EÍDOS 23

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AZIMI, et al. - Structural Behaviour of Kenaf Fibre Lightweight Concrete Beams Modelling Via FEM-Abaqus. pp. 51-62 ISSN:1390-5007

Sayed Javid Azimi,

Abdulhai Kaiwaan,

Sayed Alem Azimi

Structural Engineering Faculty of Afghan International Islamic University. PhD candidate at Civil Engineering

at Delhi Technological University. s.javidazimi@gmail.com. ORCID: 0000-0003-2149-7768

Structural Engineering Faculty of Afghan International Islamic University. PhD candidate at Civil Engineering

at Delhi Technological University. kaiwaan38@gmail.com. ORCID: 0009-0008-2427-5902

Electrical Engineering faculty of Takhar University. alem.azimi@gmail.com. ORCID: 0009-0005-1451-164X

Structural Behaviour of Kenaf Fibre Lightweight

Concrete Beams Modelling Via FEM-Abaqus

Comportamiento estructural de vigas de hormigón ligero de bra

Kenaf Modulación mediante FEM-Abaqus

EÍDOS N

Revista Cientíca de Arquitectura y Urbanismo

ISSN: 1390-5007

revistas.ute.edu.ec/index.php/eidos

Recepción: 19, 07, 2023 - Aceptación: 14, 11, 2023 - Publicado: 01, 01, 2024

Resumen:

Este estudio presenta las propiedades estructurales de

vigas de concreto ligero de cáscara de palma de acei-

te con bras de kenaf (OPS-KFLC). El objetivo principal

de esta investigación fue investigar la ventaja potencial

de las bras de kenaf para mejorar las propiedades es-

tructurales de las vigas de OPS-RC. Esta investigación

se llevó a cabo mediante dos métodos: experimental

y, consecuentemente, modelado numérico. El trabajo

experimental se centró en dos vigas. La primera viga

se construyó con refuerzo completo de cortante y sin

bras (SI = 0% y con Vf = 0%), denominada como viga

de control. Mientras tanto, se construyó una viga más

con refuerzo completo de cortante (SI = 0%) y con una

fracción de volumen de bras de Vf = 1%. El trabajo ex-

perimental incluyó pruebas de exión de cuatro puntos

en vigas simplemente apoyadas. Posteriormente, se

realizó un modelado numérico con el software de mé-

todo de elementos nitos Abaqus para la calibración y

validación de los resultados experimentales. Primero,

se realizó un análisis de sensibilidad (malla y tiempo)

para obtener la mejor correlación con los resultados

experimentales. Luego, se utilizaron los resultados de

las pruebas de las vigas para la calibración en la in-

vestigación del modelado de elementos nitos (FEM).

La comparación de los resultados mostró que hay una

buena concordancia entre las pruebas experimentales

y los resultados del análisis de elementos nitos no li-

neales (NLFEA). En general, esta investigación demos-

tró una mejora de hasta un 37% en las propiedades es-

tructurales de las vigas de OPS-RC mediante la adición

de un 2% de bras de kenaf.

Palabras clave: Fibra de kenaf, resistencia al corte,

ductilidad, capacidad de carga, modo de fallo, con-

creto ligero.

Abstract:

This study presents the structural properties of oil

palm shell kenaf bre Lightweight concrete (OPS-

KFLC) beams. The main objective of this research

was to investigate the potential advantage of kenaf

ber for improving the structure properties of OPS-RC

beams. This investigation carried out by two methods

experimental and consequently numerical modelling.

The experimental work focused on two beams. First

beam constructed with full shear reinforcement and

without bre (SI = 0% and with Vf = 0%) denoted as a

control beam. Meanwhile one more beams with full shear

reinforcement (SI = 0%) and with bre volume fraction

of Vf = 1% constructed respectively. The experimental

work has been considered four point exural tests on

simply supported beam. Consequently, numerical

modelling with nite element method FEM software

Abaqus for calibration and validation of experiment

results considered. First, sensitivity analysis (mesh

and time) conducted up to acquire the best correlation

with experimental result. Then, the experiments result

of beams was used, for calibration in FEM modelling

investigation. The results comparison showed that

there is a good agreement between the experimental

test and nonlinear nite element analysis NLFEA

results. Generally, this investigation demonstrated up

to 37% improvement on structure properties of OPS-RC

beam by addition of Vf = 2%kenaf ber.

