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The strength of hollow concrete block walls, reinforced hollow concrete block beams, and columns

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The purpose of this study was to determine the strength of hollow concrete block masonry walls, beams, and columns, and compare their values with brick masonry walls and ordinary reinforced concrete beams and columns. The specimens for the hollow concrete block and brick masonry walls were prepared and tested for compressive and flexural strengths as well as horizontal and diagonal shear strengths. Moreover, two hollow concrete blocks and two ordinary reinforced concrete beams were designed to experience flexural and shear failure and loaded under a two-point bending load. Meanwhile, a hollow concrete block and an ordinary reinforced concrete column were also constructed and subjected to centric axial loads until they collapsed. The results showed the hollow concrete block masonry walls have greater strength than those made with bricks while both flexural and shear capacity as well as the flexural ductility of reinforced hollow concrete block beams were higher than ordinary reinforced concrete beams. Meanwhile, the centric compressive axial strength of the reinforced hollow concrete block column was smaller due to the inefficient bond it has with the infilled concrete which leads to their separation under the compressive axial load.
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Original article
The strength of hollow concrete block walls, reinforced hollow concrete block
beams, and columns
Muttaqin Hasan, Taufiq Saidi, David Sarana, Bunyamin
PII: S1018-3639(21)00015-5
DOI: https://doi.org/10.1016/j.jksues.2021.01.008
Reference: JKSUES 482
To appear in: Journal of King Saud University - Engineering Sci‐
ences
Received Date: 15 November 2020
Revised Date: 25 January 2021
Accepted Date: 28 January 2021
Please cite this article as: Hasan, M., Saidi, T., Sarana, D., Bunyamin, The strength of hollow concrete block
walls, reinforced hollow concrete block beams, and columns, Journal of King Saud University - Engineering
Sciences (2021), doi: https://doi.org/10.1016/j.jksues.2021.01.008
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The strength of hollow concrete block walls, reinforced hollow concrete block
beams, and columns
A B S T R A C T
The purpose of this study was to determine the strength of hollow concrete block masonry walls, beams, and columns, and compare
their values with brick masonry walls and ordinary reinforced concrete beams and columns. The specimens for the hollow concrete
block and brick masonry walls were prepared and tested for compressive and flexural strengths as well as horizontal and diagonal
shear strengths. Moreover, two hollow concrete blocks and two ordinary reinforced concrete beams were designed to experience
flexural and shear failure and loaded under a two-point bending load. Meanwhile, a hollow concrete block and an ordinary reinforced
concrete column were also constructed and subjected to centric axial loads until they collapsed. The results showed the hollow
concrete block masonry walls have greater strength than those made with bricks while both flexural and shear capacity as well as the
flexural ductility of reinforced hollow concrete block beams were higher than ordinary reinforced concrete beams. Meanwhile, the
centric compressive axial strength of the reinforced hollow concrete block column was smaller due to the inefficient bond it has with
the infilled concrete which leads to their separation under the compressive axial load.
Keywords: strength, hollow concrete block, masonry wall, beam, column.
1. Introduction
Hollow concrete block masonry wall has been widely used
both in developing and developed countries to replace fired
clay brick masonry wall and this means it currently plays an
important role in the modern building industry (Sathivaran et
al., 2014; Yang et al., 2019). It is used for both load-bearing
and non-load-bearing walls (Zhou et al., 2019), especially due
to its ability to save energy, reduce the use of raw materials,
decrease the impact on the environment, fire-resistant, and
requires low maintenance throughout its lifetime (Sathivaran
et al., 2014; Yang et al., 2019;). It is also possible to replace
the sand used in its production with petroleum-contaminated
soil up to 60% (Dawood et al., 2010).
The compressive strength of hollow concrete block is
mainly determined by its composition, especially the binder
content in the mixture, compaction level, aggregates used, and
the curing method (Dawood et al., 2010). Ganeshan &
Ramamurthy (1992) recommended a rational method to test
the system under compressive loads while the shear strength
was determined in other studies using the mortar strength with
the values observed to have a direct relationship (Yu et al.,
2015; Bouliva et al., 2013). Meanwhile, its tensile and flexural
strengths have been reported to be influenced by the block
size and the grouting status of the cell (Hamid & Drysdale,
1988). Another study showed that unreinforced masonry
generally has good compressive strength but low tensile and
flexural strength and this makes it vulnerable to lateral loads
(Meli & Brzev, 2011; Janaraj & Dhanasekar, 2015). It is,
however, possible to increase the tensile and flexural strengths
by embedding a grid of horizontal and vertical reinforcement
into the wall panel (Janaraj & Dhanasekar, 2015). The lateral
load-bearing capacity of unreinforced hollow concrete block
can also be improved by plastering it with high strength
mortar produced with steel fibers and microsilica or those
incorporated in the head and bed joints (Al-Shugaa et al.,
2019). It is also possible to increase the shear strength of
block masonry wall with a composite material from multiaxial
hybrid glass-fibers and polypropylene fabric coated in a
hydraulic lime-based mortar (Giaretton et al., 2018) while the
out-of-plane behavior of hollow concrete blocks can be
improved using externally bonded composites (Reboul et al.,
2018).
