There is a great potential of ferrocement for strengthening reinforced concrete member. Ferrocement can be an excellent material in engineering construction. This method should be investigated and compared with conventional reinforced concrete. The beams were designed to have deficiency in shear, while strengthened beams were expected to fail in flexure. The experiments were planned to determine the load capacity and deformation of strengthened beams which were tested in static loading. The observation includes the failure mode of the beam as well as crack pattern on surface main beam and ferrocement panel. It was instructive to compare behavior between ferrocement panels and original beams.

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14

Chapter 4

Experimental Investigation on Strengthening Reinforced Concrete Beams
by Ferrocement


4.1 General

There is a great potential of ferrocement for strengthening reinforced concrete member.
Ferrocement can be an excellent material in engineering construction. This method should be
investigated and compared with conventional reinforced concrete. The beams were designed
to have deficiency in shear, while strengthened beams were expected to fail in flexure. The
experiments were planned to determine the load capacity and deformation of strengthened
beams which were tested in static loading. The observation includes the failure mode of the
beam as well as crack pattern on surface main beam and ferrocement panel. It was instructive
to compare behavior between ferrocement panels and original beams.

The research aims to determine the performance strengthened reinforced concrete beam
under different conditions such an effect of additional external steel bar and arrangements. The
effect of variable spacing of external reinforcement was considered. The experimental results
were also compared with analytical predictions such as finite element analysis in the following
chapters.

4.2 Experimental program

4.2.1 Dimensions and reinforcement details of beam specimens

The experimental program consisted of nine beams. The cross-section geometries of all
reinforced concrete beams were 200 mm in width and 400 mm in depth (Figure 4.1). The total
length was 2400 mm and the effective span was 2200 mm. The effective depth was 365 mm.
The clear concrete covering was 25 mm. The specimens were reinforced with 2-DB25 (25 mm
deformed bar) bottom longitudinal reinforcement. The top longitudinal reinforcement was 2-
DB20 (20 mm deformed bar). The transverse reinforcement consist of RB6 (6 mm rounded
bar) spaced at 175 mm center to center. Reinforcement details were illustrated in figure 4.2.
Two control beams were designed to fail in shear for these experiments. CON1 was without
shear reinforcement and CON2 was provided with low percentage of shear reinforcement. The
reference beam (CON2), tested without strengthening, and used as a baseline for comparison
with specimens strengthened by ferrocement. CON3 was designed to fail in flexural failure. It
was provided with maximum percentage of shear reinforcement which was spacing of 50mm.
The main objective of testing the control beam (CON1) was to evaluate the total shear
capacity of concrete alone. CON3 was to study behavior and deformation of flexural failure.






15




Fig. 4.1 Details of beam specimens



Fig. 4.2 Details of reinforcement specimens

4.2.2 Strengthening techniques

The specimens were strengthened by ferrocement attached onto both side faces of the
beam. The ferrocement panels were 20 mm thick. Inside ferrocement panel, the additional
external reinforcement was used for increasing shear strength. As for the bonding of
ferrocement panel with the beam, the holes were made by drilling in to the beams. The epoxy
resin was injected into drilled holes and steel are inserted into the holes. Before plastering
mortar onto beam, wide meshes were provided inside and outside of the addition external
reinforcement.
2
-
DB25

RB6@175

2-DB20

2
-
DB20

2
-
DB25

16

Table 4.1 Description of specimens
Specimens
Spacing of addition
external steel (mm)
Special detail
CON1 - -
CON2 - -
CON3 - -
S75 75 -
S150 150 -
S300 300 -
Col-S75 75 Special reinforcement
Col-S150 150 Special reinforcement
Col-S300 300 Special reinforcement
Note: Special reinforcement means alternate anchorage of dowel bars into main beams.

CON1

CON2

CON3
Fig. 4.3(a) Details of control beams
17

18

4.2.3 Preparation of test specimens

1. Setting up Formworks

This research used grade SD40 (f
y
= 400 MPa) longitudinal steel and grade SD24 (f
y
=
240 MPa) for transverse steel. A total 5 of strain gauges were attached on longitudinal and
transverse reinforcement in each specimen. Figure 4.15 showed the strain gauges arrangement
in each specimen. After the strain gauge was attached by chemical eposy, it was coated by
3M-rubber and paraffin to protect from damage during concrete casting. For the formworks,
plywood was used with thickness of 10 mm for one set of twelve beams and they were braced
with strong wood as shown in figure 4.5.