Keywords: Kenaf ber, Shear strength, ductility,

load carrying capacity, mode of failure, Lightweight

concrete.

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1. INTRODUCTION

Lightweight aggregate concrete

(LWAC) is an important economic and ver-

satile material; nonetheless, it has lower

tensile strengths and a subsequently re-

duced shear resistance. As the LWAC has

a lower modulus elasticity, the structure de-

ects more and has a lower rate of loading

in cracking than typical concrete structure

(Almousawi, 2011). In addition, the usage

of LWAC in the concrete industry is still lim-

ited due of its lack of ductility and brittle-

ness (Arisoy, 2002). Oil palm shell (OPS)

is considered as a waste material, and

Malaysia alone produces over 4 million ton

OPS annually. OPS as coarse aggregate

have been found useful by a number of re-

searchers in producing LWAC. Teo et al.

(2006) concluded that 20% dead weight

of construction would decrease by replac-

ing sand aggregate with OPS. Numerous

articles on the physical, and material prop-

erties of OPS as lightweight aggregate for

making LWAC have been published. It was

also reported that the brittleness effect of

OPS-LWAC has yet to be fully mitigated

in the concrete industry (Alengaram et al.,

2013). Several investigations on the incor-

poration of different types of bres in the

mix in order to mitigate this issue has been

reported (Hassanpour et al., 2012; Carmo-

na et al., 2013; Chaallal et al., 1993).

However, it is worth noting that the

literature regarding structural properties of

OPS-RC added with bre is rather limited.

Shagh et al. (2013) enhanced the struc-

tural properties of OPS-RC with steel ber.

However, steel ber is deemed uneco-

nomical and scarce as it comes from non-

renewable resources. Therefore, research-

ers have been investigating on a suitable

substitute for steel bers. The incorpora-

tion of natural bres in concrete as a viable

replacement of conventional steel bers is

of immense interest as it is more economi-

cal and environmentally friendly in promot-

ing “green” structures (Deka et al. (2013).

Akil et al. (2011) revealed that the tensile

strength of kenaf bre is between 400-550

MPa, which is higher than other natural

bres, such as sisal and jute. Therefore,

kenaf ber is capable of improving the

structural properties of OPS-RC. However;

study on kenaf bres added to OPS-RC

structures has yet been published. There-

fore, it is essential to investigate the poten-

tial advantages of kenaf ber in order to

enhance the structural properties of OPS-

RC beams. From a structural standpoint,

the primary reason for adding ber is to

improve structural properties of concrete

through the ber ability. Fiber bridging

over the cracks leads to increase shear,

moment, ductility, punching resistance,

stiffness and reduce cracks widths. Fibre

acts as a multi-dimensional matrix and en-

hances the bond between the matrix that

in turn increases the structural integrity of

the concrete (Hassanpour et al., 2012).

It is apparent that the inclusion of

bres brings about signicant desirable

characteristics as compared to ordinary

concrete. It could also be concluded that

natural bre, such as kenaf has the poten-

tial to serve as a bre reinforced concrete

owing to its favourable properties as dis-

cussed above. Fibre contents in excess

of 2% by volume fraction results in poor

workability which was pointed out by sev-

eral investigations. Hence, this research

tested three volume fraction (Vf = 0%,

Vf = 1% and Vf = 2%) of bre into the OPS-

RC beams experimentally. Several study

reported, addition of different types of -

bres increased the shear strength of con-

crete structures and changed the failure

mode from shear to bending. Thus, this re-

search aimed to substitute kenaf bre as a

part of shear reinforcement in beams. Sub-

stantial amount of work has been carried

out on material properties of OPS-LWAC

concrete, but limited work has been done

to study the inuence of bres on structur-

al performance of the OPS-RC, especially

kenaf bre. It is, therefore, expected that

the incorporation of kenaf ber may im-

prove the structural properties of OPS-RC

(strength, ductility, crack propagation and

mode of failure). It is also anticipated that

kenaf bre may serve as part of shear re-

inforcement to reduce the amount of shear

reinforcement from OPS-RC beams. In or-

der to investigate the efcacy of kenaf -

bres as reinforced concrete, experimental

and simulation work is carried out. Abaqus

will be used to model the OPS-KFRC as it

was proven as an effective tool to study the

issues above (Shagh, et al., 2013; Teo et

al., 2006, Mannan and Ganapathy, 2002).