Masonry structures were reported to have poor seismic
performance during an earthquake (Chi et al., 2019) and are
usually fully or partially grouted with prestressing
technologies to increase their ability to withstand seismic
loads (Janaraj & Dhanasekar, 2014; Zhao & Wang, 2015;
Janaraj & Dhanasekar, 2016; Ma et al., 2017; Chi et al., 2019;
Calderon et al., 2020) as well as through carbon fiber
reinforced polymer (Can, 2018). Several studies have,
however, been conducted on the seismic response of
reinforced concrete block wall buildings (Ezzeldin et al.,
2017; Heerema et al., 2014; Banting & El-Dakhakhni, 2014)
while some other studies focused on hollow block walls
thermal properties (Gao et al., 2020; Caruana et al., 2017;
Chen et al., 2016) as well as heat transfer characteristics of
building wall elements (Al-Sanea, 2000; Alwetaishi, 2019).
Holes were created inside the slab to reduce the concrete
volume and overall weight of the slab (de Castilho et al.,
2005; Pajari 2009; Hegger et al., 2009; Al-Negheimish et al.,
2018) but the voids have the ability to significantly cause
early shear failure and reduce the slab capacity (Azad &
Hakeem, 2016; Brunesi et al., 2015). Moreover, the hollow
composite reinforcing system through the use of glass fiber
reinforced polymer bars and four flanges to improve the bond
with the concrete has recently been developed and found to
enhance the structural performance of hollow concrete slab
(Al-Rubaye et al., 2020). Meanwhile, the reinforced hollow
concrete columns with steel bars have been used extensively
for ground piles, bridges pier, and utility poles due to their
higher structural efficiency and use of fewer concrete
materials compared to the solid concrete columns (Lignola et
al., 2007; Kusumawardaningsih & Hadi, 2010). It has been
reported that the hollow concrete columns have low
deformation capacity and experience a sudden reduction in
strength when they are not properly designed due to
longitudinal bars buckling or the concrete wall failing in
shear, thereby, causing brittle failure behavior (Pavese et al.,
2004; Kusumawardaningsih & Hadi, 2010). Therefore,
AlAjarmeh et al. (2020) critically reviewed the difference
design parameters affecting the performance of hollow
concrete columns and identified the new opportunities for safe
design and effective use of this construction system.
Furthermore, the flexural behavior of glass fiber-reinforced
polymer composite hollow profiles with double-H-planks and
round-piles structural retaining wall systems has also been
investigated (Ferdous et al., 2018).
Residential buildings in Indonesia are generally made of
reinforced concrete frames with brick masonry walls.
However, the Aceh-Nias Rehabilitation and Reconstruction
Agency and NGOs have built 30,000 houses after the 2004
Aceh earthquake and tsunami using a hollow concrete block
system due to the ease of installation, short completion time,
and the need for no skilled construction workers and
formwork. These blocks are not only used for walls but also in
frame structures such as beams and columns through the
placement of reinforcing bars into their cell after which they
are cast using concrete. The same method is applied in
installing walls but reinforcing bars are not used. Therefore, it
is necessary to examine the strength of the hollow concrete
block and this research was conducted for this purpose using
static loads while the next study is expected to focus on cyclic
loads.
The hollow concrete blocks were joined together using bed
and head joints to form masonry wall in previous studies
(Sathivaran et al., 2014; Janaraj & Dhanasekar, 2015; Yan &
Fenglai, 2015; Yu et al., 2015; Ma et al., 2017; Can, 2018;
Giaretton et al., 2018; Reboul et al., 2018; Al-Shugaa et al.,
2019; Zhou et al., 2019; Chi et al., 2019; Calderon et al.,
2020) and this means there is a need for a masonry man in the
construction process. This study, however, introduced a new
and simple method of joining the hollow concrete block
through the concept of nail joints. This involved the
preparation of the nails at the top, bottom, left, and right sides
of the hollow concrete blocks when they are being casted after
which the blocks were arranged in layers with those above and
below as well as left and right connected using the nails
prepared, and later filled with concrete or mortar. The
implementation of this method is very easy in the construction
process, does not require skilled masonry man, and can be
completed in a very fast time in comparison with the use of
the bed and head joints. Therefore, this method is expected to
be applied more widely in the construction industry. As the
first study to use the nail joints in hollow concrete block
system, this paper presented the compressive strength, flexural
strength, horizontal and diagonal shear strength of
unreinforced non-structural hollow concrete block walls,
flexural capacity and shear capacity of reinforced hollow
concrete beams, and the concentric axial compression capacity
of reinforced hollow concrete column using the same type of
connection under static loading. The findings were also
compared with the strength of solid brick masonry walls as
well as the ordinary reinforced concrete beams and columns.
