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Define development length and lap splice

Short answer

Development length is the embedded length to develop full bar stress through bond, L_d = 0.87 f_y φ/(4 τ_bd). Lap splice: overlapping bars for force transfer; lap length ≥ L_d (≥30φ in flexural tension, 2L_d in direct tension, 24φ in compression), placed staggered away from high-stress sections.

Define development length and lap splice.

  • Development length (LdL_d): the length of reinforcing bar that must be embedded in concrete beyond a section so that the bar can develop its full design stress (0.87fy0.87f_y) through bond without slipping. Ld=0.87fy ϕ4τbdL_d=\dfrac{0.87f_y\,\phi}{4\tau_{bd}}, e.g. about 47ϕ47\phi for Fe415 deformed bars in M20.
  • Lap splice: a joint between two reinforcing bars made by placing them side by side and overlapping them for a specified length, so that the force passes from one bar to the other through the concrete by bond. The lap length is not less than LdL_d or 30ϕ30\phi (whichever is greater) for bars in flexural tension, 2Ld2L_d or 30ϕ30\phi in direct tension, and LdL_d (in compression) or 24ϕ24\phi for bars in compression. Laps should be staggered and kept away from sections of maximum stress.

✓ Answer checked by Claude Opus 5.5 (high effort)

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