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 Haq 1 , Zahid Ahmad Chat 2 1 M-Tech (Structural Engineering) NIT-Srinagar 2 M-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
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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