Fig. 4.4 Reinforcement fabrication and strain gauge installation


Fig. 4.5 Formwork of beam specimen
19


Fig. 4.6 Before concrete casting

2. Beam casting

In order to control the same quality of concrete for all specimens, the concrete used was
obtained from the same batch of ready mix concrete. The slump was determined to check
workability and quality of ready mix concrete. Before casting the concrete, the plywood was
lubricated by oil on all forms to avoid difficulty when demolding. While pouring concrete into
formworks, the pores were reduced by vibrator along the concrete. After casting, the top
concrete surface of the beams was finished and covered by plastic sheets. The 100-mm
diameter by 200 mm concrete cylinders were sampled for every casting of the beam
specimens.



Fig. 4.7 Slump testing and samples of concrete cylinders

3. Formwork removal and curing

The formwork was removed after 3 days of casting, and then the beams were kept in
wetness which was conducted by covering wet sacks. Water was sprayed on the sacks every
24 hours up to 7 days from casting. The concrete cylinders were also kept in the same
conditions with the test specimens. The curing of specimens were illustrated in figure 4.9

20



Fig. 4.8 Pouring concrete



Fig. 4.9 Curing of specimens

4. Strengthening procedure

Ferrocement was used for shear strengthening the reinforced concrete beams. The
strengthening procedures consisted of surface preparation, hole drilling, fixing external steel
bars into drilled holes, and mortar plastering. Prior to bonding, the beam was drilled by an
augur on both sides at the spacing as shown in table 4.1. To allow complete bonding of the
adhesive after drilling, the air was blown into the holes for removing dust and loose particles.

After preparing surface of the beams, the prefabricated skeleton steel, made from RB6
with 2 layers of wire meshes, was attached onto beam surfaces. Then the additional external
steel bars bent in C-shape were inserted into drilled holes in the beam via a chemical epoxy
resin. This epoxy resin was produced by Sika company under the commercial name (Sikadur-
31). Two-component epoxy resin was mixed according to the proportions recommended by
the manufacturer’s instruction. Mixing was carried out in a metal container and continued until
it achieved the uniform color of mixture. The stirrup or C-bars had a length of 360 mm. All
additional external reinforcements were directed at an angle of 90 degree with respect to the
beam’s axis. The specimens S75, S150, and S300 meant the spacing of additional external
steel bars at 75, 150 and 300 mm respectively.
21



Fig. 4.10 Additional external steel


Fig. 4.11 Additional external steel of S series


Fig. 4.12 Additional external steel of COL series
RB6@7.5
RB6 Frame
RB6@7.5
RB6 Frame

RB6@7.5
on frame
22

In the second group of three beams, namely, beams Col-S75, Col-S150, and Col-S300,
the beams were strengthened with C-shape steel bars but the number of drilled holes on the
beam surface was reduced to save the construction time. It was noted that some of the external
steels were not inserted into the drilled hole. As an example, in beam Col-S75, the holes were
made at the spacing of 150 mm for additional C-clip steels. Other external bars are attached
directly to the frame with the spacing of 150 mm. In effect, the spacing of external
reinforcements in Col-S75 was 75 mm center to center as shown figure 4.12, but only
RB6@150 were fixed with the main beams.

The ferrocement frame was attached on two sides. Before plastering, double layers of
wire mesh were attached and tied together with the skeletal steel (figure 4.11). The mortar
mixed used for ferrocement was made by ordinary Portland cement and natural sand. The mix
proportions were 1:2 by weight and the water cement ratio w/c was 0.4. The average cube
compressive strength of mortar was 50 MPa. After mixing, the mortar was plastered on the
wire mesh (figure 4.13), to have a uniform thickness of 20 mm on both sides of the specimens.
The same batch of mortar was poured into the 50x50mm cubic mold for the compressive
strength testing.



Fig. 4.13 Plastering cement mortar and finishing surface

4.2.3 Material properties

The longitudinal reinforcements used in this experiment were SD40 steel grade. Tensile
properties were tested in laboratory. The yield strengths of DB25, DB20 and RB9 were
501.24, 510.68 and 406.61MPa. The ultimate strengths of DB25, DB20 and RB9 were 612.73,
620.72 and 511.85MPa, respectively. Properties of steel were given in table 4.2. The
cylindrical compressive strength of concrete with diameter of 100 mm and 200 mm high were
tested by uni-axial compression test. The average tested compressive strength of concrete and
mortar were given in table 4.3.




