Introduction / Context:
Lap splices are used to provide continuity of reinforcing bars when individual bar lengths are insufficient. In compression members (such as reinforced concrete columns), codal provisions specify a minimum lap length to ensure safe transfer of compressive forces between lapped bars without premature slip or crushing of surrounding concrete.
Given Data / Assumptions:
- Member type: reinforced concrete compression member (column).
- Quantity asked: minimum lap length as a multiple of bar diameter φ.
- Design context: basic codal/detaling rule of thumb for compression splices (no special confinement or mechanical couplers considered).
Concept / Approach:
The lap splice in compression must be long enough to develop the required compressive force in the bar through bond with the surrounding concrete. While exact development length depends on concrete grade, bar type, and bond conditions, codes provide a minimum lap length for compression to avoid unsafe reductions. A widely adopted minimum is 24 φ for bars in compression, ensuring reliable force transfer even under minor construction deviations.
Step-by-Step Solution:
Identify member action: bars are in compression → use compression splice rule.Recall minimum lap length requirement in compression: not less than 24 φ.Compare with options → select 24 φ as the smallest acceptable multiple that meets the rule.
Verification / Alternative check:
For tension splices, a larger limit (often 30 φ or more, depending on development length) is typical; the question specifically targets compression, where 24 φ suffices as the minimum.
Why Other Options Are Wrong:
12 φ / 16 φ / 20 φ: too short for a reliable compression splice in standard detailing.30 φ: conservative but not the minimum; exceeds the requirement for compression splices.
Common Pitfalls:
Confusing tension and compression lap requirements; applying development-length equations without observing codal minimums.Ignoring bar location and confinement, which affect required lengths but do not reduce the codal minimum.
Final Answer:
24 φ
Discussion & Comments