Correct Answer: A. 10 cm
Solution:
According to building codes, a stiffening wall (or cross wall) provides lateral support to a longer wall. For buildings up to three storeys, the minimum required thickness for such a wall is typically 10 cm (or half a brick thick).
Correct Answer: B. 7.5 cm
Solution:
A cavity wall consists of two separate walls or "leaves" with a gap in between. Building standards specify that for structural stability, the thickness of each individual leaf must not be less than 7.5 cm.
Correct Answer: C. 70%
Solution:
Water retentivity is a measure of a mortar's ability to hold its mixing water against the suction of the masonry units. A high water retentivity is crucial for proper cement hydration and bond strength. For brick masonry, the value should not be less than 70%.
Correct Answer: B. 60 cm
Solution:
In seismic design, the masonry pier between two vertically aligned openings is critical for resisting lateral forces. To ensure this pier is strong enough, seismic codes (like IS 4326) specify that the vertical distance between openings must not be less than 60 cm.
Correct Answer: C. 1.0 kg/cm²
Solution:
According to IS 1905, for a panel wall (non-load bearing) built with M1 type mortar (1:5 cement:sand) and subjected to out-of-plane bending, the permissible tensile stress in the vertical direction is 1.0 kg/cm² (or 0.1 N/mm²).
Correct Answer: A. Providing buttresses at certain intervals
Solution:
A long, high wall is susceptible to failure from lateral loads like wind. Providing buttresses (or piers) at regular intervals is the most effective structural solution. These buttresses act as stiffeners, breaking up the long span of the wall and providing significant resistance to bending and overturning.
Correct Answer: C. 1.6
Solution:
Building codes provide modification factors for the basic compressive stress of masonry units based on their geometry. For a height-to-width ratio of 1.5, the specified shape modification factor allows for an increase in the basic stress by a factor of 1.6.
Correct Answer: A. ¼ × height of shorter opening
Solution:
To ensure adequate strength of the masonry pier between openings in seismic zones, codes specify minimum distances. For areas with a low seismic coefficient (< 0.08), the horizontal pier width must be at least one-quarter of the height of the shorter opening.
Correct Answer: D. 10
Solution:
Mortars are graded based on their compressive strength. According to IS 1905, H1 type mortar is a high-strength mortar (typically a 1:3 cement:sand mix) and is required to have a minimum 28-day compressive strength of 10 N/mm².
Correct Answer: A. 15
Solution:
The slenderness ratio is calculated as the effective height divided by the effective thickness. For a wall supported by RCC slabs, the effective height is 0.75 times the clear height (0.75 * 3.8m = 2.85m). The effective thickness is 200mm or 0.2m. Slenderness Ratio = 2.85 / 0.2 = 14.25, which is approximately 15.
Correct Answer: D. Larger of (B) and (C)
Solution:
For structural calculations of a load-bearing cavity wall, the effective thickness is determined by considering two criteria: two-thirds of the sum of the thicknesses of both leaves, and the actual thickness of the stronger leaf. The code specifies using the larger of these two values for design.
Correct Answer: B. Vertical tensile splitting
Solution:
Very short, stocky masonry columns (with a height-to-thickness ratio less than 4) are not prone to buckling. When loaded in compression, they tend to fail due to the lateral expansion of the material, which causes vertical tensile splitting cracks to form.
Correct Answer: D. 7%
Solution:
According to structural design codes, when a single component provides lateral stability to a large group of vertical members (five or more), it must be designed to resist a notional horizontal force. This force is taken as 7% of the total vertical load from the most heavily loaded member in that group to ensure overall system stability.
Correct Answer: C. 0.85
Solution:
Building codes specify a stress reduction factor for masonry walls based on their cross-sectional area to account for scale effects. For a wall with a horizontal cross-sectional area between 1000 cm² and 1500 cm², the specified reduction factor is 0.85.
Correct Answer: A. 0.75 H
Solution:
The effective height of a wall is used to calculate its slenderness ratio. When a wall is provided with lateral and rotational restraint at the top and bottom by concrete floors that have adequate bearing, its effective height is taken as 0.75 H, where H is the actual height between support centers.