSC columns, reinforced with well-distributed and later-

ally supported longitudinal reinforcement, exhibit

improved ductility. Nagashima et al. (1992) observed,

however, that columns with six, eight, and 12 longitudinal

bar arrangements (Steel Confinement Configuration type 2,

3 and 6—see Fig. 3) did not exhibit a significant difference

in strength and ductility. Cusson and Paultre (1994) con-

cluded that columns with 12 longitudinal bar arrangements

(Type 6 in Fig. 3) did not necessarily show improved

behavior over those with an 8-bar arrangement (Type 3 in

Fig. 3).

Amount, spacing and strength of longitudinal bar

The effect of longitudinal bars, in terms of bar size and

steel grade, has been studied experimentally. Sakai (1990)

reported that columns with a higher percentage of longi-

tudinal steel showed improved ductility. Cusson and

Paultre (1994) concluded that the beneficial effects of high

reinforcement ratio of longitudinal steel increased with the

degree of confinement provided by other parameters. On

the other hand, Bjerkeli et al. (1990) showed that there was

no significant effect of longitudinal steel ratio on the

Fig. 9 Ductility variation versus confinement ratio, qsfyt=f0c


123

stress–strain relationship of confined concrete in columns

with 1.4–3.6% steel ratios. Nagashima et al. (1992) showed

that the grade of longitudinal reinforcement did not affect

the stress–strain relationship of confined concrete.

It is important to notice all these researches investigated

the axial deformability of columns regardless of their lat-

eral loading. According to this investigation (Tables 2, 3),

displacement ductility, and drift ratio increased by

increasing the amount and strength of longitudinal bars.

Furthermore, longitudinal bar spacing as parameter s1, is

another factor affecting the distribution of confinement

pressure. If the lateral force applied by longitudinal rein-

forcement on concrete is well distributed around the

boundary of the core concrete, the distribution of lateral

pressure becomes almost uniform, improving the effec-

tiveness of confinement reinforcement.

Section geometry and size

It has been well established that circular spirals are more

effective in confining concrete than rectilinear ties. The

advantage of circular spirals owes to their geometric shape,

producing unvarying and unbroken pressure around the

border of the core. According to Saatcioglu and Razvi

(1992), rectilinear ties can not produce uniform pressure,

peaking at positions of transverse legs of tie steel. Hata-

naka and Tanigawa (1992) reported that the lateral pressure

created by a square perimeter tie was approximately

0.3–0.5 times of the pressure provided by a circular tie.

Ekasit (1993) reported that strain measured in a spirally

reinforced circular column was 12% higher than that

measured in a companion tied column at the same stress

level.

Most of the HSC column tests reported in the literature

are small-scale specimens. A relative research carried out

by Martinez et al. (1982) that explained lower strength in

smaller specimens in comparison to larger specimens,

representing the size effect. However, because of the lim-

ited nature of the available experimental data, it is difficult

to generalize this conclusion.

Conclusions

This investigation collected some main information on the

ductility of 112 normal weight concrete columns with

specified compressive strength in the range of 50–130 MPa

and presented a novel database. The data included the

results of column testes under axial and reversed lateral

loading. Moreover, HSC columns were evaluated in terms

of their concrete and reinforcement strengths, bar

arrangements, tie spacing, axial load ratio, ductility, and

drift ratio. Therefore, the following conclusions are

presented:

1. In HSC columns, an increase in the specified com-

pressive strength of concrete tends to result in lower

displacement ductility.

2. Review of statistics casts doubt about capability of P/

Agfc0 ratio being inversely proportional to HSC

columns displacement ductility ratio. Indeed, increas-

ing concrete strength will reduce the P=Agf0c ratio and

according to other studies and codes, ductility of

columns will be increased by reducing P=Agf0c ratio.

Hence, codes and standard should be more concern

about range of modeling parameters for nonlinear

analysis of concrete structures with HSC columns and

therefore more studies are needed.

3. To reach the appropriate ductility, HSC columns

should be confined properly. The main parameters of

confinement include volumetric ratio, bar spacing,

arrangement of reinforcement, and strength of trans-

verse reinforcement. Regardless of the effect of axial

load, bars arrangement and lateral reinforcement

spacing, the general trend of displacement ductility,

lD, versus non-dimensional parameter, qsfyt=f0c, is

ascending.

4. If the potential lateral dilation of concrete is not high

enough to impose higher stresses in confinement steel

to its capacity, higher capacity of steel may not be

utilized. Furthermore, HSC is a brittle material and

may not develop transverse dilation high enough to

strain the steel to its yield level. In this case, before

confinement steel reaches to its appropriate strength,

concrete column core would be crushed. Therefore,

more confinement is required to reach the appropriate

ductility. Moreover, review of literature shows that

reducing the bar spacing is more useful than other

confinement parameters.

Open Access This article is distributed under the terms of theCreative Commons Attribution 4.0 International License (http://crea

tivecommons.org/licenses/by/4.0/), which permits unrestricted use,

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appropriate credit to the original author(s) and the source, provide a

link to the Creative Commons license, and indicate if changes were

made.

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Critical factors in displacement ductility assessment of high-strength concrete columnsAbstractIntroductionColumn tests consideredAnalysis of test dataEffect of concrete compressive strength and axial load on ductilityParameters related to confinementStrength of confinement barsTransverse reinforcement spacingTie arrangementAmount, spacing and strength of longitudinal barSection geometry and size

ConclusionsOpen AccessReferences

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