As per $IS \: 456:2000$ for $M20$ grade concrete and plain barsin tension the design bond stress $\tau_{bd}=1.2$ MPa. Further, $IS \: 456:2000$ permits this design bond stress value to be increased by $60 \%$ for HSD bars. The stress in the HSD reinforcing steel barsin tension, $\sigma_s=360$ MPa. Find the required development length, $L_d$, for HSD barsin terms of the bar diameter, $\phi$ ________