The 3rd International Conference on Earthquake Engineering and Disaster Mitigation 2016
(ICEEDM-III 2016)
Experimental Study of Confined Masonry Wall with Opening
Under Cyclic Load
Dyah Kusumastuti1*, Made Suarjana1, Ferdy Whisnu Prasetyo1, and Rildova2
1
Faculty of Civil and Environmental Engineering,
Institute of Technology Bandung,
Jl. Ganesha 10, Bandung 40132, Indonesia
Abstract
Behavior of confined masonry walls with openings has been studied in Indonesia following large
earthquakes in the recent years. To better understand the behavior of confined masonry walls with
opening, an experimental study has been conducted using two full scaled experimental models of 3 x 3
walls with openings. The one-story models were built based on local standard in Indonesia. The
dimension of the opening located at the center of each model was 80 x 120 cm with wooden frame to
model regular window. The first model was constructed without any reinforcement for the opening,
while the second model was constructed with continuous rebar located at the lintel and sills levels of the
opening. Lateral cyclic loads were applied to the model with increasing displacement. Parameters
evaluated were crack pattern, failure mechanism, lateral capacity, energy dissipation, ductility, and
overall structural performance. The study reveals that crack patterns are relatively similar for both
models, with cracks occurred at corners of openings and truss mechanism was later developed for walls.
Test shows that both models could withstand 3.5% drift without collapse, and the continuous rebars
provided significant increase in strength and ductility. Proper detailing allowed frames to provide
confining action to masonry walls, while anchorage of walls to columns and wooden frames limited
damage area on walls. The results confirm that structures built according to the standard will behave
satisfactorily under the design earthquake load
Keywords: Confined masonry wall, wall opening, residential building, experimental study, collapse
mechanism.
1 Introduction
Past earthquakes have shown that residential houses are prone to damage, and the vast numbers of residential
buildings damaged by earthquakes greatly affect the number of casualties. Therefore, improving the performance
of such structures under seismic loads has become top priority to reduce fatalities and economic losses due to
earthquake. Typical houses in Indonesia are of stone masonry foundation, reinforced concrete tie column and tie
beam (reinforced concrete frame), with infilled brick masonry wall. As they are usually built without appropriate
structural design processes, hence are classified as non-engineered structures, the detailing of such structure is
often far from the required standard, and varied due to disparities of workmanship and materials. These factors
contribute greatly to the failure of a simple house structure in the occurrence of lateral loading such as earthquakes.
From experience, the failures or structural damages of residential buildings were mostly caused by the absence of
connection between infilled wall and the confined frame, insufficient detailing and capacity of columns, large
distance between columns and poor quality of workmanship. In the case of walls with openings, such as windows
and doors, these structures usually experienced damage near the openings. Damages were initiated from the area
adjacent to the openings and often trigger worse condition for the walls, which result in the collapse of walls.
Several experimental studies of confined masonry and reinforced concrete frame infilled with masonry walls were
conducted to better understand the performance of simple house structure. The studies focused on the parameters
of the structural materials, such as masonry properties, mortars and concrete used, as well as details of masonry
wall confined by reinforced concrete frame resistance to the seismic loads. Various studies also suggested
improvements on confining frame and the connection of walls to the frame to increase the capacity and ductility
of masonry wall systems. Aside from these improved methods, the installation of openings on a confined masonry
wall has been considered to reduce the structural strength and stiffness of the walls, which may limit the capacity
of the structure in resisting lateral load. Although numerical studies have been conducted on the subject, few
experimental studies were carried out to study the effect of openings on the wall structure. Therefore, an
experimental study on confined masonry walls with openings was conducted based on typical structures in
Indonesia, to evaluate the behavior of such structures under seismic loads.
This research presents the performance of two specimens of confined masonry walls with openings, where one of
them uses continuous horizontal anchorages to improve the wall-frame confinement. The models were tested under
cyclic loading test with increasing intensity until collapse. Prior to the experiments, tests were also conducted on
the characteristics of the materials, i.e. red brick unit, mortar, plaster, and frame concrete, to obtain the actual
material properties. The results from this study will be compared with results from previous experimental studies
to analyze the effects of window opening, and horizontal anchorage to the response of the confined wall.
This research presents the performance of two specimens of plastered confined masonry wall, where one of them
uses continuous horizontal anchorages to improve the wall-frame confinement. The models were tested under
cyclic loading test with increasing intensity until collapse. Prior to the experiments, tests were also conducted on
the characteristics of the materials, i.e. red brick unit, mortar, plaster, and frame concrete, to obtain the actual
material properties. The results from this study will be compared with results from previous experimental studies
to analyze the effects of plaster, window opening, and horizontal anchorage to the response of the confined wall.