It is, however, possible to extend to reinforced structural
hollow concrete block walls as well as open and infilled
hollow concrete block frames under both static and cyclic
loadings in future studies.
2. Experimental Program
2.1. Preparation of hollow concrete blocks
The materials used in producing hollow concrete blocks
include Portland Pozzolan Cement from Semen Padang
Company and fine sand from the Krueng Aceh River with the
physical properties and grading of the sand shown in Tables 1
and 2 respectively. The hollow concrete blocks were designed
with no slump sand-cement based on ACI 211.3R-02 and the
three produced are shown in Figs. 1-3 for walls, beams, and
columns respectively. The nails were provided at the top,
bottom, left and right sides of the blocks for joining purposes
as shown in the figures. The beams and columns were made
using the same w/c mixture of 0.60 while 0.75 was used for
the walls with each mix proportion shown in Table 3. The
difference in the w/c of beams and columns on one side and
walls on the other side was due to planning of the beams and
columns for structural elements requiring a minimum
compressive strength of 17.5 MPa while the walls were
planned for non-structural elements with lower compressive
strength in this study. Meanwhile, the production process
involves mixing cement, sand, and water using a concrete
mixer, printed in the mold provided, and pressed using a
concrete press machine at 0.85 MPa pressure. Furthermore, 5
cylinder specimens with 150 mm diameter and 300 mm height
for each mixture were made to test the concrete compressive
strength at the age of 28 days which were 19.2 MPa and 10.04
MPa respectively as shown in Table 3.
Table 1
Physical properties of aggregates.
Physical properties
Fine sand
Coarse sand
Gravel
Bulk density (kg/m3)
1600
1600
1686
Specific gravity OD
2.604
2.555
2.677
Specific gravity SSD
2.667
2.675
2.714
Absorption (%)
2.423
4.705
1.381
Fineness modulus
2.640
3.520
7.490
Table 2
Grading of aggregates.
Sieve size
Cumulative passing (%)
(mm)
Coarse sand
Gravel
25.40
100
100
19.10
100
49.89
9.52
100
1.46
4.75
85.68
0
2.36
69.13
0
1.18
53.31
0
0.60
28.15
0
0.30
9.44
0
0.15
2.06
0
30
20130
300
300
100
150
215
6512030
9,5
14,5 120 120
150
100
9,5
120
130
150
130
this part can be
removed
R10
14,5
120 14,5 14,5
Fig. 1. Detail of hollow concrete block for walls.
Fig. 2. Detail of hollow concrete block for beams.
2.2. Hollow concrete block walls
2.2.1. Preparation of specimens
Three specimens of the hollow concrete block masonry
walls with 300 mm x 200 mm x 150 mm dimension were
made for compression test, three others with 1200 mm x 150
mm x 750 mm for flexural test, three specimens with 600 mm
x 150 mm x 450 mm for horizontal shear test, and another
three with 600 mm x 150 mm x 600 mm dimensions for
diagonal shear test. Furthermore, three specimens of brick
masonry which are commonly used for building walls in
Indonesia were also produced for each of the tests for
comparison. The compressive strength of the bricks was 5.8
MPa. The details of these specimens are presented in Table 4.
Moreover, the masonry wall specimens for the compressive,
flexural, horizontal, and diagonal shear tests were arranged
according to their respective shapes. The blocks were joined
together just by arranging them in layers with those above and
below as well as those on the left and right blocks in the same
layer connected by the nails prepared during the casting
process while the filler concrete mixture which was stirred in
a concrete mixer was poured into the hollow concrete block
holes arranged in three layers after which compaction was
conducted using steel sticks as shown in Fig. 4. The top was,
however, leveled with a cement spoon and capped with
cement paste after it has been fully filled. Meanwhile, an
adhesive from mortar mixed at a cement to sand volume ratio
of 1: 4 was used for brick masonry based on the common
construction practice in Indonesia. The specimens were
subsequently treated using a wet burlap for covering and then
watering every 24 hours.
nails
TOP VIEW
FRONT VIEW
SIDE VIEW
SECTION A-A
A
A
nails
Fig. 3. Detail of hollow concrete block for columns.
