existing beam - added shear capacity

huangyhg

existing beam - added shear capacity
how do i add shear capacity to a reinforced concrete beam that looks what is shown on the attachment. i know you can use carbon-fiber on a typical rectangular beam, but i can't do it here due to existing geometry. i'd rather not add the cost of demo'ing the extra 4" overhang around the entire opening that is being infilled.
this beam is 20' long and is supported by beams on either end. the shear capacity is needed in the middle because the shear is greater than 50% of the vc. the reinforcement is there but it is spaced at 10" oc. this does not meet the requirement of d/2 minimum spacing.
this area is getting infilled so that is why the beam does not have the required shear reinforcement, and i was wondering how we can reinforce this beam. any suggestions? i don't have the head room to put a steel beam below this beam.   
rc
all that is necessary for the triumph of evil is that good men do nothing.
    edmund burke

if you are infilling with concrete can you incorprate an edge beam to the infill with the required strength?
if you can take a core sample of the concrete and test it, maybe the f'c attained is greater than what was spec'd in the oroginal structural drawings, and just maybe that's enough to avoid having to add the extraq shear reinforcing?
mike mccann
mmc engineering
the simplest way may be to drill in from the top and insert double headed studs, set in epoxy mortar.
hokie66,
the problem with that is that they will want to diamond core it through something that deep and those sides of the hole will be as smooth as .. well as smooth as something really smooth.
rcraine,
can you put a steel channel either side of the beam?
i would second some of the suggestions above - first nail down the f'c.  also consider the idea of two c8 channels - one on either side.
harped external pt strands may be an option.   
i agree with hokie66's suggestion. another thought i had was similar except using single leg #2 or #3 rebar hooked on the tension end set in epoxy filled drilled holes. you could also use external vertical plate straping. any external solution may require fireproofing to maintain the fire rating.
apsix,
we were planning on infilling with a series of small steel beams and some metal deck. the opening is only 10' wide by 18' long, so we weren't planning on using concrete in this application.
mssquared,
that could be an option, but i don't think we'll get much benefit because the shear is about 80% of the shear provided by the concrete. so the increase wouldn't get us below the 50% required to not require stirrups. if it was closer, then possibly, that could save us in this situation.
hokie66,
i have never seen this done, as i'm pretty new (~2yrs). do you ahve information on this? i know i've read about it recently and seen mostly in pt slabs but any information you can pass along would be great.
csd72,
for the channels, would they be set with epoxy/expansion bolts as required to transfer enough shear to be below the 50% required? then i'd be able to cut this short once i'm beyond the critical point where shear provided from (vs + vc) can be used due to the spacing?
teguci,
the pt seems excessive for this application, we've [our firm, not me ] done this in the past at a pt garage we're constantly monitoring.
jike,
is the plate strapping doing the same thing as the c8, with regard to distributing the shear?
thanks for all your responses! i truly appreciate this great forum and i look forward to your continued help!
  
rc
all that is necessary for the triumph of evil is that good men do nothing.
    edmund burke

what about wrapping the tee with a steel plate?
when you checked the design of the beam did you take into account the 8" slab on top and design it as a t beam or just check it as a 12"x16" beam?  if you checked it as a t beam and it still does not work then i would add a steel channel for the full length on one or both sides as required.  i would design the steel channel to take the added infill load by itself.
you said the shear capacity is needed in the middle.  assuming you mean the middle of the span, that is where the shear would be the lowest.  please explain.