Its depends, if the level of TOC higher than top of slab concrete , then we have to crush the concrete surround rebar and clean rebar in proper way to establish overlaping for next floor column reinforcement, this should consider the availble exposed rebar lenght to do extension by mechanical overlapping or field welding if applicable , for more safe action we have to drill into old concrete and using chemical bond .
Secound senirio the TOC is same of slab concrete slab level , in this case drilling into old concrete and using welding between old and new rebar with chemical bond is required , considering the new rebar for next column shall be as extension to provide minmum distance for overlapping .