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Numerical modelling of ber rein-

forced concrete beam with different pro-

posed model for FRC was investigated

through FEM software Abaqus by Abbas

et al. (2010). The ber behaviour within ma-

trix is characterised by its tensile strength.

“Brittle cracking model” that is available in

the Abaqus material model was adopted

to describe the concrete behaviour as in

tensile cracking. From the study Lok and

Xiao (1999) proposed model demonstrat-

ed the tensile post cracking behaviour of

FRC structure better than other models

due to the following reasons. Firstly, dif-

ferent ber specication can be dened

such as ber volume fraction, aspect ratio

and bond stress. Secondly, the orientation

factor or randomness distribution of ber

can be considered. Thirdly, this model is

capable of modelling of tension softening

and hardening behaviour by considering

the variables. Finally, a good correlation

between numerical modelling and ex-

perimental result can be obtained. Fur-

thermore, Abbas et al. (2012) carried out

a study on the structural behaviour of a

simply-supported FRC beam with Abaqus.

The FRC constitutive model proposed by

Lok and Xiao (1999) was adopted in the

research to describe the tensile behav-

iour of ber with “Brittle cracking models”.

Firstly, calibration study was carried with

existing experimental data. Subsequently,

parametric study on bre content varied

from 0 – 2.5% were conducted after the ac-

curate calibration was obtained. The nd-

ing based on load deection and crack-

ing pattern indicated that the inclusion of

ber improves the structural behaviour of

the concrete structure. Hence, the present

research aimed to study the behaviour of

OPS-RC beams upon the inclusion of ke-

naf bres and to determine the potential of

kenaf bres as part of the shear reinforce-

ment in the beams.

2. PREPARATION OF REINFORCED

CONCRETE BEAMS FOR TESTING

The present research centres on

both experimental work and numerical

modelling. The experimental work focuss-

es on the addition of kenaf ber in OPS-RC

reinforced concrete beams under labora-

tory conditions. The results obtained from

the experimental work were used to cali-

brate the numerical model before further

parametric studies are carried out.

Table 1 lists three sets of concrete

mixture proportions for ve beams. Kenaf

bres included in the mixtures are 30 mm

of length with a diameter between 0.1 mm

to 2 mm as shown in Fig. 1. Super-plasti-

cizer was added to achieve the required

slump. The concrete mixture used in the

fabrication of all specimens has a slump in

the range of 95 mm to 105 mm.

Table 1. Mixture of concrete

Ingredients Kg/m³ Kg/m³

Concrete Mix 1 Mix 2

Kenaf ber (Vf = 1%) 0 1

Coarse aggregate

(OPS)

308 308

Super plasticizer

(Liter/m³)

5 5

Fine aggregate(sand) 848 848

W/C ratio 0.4 0.4

Cement 510 510

Fig. 1. Kenaf ber (cut 30 mm length)

Fig. 3. Main reinforcement arrangement

& dimensions of The beam

Fig. 2. Loading arrangement and dimensions of the beam

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2.1 Testing

Static loading test was conducted

using a hydraulic machine under two-point

loading. The three linear variable differen-

tial transducers (LVDT) in the actuator was

used to determine the mid-span displace-

ment whilst the load cell indicated the ap-

plied. The cracking of the beams was

marked by numbering all the cracks and

their location. The loading arrangement and

reinforcement properties of the beam are

shown in Fig. 2 and Fig. 3. The beams were

initially designed by Euro code 2 with shear

reinforcement less than that is required to

cause shear failure. The test was carried out

on the 56th day in order to ensure that the

OPS-RC beams added with kenaf were fully

hardened. Concrete beams under laborato-

ry conditions. The results obtained from the

experimental work were used to calibrate

the numerical model before further para-

metric studies are carried out. Table 1 lists

three sets of concrete mixture proportions

for ve beams. Kenaf bres included in the

mixtures are 30 mm of length with a diameter

between 0.1 mm to 2 mm as shown in Fig. 1.

