If Sb, is the average bond stress on a bar of diameter d subjected to maximum stress t, the length of the embedment $$l$$ is given by A. $$l = \frac{{{\text{dt}}}}{{{{\text{S}}_{\text{b}}}}}$$ B. $$l = \frac{{{\text{dt}}}}{{2{{\text{S}}_{\text{b}}}}}$$ C. $$l = \frac{{{\text{dt}}}}{{3{{\text{S}}_{\text{b}}}}}$$ D. $$l = \frac{{{\text{dt}}}}{{4{{\text{S}}_{\text{b}}}}}$$

The correct answer is $\boxed{\text{B. }l = \frac{{{\text{dt}}}}{{2{{\text{S}}_{\text{b}}}}}$}.

The bond stress is the force per unit area that resists the pull of the reinforcing bar on the concrete. The maximum stress is the highest stress that the concrete can withstand before it fails. The diameter is the width of the reinforcing bar. The length of the embedment is the length of the reinforcing bar that is embedded in the concrete.

The bond stress is calculated by dividing the maximum stress by the diameter. The length of the embedment is calculated by dividing the bond stress by the maximum stress.

Therefore, the length of the embedment is given by:

$$l = \frac{{{\text{dt}}}}{{2{{\text{S}}_{\text{b}}}}}$$

where:

• $l$ is the length of the embedment
• $d$ is the diameter of the reinforcing bar
• $t$ is the maximum stress
• $S_b$ is the bond stress

The other options are incorrect because they do not divide the bond stress by the maximum stress.