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Re: How to Retrofit a Concrete Beam

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        While a 24 x 36 deep beam is pretty hunky, at 25 c/c and 50 long, they do not support many floors my guess is two. So if the new load is substantially higher, the amount of effort in figuring out the existing reinforcing and analysis may not be worth it.
        If pretensioned, try to get to the end of a beam and look at the ends of the strand. If posttensioned, this will be harder. The stirrup configuration and top steel will still have to be ascertained. X-raying works, but no one else can be onsite and it’s expensive. There are other ways of determining reinforcing, with varying costs and clarity – and usually varying reciprocally, but in 24” some will not work.
        If prestressed and the strands are draped, then retrofitting by putting new columns along the span will cause negative moment issues. Even if mild steel reinforced, this can occur. Grooves can be cut and new bars epoxied in, carbon fiber can be placed, external post-tensioning can be placed, sister beams can be placed and other possibilities are numerous, so I am not going to go into detail sorry.
        Jim Getaz
        Precast Concrete Engineer