23

Table 4.2 Material properties of steel
Materials
Yield stress (MPa)
Ultimate stress (MPa)

Modulus of elasticity (MPa)
DB25 501.24 612.73
5
102×
DB20 510.68 620.72
5
102×
RB6 406.61 511.85
5
102×
Note: Deformed bars used in this experiment were SD40 steel grade

Table 4.3 Material properties of concrete
Specimens

c
f' (MPa)
m
f' (MPa)
Modulus of elasticity (MPa)
CON1 30.13 50.12
4
105.2 ×
CON2 30.42 50.55
4
105.2 ×
CON3 30.42 50.55
4
105.2 ×
S75 30.52 50.78
4
105.2 ×
S150 30.95 50.65
4
105.2 ×
S300 31.52 50.78
4
105.2 ×
Col-S75 30.52 50.78
4
105.2 ×
Col-S150 30.95 50.65
4
105.2 ×
Col-S300 31.52 50.78
4
105.2 ×
Note:
c
f' = compressive strength of concrete (MPa)

m
f' = compressive strength of mortar (MPa)

4.3 Test procedure

All nine beams were tested using hydraulic jack mounted vertically over the test beams.
The beam specimens were tested under simply-supported or third-point bending load set-up.
One end of the specimen was rested on a roller that allowed horizontal movement and the
other on a simple support (figure 4.16). The shear span length was 1100 mm. Specimens were
tested under monotonic loading until failure. The force was measured by a load cell of 1000
kN load capacity. To evaluate the beam deflection, five LVDTs transducers of 50 mm capacity
24

were used according to the arrangement shown in figure 4.14. Displacement transducers were
installed at mid-span and at the ends of the specimens for measuring lateral movement. All
data were recorded with a data logger. For each loading increment, the crack patterns were
observed and marked with permanent pen. Loading capacity, deflection displacement, crack
pattern and strain were compared and evaluated.




Fig. 4.14 Location of LVTDs setup




Fig. 4.16 Three-point bending setup (Front view and side view)

1
2
3
25


Fig. 4.17 Test setup of reinforced concrete beams

4.3.1 Load pattern

The load application consisted of 2 stages. In the first stage, before longitudinal
reinforcements yielded, specimens were tested under load control with monotonically
incremental load of 10 kN for each load step. In the second stage, after longitudinal
reinforcement yielded, specimens were tested under displacement control with monotonically
incremental displacement of 1 mm for each step. In each step, the load level, displacement and
cracked were recorded and compared.

4.3.2 Ultimate shear capacity of specimen

Table 4.4 summarized the prediction of shear and flexural capacities of the control
beam. The calculation was based on the tested material properties and dimension of the
control beam (beam without ferrocement panels). The shear spans to depth ration (a/d) was
3.03. The shear capacity of concrete and stirrup was calculated using ACI recommendations.
The general procedure of ACI318 has been adopted and modified to analyze beam with
ferrocement cover. Applying the ACI equations, the contribution of ferrocement to the total
shear force capacity was calculated and given in table 4.4.









26

Table 4.4 Shear and flexural strength prediction of specimens

Specimen

Concrete shear
capacity
(
)
c
V
,kN
Stirrup shear
capacity
(
)
s
V
,kN
Ferrocement
shear capacity
(
)
f
V
,kN
Total shear
capacity
(
)
u
V
,kN
Moment
capacity
(
)
u
M
,kN-m

Shear
failure load

(
)
y
P
,kN
Yield failure
load
(
)
y
P
,kN

Mode of failure

CON1 65.43 - - 65.43 159.51 130.86 290.01 Shear
CON2 65.74 47.15 - 112.90 159.51 225.80 290.01 Shear
CON3 65.78 165.04 - 230.79 159.51 461.59 290.01 Flexural
S75 65.85 47.15 110.03 223.04 159.51 446.09 290.01 Flexural
S150 66.32 47.15 55.01 168.49 159.51 336.98 290.01 Flexural
S300 66.32 47.15 27.50 141.59 159.51 283.19 290.01 Shear
Col-S75 65.85 47.15 110.03 223.04 159.51 446.09 290.01 Flexural
Col-S175 66.32 47.15 55.01 168.49 159.51 336.98 290.01 Flexural
Col-S275 66.32 47.15 27.50 141.59 159.51 283.19 290.01 Shear









