Strength and Deformability of High Strength R.C Columns Subjected to Eccentric Loading · 2017. 11....

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Strength and Deformability of High Strength R.C Columns Subjected to

Eccentric Loading

Yasser Mahmuod Mohammad 1, Zainab E. Abd El-Shafy

2,

Kamal A. Assaf3 and Yehia A. Hassanean

4

Abstract:

The use of high-strength concrete (HSC) has been widely accepted by designers and contractors in

reinforced concrete structures, especially heavily loaded column of high-rise building and bridges.

To study the strength and deformability of HSC columns subjected to eccentric loading, nine

columns were tested under eccentric loading and one column only was tested under axial loading.

The investigated parameters were concrete compressive strength, slenderness and rectangularity

ratios, and load eccentricity. The concrete compressive strength ranged from 36.0 to 75.0 MPa

and the slenderness ratio was ranged from 6.67 to 10.0 while the considered eccentricities ratios

ranged from 0.0 to 0.80. Also, comparison between experimental and analytical study was carried.

The results indicated that increasing concrete compressive strength resulted in increasing the

column strength capacity. While increasing the eccentricity are resulted in decreasing the column

strength capacity. Also the comparison between experimental and analytical study indicated that

both ACI 318R-14 and ECP 203-07 codes are acceptable and valid to determine both the load and

the moment capacity of such columns subjected to eccentric loading if take into consideration the

additional moment induced due to column deformations.

Keywords: High Strength Concrete HSC; R.C Columns; Eccentric Loading; Strength; Deformability; Stress-Strain Curves.

Introduction

One of the advantages of using HSC in columns is that it allows smaller size columns cross-

section; thus, providing more floor space and reducing cost of formwork. ACI committee 363R-92

[2], defined high strength concrete as a concrete strength of 41 MPa or greater. Now more recently,

compressive strengths approaching 138 MPa have been used [2]. Many experimental and

analytical researches have been carried out to study the effect of different parameters on the

behavior and deformability of HSC columns under eccentric loading. Previous studies [9], [10],

[11], [12] and [16] reported that:

a. Mode of failure of HSC columns was typically flexure with concrete spalling in the compression zone.

b. Increasing the concrete compressive strength could increase the capacity of the reinforced HSC columns; however, it could significantly decrease the ductility and deformability of the

columns.

c. As the eccentricity increases, the columns give more ductile behavior while columns capacity decreases.

d. Increasing transverse volumetric ratio, decreasing both tie spacing and tie yield strength and tie configuration are very effective in increasing capacity and ductility of HSC columns.

1Civil Engineering Dept, Al.Azhar University, Qena branch. E-mail: [email protected]

2Lectturer of Structural Engineering Civil Eng. Department Faculty of Engineering Assiut University. Assiut 71516,

Egypt. E-mail: [email protected] 3 Associated Prof. of Structural Eng, Civil Eng. Dept., Faculty of Eng. Assiut University,.

4Prof. of Reinforced Concrete, Civil Eng. Dept., Faculty of Eng. Assiut University, E-mail: [email protected].

mailto:[email protected]:[email protected]

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e. Increasing longitudinal reinforcement ratio and yield strength of main steel had a little effect on capacity and ductility of confined HSC columns.

f. Concrete cover spalling zone tended to be larger as concrete compressive strength and steel ratio increased, also as slenderness ratio and initial eccentricity decreased.

Abo Eleineen et al, [1], carried out an experimental and analytical program to study the general

deformational behavior of eccentrically loaded high performance concrete columns and concluded

that the ductility and the failure strain of high performance concrete are lower than those of normal

strength concrete. Canbay et al, [6] and Husem et al, [12] reported that the ultimate strength

calculated by using ACI equivalent rectangular stress block over estimates the capacity of high

strength concrete columns but the capacities calculated using CSA A23.3 stress block agree better

with the experimental results. Nadaf and Biradar [7], also reported that HSC columns tended

towards brittleness leading less deflection at mid height. Also, decreasing the spacing of lateral ties

at both the ends up to certain distance influenced the resistance to the shear generated by uniaxial

loading. Foster [14], studied the spalling of the concrete cover of HSC columns with high-axial

loads applied at small eccentricity and concluded that only one way to prevent early spalling of the

cover and to improve the ductility is to add steel fibers to concrete mixture. Antonius [4], tested

twelve HSC columns to study the effect of confinement on high-strength columns subjected to

eccentric loading and to develop stress-strain analytical model and concluded that the ductility of

reinforced concrete columns depended on the confinement provided by the lateral reinforcement

and the strength enhancement of concrete tended to associated with less ductility and more

brittleness for the failure.

