provision for future expansion in rcc frame structure

huangyhg

provision for future expansion in rcc frame structure
i have a reinforced concrete frame structure with three bays, however, there is provision in plan for constructing further three bays in future. my approach is to construct three bays, leave about 3 inches (just like expansion joint) and construct the other three bay frame when needed. however, combined foundation for last column of this frame + first of future frame should be provided now.
is this the correct approach, or some other method should be adopted to avoid duplication of columns at interframe gap.
e.g, simply supporting beam on end column etc.
please comment.
first decide if you need the expansion joint in the building.  two reasons for an ej would be the length of the building and whether the foundation system might have significant settlements upon its construction.  in most cases there is a concern that new construction will naturally deflect some amount.  the question is whether a tied-in addition can endure those settlements.
if an expansion joint is required - yes, design the end footings for the future loading.  if an expansion joint is not required - then the end columns and footings should be designed to support the future loading.  
for a connection to an end column, you could provide a corbel with extended rebar - or use threaded couplers at the corbel top face - and go from there.  other option would be to use a stepped column - i.e. the lower column is wider than the upper and creates a ledge for the future beam to rest on.
precast concrete building details could be used ie,
- corbel, to form halved joint with future beam
- steel connector protruding from column face, hidden within beam section
- rebated column face and cast-in threaded inserts for rebar into the beam
it is not very efficient to plan for a double column.