Confine Concrete 1

ASIAN JOURNAL OF CIVIL ENGINEERING (BUILDING AND HOUSING) VOL. 12, NO. 3 (2011) PAGES 337-352

INVESTIGATION OF VERSATILITY OF THEORETICAL PREDICTION MODELS FOR PLAIN CONCRETE CONFINED

WITH FERROCEMENT

S.F.A. Rafeeqi and T. Ayub*

Department of Civil Engineering, ED University of Engineering and Technology, 75270 Karachi, Pakistan

ABSTRACT

The paper presents a short investigation of theoretical prediction models for plain concrete confined with Ferrocement. Although to date scant experimental data is available for a conclusive recommendation, however, ample evidence of the versatility of the model proposed by Waliuddin and Rafeeqi [36] has been provided in this paper. The proposed model possess the capability of predicting strength of plain concrete, confined with Ferrocement for almost all the possible and practical methods of confinement by way of; integrally cast mesh layer, mesh layers in precast shell and wrapped mesh layer on precast core.

Keywords: Confinement; ferrocement; theoretical model; plain concrete; strengthening

1. INTRODUCTION

Confinement reinforcement during the turn of the century has assumed a prominent role in the art of design and detailing of reinforced concrete elements, both from the point of view of strength enhancement and increased ductility of the confined sections. Other aspects such as increase in dowel action and aggregate inter lock though not considered to be quantified; however, its qualitative role has always been the part of discussion. Several research studies and subsequent findings [1-7], since Considere [8] endeavour related to confinement have enriched the research literature and the researchers. The ductility requirements of structural section and members in earthquake zones thus have primarily been fulfilled by confinement reinforcement, establishing the important role of confinement.

While new stock of structures are added almost every day on this planet due to population explosion and other reasons; however, demand for strengthening, and retrofitting of existing stock of structures have also been witnessed with the same vigour, due to escalating cost of construction. Strengthening techniques [9-22], therefore, are in great demand due to the sole reason that no one technique can offer answer to variety of reasons associated with strengthening need within a given geographical bound. Modest strength * E-mail address of the corresponding author: [email protected] (T. Ayub)

S.F.A. Rafeeqi and T. Ayub

338

enhancement and increased ductility is becoming the major demand in most of the developing countries specifically in earthquake prone areas which some how still lack expertise and skill needed for majority of the techniques prevailing in the developed world. Ferrocement [23] which was born in Europe, and attained its youth in the developing world has once again captured the attention of the developed world due to its versatility, forgiving nature, simplicity in use and easy maintenance, and now resides in the safe hands of American Concrete Institute. Though its real application still lies in low cost housing [24-29], however, it is gaining popularity in variety of other applications [30-38] inclusive of strengthening of structures [33-35] in terms of serviceability, strength, ductility and durability. Its selection lies in its superior ability of controlling cracking and excellent ductility. Exploitation of its applicability in confining concrete dates back to almost 3 decades now and number of research papers related to experimental and theoretical investigations has emerged during this period [36-41].

In 1994 the first author of this paper presented result findings as a co-author in a paper related to confinement with Ferrocement published in Journal of Ferrocement [36]. The study at that point in time was comparatively a comprehensive study where theoretical prediction equation was proposed for three methods of confinement envisaged to be of possible practical use. In one of the recent paper [43] the authors of the paper identified the suitability of the proposed theoretical prediction equation [36] and successfully demonstrated its adaptability for predicting strength of the concrete confined with Ferrocement.

The inspiration of this present investigation thus derives its strength from the assertion put forward by Kondraivendhan and Pradhan [32].

2. OBJECTIVE OF THE STUDY

As said earlier that the inspiration gathered from Kondraivendham and Pradhem [32] led to review of all the experimental as well as theoretical studies since 1994 and to compare the results obtained from available prediction equations so as to provide guidance to the practicing engineers engaged in strengthening work. The objective of the study, therefore, remains to be the identification of most suitable prediction equation for evaluating the strength of concrete confined with Ferrocement.

3. METHODOLOGY

Research papers related to the experimental studies available to date were reviewed and were tabulated in a uniform format and each set of results were compared with the available theoretical models to arrive at a rationale for recommending a suitable prediction equation for strength of confined concrete.

