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DOI : 10.23883/IJRTER.2018.4406.IKXWE 51
Effect Of Central Openings On The Strength Of Confined Masonry
Subjected To Lateral In-Plane Loading (An Experimental Study)
Ahsan Ul Haq1, Zahid Ahmad Chat
2
1M-Tech (Structural Engineering) NIT-Srinagar
2M-Tech (Structural Engineering) NIT-Srinagar
Abstract Confined masonry construction is made up of masonry walls and confining ties, which are built on
all four sides of each wall. This system is a conventional form for constructing houses as well as a
good alternative for post-disaster reconstruction of the seismically damaged and/or collapsed
buildings in many countries. Window and door openings appear in many panels of confined masonry
buildings, but many codes do not consider the effect of these openings in the strength and the
stiffness of confined masonry panels. In this study, the influence of area of openings on the stiffness
and the strength of confined masonry walls is investigated. An experimental program is used to
investigate the strength and stiffness of confined masonry walls; four specimens were used:-confined
masonry wall without opening, confined masonry wall with opening of 20% wall area, confined
masonry wall with opening of 25% wall area, and confined masonry wall with opening of 30% wall
area.
The results show that openings significantly reduce the lateral load resistant properties of the
confined masonry.
I. INTRODUCTION In many developing countries, masonry is used for housing because of its low material cost and
simplicity of construction. Masonry is a sturdy and durable material for wind and vertical loads that
houses must routinely withstand. However, if it is unreinforced, earthquake shaking can easily render
a masonry building a pile of rubble with obvious serious consequences for the inhabitants. For many
years now, reinforced concrete frame construction has also been very popular. In this type of
construction, builders add unreinforced masonry walls after they construct the reinforced concrete
frame. Intuitively, reinforced concrete frame construction might seem a better solution to resist
earthquakes than unreinforced masonry. Unfortunately, these frames require a high degree of skill to
build properly. The interaction of the unreinforced masonry infills with the frames causes brittle
behavior that is only, at best, marginally better than unreinforced masonry construction. Given the
universal popularity of masonry and the widespread availability of cement, reinforcing steel, and
aggregate, confined masonry is a simple solution. By making some inexpensive and easy changes to
traditional construction materials and procedures, the risk of casualties can be significantly reduced.
Very few cases of collapse have been reported in past earthquakes worldwide.
To construct a confined masonry house, a builder begins with the masonry walls much in the same
way as with unreinforced masonry construction. The difference is that the builder leaves vertical
slots in the walls every three or four meters. After finishing the walls at the first floor, the builder
then places steel reinforcing in the vertical slots and along the tops of the wall. Forms (usually
wooden boards) are also placed at the same locations and concrete is cast into the wall slots and at
the top of the wall. The verticals are called “tie columns” and the horizontals are called “bond” or
“tie beams.” Although they look a lot like the more traditional columns and beams of a reinforced
concrete frame, their function during an earthquake is quite different. In essence, they confine the
International Journal of Recent Trends in Engineering & Research (IJRTER)
Volume 04, Issue 11; November - 2018 [ISSN: 2455-1457]
@IJRTER-2018, All Rights Reserved 52
masonry and force it to work together with the concrete ties. The result is dramatically better
performance during earthquakes and a major reduction in the risk of collapse.
The confining members are effective in:
• Enhancing the stability and integrity of masonry walls for in-plane and out-of-plane earthquake
loads (confining members can effectively contain damaged masonry walls),
• Enhancing the strength (resistance) of masonry walls under lateral loads, and
• Reducing the brittleness of masonry walls under earthquake loads and hence improving their
earthquake performance.
It should be noted that the term “confined masonry” is used in a general sense for different forms of
masonry construction reinforced with additional steel, timber, or concrete elements. However, the
focus of this document is on clay brick or concrete block masonry walls “confined” with reinforced
concrete tie-beams and tie-columns.
Confined masonry walls can be constructed using different types of masonry units like clay burnt
bricks, hollow clay tiles, concrete blocks etc
II. OBJECTIVES OF THE STUDY The objective of this study is to find experimentally:
a). The strength and stiffness of confined masonry walls.
b). The effect of central opening on the lateral strength of confined masonry walls.
III. METHODOLOGY
An experimental study is performed to obtain the lateral stiffness of confined masonry walls. Four
confined masonry walls were tested to investigate their characteristics and compare the same. The
four types of walls tested are:
1. CM wall without opening-“CM”.
2. CM wall with opening and area of opening 20% - “CM+O20
”.
