As per the ACI318 tables for the Development and Splice lengths in the thread, Top bar in
ACI318 is defined as the bar fixed on concrete that is 300mm thick or more.
Other bar is defined as any bar fixed below that thickness just above the
concrete cover. So those vertical or horizontal bars in a wall or a column will
only follow the Other bar lengths mentioned in the tables. This difference is
because of amount of bubbles on top are muchj higher than their amount under the
bottom reinforcement, causing less bond between the bar and the concrete.