2 Material Characteristics
The confined masonry wall specimens were constructed using moderate quality red bricks and concrete frame
with mixing specifications of 1:2:3 (volume of cement, sand and coarse aggregate, respectively) with water being
added as much as 100% of the cement volume. Frame reinforcement used 10 mm plain bars for the main re-bar
and 8 mm plain bar for the stirrup. The 8 mm plain rebar was also used for continuous anchorage. The size of the
red bricks is 55 mm × 100 mm × 205 mm. Mortar space in between bricks is approximately 15 mm thick with
mixing composition of 1:5 (volume of cement and sand, respectively), using the same volume of water as cement.
Testing of materials was carried out to obtain their properties. The results of these tests are shown in Table 1.
Table 1 Materials Test Results
No Material Properties Test Results Note
1 Compressive Strength of Bricks SII 0021-78
Number of specimen 3
Average [ MPa] 4,83
Standard Deviation [MPa] 0,79
COV (%) 16
2 Compressive Strength of Mortar SNI 03-4166-1996
Number of specimen 10
Average [ MPa] 14,00
Standard Deviation [MPa] 1,36
COV (%) 10
3 Diagonal Shear SNI 03-4166-1996
3.2 Bond Shear Strength Brick and
Mortar
Number of specimen 3
Average [ MPa] 0,22
Standard Deviation [MPa] 0,08
COV (%) 35
4 Tensile Strength of Rebars SNI 07-2529-1991
4.1 Deformed 10 mm
Number of specimen 4
Average [ MPa] 282,50
Standard Deviation [MPa] 9,57
COV (%) 3
4.2 Plain 10 mm
Number of specimen 4
Average [ MPa] 327,50
Standard Deviation [MPa] 17,08
COV (%) 5
4.3 Plain 8 mm
Number of specimen 5
Average [ MPa] 335,94
Standard Deviation [MPa] 4,01
COV (%) 1
5 Compressive Strength of Concrete SNI 1974-2011
Number of specimen 8
Average [ MPa] 23,72
Standard Deviation [MPa] 3,33
COV (%) 14
3 Experimental Setup
Two full scale (3x3m) plastered confined masonry walls with openings were used as specimens in the experimental
study. The details of the two wall specimens are shown in Figures 1 and 2. Model 1 represents simple confined
masonry wall with framed window in the middle of the wall. Model 2 is similar to Model 1, except for two
additional continuous horizontal anchorage placed right above and below the window frame. The models were
constructed and anchored to concrete block foundations.
Figure 1 Details of wall specimen Model 1.
Figure 2 Details of wall specimen Model 2.
The response of the wall specimen was measured using strain gauges and LVDT (Linear Variable Displacement
Transducers). Several LVDT were installed on the model to obtain the in-plane and out-of-plane displacements
during testing. The lateral cyclic load was applied at the top beam-column joint. The load came from a hydraulic
jack attached to the reaction wall. To simulate seismic loading, a load history of lateral cyclic load was used to
obtain the structural performance. Figure 3 shows the test setup for the lateral cyclic load of confined masonry
wall. The strain gauges locations for Model 1 and Model 2 are shown in Figure 4.
Figure 3 Experimental setup.
(a) Model 1 (b) Model 2
Figure 4 Location of strain gauges on specimens
Figure 5 shows the loading cycles that were applied during each experiment. The models were subjected to a series
of increasing cyclic lateral load. In between these cycles, smaller cycles were conducted to obtain the structural
properties. The largest drift applied on the structure was 3.5 percent or 105 mm.
150 5
100
3
2
50
Simpangan (mm)
0 0 Drift (%)
-1
-50
-2
-3
-100
-4
-150 -5
Siklus
Figure 5 Loading cycles during experiments.
Using the above loading scheme, the models were evaluated, and cracks developed were observed. Damage pattern
and failure mechanism at the end on each test were also noted. Figures 7 show various stages of the test of models.
(a) Model 2 prior to testing (b) Development of crack on Model 1
(c) Damage at the corner of the window frame for Model 1 (d) Model 2 near end cycle of test.
Figure 6 Experimental stages of Model 1 and 2.
4 Experimental Results
4.1 Hysteretic Behavior
Figures 7 present the hysteretic diagram of load-displacement for Model and Model 2 during the tests. Both models
appear to have similar hysteretic behavior, with difference only in the maximum load where Model 1 can sustain
about 8.5 tons while Model 2 with additional anchorage has a maximum load about 11.5 tons. The difference in
maximum load is presumed to be caused by the additional anchorage on Model 2. Therefore, adding continuous
anchorage on the brick masonry wall seems to improve the lateral resisting capacity.
However, there is not much difference observed in stiffness degradation both models. Model 1 has a maximum
displacement of 21.9mm, while Model 2 has a maximum displacement of 21.6mm, both models also show poor
energy dissipation capacity.
