Assertion (A): In the preparation of a structural layout, "Secondary Beams" are often used to reduce the span of the slabs. Reason (R): Reducing the slab span decreases the thickness of the slab required and limits the deflection. Choose the correct answer: (A) Both (A) and (R) are correct and (R) is the correct explanation of
- ABoth (A) and (R) are correct and (R) is the correct explanation of (A)Correct
- BBoth (A) and (R) are correct, but (R) is not the correct explanation of (A)
- C(A) is correct but (R) is incorrect
- D(A) is incorrect but (R) is correct
Solution
Concept
Secondary Beams in Structural Layouts
Formula
N/A
Step-by-step solution
1. Evaluate Assertion (A) regarding secondary beams reducing slab spans. 2. Evaluate Reason (R) that smaller spans lower required slab thickness and limit deflection, directly explaining (A). 3. Select the choice stating both (A) and (R) are correct and (R) is the correct explanation of (A).
Explanation
Secondary beams support slabs by breaking larger spaces into smaller spans, which directly allows engineers to design thinner slabs with less bending and lower deflection. Because smaller spans directly reduce the required slab thickness and control sag, the reason correctly explains why secondary beams are used.
Shortcut
To remember the role of Secondary Beams, use the rule "Smaller Span = Thinner Slab": - Secondary Beams: Added to split long spans into smaller slab panels. - Design Benefit: Shorter span reduces bending moment, which decreases required slab thickness and limits deflection.
Common mistake
A common mistake is selecting Option B by agreeing that both statements are correct but failing to recognize that Reason (R) directly explains why Assertion (A) is done in structural engineering. Reducing slab thickness and deflection is the exact design objective behind introducing secondary beams to break up larger spans. Another frequent error is confusing secondary beams with primary beams and mistakenly assuming secondary beams frame directly into columns rather than main beams.
Correct answer: A) Both (A) and (R) are correct and (R) is the correct explanation of (A)