The fundamental assumption of reinforced concrete design—that concrete and steel deform together without slipping (perfect bond)—relies entirely on the ability to transfer stresses between the two materials. If a reinforcing bar is not sufficiently embedded into the concrete, it will pull out before it can develop its full yield strength ($f_y$).

The stress transfer from the concrete to the steel is called bond.

The shortest length of bar in which the full yield stress ($f_y$) can be developed is called the development length ($l_d$). The ACI 318 / NSCP equation for deformed bars in tension is:

The term $(c_b + K_{tr}/d_b)$ accounts for the splitting resistance of the surrounding concrete cover and transverse reinforcement (stirrups). It is limited to a maximum value of 2.5 to prevent a pullout failure from preceding a splitting failure.

Development length in compression is significantly shorter than in tension. There are two main reasons: (1) The end of the bar bears directly against the concrete (end bearing), transferring some force without relying on bond. (2) There are no flexural tension cracks in the concrete compression zone to weaken the mechanical interlock.

Note: The absolute minimum $l_{dc}$ is $200 \text{ mm}$. This length can be reduced if excess reinforcement is provided ($A_{s,required} / A_{s,provided}$), or if enclosed within spirals or closely spaced ties.

When the available straight distance is insufficient to satisfy the calculated $l_d$ (e.g., at exterior beam-column joints where the beam ends), the bar must be anchored using a standard hook. The hook mechanically engages a large volume of concrete, drastically reducing the required embedment length.

In heavily congested joints (like beam-column connections in seismic zones), even standard hooks may not fit or may cause unacceptable concrete placement issues.

In continuous beams, the bending moment varies along the span. To save material, flexural reinforcement is often cut off where it is theoretically no longer needed according to the moment envelope diagram.

When the required length of a reinforcing bar exceeds standard manufacturing or transport lengths (typically 6m, 9m, or 12m), bars must be spliced together to maintain continuity.

The required lap length ($l_s$) for tension splices depends on the class of the splice, which is determined by the ratio of area provided to area required, and the percentage of steel spliced at one location.

Compression lap splices ($l_{sc}$) are shorter than tension splices because they only need to transfer compressive forces. The basic length is $0.071 f_y d_b$ (for $f_y \leq 420$ MPa), but not less than $300 \text{ mm}$. If the bars are of different sizes, the lap must be the larger of the development length of the larger bar, or the splice length of the smaller bar.

To reduce congestion in heavily reinforced members (like large columns or transfer girders), bars can be bundled together in groups of up to four.