Table 3
Mix proportion of concrete
Materials
HB1
HB2
IC1
IC2
Cement (kg)
240
300
248
310
Water (kg)
180
180
186
186
Fine sand (kg)
1860
1800
716
635
Coarse sand (kg)
0
0
133
158
Gravel (kg)
0
0
1098
1098
w/c
0.75
0.60
0.75
0.60
Slump (mm)
0
0
42.5
42.5
f'c (MPa)
10.04
19.2
7.58
17.9
Description: HB1 = hollow concrete block for walls, HB2 =
hollow concrete block for beams and columns, IC1 = infilled
concrete for walls, IC2 = infilled concrete and ordinary
reinforced concrete for beams and columns, f’c = cylinder
compressive strength at 28 days.
Table 4
Details of hollow concrete block masonry wall specimens
Specimen numbers
Specimen
Specimen size
Hollow
concrete
block
masonry
Compression
test
300 x 200 x 150
3
Flexural test
1200 x 150 x 750
3
Horizontal
shear test
600 x 150 x 450
3
Diagonal
shear test
600 x 140 x 600
3
Fig. 4. Placement of infilled concrete in the hollow concrete
block masonry.
The materials used in the infilled concrete consist of
Portland Pozzolan Cement and water as well as fine sand,
coarse sand, and gravel obtained from the Krueng Aceh River
with the physical properties and gradation provided in Tables
1 and 2. The mix proportion of the infilled concrete mixture
which was marked as IC1 was designed based on ACI 211.1-
91 with w/c being 0.75, design slump was 25 - 50 mm as
shown in Table 3. Moreover, the slump for the infilled
concrete mixture and the compressive strength of the 150 mm
x 300 mm cylinder for 28 days was 42.5 mm and 7.58 MPa,
respectively, as shown in Table 3.
2.2.2. Loading tests
The masonry wall specimens were tested after the infilled
concrete reached 28 days of age with the compression
determined using a compression testing machine with a 100
tons capacity. The process involved placing the specimen
vertically on the loading plates as shown in Fig. 5 after which
the load was applied slowly until the specimen was crushed.
Moreover, the flexural strength was tested with the specimen
placed horizontally on two simple supports with a span of 550
mm while two solid steel rollers with 5/3 inches diameter
were placed at the top to transmit the load to the specimen.
The distance between the support and the load points was
137.5 mm. Meanwhile, an H-steel beam was placed on the top
of the steel roller while the load was provided by a 30-tons
capacity hydraulic jack channeled through the H steel beam as
shown in Fig. 6 and the load was increased slowly up to the
moment the specimen breaks. Furthermore, the horizontal
shear was tested by applying pressure to the hollow concrete
block in the middle and this caused a shift of the sample
between to left and right as shown in Fig. 7 while the diagonal
shear was determined by placing the specimen at an angle and
applying a load in a diagonal direction as shown in Fig. 8.
Fig. 5. Compression test of hollow concrete block
masonry wall specimen.
nails
FRONT VIEW
TOP VIEW
Fig. 6. Flexural test of hollow concrete block masonry
wall specimen.
Fig. 7. Horizontal shear test of hollow concrete block
masonry wall specimen.
Fig. 8. Diagonal shear test of hollow concrete block
masonry wall specimen.
2.3. Hollow concrete block beams
Two reinforced hollow concrete blocks and two ordinary
reinforced concrete beams were prepared with one specimen
designed for each of the samples to have a flexural failure
while another was designed to experience shear failure. The
shear and ultimate moment capacity calculated based on SNI
2847: 2013 and ACI 318-14 are shown in Table 5 with HBF
and RCF used to indicate reinforced hollow concrete block
and ordinary reinforced concrete beam which experienced
flexural failure while HBS and RCS represented those that
experienced shear failure respectively.
Table 5
Calculated and experimental shear and moment capacity of tested beams.
Specimen
Vn (kN)
Mn (kNm)
Pf (kN)
Pv (kN)
Vnexp (kN)
Myexp (kN)
Mnexp (kN)
HBF
38.31
5.14
22.84
76.62
-
3.92
5.22
RCF
38.05
5.13
22.80
76.10
-
3.96
4.28
HBS
11.90
13.72
60.98
23.80
11.85
-
-
RCS
11.90
13.72
60.98
23.80
11.00
-
-
Description: Vn = calculated shear capacity; Mn = calculated flexural capacity; Pf = calculated flexural failure load; Pv = calculated
shear failure load; Vnexp = experiment shear capacity, Myexp = experiment yield moment; Mnexp = experiment flexural capacity;
=
ductility index.