1. Experimental program

Experimental program of this work was consisted of ten HSC columns with cross section of

150×150 mm, 150×200 mm and 150×250 mm and overall height of 1000 mm, 1250 mm and 1500

mm with two end cantilevers to apply eccentricity and prevent boundary effects. Columns

longitudinal reinforcement was 6Ф10 mm and lateral reinforcement of 1 Ø 8/150 mm. Three

different strengths of concrete with target compressive strength of 36, 60 and 75 MPa were used.

All tested columns have concrete cover of 25 mm. Columns were tested under eccentric loading

with eccentricity ratio, e/t = 0, 0.2, 0.5 and 0.8. The tested reference column R and Nine columns

were arranged in four groups B, C, D and E as presented in table No. 1. Also complete details of

specimens were shown in Figure (1).

2. Material Properties Concrete mixes were designed to produce concrete target cubic concrete compressive strength of

36, 60 and 75 MPa. The properties of the material used in the mixes were as follows:

Cement: Ordinary Portland cement with chemical, physical and mechanical properties complied with Egyptian Standard Specifications E.S.S.

Coarse aggregate: The coarse aggregate used in normal-strength concrete was local gravel of 20 mm maximum nominal size, 2.65 specific gravity and 1.67 t/m

3 volume weight. The coarse

aggregate used in high-strength concrete was crushed basalt of 20 mm maximum nominal size, 2.7

specific gravity and 2.35 t/m3 volume weight.

Fine aggregate: The fine aggregate used was local natural siliceous sand with 2.60, 1.58 and 2.58 specific gravity, volume weight and fineness modules respectively.

Water: Drinking water was used for mixing and curing.

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Silica fume: Silica fume was used in producing high-strength concrete specimens with average particle size of 0.1µm, the specific surface area is (12 – 15m

2/g) and the specific gravity is 2.2.

Superplasticizer: High-range-water-reducing admixture (HRWRA) was added to concrete composites to improve workability without increasing water content. Product density is 1.21t/m

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and for doses about 3% by weight of cement content.

Steel reinforcement: Longitudinal reinforcement steel was deformed bars of high tensile steel with diameter of 10 mm, while lateral reinforcement steel were plain bars of normal mild steel

with diameter of 8 mm.

Tables (2) and (3) are summarized the concrete mix proportions and mechanical properties of the

used steel.

Table (1): Details of the tested columns

Group Column

No. As

b

mm

t

mm e/t

fcu (MPa)

t/b h/b Ties / Spacing

(mm)

R R 6Ф10 150 250 0.0 75 1.66 10.0 1 Ø 8/150

B

A2 6Ф10 150 250 0.5 75 1.66 10.0 1 Ø 8/150

B1 6Ф10 150 150 0.5 75 1.00 10.0 1 Ø 8/150

B2 6Ф10 150 200 0.5 75 1.33 10.0 1 Ø 8/150

C C1 6Ф10 150 250 0.2 75 1.66 10.0 1 Ø 8/150

C2 6Ф10 150 250 0.8 75 1.66 10.0 1 Ø 8/150

D D1 6Ф10 150 250 0.5 36 1.66 10.0 1 Ø 8/150

D2 6Ф10 150 250 0.5 60 1.66 10.0 1 Ø 8/150

E E1 6Ф10 150 250 0.5 75 1.66 6.67 1 Ø 8/150

E2 6Ф10 150 250 0.5 75 1.66 8.33 1 Ø 8/150

fcu Target cubic concrete compressive strength.

As Longitudinal reinforcement.

b Breadth of column cross-section.

t Depth of column cross-section.

h Column height

e Load eccentricity.

Table (2): Mix by weight for the different mixes.

Mix

No.

Amount of constituent materials/m3

fcu

MPa Cement

(kg)

Aggregate (kg) Water

(Liter)

Silica fume

(kg)

HRWRA

(kg) Sand Gravel Basalt

1 450 610 1220 ------- 175 --- -- 36

2 500 600 ----- 1200 155 75 12 60

3 550 570 ----- 1140 145 90 16 75

Table (3): Mechanical properties of the used steel

Commercial diameter in mm 6 8 10 12

Yield strength in MPa 299.4 242.0 617.5 512.1

Ultimate strength in MPa 445.9 398.0 719.4 673.9

Elongation % 30.00 26.0 11.0 12.0

Grade according to ECP203 280/450 240/350 400/600 400/600

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Figure (1): Details of the tested Columns.

