Difficulty: Easy
Correct Answer: 20%
Explanation:
Introduction / Context:
Bundling bars reduces the perimeter available for bond for each individual bar, which lowers bond efficiency. To compensate, codes require an increase in development length (Ld) for bars in bundles, with the increment depending on the number of bars bundled.
Given Data / Assumptions:
Concept / Approach:
Typical tabulated increments are: +10% for two bars, +20% for three bars, and +33% for four bars bundled together. These multipliers reflect the reduction in effective surface area per bar and the tendency for slip within bundles.
Step-by-Step Solution:
Step 1: Identify number of bars n = 3 in the bundle.Step 2: Apply codal increment: Ld_increase = +20% for n = 3.Step 3: Hence, required Ld per bar = 1.20 × Ld (for a single bar).
Verification / Alternative check:
Detailing handbooks and solved examples reproduce the same 10/20/33% sequence for 2/3/4 bars respectively, confirming the 20% increase for triplets.
Why Other Options Are Wrong:
10%: Applies to two-bar bundles, not three.33%: For four-bar bundles.50%: Excessively conservative; not specified for three-bar bundles.5%: Too small; not a recognized increment.
Common Pitfalls:
Final Answer:
20%
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