3. CM wall with opening and area of opening 25% - “CM+O25
”.
4. CM wall with opening and area of opening 30% - “CM+O30
”.
Two model specimens were tested for each type of wall. All the model specimen had brick masonry
panel confined by tie columns and tie beams. The walls of height 1.3m, width 1.2m and thickness
0.1m were used. The size of bricks used is 230mm×100mm×67.5mm. The thickness of bond used is
10mm. The size of columns and beams is 100mm×100mm. The size of opening were: 62mmx50mm
(20% opening area), 75mm×52mm (25% opening area) and 75mmx62mm ( 30% opening area).
Guidelines For The Confined Masonry: Following are some guidelines which have been taken into account for the construction of confined
masonry walls:
Guidelines From The Earthquake Resistant Confined Masonry Construction, By Svetlana
Brzev:
• The tie-column reinforcement should consist of four 10 mm diameter deformed bars (4-10 mm
bars) for longitudinal reinforcement, and 6 mm ties at 200 mm spacing (6mm @200 mm). Vertical
bars should be lapped by a minimum of 500 mm (or by at least 40 times the bar diameter).
• The minimum tie-column cross sectional dimensions are 100 mm by 100 mm.
• The tie-beam reinforcement should consist of four 10 mm diameter deformed bars for longitudinal
reinforcement, and 6 mm stirrups at 200 mm spacing. The tie-beam reinforcement needs to be
continuous, with the longitudinal reinforcement bars lapped by at least 500 mm.
International Journal of Recent Trends in Engineering & Research (IJRTER)
Volume 04, Issue 11; November - 2018 [ISSN: 2455-1457]
@IJRTER-2018, All Rights Reserved 53
IS Code Guidelines For Openings In Bearing Walls: The IS code is silent about confined masonry, but for openings in the bearing walls it recommends
the following guidelines:
● The guidelines on the size and position of opening are given in the clause 8.3.1 of IS 4326:
1993.
Characteristics of Materials To better understand the structural behavior of masonry wall it is important to have some knowledge
of the properties of component materials. Masonry is a multi-component assembly; in the current
study the wall specimens consisted of clay burnt bricks, cement mortar, concrete, and reinforcing
steel.
The main purpose of testing the component materials was to characterize the materials, to facilitate
the comparisons with other published results and design standards and to ensure that the quality of
materials was being maintained.
Material
Strength
Mean value(MPa)
Bricks Compressive strength 8.3
Mortar (1:6) Compressive strength 3.8
Concrete(1:2:4) Compressive strength 16.2
Steel Yield strength 425
Parameters Studied The parameters studied in this experimental program were the effect of central opening and effect of
reinforcement around the opening on the strength and stiffness of confined masonry walls.
Construction The specimens were built upon a concrete floor in the loading frame. The bricks were placed in
stretcher courses. The construction is carried in such a way so that toothed wall is made. After every
two layers of brick course the concrete is poured in form-work of columns, already placed at the
sides of constructing wall, so that the monolithic confined masonry wall is prepared. The tie-beam is
finally laid at the top.
To cure them, the specimens were wetted for seven days. The mortar joints of the concrete masonry
unit specimens were wetted twice a day.
Testing Procedures The testing set up is shown in Figure below. A horizontal load was applied along the axis of the top
beam using hydraulic jack. The walls were vertically confined. The walls were also restrained to
translation. During testing, the development of cracks and damage were registered. The load and
deformation of the walls at top were recorded manually.
Qualitative Behaviors Of The Specimens All the specimens failed in shear. The walls show almost linear behaviour initially followed by the
development and propagation of cracks, thus the later non-linear load deformation zone. The cracks
were mostly diagonal. The bottom of the compression tie-column got crushed and deformed i.e.
formation of plastic hinge. The cracks propagate though the mortar joint due to a low adherence
between the mortar and the masonry units.
International
IV.