The ductility capacity of Model 1 was found to be 1.48, while Model 2 developed ductility capacity of 2.1.
Therefore, adding horizontal rebars for anchorage have increased the structural ductility by 1.4 times.
10 12
10
8
8
6
6
4
4
Gaya Lateral (tonf)
Gaya Lateral (tonf)
2
2
0
-100 -80 -60 -40 -20 0 20 40 60 80 100 120 0
-2 -120 -100 -80 -60 -40 -20 0 20 40 60 80 100 120
-2
-4
-4
-6
-6
-8
-8
-10
-10
-12
-12
Perpindahan Lateral (m m )
Perpindahan Lateral (mm)
(a) Model 1 (b) Model 2
Figure 7 Hysteretic behavior of structural models
4.2 Crack Patterns and Failure Modes
The development of cracks and damage propagation were also observed during the experiments. Figure 8 presents
the crack patterns of Model 1 and 2 after the tests. In both cases, crack initiated at the corner of window frame and
formed diagonal cracking from there. At the end of the experiment, both models show similar failure mechanism.
(a) Model 1 (b) Model 2
Figure 8 Crack patterns of wall specimens.
Model 1 specimen shows a typical development of diagonal crack pattern, which subsequently developing strut
and tie mechanism between the wall and the confining column for lateral load resistance mechanism. The damage
was observed on the corners of the opening, as well as the column ends. Due to inability of the cracks on to
perfectly fill back at zero drift, the gap consequently added to the volume of the wall panel, which then pushed the
columns outward. The confined frame columns were then inflated out in the wall plane (bulging effect). Bulging
effect on the confined columns subsequently weakened the confinement and thus reduced the wall strength. The
effect was reduced by the existence of plaster, which also confined the masonry wall. A slight increase in ductility
is also observed in the plastered wall specimen, compared to unplastered one from previous study. Although the
significant effect of plaster is assumed to be in the out-of-plane direction, in the in-plane direction, the plaster acts
as an additional confinement for the brick masonry wall, thus allowing the model to developed more ductile
behavior.
Similarly, the diagonal crack pattern was also observed for Model 2. Therefore, the strut and tie mechanism was
also developed in this model. However, less bulging of columns were observed on the columns. The installed
continuous anchorage seemed to limit the bulging effect on columns, and the model was able to maintain its shape
for larger displacement. With the additional strength from the anchorage, the model was able to resist more lateral
load, compared to Model 1. Although less column deformation was observed, Model 2 specimen developed large
crack at the bottom of the right column frame and further observation reveals that two of the longitudinal
reinforcement failed near the end of testing. Therefore, the damage is much severe on this column compared to
the other model.
The window frames installed at the perimeter of the openings also show that their performance greatly affect the
structural performance of the walls. Provided that the window frames were intact, they acted as confinement for
the masonry walls, thus limiting the walls’ deformation or cracks developed on the walls. Contrary to the predicting
results, continuous anchorages do not have superior effect on the performance of the wall. The locations of the
anchorage that are next to the window frame were unable to provide additional benefit as expected, since cracks
did not develop through the anchorage. The effect of anchorage will be maximum when cracks went through the
anchorage, thus allowing the anchorage to develop its tensile strength. From the crack pattern, the possibility of
optimum location for the anchorage can be deducted. Using two levels of horizontal anchorage, these locations
are: (i) at two thirds of the height of the wall portion between the tie beam and the bottom window frame
(approximately 70 cm from the bottom of the wall), and (ii) above the diagonal bricks at the top of the window
frame (approximately 30 cm from the top of the window frame). If the anchorages were provided at these locations,
it is expected that the better performance of the wall will be obtained.
5 Concluding Remarks
Based on the experimental results, the following conclusions were drawn:
1. Providing plaster on confined masonry walls increases both capacity and ductility of the masonry wall. Cracks
were observed at larger displacements compared to the non-plastered model. The plaster added confining
effect on the masonry walls, and delayed the formation of the initial crack. Thus, better structural performance
was observed for the specimens.
2. Installing window frames on the perimeter of the opening is important in obtaining better behavior of the
structure. The performance of window frames on the perimeter of the opening significantly affects the
structural performance of the walls. As long as the window frames remain intact, the development of cracks
can be limited thus delay the collapse mechanism.
3. Installing continuous anchorage seems to have less effect than expected. Observation shows that the locations
of the anchorage that are next to the window frame do not provide additional benefit as expected, since cracks
did not develop through the anchorage.
Therefore, the study shows that installing plaster as well as proper wall-frame connection strategies, i.e. type and
location, is crucial in improving the structural performance.
Acknowledgment
Parts of this research is funded by ITB Research Grant No.176.j/K01.10/PL/2010. The support is gratefully
acknowledged.
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