Correct Answer  Option 4 :
\({f_w} = {K_w}\sqrt {{f_b}{f_m}} \)
Concept:
The basic compressive stress of masonry depends upon the crushing strength of masonry units (bricks) and type of mortar used.
Basic compressive stress also depends upon surface characteristics, water absorption property of units, uniformity of shape and size of units, thickness of joints etc.
For a wall, the slenderness ratio shall be the effective height divided by the effective thickness and stiffening coefficient (Kn) or the effective length divided by the effective thickness, whichever is less.
Thus, \(SR = \frac{h}{{t{K_n}}}\)
The relation between the strength of brick masonry fw, the strength of bricks fb, and the strength of mortar fm is given by,
\({f_w} = {K_w}\sqrt {{f_b}{f_m}} \)
No. of storeys

Thickness of wall

Maximum values of S.R

Mortar containing cement

Mortar not containing cement

Not exceeding 2

Any

27

20

Exceeding 2

Walls of 90 mm thickness or more

27

13

Wall less than 90 mm thickness

20

13