Super-plasticizer was added to achieve the

required slump. The concrete mixture used

in the fabrication of all specimens has a

slump in the range of 95 mm to 105 mm.

The load arrangement and dimension of the

beams are given in Figure 3.11. The exural

test was carried out using the MTS hydraulic

machine with a capacity of 300 kN. The hy-

draulic pressure was connected to a com-

puter that records the data and displays the

force applied on a graph. A thin coat of ‘best

temp’ paint (white wash) was applied on the

surface of the beams to improve the con-

crete cracking visualization during the test-

ing. The strain gauge was attached at the

middle of shear span with a position of 45

degree in order to record the shear strain.

The exural strain of concrete is measured

through the strain gauge attached at the

bottom of the mid span of beam based on

recommendation of Fernando et al (2003).

The deection of the beams during testing

were obtained from three linear variable dif-

ferential transducers (LVDT) placed on the

mid span of the beams.

3. NUMERICAL SIMULATION

PROCEDURE

The numerical modelling is ac-

complished by means of NLFEA built in

Abaqus. Fig. 4 briey explains the numeri-

cal work procedure conducted through

Abaqus.

Figure 4. Numerical analysis procedure with FEM software

(Abaqus)

The geometry of the beam is mod-

elled similarly to the beam considered

in the experimental work created in the

part module by entering the dimensions

(length, width and height), thickness of

the cover, as well as reinforcements. In

order to simulate the experimental con-

ditions, steel plates of 10 mm thickness

and 20 mm width extending across the

breadth of the beam were added at the

support and loading points. The steel

plate for loading points and support point

assigned linear elastic property where the

cracking is not allowed. This was done to

prevent convergence, where the model

could become numerically unstable. In

order to reduce the duration for the ana-

lysing, a half beam (1500 mm long, 150

mm high and 75 mm wide) was modelled

symmetrically along the z-axis as illustrat-

ed in Figure 5.

After the geometry model has

been constructed, the material proper-

ties of OPS-KFRC and reinforcement are

assigned into brittle cracking concrete

model. The effect of the bres as rein-

forcement was adopted in the tension

part of the concrete models, as post peak

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tensile strain softening or hardening de-

pends on the amount of bres. Also, the

bres effect on shear response concrete

structure considered by using the “shear

retention” part of Abaqus concrete mod-

el. Shear retention is used to allow for the

impact of aggregate interlock and dowel

action. After all the aforementioned set-

tings are arranged, the model is then sub-

mitted to the analysis procedure. At the

calibration stage of this study, numerical

modelling is carried out by using beams

with Vf = 0%, Vf = 1% ber content and

full shear reinforcement SI = 0%. Once an

acceptable correlation was obtained, the

parametric studies based on two distinct

parameters volume fraction of ber (Vf)

and stirrups spacing incensement (SI)

were performed. The NLFEM is used to

calibrate and validate the results obtained

from the experimental work, and then fol-

lowed by further parametric studies. The

numerical modelling was carried out by

using quasi-static analysis in Abaqus/Ex-

plicit with brittle cracking concrete model.

