Lap splicing in compression members: The lap length shall not be less than bar_dia * (permissible_stress / (5 * bond_stress)) or which minimum value expressed in bar diameters, whichever is greater?

Introduction / Context:
Lap splices in compression must safely transfer force between bars through bond with concrete. Codes specify a calculated lap length and also a minimum bar diameter multiple to cover variability in workmanship and conditions.

Given Data / Assumptions:

• Compression member with lapped longitudinal bars.
• Design stresses and bond stresses per standard practice.
• Requirement: adopt the larger of calculated or minimum lap.

Concept / Approach:
The calculated lap uses permissible stress and bond stress values; however, a minimum of 24φ (φ = bar diameter) is typically specified for compression laps to ensure adequate embedment and confinement length even when calculated values are small.

Step-by-Step Solution:
Compute L_calc = φ * (permissible_stress / (5 * bond_stress)).Compare with L_min = 24φ.Provide lap length = max(L_calc, 24φ) within a zone of adequate transverse reinforcement.

Verification / Alternative check:
Confinement via closer ties in splice regions enhances bond behavior; design guides consistently adopt 24φ as the baseline for compression laps in normal conditions.

Why Other Options Are Wrong:

• 12φ and 18φ: usually insufficient for reliable compression splices.
• 30φ or 36φ: conservative but not the commonly mandated minimum for compression laps in ordinary conditions.

Common Pitfalls:
Placing splices at highly stressed sections, inadequate tie spacing, and ignoring cover limitations which reduce bond effectiveness.

Final Answer:
24 bar diameters.