huangyhg

adding stirrups
a contractor got creative with one of my designs and some stirrups were omitted.
is it possible to drill & epoxy #3 vertical rods into the beam? does the stirrup leg still need to hook around the tension reinforcement per aci 318-99 11.5.1.2?
i doubt if this would be practical to do in the same plane as the existing stirrups since i would worry about drilling bars so close to the face of the beam. perhaps they can be drilled inside the longitundinal steel and hooked over the top.
i have seen steel straping used for this problem but this is a grade beam so i would be worried about corrosion unless i used stainless steel.
any other ideas?
consider exterior composite reinforcement
if it is a grade beam, and you are worried about shear - then i presume you have a grade beam that is spanning some distance from underlying supports such as piers or footings?
the first thing to do is re-verify your calculations and eliminate any sluff / extra loads you put on the beam that really won't occur. next take a look at the f'c that you get from the test results since shear is very dependent on f'c.
you could possibly drill down and use a bolted end to a top cap plate but that sounds really difficult to do - lots of drilling = lots of money.
i'd agree that exterior strapping would be subject to corrosion and boo1's suggestion might be workable - but its usually expensive also - and takes time to get the sub-contractor specialist in to do it.
perhaps some strategic underpinning with additional supports to minimize shear?
or perhaps an adjacent grade beam on the inside to add strength and span from the same supports.
you likely know of this, but aci 318 section 11.1.3.1 allows you to design for shear using the factored shear value at a distance "d" from the face of the support. this might allow for a greater stirrup spacing so you can use what the contractor installed. doesn't help if he left out all of the stirrups, tho.
also, determine the required spacing of stirrups for your shear, not the minimum spacing per the code. this can sometimes be vastly different.
if you have to go with external composites, perhaps this will help
consider making him replace the beam.
whatever you do, don't work to find calculations and allowances in aci that end up showing the beam to be okay and then just come back and say to the contractor "oh it's okay" without further explanation. we have enough problems in this field of contractors thinking us engineers just overdesign everything so we don't have to do any work. let him no what a pain in the --- it is and how much extra work you will have to do to find a workable solution. if you can make what the contractor actually installed work, by all means let him know how you saved his tail and that he owes you (even if it's just lunch).
zcp

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