4. RESULTS AND DISCUSSION

The load-deection relationships

of beams that were acquired in the experi-

mental works were used to calibrate and

validate the FE predictions. The modulus

of elasticity of 18.5 GPa was used for all

beams. A number of sensitivity studies

mesh were also performed as shown in

Figures 6 and sensitivity of time as shown

in Figure 7. This was conducted to corre-

late experimental results with our nite ele-

ment model as it is both mesh and time

dependent. The mesh adopted has an el-

ement size of 15 mm was selected once

the sensitivity analysis mesh and time was

Figure 5. Half of the beam model in Abaqus with dened boundary condition along-z- symmetrical

Table 3.3. Material properties of concrete and steel reinforcement

Material properties of concrete Material properties of steel reinforcement

Compressive strength 20 MPa Density 7850 kg/m³

Density 2000 kg/m³ Modulus of elasticity 200 GPa

Modulus of elasticity 18.5 GPa Poisson’s Ratio 0.3

Poisson’s Ratio 0.2 Yield stress for main reinforcement 610 MPa

Strain value for compression -0.0035

Ultimate stress for main

reinforcement

650 MPa

Strain value for tension of OPS-RC 0.001 Yield strain for main reinforcement 0

Strain value for tension of OPS-

KFRC

0.006 Ultimate strain for main reinforcement 0.1

Tensile strength of concrete 2 MPa Yield stress for shear reinforcement 510 MPa

Shear retention factor 0.5 Density 7850 kg/m³

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performed. By reducing the mesh size to

15 mm the duration of the analysis of each

model increased up to 10 hours. There-

fore, the mesh sizing associated with 15

mm together with T2 were selected it pos-

sesses a good correlation with the experi-

mental data. Figure 6 shows kinetic en-

ergy plots to determine failure for beams

of calibration work. The failure point on the

FE investigation in Abaqus is decided via

the kinetic energy of the beam. In present

calibration work and following parametric

modelling, the failure point is determined

based on the sudden high jump in the ki-

netic energy. The sudden high rise of ki-

netic energy indicates that the sudden

movement of structure which specied the

presence of wide cracks within the mem-

ber which representing the structure was

under failure stage as demonstrated by

Syed Mohsin (2012).

The failure point on the FE investi-

gation in Abaqus is decided via the kinetic

energy of the beam. In present calibration

work and following parametric modelling,

the failure point is determined based on

the sudden high jump in the kinetic en-

ergy. The sudden high rise of kinetic en-

ergy indicates that the sudden movement

of structure which specied the presence

of wide cracks within the member which

representing the structure was under

failure stage. The comparisons between

the experimental and numerical results

are shown in Fig. 7 and Fig. 8 with the

key parameters summarised in Table 2.

It was discovered that load-deection

curves of the FE model results were in

good agreement with the experimental

results. It is observed that experiment

result has stiffer load-deection curve

as compared to FE model with volume

fraction of Vf = 0%. In addition, the beam

with ber volume fraction of Vf = 1% cor-

relates better in terms of stiffness and ul-

timate displacement.

A comparison between the exper-

imental and numerical MESH and TIME

analysis results is presented in Fig. 9 and

Fig. 10, for both beams without and with

bres denoted by symbols (Vf = 0%) and

(Vf = 1%), respectively. The key values

are summarised in Table 2. There is good

agreement between the two sets of data.

Figure 6. Kinetic energy plots to determine failure for

calibration work

Figure 7. Load-deection curves for mesh

analysis with SI = 0%

Figure 8. Load-deection curves for time analysis

with SI = 0%

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4.1 Parametric Studies

Following the calibration work,

parametric studies are conducted with two

broad parameters, kenaf bres volume

fraction (Vf) and the increase in stirrups

spacing (SI). The effects of bres amount

on structural enhancements are studied by

six-volume fraction of kenaf bres which

are Vf = 0%, Vf = 0.5%, Vf = 1%, Vf =

1.5%, Vf = 2% and Vf = 2.5% on three

stirrups spacing arrangement of SI=0%,

SI=50% and SI= 100%. Furthermore, the

beams were modelled with reduced shear

reinforcement in order to induce a shear

mode of failure. The additions of bres

for improving shear strength of the beam

in case of changing the mode of failure

from shear to bending are examined. The

stress-strain relationship in tension that

was adopted in the parametric studies are

shown in Fig. 11 and with the main values

summarised in Table 3.

The load- deection curves in Fig.

12 and Fig. 13 display that the beam with-

out bres failed prematurely suggesting a

sudden brittle mode of failure which as-

sociated with shear strength insufciency.