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3. Fabrication of the tested columns

This program was carried out in the R.C. laboratory at Assiut University. The mixing of

constituent materials was achieved by means of horizontal pan mixer of 0.1 m3 capacity. For

normal-strength concrete, the dry aggregates and cement were first mixed for one minute, then; the

water was added and mixing was continued for two minutes. The same steps were followed for

HSC, where the dry aggregates, cement and silica fume were mixed for one minute, then the

HRWRA was added to the water and poured it gradually and mixing was continued for two

minutes. All columns were cast vertically in steel forms. Before casting, the interior faces of the

form were greased to facilitate the extraction of concrete columns. Casting of concrete was done in

layers, where each layer was compacted with an electrical internal rod vibrator. For all columns,

the time of mixing and the method of compaction were held constant. Concrete samples of three

cubes 15cm side length were cast with each column at the same time. The measured slump for mix

no. 1 was 65 mm, while mixes no.2 and 3 were wet and sloppy due to its content of HRWRA. The

columns and cubes were sprayed with fresh water two times per day until 28 days from casting.

Electrical resistance strain gauges were mounted on the reinforcing bars at the proposed position

before casting. The gauges were covered with a water-tight material to protect strain gauges

against moisture.

4. Test set up and procedure

All columns were white painted one day before testing to facilitate cracks observations during

loading test. Deformations of the longitudinal reinforcement steel were measured by electrical-

resistance strain gauges. Two adjacent longitudinal steel bars were instrumented at the middle

height by two electrical strain gauges which glued and isolated to protect it before casting .To

measure concrete deformations; one electrical strain gauge was instrumented on expected

compression side at the mid-height of specimens to predict strains in compression zone. All strain

gauges were connected to a digital strain indicator to collect readings at different loading stages.

Longitudinal displacement was measured using a dial gauge with an accuracy of 0.01mm fixed on

bottom head of the testing machine. Also lateral deformations were measured by two dial gauges

fixed on two adjacent sides of specimens at the mid-height region. To apply eccentricity, load was

applied with two special roller bearing systems to ensure eccentricity on specimens. Column was

placed between heads of compression machine and adjusted the assembly roller bearing system on

the top and bottom of tested column to control eccentricities. Load was applied with a constant

increment of 5 ton for each load level up to failure and was kept constant for about three minutes.

During this period, reading of electrical strain gauges of steel and concrete strains, dial gauges.

Also cracks width and the cracks propagation were recorded at the beginning and end of each

increment of loading.

5. General Behavior and Mode of Failure of Tested Columns

Due to big eccentricity applied on the tested columns, first crack initiated prematurely. For all

tested column under eccentric loading the first crack initiated horizontally at mid height of the

tension side. By increasing load, the width of first crack increased and other horizontally cracks

initiated parallel to first crack along the tension side of the tested columns. Subsequently, by

increasing load, all these cracks had trended towards compression side in horizontal direction till it

reached to the neutral axis of cross-section then it moved in inclined direction. Before failure

occurred; vertical cracks appeared suddenly at mid third or close to mid third of compression side

for columns A2, B1, C1, D1 and E1. The vertical cracks are appeared at upper third of

compression side for column B2, D2, E2 and, R while these cracks were appeared at lower third of

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compression side for column C2 till failure took place. Failure was associated with separated of

concrete cover in compression zone for. Figures (2 and 3) showed Failure mode and pattern of

cracks of tested column. Table (4) summarized test results for tested columns.

Column (A2) Column (B1) Column (B2) Column (C1) Column (C2)

Column (D1) Column (D2) Column (E1) Column (E2) Column (R)

Figure (2): Failure Mode and Pattern of Cracks for Tested Columns.

Figure (3): Crack zones of the tested columns.

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Table (4): Test Results

Group

No.

Column

No. 𝑓𝑐ˋ

(Mpa)

ei

(mm)

△fail efail (mm)

Pcr

(KN)

Pult

(KN)

Mult

(KN.m) △1

(mm)

△2 (mm)

R R 63.2 0 17.1 13.6 0 1600 1950 0

B

A2 64.3 125 25.5 6.55 143.95 50 500 71.975

B1 63.5 75 27.4 5.00 97.40 50 300 29.22

B2 64.8 100 26.6 5.60 121.00 50 450 54.45

C C1 64.40 50 21.2 10.70 60.50 600 1050 63.525

C2 64.7 200 41.8 3.55 238.25 40 260 61.945

D D1 28.92 125 27.3 7.70 144.60 50 250 36.15

D2 52.7 125 26.5 6.80 144.70 50 450 65.11

E E1 64.6 125 20.7 8.10 137.6 200 600 82.56

E2 64.5 125 24.8 7.40 142.4 100 550 78.32

Where:

𝑓𝑐ˋ : Cylinder concrete compressive strength (MPa).

ei : Initial load eccentricity (mm).