27

4.4 Experimental results

4.4.1 General behavior of reinforced concrete beam specimens

For three control beams (CON1-CON3), the first flexural crack formed at mid span at
a load P = 78 kN. As the applied load increased further, more flexural cracks appeared and at
the same time the length of generated cracks extended. At the later stages of loading, crack
formation had stabilized, so no new cracks formed but the increase in load could only cause an
increase in crack length and width of cracks. At a load P=157.74 kN, diagonal crack appeared
in the shear span and suddenly caused a brittle shear in CON1. It was recorded that the
ultimate shear force carried by the concrete alone was 157.74 kN. In the case of CON2, the
first diagonal shear crack occurred at a load P = 160 kN (close to CON1). The applied load
can be increased further beyond shear force carried by concrete. After exceeding P = 160 kN
load level, shear cracks started to develop and propagate. The excess shear force was carried
by internal stirrups, resulted in the enhancement in shear capacity in comparison to the case of
beam (CON1). This behavior continued until at the load P=227 kN when the beam suddenly
failed in a shear failure. The failure mode was more ductile than beam (CON1). Comparing
the result of the ultimate shear force carried by internal stirrups, it was concluded that the
contribution of the transverse steel was 69.26 kN. Figure 4.19 and figure 4.20 showed the
cracking patterns of both control beams CON1 and CON2 after failure. As for CON3 with
largest amount of internal stirrups, the beam CON3 illustrated a high ductility in comparison
with the case of other beams. Also, the first diagonal shear crack was formed 186 kN. Figure
4.21 showed the cracking patterns of beam CON3 after failure.


Fig. 4.18 First diagonal shear crack


Fig. 4.19 Cracking patterns of CON1 after failure

28


Fig. 4.20 Cracking patterns of CON2 after failure


Fig. 4.21 Cracking patterns of CON3 after failure

0
50
100
150
200
250
300
350
400
0 10 20 30 40 50 60
Mid-span deflection (mm)
Load (kN)
CON1
CON2
CON3
First shear crack
First Flexure crack

Fig. 4.22 Load-displacement relationships of control beams


29

4.4.2 General behavior of strengthened beams

At the service stage, the strengthened beams showed improved performance. The test
results of strengthened beams in terms of the ultimate load P and the mode of failure were
shown in table 4.5. The table also showed the percent load increase compared to the control
beam. It was concluded that the application of externally additional reinforcement with
ferrocement jacket in the form of stirrups could increase the shear capacity of the beams.
Ferrocement was efficient to strengthen reinforced concrete beams in shear. However, it can
be also observed from the table 4.5 that beams Col-S75, Col-S150 and Col-S300 were less
efficient than S-75, S-150, and S-300. In terms of amount of externally additional steel, it the
less spacing of externally additional steel (S75) was more efficient than S150 and S300
respectively.

The failure of the connection between concrete and steel bar occurred at the bottom of
the beams. As a result, these steel bars were detached from the concrete surface and the load
decreased (figure 4.23).

4.4.3 Mode of failure

All beam specimens failed in shear, excepted beam CON3 which failed in flexure. The
mechanism of failure started with the formation of a diagonal crack in shear span and the
subsequent extension of cracks upon further loading. The shear failure was characterized by a
sudden diagonal shear crack in the shear span. The beams were considered to fail when it
could no longer resisted further load or vertical stirrups ruptured. The failure mode was
considered as shear because cracks caused failure to appear in large diagonal shear cracks. In
the strengthened beams, the beams failed due to separation of the ferrocement panel and
tearing of the concrete cover.

However, the increase in shear capacity was found in strengthened beams. Almost all
the failures were shear failures but the presence of ferrocement could significantly increased
the shear capacity. A great number of cracks and sufficient ductility were apparent in
strengthened beams.

4.4.4 Deformation ability

In the tests, beams deflection was measured at the mid-span of the beams. Load-
deflection curve was constructed. The relationship between the force and the deflection at the
mid span of the strengthened beams was depicted in figure 4.24 to figure 4.29. It was observed
that strengthening by ferrocement resulted in a significant improvement in maximum loading
in comparison to control beam (CON2).