Figure 11. Stress-strain relations in tension for parametric

studies

Figure 9. Load-deection curve of OPS-RC beam with

SI = 0%

Figure 10. Load-deection curve of OPS-KFRC beam with

SI = 0%

Table 2. Calibration results summary for beams with full shear reinforcement

Beam

δy

δu

Pma

µ=δu/δy

EX (Vf = 0%) 58.0 6.9 73.0 13.0 77.0 1.8

FE(Vf = 0%) 61.0 9.0 73.9 12.9 73.9 1.4

EX(Vf = 1%) 69.0 9.9 70.1 28.1 84.5 2.8

FE (Vf = 1%) 64.5 9.0 70.4 27.9 81.9 3.1

Table 3. Tensile stress-strain parameters

or OPS-RC

Point Strain (‰)

Stress, Vf = 0%

(MPa)

Origin 0.00 0.00

Peak tensile

stress (A)

0.10 2.00

Ultimate tensile

strain(B0)

1.00 0.00

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As compared to control beam, the beam

with ber illustrates signicant increase in

strength, stiffness and ductility that is more

vital pertaining for design considerations.

Inspection of the load deection show

that by increasing the amount of ber the

stiffness, load at yield (Py), and maximum

load (Pmax) consistently increases. The

ductility ratio shows improvement upon

the inclusion of bre up to a certain extent,

nonetheless beyond this limit, the ductility

behaves otherwise. This is due to the ad-

dition of more kenaf ber, as the amount of

kenaf ber increases, the beam became

stiffer and deects less which is essentially

contributed by the ber acting as pull-out

mechanism and cracks arrestor which

cause multiple cracking to the beam.

Hence, it is apparent that kenaf ber in-

creased the shear capacity of the beam

as the mode of failure changed from shear

failure to more bending ductile one. There-

fore, the improvement of shear strength

due to bres endorses their possibility to

substitute conventional shear reinforce-

ment that in turn suggests that the bres

signicantly increase structure properties

of OPS-RC beam.

Fig. 13. Load-deection curves for OPS-KRFC beams with

SI = 50%

Fig. 12. Load-deection curves for OPS-KRFC beams

with SI = 100%

Table 4. Results summary for parametric studies for beams with SI = 100%

Vf (%)

(KN)

δy

(mm)

(KN)

δu

(mm)

Pmax

(KN)

µ=δu/δy

0% 50.30 8.00 50.30 8.00 50.40 1.00

0.50% 57.80 9.20 70.90 10.60 67.44 1.15

1% 61.50 9.20 79.98 16.94 78.16 1.84

1.50% 63.00 9.20 75.38 21.90 79.11 2.38

2% 64.50 9.20 74.48 24.93 80.49 2.71

2.50% 66.00 9.20 80.10 20.90 81.63 2.27

Table 5. Results summary for parametric studies for beams with SI =50%

Vf (%)

(KN)

δy

(mm)

(KN)

δu

(mm)

Pmax

(KN)

µ=δu/δy

0% 33.61 6.00 33.61 6.00 33.61 1.00

0.50% 51.46 9.00 51.46 9.00 51.46 1.00

1% 58.60 9.40 64.50 10.90 64.50 1.16

1.50% 60.20 9.40 73.87 15.50 74.84 1.65

2% 61.60 9.40 74.24 16.95 77.59 1.80

2.5% 62.80 9.40 72.48 20.50 79.69 2.18

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4.2 Principal Strain Contour

The principal strain contours of

beams at failure phase with SI = 0%, is

presented in Fig. 14. In order to observe

the contours at failure, the principal strain

range is selected between an ultimate

tensile strain of 0.001 cracking strain for

beams without bres and 0.006 pull-out

strain for OPS-KFRC beams and an ulti-

mate compressive strain of -0.0035. The

grey colour highlighted as tensile failure in

principal strain contour of beam represent-

ing the area where exceeding the ultimate

tensile strain 0.006 for OPS-KFRC and

0.001 for OPS-RC while the region of com-

pressive failure are highlighted in black

where the value exceeds the maximum

compressive strain. It was found that the

failure of beams were considered by ten-

sile cracking at the bottom of middle point

of the longest span of beam (at the sec-

tion where the loads (P) were applied) and

top of central support. By associating the

contour of beams with different percent-

age of ber (Vf), it is observed cracking

formation decreases by increases in bre

amount. Throughout the analysis, only one

of these small cracks developed earlier

will continue to propagate into a large one.