INVESTIGATION OF VERSATILITY OF THEORETICAL PREDICTION...

339

4. EXPERIMENTAL RESULTS

In all five (05) experimental studies [36-38,43 and 44] were identified where 144 specimens were tested by Waliuddin and Rafeeqi [36], twenty specimens of each 0,1,2,3,4 layers by Balaguru [37], three (03) tested by Kaushik and Singh [38], seven (07) tested by Kondraivendhan and Pradhan [43] and twelve (12) tested by Mourad [44].

It was only in study [36] that three methods of confining concrete were used; Integrally Cast Mesh Mayer, Mesh Layer in Precast Shell and Wrapped Mesh Layer on Precast Core referred to as Method-1, Method-2 and Method-3.

None of the other studies used Method-2, where as studies [37, 38] used only Method-1 and studies [43, 44] used Method-3 only.

In some of the studies where specimen label/nomenclature were not available, the specimens have been assigned labels by using the first letter of the name of the author(s).

The nomenclature, parameters of the study, unconfined compressive strength and experimentally obtained confined compressive strength for all the studies have been provided in Table A1 to Table A5. In two of the studies [37, 38] the yield strength of wire mesh was not provided which have been obtained through reverse calculations.

5. PREDICTION EQUATIONS AND THEORETICAL RESULTS

The review of the literature revealed that only three (03) researchers [36-38] presented theoretical prediction equations, which are presented, defined and elaborated underneath:

By Waliuddin and Rafeeqi [36]

ycuct fKff

(1)

Where,

pgm KKKK

From this study, Km is evaluated to be:

mK , for integrally cast wire mesh layers = 1

mK , for wrapped wire mesh layers impregnated with mortar = 0.88

mK , for already cast shell with wire mesh layers = 0.83

and,

gK = Coefficient to account for the grade of concrete = 1

pK is proposed as: rp KpK 35 pK = 35 p Kr

Where, p = volume fraction of transverse wires taken over shell area

rK = ratio of cross- sectional and surface area of shell

By Balaguru [37]

yS fAP


340

Table A1: Details and related engineering properties of specimens [36]

Specimen*

label

Cylinder dimension

(mm)

Mesh layers

Yield strength (MPa)

Unconfined compressive strength fcu (MPa)

Experimental confined

compressive Strength (MPa)