4.4.5 Effect of spacing of additional steel bars

The spacing of additional steel bars in beam (S75) and beam (S300) was 75 mm and
300 mm, respectively. The number of additional steel bars in beam (S75) was therefore more
than that in beam S300. In general, the lower the spacing is, the higher the shear strength of
the beam is obtained. The beams (S75, S150 and S300) with all C-shaped bars fixed into the
30

main beams also show better performance compared with the Col-S75, Col-S150 and Col-
S300 despite it has the same spacing.


Fig. 4.23 Plate separation with the concrete cover

0
50
100
150
200
250
300
350
400
0 10 20 30 40 50 60
Mid-span deflection (mm)
Load (kN)
S-75
Col-S75
CON2

Fig. 4.24 Load-displacement relationships of S75 and Col-S75

31

0
50
100
150
200
250
300
350
400
0 10 20 30 40 50 60
Mid-span deflection (mm)
Load (kN)
S-150
Col-S150
CON2

Fig. 4.25 Load-displacement relationships of S150 and Col-S150
0
50
100
150
200
250
300
350
400
0 10 20 30 40 50 60
Mid-span deflection (mm)
Load (kN)
S-300
Col-S300
CON2

Fig. 4.26 Load-displacement relationships of S300 and Col-S300

32

0
50
100
150
200
250
300
350
400
0 10 20 30 40 50 60
Mid-span deflection (mm)
Load (kN)
CON2
S-75
S-150
S-300

Fig. 4.27 Load-displacement relationships of S series
0
50
100
150
200
250
300
350
400
0 10 20 30 40 50 60
Mid-span deflection (mm)
Load (kN)
CON2
Col-S75
Col-S150
Col-S300

Fig. 4.28 Load-displacement relationships of Col series

33

0
50
100
150
200
250
300
350
400
0 10 20 30 40 50 60
Mid-span deflection (mm)
Load (kN)
CON2
S-75
S-150
S-300
Col-S75
Col-S150
Col-S300

Fig. 4.29 Load-displacement relationships of specimens strengthened with ferrocement

Figure 4.29 showed that the ferrocement increased the shear resistance of the
reinforced concrete beams significantly. When compared to the maximum load of CON2, it is
found that ferrocement provided an increase in the loading capacity ranging from 7% to 37%.
The highest capacity increases was recorded in beam S75 and the lowest capacity was
recorded in beam Col-S300.

4.4.6 Strains

The strains were measured in the vertical stirrups at the middle of the left shear span
and one-third and two-third of the right shear span (Figure 4.15). On the ferrocement panel,
the measured strains are also measured in the additional steel at the same position as vertical
stirrups shown in figure 4.15.

0
50
100
150
200
250
300
350
400
0 10 20 30 40 50
Deflection (mm)
Load (kN)

0
50
100
150
200
250
300
350
400
0 500 1000 1500 2000 2500
Strain (micron)
Load (kN)

(a) Load-deflection relationships (b) Load-strain relationships for the vertical
stirrups and external reinforcement
Fig. 4.30 Specimen S75
Debond failure
Debond failure
34

0
50
100
150
200
250
300
0 5 10 15 20 25 30
Deflection (mm)
Load (kN)

0
50
100
150
200
250
300
0 500 1000 1500 2000 2500
Strain (micron)
Load (kN)

(a) Load-deflection relationships (b) Load-strain relationships for the vertical
stirrups and external reinforcement
Fig. 4.31 Specimen S150

0
50
100
150
200
250
300
0 5 10 15 20
Deflection (mm)
Load (kN)

0
50
100
150
200
250
300
0 500 1000 1500 2000 2500 3000 3500
Strain (micron)
Load (kN)

(a) Load-deflection relationships (b) Load-strain relationships for the vertical
stirrups and external reinforcement
Fig. 4.32 Specimen S300

Figures 4.30-4.32 show the relations between load and strains of specimens in “s”
series. The strain in these figures is recorded at location 2 in Figure 4.15. In the initial load
step, a linear-elastic behavior is obtained, followed by a first flexural crack introduced in the
maximum moment region of the beam. After that, a large diagonal shear cracks appeared with
the development of strain in the stirrups and external reinforcement as well as beam
deflection. All specimens reached failure by detachment of ferrocement cover before yielding
of the longitudinal bars. Specimens S75, S150, and S300 showed a debonding failure at the
adhesive-concrete interface. In these specimens, the debonding started at one of the end of
critical diagonal shear crack region. Finally, the ferrocement cover was fully detached from
the main concrete beam. For all strengthened beams, the maximum strains developed in
external reinforcement were as large as two-third of the corresponding values of stirrups in the
main specimens (See figure 4.30 to figure 4.32). This indicates that the stirrups in ferrocement
cover were not as efficient as that in the main beams.