Confined Masonry Wall Without Opening
Model 1
S.No Load(tons) Deflection(cm)
1. 0 0
2. 1 0.05
3. 2 0.1
4. 3 0.3
5. 4 0.4
6. 5 1.0
7. 5.5 1.5
8. 6 2.0
9. 5 4.0
10. 3.5 6.0
11. 3 8
12. 3 10
13. 2.5 12
International Journal of Recent Trends in Engineering & Research (IJRTER)
Volume 04, Issue 11; November - 2018
RESULTS AND DISCUSSIONS
Masonry Wall Without Opening-“CM”
Model 1 Model 2
Deflection(cm) S.No Load(tons) Deflection(cm)
1. 0 0
0.05 2. 1 0.05
3. 2 0.1
4. 3 0.3
5. 4 0.4
6. 5 0.7
7. 6 1.0
8. 6.5 1.6
9. 6 1.8
10. 5 2.0
11. 3.5 3.5
12. 3 5
13. 3 8
14. 3 10
15. 2.5 13
Journal of Recent Trends in Engineering & Research (IJRTER)
[ISSN: 2455-1457]
Deflection(cm)
International
Average values:
Peak load = 62.5 KN
Initial stiffness = 10 KN/mm
Deformation capacity = 12.5 cm
Confined masonry wall with opening
Model 1
S.No Load(tons) Deflection(cm)
1 0 0
2 1 0.2
3 1.5 0.3
4 2 0.8
5 2.5 1.2
6 3.2 1.8
7 2 2.5
8 1.5 3.5
9 1.5 5
10 1 6
International Journal of Recent Trends in Engineering & Research (IJRTER)
Volume 04, Issue 11; November - 2018
Confined masonry wall with opening-“CM+O20
”
Model 1 Model 2
Deflection(cm) S.No Load(tons) Deflection(cm)
1. 0 0
2. 1 0.2
3. 1.5 0.3
4. 2 0.9
5. 2.5 1
6. 3 1.3
7. 3.5 1.6
8. 2 2.2
9. 1.5 3
10. 1.5 6
11. 1 8
Journal of Recent Trends in Engineering & Research (IJRTER)
[ISSN: 2455-1457]
Deflection(cm)
International
Average values:
Peak load = 33 KN
Initial stiffness = 5 KN/mm
Deformation capacity = 7 cm
Confined masonry wall with opening
Model 1
S.No Load(tons) Deflection(cm)
1 0 0
2 1 0.3
3 1.5 0.5
4 2 1.0
5 2.5 1.5
6 2 2.0
7 1.5 3.0
8 1.5 4.0
9 1 6.0
International Journal of Recent Trends in Engineering & Research (IJRTER)
Volume 04, Issue 11; November - 2018
Confined masonry wall with opening-“CM+O25
”
Model 1 Model 2
Deflection(cm) S.No Load(tons) Deflection(cm)
1. 0.0 0.0
2. 1.0 0.3
3. 1.5 0.5
4. 2.0 0.8
5. 2.8 1.0
6. 2.5 1.5
7. 2.0 2.0
8. 1.5 3.0
9. 1.5 4.0
10. 1 7.0
Journal of Recent Trends in Engineering & Research (IJRTER)
[ISSN: 2455-1457]
Deflection(cm)
International
Average values:
Peak load = 26.5 KN
Initial stiffness = 3 KN/mm
Deformation capacity = 6.5 cm
Confined masonry wall with opening
Model 1
S.No Load(tons) Deflection(cm)
1 0 0
2 1 0.6
3 1.5 1
4 1.8 2
5 1.5 4
6 1.5 6
7 1 6.5
Average values:
Peak load = 17.7 KN
Initial stiffness = 1.58 KN/mm
Deformation capacity = 6.25 cm
International Journal of Recent Trends in Engineering & Research (IJRTER)
Volume 04, Issue 11; November - 2018
Confined masonry wall with opening-“CM+O30
”
Model 1 Model 2
Deflection(cm) S.No Load(tons) Deflection(cm)
1. 0 0
2. 1 0.6
3. 1.5 0.9
4. 1.7 2.2
5. 1.5 4
6. 1.5 5
7. 1 6
Journal of Recent Trends in Engineering & Research (IJRTER)
[ISSN: 2455-1457]
Deflection(cm)
International
From the above graph of Load-deflection of all the three types of wall specimens, the maximum load
was carried by confined masonry wall without opening i.e. “CM” and least by the confined masonry
wall with opening 30% i.e. “CM+O
masonry wall without opening i.e. “CM” and minimum in the “CM+O
stiffness was also seen in the “CM” and the least initial stiffness was observed in the “CM+O
From the crack pattern (diagonal cra
In case of “CM” the crack was diagonal and propagated from central portion towards corners. In case
of wall with opening i.e. “CM+O” the cracks were diagonal and concentrated around the open
corners.
