masonry lap splices

huangyhg

masonry lap splices
    hello all,  i have an existing masonry block wall that i am looking to extend up.  it is a site retaining wall and i would like to extend the reinforcing up into block that i am extending.  the existing wall is reinforced with #6 bars at 24" oc.  i have gone to the site and can see the grouted cores and the bond beam is 3 block courses down.
    i need a lap splice of 36", but with the bond beam 24" down i cannot get that.  i could used mechanical connectors but then i would need to demo into the grouted cells to expose the existing rebar, potentially splitting the block.  my boss suggested that we could put bars into the cores on either side.  the theory being that two bars lapped 24" is equivalent to one bar lapped at 36".  is that a credible idea?  code only gives lapped, welded or mechanical connectors.
    tia
    roland bokma
    structural e.i.t.
    progressiveae
how do you get rebar lap if you put the new bars in the adjacent cores?  rebar lap requirements, in my experiance, mean rebar contact over the length of the lap.
my suggestion would be to put the new rebar in adjacent cores as you suggest, grout those cores, run the new rebar up into the new block and the first new course of block should be a bond beam.  this doesn't really lap the rebar, but it would lock it into the existing wall.  the new bond beam would provide additional stiffness and bond for the new rebar.  the new bond beam would have horizontal rebar too.
  code permits noncontact lap splices to occur in the adjacent core providing they are not spaced further than 1/5th the required lap length nor more than 8 inches (aci 530-99, section 2.1.8.6.1.2).
  thanks for the response, roland
rolin, you can also reduce the required lap splice (development length) based on area required/area provided - so having extra rebar does allow a diminished length.  
jae,
wouldn't the reduction in lap length for excess area only apply if the rebar at both ends of the lap joint has excess area?  ie not only do you need the new bars to have excess area, but the existing bar as well??
whislt concentrating on the lap/splice detail don't forget to check the overall design of the new "higher" wall, especially for the lower section of wall which will be subject to greater forces and moments at the the base....then it was originally designed for.