By comparing specimen S75 and S300, specimen S75 could attain higher load capacity
compared with specimen S300 but the mechanism was the same in both specimens. This is as
expected as small spacing of external bars produces higher shear reinforcing areas, thus higher
load capacity. The load-strain diagrams for all specimens indicated that the strains in
ferrocement do not yield.

Debond failure
Debond failure
Debond failure
Debond failure
35

0
50
100
150
200
250
300
0 5 10 15 20 25 30 35 40
Deflection (mm)
Load (kN)

0
50
100
150
200
250
300
0 500 1000 1500 2000
Strain (micron)
Load (kN)

(a) Load-deflection relationships (b) Load-strain relationships for the vertical
stirrups and externally addition
reinforcement
Fig. 4.33 Specimen Col-S75

0
50
100
150
200
250
300
0 5 10 15 20 25
Deflection (mm)
Load (kN)

0
50
100
150
200
250
300
0 500 1000 1500 2000 2500
Strain (micron)
Load (kN)

(a) Load-deflection relationships (b) Load-strain relationships for the vertical
stirrups and externally addition
reinforcement
Fig. 4.34 Specimen col-S150

0
50
100
150
200
250
300
0 5 10 15 20 25
Deflection (mm)
Load (kN)

0
50
100
150
200
250
300
0 500 1000 1500 2000 2500
Strain (micron)
Load (kN)

(a) Load-deflection relationships (b) Load-strain relationships for the vertical
stirrups and externally addition
reinforcement
Fig. 4.35 Specimen col-S300

The load-strain relation of specimens in col-s series are shown in figure 4.33 to figure
4.35. All strengthened beams reached the failure by detachment of ferrocement cover before

yielding of the longitudinal steel. In those beams, the debonding failed at the adhesive
concrete interface and started at the end of diagonal shear crack.
Debond failure
Debond failure
Debond failure
Debond failure
Debond failure
Debond failure
36

The effect of reduced drilling holes can be observed by comparing the load-strain
relation of specimen S75 with Col-S75. Obviously, Col-S75 has lower load capacity but the
mechanism was slightly to S150 both ultimate load and deflection. Reducing the number of
anchorages into the main beam resulted in a strength reduction. This is because the shear force
was not transferred to external steel bars that were not connected with the main beam.

Figure 4.30(b) to figure 4.35(b) show the relationships between the applied load (P)
and the strain in the vertical steel. It can be seen from the figure that there was almost no
contribution from the vertical stirrups to the shear strength of the beam until the first shear
crack formed at loading P=187 kN. After that the strains in both stirrups and external bar
started to develop. The strain in internal stirrups was much greater than that in external
additional steel located at the same position. As can be observed in these figures, the strain of
external steel decreased at the ultimate load capacity corresponding to the point of detachment
of ferrocement cover from the main beam.

The comparison of strains in dowel bars and internal stirrups are shown in figure 4.30
to figure 4.35. It can be seen that the strains in internal stirrups are always larger than those of
dowel bars in ferrocement panel at the same position. Hence, the shear force carried by
internal stirrups is larger than that carried by dowel bars. The difference in strain could be an
indicator of the efficiency of the technique. It is found that the difference is larger in “col-s”
series than in “s” series because of the higher bond efficiency in the latter series.