Mult : Failure moment (KN.m)

△fail : Deflection at Pult (mm). Pcr : Cracking load (KN).

Pult : Failure load (KN).

efail = ei + △fail (mm). △1 : Mid-height axial displacement (mm). △2 : Mid-height lateral displacement (mm).

6. Discussion of test results 6.1 : Cracking and Ultimate loads:

The relation between both the cracking and ultimate loads, and the studied parameters are plotted

in Figure (4.a) to Figure (4.d). The cracking load is not affected by both rectangularity of the

column cross-section and concrete compressive strengths but pronounced effect is observed due to

increase of the load eccentricity. Increasing of load eccentricity ratio from 0.0 to 0.80 is leads to

decrease the cracking load by 97.5 %. The decreasing of cracking load this is may be due to the

higher tensile stresses induced due to higher induced bending moment. Also, the higher

slenderness ratio meets low cracking load this is may be due to the higher values of added bending

moment. Increasing the slenderness ratio from 6.33 to 10.0 is decreasing the cracking load by

75%.

The same behavior is almost observed for the affects of the studied parameters on the ultimate

loads. Increasing rectangularity ratio from 1 to 1.67 resulted in increasing column load capacity

with 67% as shown in Figure (4.a). Also, increasing load eccentricity ratio from zero to 0.8 of

column thickness led to decrease load capacity by 87%, as shown in figure (4.b). This is due to the

higher tensile stresses induced due to higher induced bending moment. Figure (4.c) indicated that

increasing concrete compressive strength (𝑓𝑐ˋ) from 30 MPa to 64.0 MPa resulted in increasing

column capacity by 100%. Also increasing slenderness ratio from 6.67 to 10.0 is leads to decrease

the load capacity 16.67% as shown in Figure (4.d).

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Figure (4-a): Effect of rectangularity ratio on ultimate and cracking

load.

Figure (4-b): Effect of load eccentricity on ultimate and cracking load.

Figure (4-c): Effect of concrete compressive strength on ultimate and

cracking load. Figure (4-d): Effect of slenderness ratio on ultimate and cracking load.

6.2 Maximum Mid-height Deformations:

Both rectangularity ratio and concrete compressive strength have slightly affected on the

maximum axial mid-height displacements of the tested columns. Increasing rectangularity ratio

from 1.0 to 1.67 resulted in decreasing mid-height displacement by 7%. This reduction is due to

increase column dimension in the direction of load eccentricity. Likewise increasing concrete

compressive strength from 29.0 MPa to 64.0 MPa resulted in decreasing maximum axial mid-

height displacement 6.6%. On the other hand load eccentricity has pronounced affect on the

maximum axial mid-height displacement. As the load eccentricity increased from zero to 0.8 of

column thickness leads to increase in maximum axial mid-height displacement by 144% this could

be attributed to the increase in moment acting on tested columns. Furthermore, increasing

slenderness ratio from 6.67 to 10 led to increase maximum axial mid-height displacement by

23.19%. Figure (5.a) to Figure (5.d) show the effect of the investigated parameters on the

maximum axial mid-height displacements.

B1

B2A2

B1 B2 A2

0

100

200

300

400

500

600

0.5 1 1.5 2

Load

(K

N)

Rectangularity ratio (t/b)%

Ultimate Load

Cracking Load

C2

A2

C1

R

C2A2C1

R

0

500

1000

1500

2000

2500

0 0.2 0.4 0.6 0.8 1

Load

(K

N)

Load Eccentricity ratio (e/t)%

Ultimate Load

Cracking Load

D1

D2A2

D1 D2 A2

0

100

200

300

400

500

600

20 30 40 50 60 70

Load

(K

N)

Concrete Compressive Strength (fcˋ)

Ultimate Load

Cracking Load

E2 E2A2

E2

E1A2

0

100

200

300

400

500

600

700

5 6 7 8 9 10 11L

oad

(K

N)

Slenderness ratio (h/b)%

Ultimate Load

Cracking Load

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Figure (5-a): Effect of rectangularity ratio on mid-height displacement. Figure (5-b): Effect of load eccentricity on axial mid-height

displacement.