2.3.1. Materials
No slump sand-cement concrete was designed based on
ACI 211.3R-02 and used for the hollow concrete block with
the cylinder compressive strength recorded to be 19.2 MPa as
shown in Fig. 2. The normal cylinder compressive strength of
17.9 MPa was used for the infilled concrete and ordinary
reinforced concrete specimens with the mix proportion shown
in Table 3. Moreover, bars with the 21 mm, 12 mm, and 10
mm diameters were used for longitudinal reinforcement while
6 mm diameter was used for shear reinforcement and their
yield strength was 308 MPa, 303 MPa, 298 MPa, and 246
MPa, respectively.
2.3.2. The detail of specimens and instrumentations
The beams had 150 x 200 mm cross-sectional areas as
shown in the details presented in Fig. 9. They are also 2100
mm long and simply supported with 1800 mm span and the
tensile reinforcement for HBF and RCF specimen was made
with one 12 mm diameter bar while the compressive
reinforcement used two 10 mm bars and 6 mm diameter
stirrups with 100 mm (c/c) spacing were provided in shear
span. Meanwhile, one 21 mm diameter bar and two 10 mm
bars were used for HBS and RCS respectively. Moreover, 6
mm diameter stirrups with 300 mm (c/c) spacing were used as
shear reinforcement in observed shear span while other 6 mm
diameter stirrups with 100 mm (c/c) spacing were also
provided in another shear span.
Strain gauges were mounted at the midspan of tensile and
compressive reinforcing bars of HBF and RCF to respectively
measure the tensile and compressive strain at the longitudinal
bars. Three gauges were mounted on the compression area of
the beams at the midspan to measure the concrete compressive
strain during the loading test. Meanwhile, strain gages were
mounted at the midspan of tensile reinforcing bar and stirrup
of HBS and RCS respectively to measure tensile strain at
longitudinal bars and shear strain at stirrup while 2 strain
gauges were mounted on the surface of the specimens to
measure concrete strain at the shear span.
Fig. 9. Details of the beam specimens.
Fig. 10. Detail of column specimens.
2.2.3. Loading test
There was the placement of six transducers on the test
beams before the loading test with two located on the midspan
and the remaining four at the loading points to measure the
deflections of the beams. The load was applied using a 30-
tons hydraulic jack and controlled until the specimens failed
with the value of the load, strains, and deflections recorded
using a data logger installed to a computer.
2.3. Hollow concrete block columns
2.3.1. The details of specimens and instrumentation
A reinforced hollow concrete block column (HBC) and an
ordinary reinforced concrete column (RCC) with a cross-
section size of 150 mm x 150 mm and a length of 1500 mm
were produced using the same materials used for the beams.
Moreover, the longitudinal reinforcement was made with 4
reinforcing bars having 10 mm diameter while the shear
reinforcement used stirrups with 6 mm diameter which were
installed at every 200 mm. The ends of the reinforcing bars
were welded to the steel plate surface measuring 450 mm x
300 mm with a thickness of 5 mm after they were arranged
and the welding was meant to support the column anchored to
the loading frame on the steel plate during the load test. A
strain gauge was, however, attached to each longitudinal
reinforcement. Meanwhile, the infilled concrete was cast into
the hollow concrete block after the reinforcement has been
HBF
RCF
HBS
RCS
150
450
900
450
150
300
P/2
P/2
P/2
P/2
P/2
P/2
P/2
300
100
200
100
300
150
200
200
200
200
21
12
10
10
10
10
21
12
6
6
12
6
6
P/2
RCC
HBC
assembled for the reinforced hollow concrete block column
while the concrete was cast in the provided mold for the
ordinary reinforced concrete column. The details of the
specimens are, however, indicated in Fig. 10.
2.3.2. Loading test
The end of the specimen provided with a steel plate was
anchored to the loading frame using 12 bolts with ½ inch
diameter while the other end was left free. Meanwhile, 2
transducers were installed at a distance of 100 mm from the
free end of the column and 2 others in the middle of the
column span before loading as shown in Fig. 11. A plate was
laid above the free end of the column and a centric
compressive load was transferred to the column through the
plate. This was followed by the application of load through a
30-tons hydraulic jack and read by a load cell. The load was
increased slowly until the column specimens were crushed
completely and the load, strain, and deflection data were
recorded using a data logger during the loading process.