0
500
1000
1500
2000
2500
3000
0 500 1000 1500 2000
Beam length (mm)
Strain (micron)


(a) Main beam
Fig. 4.36 Strain distribution of CON2

0
500
1000
1500
2000
2500
3000
0 500 1000 1500 2000
Beam length (mm)
Strain (micron)

0
500
1000
1500
2000
2500
3000
0 500 1000 1500 2000
Beam length (mm)
Strain (micron)

(a) Main beam (b) Ferrocement
Fig. 4.37 Strain distribution of S75

37

0
500
1000
1500
2000
2500
3000
0 500 1000 1500 2000
Beam length (mm)
Strain (micron)

0
500
1000
1500
2000
2500
3000
0 500 1000 1500 2000
Beam length (mm)
Strain (micron)

(a) Main beam (b) Ferrocement
Fig. 4.38 Strain distribution of S150

0
500
1000
1500
2000
2500
3000
0 500 1000 1500 2000
Beam length (mm)
Strain (micron)

0
500
1000
1500
2000
2500
3000
0 500 1000 1500 2000
Beam length (mm)
Strain (micron)

(a) Main beam (b) Ferrocement
Fig. 4.39 Strain distribution of S300

0
500
1000
1500
2000
2500
3000
0 500 1000 1500 2000
Beam length (mm)
Strain (micron)

0
500
1000
1500
2000
2500
3000
0 500 1000 1500 2000
Beam length (mm)
Strain (micron)

(a) Main beam (b) Ferrocement
Fig. 4.40 Strain distribution of COL-S75

0
500
1000
1500
2000
2500
3000
0 500 1000 1500 2000
Beam length (mm)
Strain (micron)

0
500
1000
1500
2000
2500
3000
0 500 1000 1500 2000
Beam length (mm)
Strain (micron)

(a) Main beam (b) Ferrocement
Fig. 4.41 Strain distribution of COL-S150

0
500
1000
1500
2000
2500
3000
0 500 1000 1500 2000
Beam length (mm)
Strain (micron)

0
500
1000
1500
2000
2500
3000
0 500 1000 1500 2000
Beam length (mm)
Strain (micron)

(a) Main beam (b) Ferrocement
Fig. 4.42 Strain distribution of COL-S300
38

Figure 4.36-4.42 showed the experimental strain distribution recorded along beam span
for all strengthened beams. The figures show strain plots at three load level, namely, the load
at the first shear crack, half load between the first shear crack load and the ultimate load, and
the ultimate load. In these specimens, six strain gauges were attached onto the external steel
bar and stirrup of main beam. The location of strain gage attachment was shown in the figure
4.15. The higher strains indicate the location of expanding diagonal shear crack. As can be
seen, the internal stirrups could develop the strain in the yielding range. But the external steel
bar could develop lower strains.


4.4.7 Crack pattern

The crack patterns of the specimens after the test were shown in figure 4.43 to figure
4.48. It can be seen that there were more cracks in ferrocement panel than in the main beam.
Almost all failures of the beams in series S and Col-s series can be classified as shear failure
caused by the occurrence of one large shear crack in one of the shear span of the beam. After
the development of a few bending cracks, shear crack formed. In ferrocement cover, most
bending cracks were formed at the location of additional steel bars and penetrated along the
ferrocement panel at the location of drilled holes. When the load increases, the crack width
increased continuously until the beam fails. Inside the main beams, two shear cracks appeared,
one in each beam shear span. The crack width in one of these cracks was large, and caused the
stirrup that crossed the crack to fracture. Delamination between ferrocement panel and
concrete surface of main beam was also observed. The concrete of original beam crossing the
failure shear crack was ruptured at the beam edges (figure 4.23) and causing the load to drop.

4.4.8 Ultimate load capacity

The results showed that a smaller spacing of additional external steel bars in the
ferrocement cover increased the ultimate strength. The shear strength of beam S75 was
improved after strengthening by about 50% compared to beam CON2. The ultimate load for
beam S150 and beam COL-S75 was the same, which was 283 kN. This represents an increase
of about 25% compared to the ultimate load of the control specimen. While the ultimate load
capacity of beam S300, Col-S150, and Col-S300 were 263.30 kN, 255.06 kN, and 264.87 kN
respectively. The strengthened beams showed an improvement in ultimate load, but the failure
mode was ferrocement detachment.

The results showed that the shear strength of the beams improved after strengthening
by about 12% to 50%. The strengthened beams that acted compositely showed higher
improvement in ultimate load. While the strengthened beams in “col” series showed smaller
improvement in ultimate strength, because the shear force could not transfer to external
vertical reinforcements which were not anchored with the main beam.