This led to a different location for the single

main crack at failure in the beams. More-

over, the pull-out failure region is limited to

the narrow zone that situated at the areas

of tensile cracking as show for OPS-KFRC

beams. Furthermore, it is observed from

the cracking pattern the beams without -

ber showed high expanded compression

zone and diagonal cracking since more

ber added the cracking pattern concen-

trated at mid-span and showed altering of

mode of failure. However, the beams with

insufcient amount of ber did not exhibit

cracking pattern more limited at mid-span

of the beam that indicates the importance

of the amount of ber for altering the mode

of failure. For instance the beams with full

shear reinforcement when added ber up

to Vf = 0.5% the cracking pattern indicated

Figure 14. Principal strain vector for beams with SI = 0% and (a)Vf = 0%, (b) Vf = 0.5%, (c) Vf = 1%, (d) Vf = 1.5%, (e) Vf = 2%

and (f) Vf = 2.5%

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mode of failure not altered since added -

ber up to Vf = 1% the cracking pattern con-

centrated at mid-span and mode of failure

properly altered from shear to bending.

This suggest that the pull-out mechanism

and bridging mechanism of bres caused

to restrained cracks propagation and in-

creased the tensile characteristic of OPS-

KFRC structure and prevent from diagonal

cracking. Meanwhile the mode of failure of

beam with sufcient amount of ber altered

from sudden shear to ductile bending.

4.3 Comparative Study of Control Beam

Using Non-Dimensional Ratios

In this section, the overall compari-

son between the beams with various -

bres content and stirrups arrangement are

made by taking the control beam (Vf = 0%

and SI = 0%). Normalised value with duc-

tility and energy absorption is by dividing

them with associated control beam. Con-

siderations on each normalised value are

made to conclude the effectiveness of -

bres on mentioned structural response.

4.3.1 Strength Ratio

The ratio of load at yield to the con-

trol beam (Py/Py0) and load at max to con-

trol beam (Pmax/ Pmax,0) shown in Fig. 15

and Fig. 16 respectively. Similar trend was

observed for the load at max (Pmax) and

load yield (Py) as compared to the control

beam. By the the addition of more bres

(Vf) both values increased steadily. Beams

without bres and with reduced shear re-

inforcement (SI = 50% and SI = 100%)

showed a decrease in load at max and

load at yield ratios as compared to control

beam. The bre act multi-dimensional into

the matrix that improve the bond between

the matrix and caused to increase the load

at yield (Py ). Also, upon crack initiation,

the ber act as crack bridging or pull-out

mechanism and the occurrence of multiple

cracking causes the load at max (Pmax) to

increase.

Adding bres at Vf = 0.5% and at

Vf = 1% with SI = 50% restored the capa-

bility of Py and Pmax level of the control

beam respectively. Meanwhile, the beam

with SI = 100% at Vf = 1% and Vf = 1.5%

restored the capability of Py and Pmax

level of the control beam respectively. The

highest improvement of Py/Py0 and Pmax/

Pmax, 0 ratio was achieved beams with

SI = 0% at Vf = 2.5% up to 12.2% and

11.2% respectively. This concludes that

the addition of kenaf ber into the mixture

considerably enhanced the strength (Py

and Pmax) of OPS-RC structures.

4.3.2 Ductility Ratio

Fig. 17 illustrates the results for the

ratio of ductility ratio for each beam and

that in the control beam plotted against -

bre volume fraction on three stirrups spac-

ing arrangement SI = 0%, SI = 50% and

SI = 100%. There was a considerable in-

crease in the ductility ratio especially for

beams with SI = 0% at Vf = 1.5% up to

212% as compared to control beam. For

beams SI = 50% and SI = 100% the maxi-

mum ductility enhancements are achieved

at Vf = 2% and Vf = 2.5% respectively.