3. Results and Discussion
3.1. Hollow concrete block masonry wall test results
The average results of compressive strength, flexural
strength, horizontal shear strength, and diagonal shear strength
for the 3 hollow concrete block masonry walls specimens are
presented in Table 6 and the average strength of hollow
concrete block masonry walls was found to be greater than
brick masonry walls. One reason for the higher strength
recorded for the hollow concrete block masonry was the
higher compressive strength of the hollow concrete block
compared to the the value for the brick since the compressive
strength, flexural strength, horizontal shear strength and
diagonal shear strength of masonry walls are usually
formulated as the function of a root square of their material
compressive strength. In this study, the ratio between the
compressive strength root square of infilled concrete used for
the hollow concrete block masonry walls was 1.31 times of
the value used for the brick masonry walls while the ratios
between the compressive strength, flexural strength,
horizontal shear strength, and diagonal shear strength of
hollow concrete block walls to those of solid brick masonry
were 1.60, 1.64, 3.91, and 4.11 respectively. Moreover, the
high ratios recorded were believed to be due to the
confinement effect on the infilled concrete in hollow concrete
block walls provided by the surrounding concrete block which
was not possible in solid brick masonry walls. This, therefore,
means the hollow concrete block wall is better in terms of
strength as well as ease of installation. The failure mode of the
hollow concrete block masonry walls after being loaded is,
however, shown in Fig. 12.
Fig. 11. Set up of loading test for column specimen.
Table 6
Strength of hollow concrete block masonry wall
Parameters
Hollow block concrete masonry wall
Brick masonry wall
Compressive strength (MPa)
8.56
5.35
Flexural strength (MPa)
0.46
0.28
Horizontal shear strength (MPa)
0.43
0.11
Diagonal shear strength (MPa)
0.37
0.09
Fig. 12. Failure mode of hollow concrete block masonry walls under (a) compression load, (b) flexural load, (c) horizontal shear load,
and (d) diagonal shear load.
3.2. Hollow concrete block beam test results
3.2.1. Beams failed in flexural
Figs. 13-15 show the load-deflection, load-strain at tensile
reinforcement and load-strain at stirrup curves for the flexural
failure of the tested beams respectively. The reinforced hollow
concrete block beam was observed to have higher flexural
capacity compared to the ordinary reinforced concrete beams
due to the confinement effect discovered on the infilled
concrete provided by the surrounding hollow concrete block
to produce higher strength for the infilled concrete. Moreover,
the ability to deform after yielding of main reinforcing bar, of
reinforced hollow concrete block beam failed in flexural was
higher than that of ordinary reinforced concrete beam. The
comparison between yield moment, ultimate moment, and
ductility index between reinforced hollow concrete block and
ordinary reinforced concrete beams is shown in Table 5. The
confinement effect of the infilled concrete in the reinforced
hollow concrete beam failed in flexural also caused the
infilled concrete to have the ability of deforming more before
its compression zone crushed since the ultimate strain of the
confined concrete is much higher than the value for the
unconfined concrete, thereby, causing the increase in its
ductility. The ductility index of reinforced hollow concrete
block beam failed in flexural was 1.5 times of that of ordinary
reinforced concrete beam as shown in Table 5. Fig. 13 also
shows that the stiffness of reinforced hollow concrete block
beam failed in flexural was almost the same with that of
ordinary reinforced concrete beam.
The vertical crack for RCF specimen started at the tensile
fiber of concrete between the two loading points at a load of
3.7 kN and propagated to the compression zone of the beam
due to an increment in the load. The load at the yield of tensile
reinforcement was 17.6 kN as shown in Fig. 14 while the
maximum was 19 kN after which the deflection increased and
the crack propagated to the compression zone of the beam
with a small decrease in the load until it crushed and the beam
failed at 16.6 kN. Meanwhile, the vertical crack for the HBF
specimen only occurred at the gap between two hollow
concrete blocks with the width observed to be expanding with
an increase in the load. The tensile reinforcement was yielded
at 17.4 kN while the maximum load was 23.2 kN and the
compression zone of concrete was crushed at 21 kN leading to
the failure of the beam. Up to maximum load, the strains at
stirrup were still below the yield point as shown in Fig. 15.
The crack patterns of the tested beams failed in flexural are
shown in Fig. 16.
0
5
10
15
20
25
0
10
20
30
40
50
HBF
RCF
Midspan Deflection (mm)
Load (kN)
Fig. 13. Load-midspan deflection curve of tested beams
failed in flexural.
(a)
(b)
(c)
(d)
0
5
10
15
20
25
0
0.002
0.004
0.006
0.008
0.01
HBF
RCF
Strain at tensile rebar (mm)
Load (kN)
y = 0.0015
Fig. 14. Load-strain at tensile reinforcement of tested
beams failed in flexural.
0
5
10
15
20
25
0
0.0002
0.0004
0.0006
0.0008
0.001
HBF
RCF
Strain at stirrup (mm)
Load (kN)
Fig. 15. Load-strain at stirrup curves of tested beams failed
in flexural.
Fig. 16. Crack pattern of the tested beams failed in flexural.
