If $$\psi$$ is the nominal diameterofreinforcing bar, $$f_{x}$$, is compressive stress in the bar and $$f_{bd}$$ is design bondstress of concrete,the anchorage length $$l_{a}$$ of straight bar in compression is equalto:

A

$$L_{a}=\frac{\psi f_{x}}{f_{bd}}$$

B

$$L_{a}=\frac{\psi f_{x}}{2 f_{bd}}$$

C

$$L_{a}=\frac{\psi f_{x}}{\pi f_{bd}}$$

D

$$L_{a}=\frac{\psi f_{x}}{4 f_{bd}}$$