TITLE:
TO DETERMINE THE STRENGTH OF A MASONRY WALL
OBJECTIVES:
THEORY:
Masonry structure gains stability from the supports offered by the cross walls, floors and other elements such as piers and buttresses.
A structural code of practice or standard contains recommendations for dealing with various aspects of design. Such a document is not, however, a textbook and doesn't relieve the designer from the responsibility of acquiring a full understanding of materials used and of the problems of structural actions. It follows therefore that, in order to use a code of practice satisfactory, and perhaps even safely,the engineer must make a careful study of its provisions and, as far as possible, their un....Show More
TITLE:
TO DETERMINE THE STRENGTH OF A MASONRY WALL
OBJECTIVES:
THEORY:
Masonry structure gains stability from the supports offered by the cross walls, floors and other elements such as piers and buttresses.
A structural code of practice or standard contains recommendations for dealing with various aspects of design. Such a document is not, however, a textbook and doesn't relieve the designer from the responsibility of acquiring a full understanding of materials used and of the problems of structural actions. It follows therefore that, in order to use a code of practice satisfactory, and perhaps even safely,the engineer must make a careful study of its provisions and, as far as possible, their unyielding intention. We are dealing with following codes of masonry design:
OBSERVATIONS:
BRICK NAME: BIRLA
Sno | Length (mm) | Breadth (mm) | Load at failure (KN) | Compressive strength `(N/(mm)^2)` | Average compressive strength |
1 | 245 | 120 | 345 | 11.735 |
|
2 | 244 | 121 | 165 | 5.589 | 9.006 |
3 | 245 | 120 | 285 | 9.694 |
|
Thus average ultimate strength =9.006 N/`(mm)^2`
DESIGN:
Let us now design the wall of a two storey building to carry 120 mm thick RCC slab with 3m ceiling height. Let the walls are unstiffened and support a 2.5 m wide slab on both sides.
Let,
Live load on roof = 1.5 KN/`m^2`
Live load on floor = 2 KN/`m^2`
Weight of surface finish = 1.2 KN/`m^2`
Let us assume the thicknesd of wall to be 120 mm.
Assuming that the joints are not racked,
The effective thickness is =120-10=110 mm
And
Effective height,`h=0.75H=0.75 (3+0.12)=2.34 m`
Let effective height is less than effective length.
`SR=2.34/0.110=21.28 <27`
From IS table 9, stress reduction factor for slenderness ratio 21.28 and zero eccentricity is,
`K_s-0.62=(0.56-0.62)/(22-20)**(21.28-20)`
`K_s=0.5816`
Also,
Area=2.5**0.11
`A=0.275>0.2m^2`
Thus,`K_a=1`
Again,
The ratio of geight and widtg of brick unit is less than 0.75 so,
`K_p=1`
Now,
Load from roof is,
Weight of slab,`w=25**0.12**2.5=7.5`KN/m
Weight of surface finish=1.2**2.5=3 KN/m
Live load=1.5**2.5=3.75 KN/m
Total load from roof=14.25 KN/m
Load from floor is,
Weight of slab,`w=25**0.12**2.5=7.5`KN/m
Weight of surface finish=1.2**2.5=3 KN/m
Live load=2**2.5=5 KN/m
Total load from roof=15.5 KN/m
Self weight of wall is,
`W=20**3**0.11**2=13.2`KN/m
Thus total load is,
`=14.25+15.5+13.2 =42.95` KN/m
And total stress applied is,
`=42.95/0.11=390.45` KN/m^2
`=0.390` N/`(mm)^2`
We know,
The allowable stress is,
`f_(ca)=f_b*K_s*K_p*K_a`
For safe design, the allowable stress must be greater than the applied stress i.e,
`f_(ca)=f_b*K_s*K_p*K_a > 0.390`
`f_b**0.5816**1**1>0.390`
`f_b>0.671` N/`(mm)^2`
Thus, we get,
Crushing strength = 7.5 N/`mm^2`
Grade of mortar: `M_1`
And allowable stress,
`f_(ca)=0.74**1**0.5816**1=0.43`
RESULTS:
Thus it is found that,
Ultimate stress > permissible stress > applied stress in the wall
CONCLUSIONS:
Thus the ultimate compresdive strength was determined and the wall for two storeyed building was designed.
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