Figure (5-c): Effect of concrete compressive strength on axial mid-height

displacement. Figure (5-d): Effect of slenderness ratio on axial mid-height

displacement.

On other hand maximum mid-height lateral displacement is increased by 31% when the

rectangularity ratio increased from 1.0 to 1.67. Also, decreasing in maximum lateral displacement

by 73.9% is observed when the load eccentricity increased from zero to 0.8 of column thickness.

Also, the maximum mid-height lateral displacement is decreasing by 15% , when concrete

compressive strength increase from 29.0 MPa to 64.0 MPa because of HSC columns are behave

more brittle than those of NSC. On the other hand, increasing slenderness ratio from 6.67 to 10

resulted in decreasing in maximum mid-height lateral displacement by 19.1%; this is because of

column with small slenderness ratio failed in brittle manner with compression failure mode

causing large lateral displacement. Figures from (6-a) to (6-d) illustrated the effect of investigated

parameters on lateral mid-height displacement.

Figure (6-a): Effect of rectangularity ratio on lateral mid-height

displacement.

Figure (6-b): Effect of load eccentricity on lateral mid-height

displacement.

0

100

200

300

400

500

600

0 5 10 15 20 25 30

Lo

ad

(K

N)

Axial Mid-hieght Displacement (mm).

B1, t/b=1

B2, t/b=1.33

A2, t/b=1.67 0

500

1000

1500

2000

2500

0 10 20 30 40 50

Lo

ad

(K

N)


C1, e/t = 0.2

C2, e/t = 0.8

A2, e/t = 0.5

R, e/t = 0

0

100

200

300

400

500

600

0 5 10 15 20 25 30

Lo

ad

(K

N)


D1, fc' = 31.09 MPaD2, fc' =52.68 MPaA2, fc' = 64.28 MPa

0

200

400

600

800

0 5 10 15 20 25 30L

oa

d (

KN

)


E1, h/b = 6.67

E2, h/b = 8.33

A2, h/b = 10

0

100

200

300

400

500

600

0 2 4 6 8

Lo

ad

(K

N)

Lateral Mid-hieght Displacement (mm).

B1, t/b=1

B2, t/b=1.33

A2, t/b=1.670

500

1000

1500

2000

2500

0 5 10 15

Lo

ad

(K

N)


C1, e/t = 0.2

C2, e/t = 0.8

A2, e/t = 0.5

R, e/t = 0

10

Figure (6-c): Effect of concrete compressive strength on lateral mid-

height displacement.

Figure (6-d): Effect of slenderness ratio on lateral mid-height

displacement.

6.3 Ultimate Induced Strains

Figures from (7-a) to (9-d) illustrated relation between ultimate mid-height induced strains in both

concrete and steel and investigated parameters. Both concrete compressive strain and steel

compression strain are almost having the same observed behavior of mid-height displacements.

Where increase rectangularity ratio or load eccentricity led to increase both concrete compressive

strain and steel compression strain. On other hand increase concrete compressive strength or

slenderness ratio decrease both concrete compressive strain and steel compression strain.

Likewise; increasing rectangularity and slenderness ratio, concrete compressive strength and load

eccentricity resulted in increasing tension steel strain. Table (5) summarized results of ultimate

induced strain for tested columns.

Figure (7-a): Effect of rectangularity ratio on concrete compressive

strain.

Figure (7-b): Effect of load eccentricity on concrete compressive

strain.

Figure (7-c): Effect of concrete compressive strength on concrete

compressive strain.

Figure (7-d): Effect of slenderness ratio on concrete compressive

strain.

0

100

200

300

400

500

600

0 2 4 6 8 10

Lo

ad

(K

N)


D1, fc' = 31.09 MPaD2, fc' = 52.68 MPaA2, fc' = 64.28 MPa

0

200

400

600

800

0 2 4 6 8 10

Lo

ad

(K

N)


E1, h/b = 6.67

E2, h/b = 8.33

A2, h/b = 10

0

100

200

300

400

500

600

-0.003-0.0025-0.002-0.0015-0.001-0.00050

Lo

ad

(K

N)

Concrete Compressive Strain

B1, t/b=1

B2, t/b=1.33

A2, t/b=1.670

500

1000

1500

2000

2500

-0.004-0.003-0.002-0.0010

Lo

ad

(K

N)