Method of attachment

of ferro-mesh layer

Remark

Aa-ii-1 152 x 305 1 345 27.62 30.8

Aa-ii-2 152 x 305 2 345 27.62 34.24

Aa-ii-3 152 x 305 3 345 27.62 37.52

Aa-iii-1 152 x 305 1 345 26.37 29.6

Aa-iii-2 152 x 305 2 345 26.37 33

Aa-iii-3 152 x 305 3 345 26.37 36.22

Ab-i-1 152 x 305 1 345 32.14 35.37

Ab-i-2 152 x 305 2 345 32.14 38.37

Ab-i-3 152 x 305 3 345 32.14 41.42

Ab-ii-1 152 x 305 1 345 30.73 33.84

Ab-ii-2 152 x 305 2 345 30.73 36.95

Ab-ii-3 152 x 305 3 345 30.73 40

Integrally cast mesh

layers

Ba-ii-1 152 x 305 1 345 27.62 30.45

Ba-ii-2 152 x 305 2 345 27.62 33.1

Ba-ii-3 152 x 305 3 345 27.62 35.82

Ba-iii-1 152 x 305 1 345 26.37 29.03

Ba-iii-2 152 x 305 2 345 26.37 31.86

Ba-iii-3 152 x 305 3 345 26.37 34.41

Bb-i-1 152 x 305 1 345 32.14 34.8

Bb-i-2 152 x 305 2 345 32.14 37.35

Bb-i-3 152 x 305 3 345 32.14 39.73

Bb-ii-1 152 x 305 1 345 30.73 33.39

Bb-ii-2 152 x 305 2 345 30.73 35.93

Bb-ii-3 152 x 305 3 345 30.73 38.48

Mesh layer in precast

shell

Ca-ii-1 152 x 305 1 345 27.62 30.45

Ca-ii-2 152 x 305 2 345 27.62 33.27

Ca-ii-3 152 x 305 3 345 27.62 36.39

Ca-iii-1 152 x 305 1 345 26.37 29.31

Ca-iii-2 152 x 305 2 345 26.37 32.14

Ca-iii-3 152 x 305 3 345 26.37 34.97

Cb-i-1 152 x 305 1 345 32.14 37.63

Cb-i-2 152 x 305 2 345 32.14 40.29

Cb-i-3 152 x 305 3 345 32.14 28.75

Cb-ii-1 152 x 305 1 345 30.73 33.56

Cb-ii-2 152 x 305 2 345 30.73 36.22

Cb-ii-3 152 x 305 3 345 30.73 38.93

Wrapped mesh layer on precast

core

After [36]

Specimen label retained as in original paper


341


Specimen*

label

Cylinder dimension

(mm)

Mesh layers




compressive strength (MPa)

Method of attachment

of ferro-mesh layer

Remark

PB-1 150 x 300 1 1585 37.895 42.37

PB-2 150 x 300 2 1585 37.895 49.61

PB-3 150 x 300 3 1585 37.895 52.364

PB-4 150 x 300 4 1585 37.895 54.78


layers

After [37]

* Specimen label assigned by using the first letter of the name of the authors


Specimen*

label

Cylinder dimension

(mm)

Mesh layers


Unconfined compressiv

e load fcu

(MPa)


compressive strength (tons)

Method of attachment of Ferro-

mesh layer

Remark

SKSP-1 150 x 300 1 340 26.65 46.5

SKSP-2 150 x 300 2 340 26.65 50

SKSP-3 150 x 300 3 340 26.65 53.5


layers Aftter [38]

* Specimen label assigned by using the first letter of the name of the authors


Specimen*

label

Cylinder dimension

(mm)

Mesh layers


Unconfined compressive strength fcu (tons)


compressive strength

(tons)

Method of attachment of ferro-mesh layer

Remark

M25 180 x 900 1 310 36.5 65

M30 180 x 900 1 310 46.5 72

M35 180 x 900 1 310 48.5 75

M40 180 x 900 1 310 54 86.5

M45 180 x 900 1 310 60.5 88.5

M50 180 x 900 1 310 61.5 90.5

M55 180 x 900 1 310 69.5 101

Wrapped mesh layer on precast

Core

After [43]

* Specimen label retained as in original paper


342


Specimen*

label

Cylinder dimension

(mm)

Mesh layers





Method of attachment of

ferro-mesh layer

Remark

A1-2 150 x 300 2 530 41.13 51.38

A2-2 150 x 300 2 530 41.13 50.76

A1-4 150 x 300 4 530 41.13 52.71

A2-4 150 x 300 4 530 41.13 48.82

A1-8 150 x 300 8 530 41.13 50.74

A2-8 150 x 300 8 530 41.13 55.99

Wrapped mesh layers on precast

core using special fasteners

B1-2 150 x 300 2 530 41.13 48.8

B2-2 150 x 300 2 530 41.13 53.3

B1-4 150 x 300 4 530 41.13 49.57

B1-8 150 x 300 8 530 41.13 60.3

wrapped mesh layers on precast core bonded on

the edges

C1-4 150 x 300 4 530 41.13 59.87

C1-8 150 x 300 8 530 41.13 71.78

Wrapped mesh layers on precast core by bonding first two layers

After [44]

* Specimen label retained as in original paper

Where SA is the area of cross section of all the wires across the height of the cylinder and

yf is the yield strength of the reinforcement. The ring tension R , resulting from the force

P can be computed using the equation:

)/(/ mmNinlb

l

PR

Where l is the height of the cylinder. The ring tension R produces a confining pressure p computed using the equation:

)mm/N(psid

Rp 22 (2)

Where, d is the diameter of the cylinder. The confining pressure produced by the variable ferro-mesh layers and the data of SH Ahmad and SP Shah [3] were used to estimate the increased compressive strengths.

