Effective Height, Opening in walls, Effective length, Effective
thickness, Slenderness Ratio
EFFECTIVE HEIGHT : The height of a wall or column to be considered for
calculating slenderness ratio (IS1905-1987) .
Refer IS1905-1987 Of Page num 11.
DEPARTMENT OF CIVIL ENGINEERING , VVIT , B'lore Page 1
Effective Height, Opening in walls, Effective length, Effective
thickness, Slenderness Ratio
DEPARTMENT OF CIVIL ENGINEERING , VVIT , B'lore Page 2
Effective Height, Opening in walls, Effective length, Effective
thickness, Slenderness Ratio
DEPARTMENT OF CIVIL ENGINEERING , VVIT , B'lore Page 3
Effective Height, Opening in walls, Effective length, Effective
thickness, Slenderness Ratio
OPENING IN WALS :
From SP20( S&T):1991 page num-10,11
An RCC slab bearing on a wall is assumed to provide full restraint to the wall while a timber
floor comprising timber joints and planking is assumed to provide only partial restraint. The
clause makes stipulations for reckoning effective height of columns formed by openings in a
wall for the two cases:
wall has full restraint at top and bottom wall has partial restraint at top and bottom
If height of neither opening exceeds 0.5H, wall masonry would provide some support to the
column formed by openings in the direction parallel to the wall and for this reason effective
height for the axis perpendicular to the wall is taken as H and otherwise it is to be taken as
2H. For the direction perpendicular to the wall, there is a likelihood of a situation when no
joist rests on the column formed between the openings and thus effective height is taken as
2H that is, for a column having no lateral support at the top.
DEPARTMENT OF CIVIL ENGINEERING , VVIT , B'lore Page 4
Effective Height, Opening in walls, Effective length, Effective
thickness, Slenderness Ratio
From IS 1905-1987 Page no 11
DEPARTMENT OF CIVIL ENGINEERING , VVIT , B'lore Page 5
Effective Height, Opening in walls, Effective length, Effective
thickness, Slenderness Ratio
EFFECTIVE LENGTH
When a wall has more than-one opening such that there is no opening within a distance of
H/8 from a cross wall and wall length between openings are not columns by definition, the
design of the wall should be based on the value of SR obtained from the consideration of
height or length, whichever is less.
The length of wall to be considered for calculating slenderness ratio.
From IS1905-1987 Page num 12
DEPARTMENT OF CIVIL ENGINEERING , VVIT , B'lore Page 6
Effective Height, Opening in walls, Effective length, Effective
thickness, Slenderness Ratio
DEPARTMENT OF CIVIL ENGINEERING , VVIT , B'lore Page 7
Effective Height, Opening in walls, Effective length, Effective
thickness, Slenderness Ratio
EFFECTIVE THICKNESS
In case of masonry using modular bricks, actual thickness of a one-brick wall for design
calculation is taken as 19 cm, though nominal thickness is 20 cm. Similarly in case of brick
masonry with bricks of old size actual thickness of one-brick wall would be taken as 22 cm
though nominal size of brick is 23 cm.
Refer IS1905-1987 page num 13-14
Effective thickness to shall be used for calculating slenderness ratio of wall or column shall
be obtained below.
1) For solid wall, faced walls or columns, effective thickness shall be the actual thickness.
2) For solid walls adequately bonded into piers, effective thickness for determining
slenderness ratio based on effective height shall be the actual thickness of wall multiplied by
stiffening coefficient as given in table 6. No modification in effective thickness, however
shall be made when slenderness ratio is to be based on effective length of walls.
3) For solid wall or faced walls stiffened by cross walls, appropriate stiffening coefficient
may be determined from Table 6 on the assumption that the cross walls are equivalent to
piers of width equal to the thickness of the cross wall and of thickness equal to three times the
thickness of stiffened wall.
4) For cavity walls with both leaves of uniform thickness throughout, effective thickness to
be taken as two-thirds the sum of the actual thickness of the two leaves.
DEPARTMENT OF CIVIL ENGINEERING , VVIT , B'lore Page 8
Effective Height, Opening in walls, Effective length, Effective
thickness, Slenderness Ratio
DEPARTMENT OF CIVIL ENGINEERING , VVIT , B'lore Page 9
Effective Height, Opening in walls, Effective length, Effective
thickness, Slenderness Ratio
SLENDERNESS RATIO
It is the ratio of effective length to the radius of gyration.
Refer IS 1905-1987 page num 14-15
Walls : For a wall, slenderness ratio shall be effective height divided by effective thickness
or effective length divided by the effective thickness, whichever is less. In case of a load
bearing wall, slenderness ratio shall not exceed that given in table 7
Columns : For a column, slenderness ratio shall be taken to be the greater of the ratios of
effective heights to the respective effective thickness in the two principal directions.
Slenderness ratio for a load bearing column shall not exceed 12.
DEPARTMENT OF CIVIL ENGINEERING , VVIT , B'lore Page 10