C1, e/t = 0.2

C2, e/t = 0.8

A2, e/t = 0.5

R, e/t = 0

0

100

200

300

400

500

600

-0.0035-0.003-0.0025-0.002-0.0015-0.001-0.00050

Lo

ad

(K

N)

Concrete compressive Strain

D1, fc' = 31.09 MPa

D2, fc' = 52.68 MPa

A2, fc' = 64.28 MPa

0

200

400

600

800

-0.004-0.003-0.002-0.0010

Lo

ad

(K

N)


E1, h/b = 6.67

E2, h/b = 8.33

A2, h/b = 10

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Figure (8-a): Effect of rectangularity ratio on steel compression

strain.

Figure (8-b): Effect of load eccentricity on steel compression

strain.

Figure (8-c): Effect of concrete compressive strength on steel

compression strain.

Figure (8-d): Effect of slenderness ratio on steel compression

strain.

Figure (9-a): Effect of rectangularity ratio on steel compression

strain.

Figure (9-b): Effect of load eccentricity on steel compression

strain.

Figure (9-c): Effect of concrete compressive strength on steel compression

strain.

Figure (9-d): Effect of slenderness ratio on steel compression strain.

0

100

200

300

400

500

600

-0.002-0.0015-0.001-0.00050

Lo

ad

(K

N)

Steel Compression Strain

B1, t/b=1

B2, t/b=1.33

A2, t/b=1.670

500

1000

1500

2000

2500

-0.002-0.0015-0.001-0.00050

Lo

ad

(K

N)


C1, e/t = 0.2

A2, e/t = 0.5

R, e/t = 0

0

100

200

300

400

500

600

-0.002-0.0015-0.001-0.00050

Lo

ad

(K

N)


D1, fc' = 31.09 MPa

D2, fc' = 52.68 MPa

A2, fc' = 64.28 MPa0

200

400

600

800

-0.003-0.002-0.0010L

oa

d (

KN

)


E1, h/b = 6.67

E2, h/b = 8.33

A2, h/b = 10

0

100

200

300

400

500

600

0 0.002 0.004 0.006 0.008 0.01

Lo

ad

(K

N)

Steel Tension Strain

B1, t/b=1

B2, t/b=1.33

A2, t/b=1.670

200

400

600

800

1000

1200

0 0.005 0.01 0.015

Lo

ad

(K

N)


C1, e/t = 0.2

C2, e/t = 0.8

A2, e/t = 0.5

0

100

200

300

400

500

600

0 0.002 0.004 0.006 0.008 0.01

Lo

ad

(K

N)


D1, fc' = 31.09 MPa

D2, fc' = 52.68 MPa

A2, fc' = 64.28 MPa0

200

400

600

800

0 0.002 0.004 0.006 0.008 0.01

Lo

ad

(K

N)


E1, h/b = 6.67

E2, h/b = 8.33

A2, h/b = 10

12

Table (5): Induced strains for tested columns

Group

No.

Column

No. 𝑓𝑐ˋ

(Mpa)

Pcr

(KN)

Pult

(KN) cu s Mode of

failure sc st R R 63.19 1600 1950 0.00192 0.00182 ------ Compression

B

A2 64.28 50 500 0.00269 0.00169 0.00823 Tension

B1 63.51 50 300 0.00156 0.00105 0.00147 Compression

B2 64.79 50 450 0.00186 0.00124 0.00442 Tension

C C1 64.40 600 1050 0.00222 0.00188 0.00292 Compression

C2 64.66 40 260 0.00334 ------ 0.01170 Tension

D D1 28.92 50 250 0.00298 0.00118 0.00272 Compression

D2 52.68 50 450 0.00281 0.00126 0.00344 Tension

E E1 64.60 200 600 0.00333 0.00256 0.00210 Compression

E2 64.47 100 550 0.00289 0.00225 0.00252 Compression

Where:

cu : Mid-height concrete strain

s : Mid-height steel strain

st : Mid-height steel compression strain

st : Mid-height steel tension strain

7. Interaction diagram of the tested columns

In order to determine capacity (maximum load and moment) of high strength concrete column

sections, interaction diagram should be drawn. To get applicable interaction diagrams for high

strength concrete sections, equivalent rectangular stress blocks of both ECP 203-07 [5] and ACI

318R-14 [3] were used. Then, strain compatibility and equilibrium of forces were applied to

determine ultimate load and moment capacities of the section .By using Excel sheet, interaction

diagrams for tested columns were drawn. Figures from (10) to (14) show these interaction

diagrams and experimental results (axial load and bending moments) attached to it, in order to

check applicability of these diagrams. Figures indicated that all tested columns are safe and valid

except column (D1), this may be attributed to normal concrete compressive strength.