By Kaushik and Singh [38] In 1999, Kaushik and Singh [38] obtained an analytical model using the analytical model of mander et al. [45] to evaluate the strength MP of axially loaded cylinders confined with


343

Ferrocement and/or containing longitudinal reinforcement. The value of 1K is taken as 4.2

as this value was found to be reasonably accurate. The model is given as:

)(2/).(( 1

2CSstysCfMOM YAwRRVKRRP (3)

Where:

O = Strength of unconfined concrete

R = Radius of column

MR = Radius of mesh layer (mean radius)

CR = Radius of core concrete

stA = Cross sectional area of longitudinal rebar

SY = Yield stress of longitudinal rebar

ysw = Mean yield stress of single wire

SY = Yield strength of longitudinal rebar

C = Strength of confined concrete

And, fV = Volume fraction of mesh in the casing and is given as

))((/..2 2

Cpmrf RRSnwV

Related needed data for evaluation of the theoretical confined strength using the three

prediction equations along with the theoretical confined strength has been provided in Table B1 to Table B5 for each study separately.

6. ANALYSIS AND DISCUSSION OF RESULTS

As intra-study discussion of the results of each study is already available in the respective research papers, therefore, the analysis of the results have been confined only to the objective of the present study.

While all the prediction equations have been shown to predict the confined compressive strength of concrete within their own parameters, however, in order to evaluate the viability of each equation all the specimens with varying number of Mesh Layers and unconfined compressive strength have been plotted in Figures 1 to 3.

The possible ways of strengthening compression members which may be encountered in practice could be by Method-1 integrally cast wire mesh layers which may be used in general enhancement of strength and ductility of columns and masonry walls where new structure is being built, in case where fair face permanent forms may be practical the Method-2 may have more practical significant, where as, Method-3, wrapped wire mesh layers impregnated with sand-cement mortar around an existing compression member would be the most viable solution.


344

Table B1: Evaluation of the theoretical confined strength [36]

Theoretical confined compressive strength Specimen

label

Cylinder dimension

(mm)

Mesh layers

Unconfined compress.

strength fcu

(MPa) Eq. (1) (MPa)

Eq. (2) (MPa)

Eq. (3) (MPa)