39

Table 4.5 Test results
Cracking load (kN)

Specimens

Flexure
Shear
Ultimate load
u
P
(kN)
Increase in ultimate
load after
strengthening
(
)/
2,,conunu
PP

Maximum
deflection
(mm)
Increase in ultimate
displacement after
strengthening
(
)/
2,,conunu
δδ

Mode of failure
CON1 78 157 157.74 - 4.02 - Shear
CON2 78 157 227.00 - 9.61 - Shear
CON3 78 157 379.94 1.67 54.34 5.65 Flexure
S75 78 157 340.01 1.49 17.08 1.77 shear
S150 78 157 283.99 1.25 25.02 2.60 Shear
S300 78 157 263.30 1.15 15.87 1.65 Shear
Col-S75 78 157 282.62 1.24 30.09 3.13 Shear
Col-S150 78 157 255.06 1.12 21.84 2.27 Shear
Col-S300 78 157 264.87 1.16 15.09 1.57 Shear







40

Table 4.6 Comparison of experimental and analytical results
Experimental (kN)
Calculated strengths
(kN)
Calculated
strengths for
ferrocement
Total ultimate
shear strength

Experimental/
Calculated

Specimens

exp
M
(kN-m)
exp
V
(kN)

cal
M
(kN-m)

cal
V
(kN)

cal
V
(kN)
cal
V
(kN)
cal
VV/
exp

CON1 86.75 78.87 159.51 65.43 - 65.43 1.21
CON2 124.85 113.50 159.51 112.90 - 112.90 1.01
CON3 208.96 189.97 159.51 230.79 - 230.79 0.82
S75 187.00 170.00 159.51 113.01 110.03 223.04 0.76
S150 156.18 141.99 159.51 113.47 55.01 168.49 0.84
S300 144.81 131.65 159.51 114.08 27.50 141.59 0.93
Col-S75 155.44 141.31 159.51 113.01 110.03 223.04 0.63
Col-S150 140.28 127.53 159.51 113.47 55.01 168.49 0.76
Col-S300 145.67 132.43 159.51 114.08 27.50 141.59 0.93
41




Fig. 4.43 Cracking patterns of S75 after failure








Fig. 4.44 Cracking patterns of S150 after failure






Ferrocement cover
Ferrocement cover
Main beam

Main beam

42




Fig. 4.45 Cracking patterns of S300 after failure









Fig. 4.46 Cracking patterns of Col-S75 after failure





Ferrocement cover
Ferrocement cover
Main beam

Main beam

43




Fig. 4.47 Cracking patterns of Col-S150 after failure









Fig. 4.48 Cracking patterns of Col-S300 after failure




Ferrocement cover
Ferrocement cover
Main beam

Main beam

44

4.5 Comparison of test results and design equations

The comparison of analytical and experimental moment and shear force capacity was
presented in table 4.5. The flexure moment capacities of specimens were calculated according
to ACI 318-99 code. For calculations of the moment capacities of the specimens, the
maximum concrete strain was taken as 0.003 at crushing failure. The shear capacity of
strengthened specimens was calculated according to equation 4.1 as follows,

fscu
VVVV ++= (4.1)

Shear strength of the beam could be expressed as the sum of three components, that is
c
V (the contribution of concrete),
s
V (the contribution of steel stirrups) and
f
V (the contribution
of ferrocement). They can be calculated according to ACI 318-99 code as follows.

6
dbf
V
wc
c

= (4.2)

s
dfA
V
yv
s
= (4.3)

f
fyfvf
f
s
dfA
V = (4.4)

where:
vf
A: Area of external reinforcement
yf
f: Yield strength of external reinforcement
f
d: Effective depth of ferrocement reinforcement
f
S: Spacing of external reinforcement

Equation 4.2 and 4.3 were used for calculating the shear load carried by concrete and
reinforcement, while equation 4.4 was used for calculating the shear load carried by
ferrocement.
f
V was calculated by assuming that there was no debonding of the external steel
bar when the maximum shear stress of the steel bar was reached.

Analytical shear load capacities of beams in S series were more than the experimental
values by 24%, 16%, and 7% for S75, S150 and S300, respectively. The similar figures for
beams in “Col-s” series were 37%, 24%, and 7% for col-s75, col-s150 and col-s300,
respectively. The beam could not reach desired shear strength because of debonding of
externally additional steel. The influence of anchorages to shear force capacity was not
included in the analytical equations that were suggested by the code. Thus the experimental
results and analytical values did not have close results. The better performance of the
strengthened beam could be expected if the premature anchorage failure could be prevented.