Results indicated that both ACI 318R-14 and ECP 203-07 are valid and safe for all tested columns

except columns C1 and D1, this could attributed to small eccentricity for column C1 and lower

compressive strength for column D1. All columns except columns C1 and D1 revealed

experimental values higher than interaction diagram this could attributed to additional moment

according to mid-height deformations.

Table (6) summarizes a comparison between loads obtained from experimental program and loads

calculated by interaction diagrams according to both ACI 318R-14 and ECP 203-07. It was

observed that ACI 318R-14 interaction diagram was more conservative than ECP 203-07.

13

Figure (10) Interaction diagram for column (B1) according to ACI 318 R-14 and ECP203-07 with experimental results attached to it.

Figure (11) Interaction diagram for column (B2) according to ACI 318 R-14 and ECP203-07 with experimental results attached to it.

Figure (12) Interaction diagram for column (A2), (C1), (C2), (E1) and (E2) according to ACI 318 R-14 and ECP203-07 with

experimental results attached to it.

Figure (13) Interaction diagram for column (D1) according to ACI 318 R-14 and ECP203-07 with experimental results attached to it.

B10

200

400

600

800

1000

1200

1400

1600

0 5 10 15 20 25 30 35

Lo

ad

(K

N)

Moment (KN.m)

ECP 203-07

B1

0

200

400

600

800

1000

1200

1400

1600

0 5 10 15 20 25 30 35

Lo

ad

(K

N)

Moment (KN.m)

ACI318R-14

B2 0

500

1000

1500

2000

2500

0 10 20 30 40 50 60

Lo

ad

(K

N)

Moment (KN.m)

ECP 203-07

B2 0

500

1000

1500

2000

2500

0 10 20 30 40 50 60

Lo

ad

(K

N)

Moment (KN.m)

ACI318R-14

E2 A2C2

C1

E1

0

500

1000

1500

2000

2500

0 20 40 60 80 100

Lo

ad

(K

N)

Moment (KN.m)

ECP 203-07

E2 A2 C2

C1

E1

0

500

1000

1500

2000

2500

0 20 40 60 80 100

Lo

ad

(K

N)

Moment (KN.m)

ACI318R-14

D1

0

200

400

600

800

1000

1200

1400

0 10 20 30 40 50

Lo

ad

(K

N)

Moment (KN.m)

ECP 203-07

D1

0

200

400

600

800

1000

1200

1400

0 10 20 30 40 50

Lo

ad

(K

N)

Moment (KN.m)

ACI318R-14

14

Figure (14) Interaction diagram for column (D2) according to ACI 318 R-14 and ECP203-07 with experimental results attached to it.

Table (6) Comparison between experimental and analytical loads

Group No. Colum No. PExp (KN) PACI (KN) PECP (KN) (PExp

PACI) (

PExp

PECP)

R R 1950 2279.86 2137.72 0.86 0.91

B

A2 500 550.00 552.48 0.91 0.90

B1 300 340.93 365.20 0.88 0.82

B2 450 453.50 476.25 0.99 0.94

C C1 1050 1356.68 1330.4 0.77 0.79

C2 260 255.00 261.50 1.02 0.99

D D1 250 344.65 339.52 0.72 0.73

D2 450 483.92 494.88 0.93 0.91

E E1 600 551.68 553.68 1.09 1.08

E2 550 551.12 553.20 0.99 0.99

10. Conclusions

This research program was conducted to investigate an experimental study on strength and

deformability of high strength reinforced concrete columns subjected to eccentric loading. From

tests carried out, herein, the following main conclusions can be drawn:

1. The concrete cover spalling zone of the tested columns was tended to be larger for higher concrete strengths. On the other hand, such zone tended to be smaller for higher slenderness

ratios or load eccentricities.

2. Increasing rectangularity ratio for columns leads to increase the column capacity as well as decrease the column ductility. Increasing rectangularity ratio by 67% increasing in column

capacity by 67% but decreasing mid-height displacement by 7%.

3. Increasing concrete compressive strength increasing the column load capacity and decreasing the ductility and deformability of reinforced high-strength concrete columns. Increasing

concrete compressive strength by 106% increasing column load capacity by 100%, on the

contrary; decreasing both of mid-height axial displacement by 3.0 and 6.6% and mid-height

lateral displacement by 15%.