Aa-ii-1 152 x 305 1 27.62 30.88 29.0 29.63 30.8

Aa-ii-2 152 x 305 2 27.62 34.15 30.5 31.65 34.24

Aa-ii-3 152 x 305 3 27.62 37.41 32.0 33.66 37.52

Aa-iii-1 152 x 305 1 26.37 29.63 27.8 28.38 29.6

Aa-iii-2 152 x 305 2 26.37 32.90 29.3 30.40 33

Aa-iii-3 152 x 305 3 26.37 36.16 30.9 32.41 36.22

Ab-i-1 152 x 305 1 32.14 35.40 33.4 34.15 35.37

Ab-i-2 152 x 305 2 32.14 38.67 34.8 36.17 38.37

Ab-i-3 152 x 305 3 32.14 41.93 36.2 38.18 41.42

Ab-ii-1 152 x 305 1 30.73 33.99 32.1 32.74 33.84

Ab-ii-2 152 x 305 2 30.73 37.26 33.5 34.76 36.95

Ab-ii-3 152 x 305 3 30.73 40.52 34.9 36.77 40

Ba-ii-1 152 x 305 1 27.62 30.38 28.20 29.63 30.45

Ba-ii-2 152 x 305 2 27.62 33.16 28.81 31.65 33.1

Ba-ii-3 152 x 305 3 27.62 35.93 29.43 33.66 35.82

Ba-iii-1 152 x 305 1 26.37 29.14 26.96 28.38 29.03

Ba-iii-2 152 x 305 2 26.37 31.91 27.59 30.40 31.86

Ba-iii-3 152 x 305 3 26.37 34.68 28.23 32.41 34.41

Bb-i-1 152 x 305 1 32.14 34.91 32.68 34.15 34.8

Bb-i-2 152 x 305 2 32.14 37.68 33.24 36.17 37.35

Bb-i-3 152 x 305 3 32.14 40.45 33.82 38.18 39.73

Bb-ii-1 152 x 305 1 30.73 33.49 31.28 32.74 33.39

Bb-ii-2 152 x 305 2 30.73 36.27 31.86 34.76 35.93

Bb-ii-3 152 x 305 3 30.73 39.04 32.45 36.77 38.48

Ca-ii-1 152 x 305 1 27.62 30.35 28.20 29.63 30.45

Ca-ii-2 152 x 305 2 27.62 33.08 28.81 31.65 33.27

Ca-ii-3 152 x 305 3 27.62 35.81 29.43 33.66 36.39

Ca-iii-1 152 x 305 1 26.37 29.10 26.96 28.38 29.31

Ca-iii-2 152 x 305 2 26.37 31.83 27.59 30.40 32.14

Ca-iii-3 152 x 305 3 26.37 34.56 28.23 32.41 34.97

Cb-i-1 152 x 305 1 32.14 34.87 32.68 34.15 37.63

Cb-i-2 152 x 305 2 32.14 37.60 33.24 36.17 40.29

Cb-i-3 152 x 305 3 32.14 40.33 33.82 38.18 28.75

Cb-ii-1 152 x 305 1 30.73 33.46 31.28 32.74 33.56

Cb-ii-2 152 x 305 2 30.73 36.19 31.86 34.76 36.22

Cb-ii-3 152 x 305 3 30.73 38.92 32.45 36.77 38.93


345

Table B2: Evaluation of the theoretical confined strength [37]

Theoretical confined compressive strength

Specimen label

Cylinder dimension

(mm)

Mesh layers

Unconfined

compress. strength fcu

(MPa) Eq. (1) (MPa)

Eq. (2) (MPa)

Eq. (3) (MPa)



Balaguru [ 37]

PB-1 150 x 300 1 37.895 42.10* 42.20 ** 43.52* 42.72 **

PB-2 150 x 300 2 37.895 46.31* 46.51 ** 49.15* 49.95 **

PB-3 150 x 300 3 37.895 50.52* 50.47 ** 54.77* 51.675 **

PB-4 150 x 300 4 37.895 54.73* 55.12 ** 60.40* 54.78 **

* Values are estimated for fy = 585 MPa (fy = 85 ksi), estimated using by reverse calculation using equation 1 (Waliuddin and SFA Rafeeqi ** Values are taken from Figure 7 (Ref. 37)

Table B3: Evaluation of theoretical confined strength [38]

Theoretical Confined Compressive Strength

Specimen label

Cylinder dimension

(mm)

Mesh layers

Unconfined compress.

strength fcu

(MPa) Eq. (1) (MPa)

Eq. (2) (MPa)

Eq. (3) (MPa)



Kaushik and Singh [38]

SKSP-1 150 x 300 1 26.65 28.53* 27.51 * 27.63 ** 25.80 **

SKSP-2 150 x 300 2 26.65 30.41 * 28.42 * 28.62 ** 27.75 **

SKSP-3 150 x 300 3 26.65 32.3 * 29.35 * 29.6 ** 29.69 **

* Values are estimated for fy = 340 MPa (fy = 50 ksi), which was estimated using equation 1 and 3 by reverse calculation ** Values are taken from Figure 1 (Ref. 38) and converted into stress


346


Theoretical Confined Compressive Strength Specimen

label

Cylinder dimension

(mm)

Mesh layers


Eq. (1) (MPa)

Eq. (2) (MPa)

Eq. (3) (MPa)



M25 180 x 900 1 20.25 26.25 24.49 25.05

M30 180 x 900 1 25.80 31.80 28.35 27.75

M35 180 x 900 1 26.91 32.91 29.12 28.90

M40 180 x 900 1 29.97 35.96 31.24 33.33

M45 180 x 900 1 33.57 39.57 33.74 34.10

M50 180 x 900 1 34.13 40.13 34.13 34.87

M55 180 x 900 1 38.57 44.57

Relevant data

required to use this equation

is not available in paper

[42] 37.21 38.92


Theoretical confined compressive strength Specimen

label

Cylinder dimension

(mm)

Mesh layers


Eq. (1) (MPa)

Eq. (2) (MPa)

Eq. (3) (MPa)