It is possible to calculate the flexural capacity of
reinforced hollow concrete block beam based on the same
theory used for ordinary reinforced concrete beam which
involves using the equilibrium of internal forces and moment.
Moreover, the height of the stress block can be calculated with
the equilibrium of internal forces such as the compressive
force of infilled concrete, the compressive force of the hollow
concrete block, the compressive force of compressive
reinforcement, and tensile force of tensile reinforcement. The
flexural capacity is, therefore, obtainable by taking moment of
all these internal forces to the point at tensile reinforcement.
3.2.2. Beams failed in shear
Figs. 17-19 show the load-deflection, load-strain at tensile
reinforcement and load-strain at stirrup curves for the shear
failure of the tested beams respectively. The reinforced hollow
concrete block beam was observed to have higher shear
capacity compared to the ordinary reinforced concrete beams
due to the confinement effect of the infilled concrete caused
by the surrounding hollow concrete block as previously
explained. The comparison between shear capacity of
reinforced hollow concrete block and ordinary reinforced
concrete beams is shown in Table 5. Figs 17 also shows that
the stiffness of reinforced hollow concrete block beam failed
in shear was almost the same with that of ordinary reinforced
concrete beam.
The vertical crack of RCS beam started at the tensile fiber
of concrete between two loading points at the load of 3.1 kN
and the shear crack was observed at the 6.9 kN propagating to
the longitudinal beam axis. Before the shear crack occurred,
the load and strain at the stirrup curve of RCS beam was
almost linear. After the shear crack occurred, the shear load
was carried almost entirely by the stirrup which causes the
strain of the stirrup to accelerate for the further increase in
shear load as shown in Fig. 19. The stirrup yielded at a load of
18.3 kN. The crack propagation became very fast at 19 kN,
extended to the concrete compression zone of the beam near
the loading point, and the shear failure occurred at 22 kN load.
The vertical crack of HBS beam started on the gap between
two hollow blocks at a load of 9.8 kN while the shear crack
was observed at 17.3 kN, propagated to the direction of
loading point, and the shear failure occurred at 23.7 kN.
Before shear crack, the strain at the stirrup of the HBS beam
was also linear with the load and began to accelerate after the
shear crack at the 17.3 kN. The stirrup yielded at a load of
22.2 kN just before shear failure at 23.7 kN. Meanwhile, the
tensile reinforcements for both RCS and HBS were still elastic
and have not yielded as shown in Fig. 18. The crack patterns
of the tested beams are shown in Fig. 20.
The test results led to the modification of the equation in
SNI 2847: 2013 and ACI 318-14 to calculate the shear
capacity of reinforced hollow concrete block beam by
considering the contribution of the hollow block as follows:
(1)
𝑉
𝑛
=
𝑉
𝑐
+
𝑉
𝑠
+
𝑉
(2)
𝑉
𝑐
=
1
6
𝑓
𝑐
𝐴
𝑓
HBF
RCF
(3)
𝑉
𝑠
=
𝐴
𝑠
𝑓
𝑦
(4)
𝑉
=
1
6
𝑓
𝑐ℎ
𝐴
where: Vn = shear capacity of reinforced hollow concrete
block beam, Vc = shear capacity contributed by filled concrete,
Vs = shear capacity contributed by the stirrup, Vh = shear
capacity contributed by hollow concrete block, f’c =
compressive strength of filled concrete, Af = section area of
filled concrete, As = section area of the stirrup, fy = yield
strength of stirrup, d = effective depth of section, s = stirrup
spacing, f’ch = compressive strength of the hollow concrete
block, and Ah = section area of hollow concrete block.
0
5
10
15
20
25
0
10
20
30
40
50
HBS
RCS
Midspan Deflection (mm)
Load (kN)
Fig. 17. Load-deflection curves of tested beams failed in
shear.
0
5
10
15
20
25
0
0.0005
0.001
0.0015
HBS
RCS
Strain at tensile rebar (mm)
Load (kN)
Fig. 18. Load-strain at tensile reinforcement of tested
beams failed in shear.
0
5
10
15
20
25
0
0.001
0.002
0.003
0.004
HBS
RCS
Strain at stirrup (mm)
Load (kN)
y = 0.0012
Fig. 19. Load-strain at stirrup curves of tested beams failed in
shear.
Fig. 20. Crack pattern of the tested beams failed in shear.