4. Increasing load eccentricity decreasing the column load capacity and increasing ductility of tested column. Increasing load eccentricity ratio from zero to 80% decreasing column load

capacity by 87%. On the contrary; such an increasing of load eccentricity increasing of both

mid-height axial displacement 144%, and mid-height lateral displacement 73.9%.

D2

0

500

1000

1500

2000

2500

0 10 20 30 40 50 60 70

Lo

ad

(K

N)

Moment (KN.m)

ECP 203-07

D2

0

500

1000

1500

2000

2500

0 10 20 30 40 50 60 70

Lo

ad

(K

N)

Moment (KN.m)

ACI318R-14

15

5. Increasing load eccentricity increasing concrete compressive strain and exceeding maximum concrete compressive strain.

6. Increasing the slenderness ratio of column decreasing column load capacity but increasing ductility of tested column. Increasing ratio by 50% decreasing the column capacity by

16.67%, on the contrary; increase mid-height lateral displacement by 23.19%.

References

1- Abd-Elwahab Abo Eleineen; Ali Shereif Abd-Elfaiad; Amr H. Abd-Elazim and Weal

Mohamed Montaser “Behavior of High Performance Concrete Columns under Eccentric

Loading” Second International Conference on Civil Engineering, 1-3 April 2000, pp. 98-109.

2- ACI committee 363R-92 “State-of-the-Art Report on High-Strength Concrete” ACI Structural

Journal, July-August 1997.

3- ACI committee 318 “Building Code Requirement for Reinforced Concrete (ACI 318-14) and

Commentary (318R-14)” American Concrete Institute.

4- Antonius “Confinement Effects on High-Strength Concrete Columns Subjected eccentric

loading” Proceedings of the 4th

ASEAN Civil Engineering Conference, Yogyakarta, 22-23

November 2011.

5- CSA (Canadian Standards Association) (1994): “Design of Concrete Structures” CSA A23.3-

94, Dec., 1994, 200pp.

6- Egyptian Code of Practice for design and construction of R.C. Structures, ECP 203-2007

7- Erdem Canbay, Guney Ozcebe and Ugur Ersoy “High-Strength Concrete Columns under

Eccentric Load” Journal of Structural Engineering, Vol. 132, No.7, July 2006. pp. 1052-1060.

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Loading” International Journal of Innovations in Engineering Research and Technology, Vol.

2, Issue 4, April 2015.

9- Halit Cenan Mertol, Sami Rizkalla, Pual Zia and Amir Mirmiran “Characteristics of

Compressive Stress Distribution in High-Strength Concrete” ACI Structural Journal, Vol. 105,

No. 5, September-October 2008, pp.626-633.

10- Hisham H. H. Ibrahim, and James G. MacGregor “Test of Eccentrically Loaded High-Strength

Concrete Columns” ACI Structural Journal, Vol. 93, No. 5, September-October 1996. pp. 585-

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11- Hisham H. H. Ibrahim, and James G. MacGregor “Flexural Behavior of Laterally Reinforced

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December 1996. pp. 674-684.

12- Jae-Hoon Lee and Hyeok-Soo Son “Failure and Strength of High-Strength Concrete Columns

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13- Metin Husem, Selim Pul, Selcuk E. Gorkem and Serhat Demir “The Behavior of High-

Strength Reinforced Concrete Columns under Low Eccentric Loading” European Journal of

Environmental

14- and Civil Engineering, April 2015.

15- Natalie Anne Lloyd and B. Vijaya Rangan “Studies on High-Strength Concrete Columns under

Eccentric compression” ACI Structural Journal Vol. 93, No.6, November-December 1996,

631-638.

16- Stephen J. Foster “On Behavior of High-Strength Concrete Columns: Cover Spalling, Steel

Fibers, and Ductility” ACI Structural Journal Vol. 98, No.4, July-August 2001, pp. 583-589.

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17- S. Kim, H. C. Mertol, S. Rizkalla and P. Zia “Behavior of High-Strength Concrete Rectangular

Columns” Seventh international Congress on Advances in Civil Engineering, October11-13,

2006, Yildiz Technical University, Istanbul, Turkey, pp.1-10.

18- Teng-Hooi Tan and Ngoc-Ba Nguyen “Flexural Behavior of Confined High-Strength Concrete

Columns” ACI Structural Journal Vol. 102, No.2, March-April 2005, pp. 198-205.

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