A1-2 150 x 300 2 41.13 46.31 43.08 44.40 51.38

A2-2 150 x 300 2 41.13 46.31 43.08 44.40 50.76

A1-4 150 x 300 4 41.13 50.75 45.13 47.38 52.71

A2-4 150 x 300 4 41.13 50.75 45.13 47.38 48.82

A1-8 150 x 300 8 41.13 59.36 49.36 53.21 50.74

A2-8 150 x 300 8 41.13 59.36 49.36 53.21 55.99

B1-2 150 x 300 2 41.13 46.31 43.08 44.40 48.8

B2-2 150 x 300 2 41.13 46.31 43.08 44.40 53.3

B1-4 150 x 300 4 41.13 50.75 45.13 47.38 49.57

B1-8 150 x 300 8 41.13 59.36 49.36 53.21 60.3

C1-4 150 x 300 4 41.13 50.75 45.13 47.38 59.87

C1-8 150 x 300 8 41.13 59.36 49.36 53.21 71.78


347

25

30

35

40

45

50

55

60

25 30 35 40 45 50 55 60

Theoratical Results (MPa)

Exp

erim

enta

l Res

ult

s (M

Pa)

Waliuddin and Rafeeqi

Balaguru

Kaushik and Singh

25

30

35

40

45

50

55

60

25 30 35 40 45 50 55 60


Exp

erim

enta

l Res

ult

s (M

Pa)


Balaguru

Kaushik and Singh

Figure 1(a). Integrally cast mesh layers (using Eq. (1))

Figure 1(b). Integrally cast mesh layers (using Eq. (2))

20

25

30

35

40

45

50

55

60

20 25 30 35 40 45 50 55 60


Th

eora

tica

l Res

ult

s (M

Pa)


Balaguru

Kaushik and Singh

Figure 1(c). Integrally cast mesh layers (using Eq. (3)) As has already been mentioned that the only theoretical model which possess capability

of predicting confined strength for all possible methods of confinement is that of Waliuddin and Rafeeqi [36].

Figure 1(a) to Figure 1(c) demonstrates that with integrally cast mesh layers, the model presented by [36] provides better accuracy than prediction models proposed by [37, 38].

Experimental confined strength for mesh layers in precast shell as presented in Figure 2(a) to Figure 2(c) also shows that the prediction model proposed by [36] provides the best accuracy.


348

25

30

35

40

45

25 30 35 40 45Theoratical Results (MPa)

Exp

erim

enta

l Res

ult

s (M

Pa)


25

30

35

40

45


Exp

erim

enta

l Res

ult

s (M

Pa)


Figure 2(a). Mesh layers in precast shell (using Eq. (1))

Figure 2(b). Mesh layers in precast shell (using Eq. (2))

25

30

35

40

45


Exp

erim

enta

l Res

ult

s (M

Pa)


Figure 2(c). Mesh layers in precast shell (using Eq. (3)) Figure 3(a) to Figure 3(c) shows that there is a considerable difference in the predicted

values of confined strength for all the three models for the experimental results of [44]. This difference can be attributable to the additional restraint provided by wrapping ferro-mesh layers on precast core using special fasteners (Series A), bonding the edges (Series B) and bonding first two layers of ferro-mesh layers (Series C) by [44]. Although, the experimental results from study by [44] do not correspond well with any of the prediction equation, however, better accuracy could still be noticed for the model proposed by [36].


349

25

30

35

40

45

50

55

60

65

70

75

25 30 35 40 45 50 55 60 65 70 75

Theoratical results (MPa)

Exp

erim

enta

l Res

ult

s (M

Pa)


Murad

Kondraivendhan and Pradhan

25

30

35

40

45

50

55

60

65

70

75

25 30 35 40 45 50 55 60 65 70 75

Theoratical results (MPa)

Exp

erim

enta

l Res

ult

s (M

Pa)


Murad


Figure 3(a). Wrapped mesh layers on precast core (using Eq. (1))

Figure 3(b). Wrapped mesh layers on precast core (using Eq. (2))

25

30

35

40

45

50

55

60

65

70

75

25 30 35 40 45 50 55 60 65 70 75Theoratical results (MPa)

Exp

erim

enta

l Res

ults

(MP

a


Murad


Figure 3(c). Wrapped mesh layers on precast core (using Eq. (3))

7. CONCLUSIONS AND RECOMMENDATIONS

Following conclusions and recommendations can be drawn from this short investigation of theoretical prediction models for plain concrete confined with Ferrocement.

1. Of the three prediction models available to date, the model proposed by Waliuddin and Rafeeqi [36] possess capability of better accuracy for all the possible practical


350

methods of confinement. 2. More experimental results are needed for validation of the theoretical models

before conclusively proposing a versatile theoretical model.

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Confine Concrete 1

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