bundling rebar

huangyhg

bundling rebar
good morning all,
i have a question about bundling rebar. in general, most designs that have bundled rebar have equal size bars in the bundle, but is it a problem to bundle two different sizes of rebar?
it would be ideal for me to place a 35m bar with a 20m bar in one bundle. can this be done well in the field? will i lose any capacity? is it not considered good practice to do this?
for background: this rebar bundle would be placed in a railway bridge abutment and embedded into the rock. the abutment is to be built in ontario, canada.
aci 318 section 12.4 states that develpoment length for compression and tension for three bars bundles shall be increased 20%; four bar bundles 33%.  there are other things to consider that section 7.6.6 talks about, one being staggering of the bundle terminations.
you can bundle unequal bar sizes, no prob.
mike mccann
mmc engineering