The ductility trend shows improve-

ment for all beams with shear reinforce-

ment arrangement SI = 0%, SI = 50% up

to a certain limit, beyond that the ductility

dropped. The optimum amount of ber was

found to be Vf = 1.5% and Vf = 2% with

Fig. 16. Ratio of yield load to that of the control beam

(SI = 0%, Vf = 0%)

Fig. 15. Ratio of maximum load to that of the control

specimen (SI = 0%, Vf = 0%)

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SI = 0% and with SI = 50% respectively.

The beams with SI = 100% the ductility

consistently increased by increasing the

amount of ber. This is due to the shear re-

inforcement taken-out from the beam. Itis

observed, that the ductility ratio decreas-

es when the shear reinforcement reduced

from the beams. As the shear reinforce-

ment reduced, a high amount of bres was

needed for achieving the same capability

of ductility. It was found that when shear

reinforcement spacing increased from the

beam up to 50% and 100%, with addition

of Vf = 1% and Vf = 1.5% the same capac-

ity of ductility with control beam was re-

stored. It indicates that the improvements

in ductility are reduced when more than

optimum amounts of bres are added.

This can be explained as effectiveness of

bres’ in bridging cracks and limiting their

opening. It was observed, crack propa-

gation was delayed leading to enhanced

ductility of the OPS-KFRC structures as

more ber content added to the beam,

caused the became stiffer and result in

failure at small amount of deformation as

explained by Syed Mohsin (2012).

5. CONCLUSION

It can be concluded; Kenaf ber

showed good compatibility in order to im-

prove the structure properties of OPS-RC

beams. Thus, ber with crack-bridging

mechanism or pull-out mechanism re-

strained the crack opening and increased

the strength (Py and Pmax) and as well as

increased the ductility up to certain limit.

In addition, kenaf bres were efcient for

improving the tensile strength of OPS-RC

to prevent from diagonal-tension cracking

and caused to change the mode of failure

of OPS-RC beams from shear to bending.

Hence, it is claried that kenaf ber with

adequate amount could increase the shear

capacity of beam as the mode of failure

of beam changed from shear to bending.

Therefore, this is conrmed that by addi-

tion of a proper amount of kenaf ber pos-

sible to reduce the amount of shear rein-

forcement from OPS-RC beams. It is highly

recommended to use kenaf ber with an

adequate amount into OPS-RC structure

for producing green concrete structure

and improving the structure properties of

OPS-RC beams.

• Then nonlinear nite element analy-

sis program (Abaqus) successfully

had been used to calibrate and vali-

date against experimental results.

Abaqus has shown the capabil-

ity to model the OPS-KFRC beams,

and the calibration results showed a

good agreement with experimental

results

• Kenaf bre showed favourable con-

tribution in improving the strength

(Py and Pmax) and ductility as well

as changing the mode of failure of

OPSKFRC beams. The addition of

ber at Vf = 2% into the beam with

SI = 0% demonstrates the increase

in strength of Py and Pmax up to

31% and 37%, respectively.

• It is also observed that the ductility

ratio is increased; nonetheless only a

certain limit of bre inclusion should

be observed as the inclusion beyond

this limit exhibits poor ductility.

• mode of failure of beams with an

adequate amount of ber changed

from shear to bending as illustrated

by the beam with SI = 100% added

ber at Vf = 2%.

• Cracking pattern indicated that with

a sufcient quantity of ber the mode

of failure of beams changes from

shear to bending as illustrated by

adding a minimum bre of Vf = 1%

Vf = 1.5% and Vf = 2% into the

beams with SI = 0%, SI = 50% and

SI = 100% respectively.

Fig. 17. Ratio of ductility ratio to that of the control beam

(SI = 0%, Vf = 0%)

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ACKNOWLEDGMENT

This study is partly funded by the

Ministry of Higher Education, Afghanistan.

Sayed Javid Azimi wishes to thank Minis-

try of Higher education of Afghanistan for

support by this research grant.

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