3.3 Reinforced hollow concrete block column test results
The largest deflection of the columns was recorded by
transducer 2 which is at a distance of 100 mm from the free
end of the column with the load and deflection relationships at
this point shown in Fig. 21. It was observed from the figure
that the ordinary reinforced concrete column has a maximum
load and stiffness which is greater than the reinforced hollow
concrete block column which is 57.0 kN and 37.3 kN
respectively. This is due to the lack of bond between the
hollow concrete block, as a column concrete cover, with the
infilled concrete as indicated by their separation at a load of
33.9 kN, thereby, the further load was carried by only the core
concrete and the reinforcing bars to carry the load. This finally
HBS
RCS
causes local buckling such that the reinforcing bars are bent at
the top which further leads to the dropping of the load during
the compressive test. Therefore, it is necessary to provide a
bond adhesive between the hollow concrete block and the
infilled concrete in further research. Moreover, the ordinary
reinforced concrete column also started to experience failure
with the separation of the concrete cover from the reinforcing
bars which made the load to be carried only by the bars and
core concrete. This was associated with the separation of the
concrete cover at a higher load, such as 43.9 kN, in ordinary
reinforced concrete, because the monolithic between cover
concrete and core concrete. The separation occurred slowly,
unlike the reinforced hollow concrete block column which
occurs suddenly, starting with cracks in the cover as the load
increases and this means the column still has the ability to
bear load up to 57.0 kN. However, the addition of the load
subsequently led to the inability of the reinforcing bars to
retain more loads and this eventually caused their bending or
buckling at the top of the column which further caused the
column lost its ability to retain compressive loads.
Furthermore, the failure of the ordinary reinforced concrete
column was ductile in contrast to brittleness recorded in the
hollow concrete block column. The longitudinal bars of both
hollow concrete block and ordinary reinforced concrete
columns have not yielded until the maximum load and the
linear relationships between the load and their strain were
observed as shown in Fig. 22. These results are in line with
the findings of AlAjarmeh et al. (2020) which showed that the
hollow concrete columns exhibit brittle failure behavior due to
the buckling of longitudinal bars and the falling of the
concrete wall in shear. Hollow concrete columns have also
been reported to have a low deformation capacity and
experience a sudden strength reduction which leads to brittle
failure behavior (Pavese et al., 2004; Kusumawardaningsih &
Hadi, 2010). The brittle failure is also caused by the yielding
of longitudinal bars which limit the resistance of the
reinforcing bar and leads to the overstressing and crushing of
the concrete wall (AlAjarmeh et al., 2020).
0
10
20
30
40
50
60
0
1
2
3
4
5
6
HBC
RBC
Deflection (mm)
Load (kN)
Fig. 21. Load-deflection curves of tested columns.
0
10
20
30
40
50
60
0
0.0001
0.0002
0.0003
HBC
RBC
Strain at longitudinal bars
(mm)
Load (kN)
Fig. 22. Load-strain at longitudinal bar curves of tested
columns.
4. Conclusions
The following conclusions were drawn from the tests and
results:
1. The compressive, flexural, horizontal shear, and diagonal
shear strength of hollow concrete block masonry walls
were greater than brick masonry walls which are often
used in building construction in Indonesia. This is due to
the higher compressive strength of the hollow concrete
block when compared with the brick material and the
presence of confinement effect of the infilled concrete in
its wall system.
2. The flexural capacity of reinforced hollow concrete block
beam was higher than the ordinary reinforced concrete
beam due to the confinement effect provided by hollow
concrete block on the infilled concrete. Flexural capacity
of reinforced hollow concrete block beam can be
calculated based on the same theory of that of ordinary
reinforced concrete beam which is based on the
equilibrium of internal forces and moment.
3. The shear capacity of reinforced hollow concrete block
beam was higher than the ordinary reinforced concrete
beam due to the confinement effect provided by hollow
concrete block on the infilled concrete. The equation to
calculate shear capacity of reinforced hollow concrete
block beam was proposed by taking into account the
contribution of hollow concrete block.
4. The confinement effect of the infilled concrete in the
reinforced hollow concrete beam failed in flexural also
caused the infilled concrete to have the ability of
deforming more before its compression zone crushed
since the ultimate strain of the confined concrete is much
higher than the value for the unconfined concrete,
thereby, causing the increase in its ductility. The ductility
index of reinforced hollow concrete block beam failed in
flexural was 1.5 times of that of ordinary reinforced
concrete beam.
5. The crack in reinforced hollow concrete block beam
failed in flexural propagated through the spacing between
two hollow concrete blocks.
6. The centric axial strength of the reinforced hollow
concrete block column was found to be lower than the
ordinary reinforced concrete column due to the lack of
good bond between infilled concrete and hollow concrete
blocks which led to separation under axial compression,
thereby, causing the load to be carried only by the core
concrete and reinforcing steel.
Conflict of interest
The authors state that there is no conflict of interest.
Acknowledgments
The authors acknowledge the financial support provided
for this study by Gitec Consult Banda Aceh Branch.
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