Development Length of Steel Bar in R.C.C.

Dear members.

In BIS code the development length of steel bar was 40X Dia. of bar in 1980 right?

In 1990 revision it was changed to 48 XDia. of bar.

Now there is formula Given in IS456:2000 reaffirmed in 2005 which shows

Develop length=(nominal Dia.of bar)x Stress in bar /4 x design bond stress

Ld = fi * sigma/ 4 tau bd.

This formula is giving too much more development length than previous formulas

My question is I am not properly understanding it or it is like that?

Please guide me.

Pravin dhameliya