COMPARISON OF RESULTS:
1. MAXIMUM LATERAL STRENGTH:a). [CM+O
20] / [CM] = 0.528
b). [CM+O25
] / [CM] = 0.424
c). [CM+O30
] / [CM] = 0.28
2. DEFORMATION CAPACITY: a). [CM+O
20] / [CM] = 0.56
b). [CM+O25
] / [CM] = 0.54
c). [CM+O30
] / [CM] = 0.52
3. INITIAL STIFFNESS: a). [CM+O
20] / [CM] = 0.50
b). [CM+O25
] / [CM] = 0.30
c). [CM+O30
] / [CM] = 0.158
International Journal of Recent Trends in Engineering & Research (IJRTER)
Volume 04, Issue 11; November - 2018
deflection of all the three types of wall specimens, the maximum load
was carried by confined masonry wall without opening i.e. “CM” and least by the confined masonry
wall with opening 30% i.e. “CM+O30
”. The maximum deflection was also observed in the confined
masonry wall without opening i.e. “CM” and minimum in the “CM+O30
”. The maximum initial
stiffness was also seen in the “CM” and the least initial stiffness was observed in the “CM+O
From the crack pattern (diagonal cracking) it was evident that all the wall specimen failed in shear.
In case of “CM” the crack was diagonal and propagated from central portion towards corners. In case
of wall with opening i.e. “CM+O” the cracks were diagonal and concentrated around the open
MAXIMUM LATERAL STRENGTH:
2. DEFORMATION CAPACITY:
V. CONCLUSION
Journal of Recent Trends in Engineering & Research (IJRTER)
[ISSN: 2455-1457]
deflection of all the three types of wall specimens, the maximum load
was carried by confined masonry wall without opening i.e. “CM” and least by the confined masonry
was also observed in the confined
”. The maximum initial
stiffness was also seen in the “CM” and the least initial stiffness was observed in the “CM+O30
”.
cking) it was evident that all the wall specimen failed in shear.
In case of “CM” the crack was diagonal and propagated from central portion towards corners. In case
of wall with opening i.e. “CM+O” the cracks were diagonal and concentrated around the opening
International Journal of Recent Trends in Engineering & Research (IJRTER)
Volume 04, Issue 11; November - 2018 [ISSN: 2455-1457]
@IJRTER-2018, All Rights Reserved 59
The research presented in this thesis investigated the structural performance of confined masonry
walls under lateral in-plane loading. The test data consists of results obtained for-confined masonry
wall without opening and confined masonry wall with opening.
Taking into account the findings from this study, the following conclusions can be drawn:
1. The presence of openings in the walls drastically reduces the earthquake resistant properties
of the buildings.
2. The incorporation of opening of area 20% of the wall area causes: decrease in lateral strength
by about 47%, decrease in deformation capacity (or ductility) by 44% and initial stiffness by about
50%.
3. The incorporation of opening of area 25% of the wall area causes: decrease in lateral strength
by about 46%, decrease in deformation capacity (or ductility) by 50% and initial stiffness by about
70%.
4. The incorporation of opening of area 72% of the wall area causes: decrease in lateral strength
by about 60%, decrease in deformation capacity (or ductility) by 48% and initial stiffness by about
86%.
5. The strength of confined masonry walls with 20% opening area is about twice as that of
confined masonry wall with 30% opening area.
6. The stiffness of confined masonry walls with 20% opening area is more than thrice as that of
confined masonry wall with 30% opening area.
7. There is hardly any change in deformation capacity between the wall with 20% opening area
and wall with 30% opening area.
REFERENCES 1. IS 2250: 1981, “Code of practice for preparation and use of masonry mortars”.
2. is 2212: 1991, “Brick works- code of practice”.
3. is 1077: 1992, “Common burnt clay building bricks and specifications”.
4. IS 4326: 1993, “Earthquake resistant design and construction of buildings- code of practice”.
5. Svetlana Brzev, Earthquake-resistant confined masonry construction, National Information Center of
Earthquake Engineering, Indian Institute of Technology Kanpur(India), December 2007
6. Eshghi, S. & Pourazin, K. 2009. In-Plane Behavior of Confined Masonry Walls – with and without
Opening, International Journal of Civil Engineering, 7(1): 49-60.
7. Sassan Eshghi & Behrang Saffari, 2009. Effect of openings on the lateral stiffness and strength of
confined masonry walls, International Journal of Civil Engineering.
8. Masayuki kasoki, kenji Kikuchi & Hideko Nonaka, Experimental study on reinforcing methods for
window openings in confined masonry walls, 35th conference on our world in concrete and structures : 25-27
August 2010, Singapore.
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