1927 Concrete Building
1927 Concrete Building
(OP)
I am analyzing a concrete building to determine the capacity of the 8th floor. Surprisingly, I have drawings. The joists and beams are scheduled, so I have the reinforcing. The schedules list, for example, '1 7/8" dia. mark 703'. The bar bending diagram tells me what mark 703 looks like. However, each joist has one or two bars marked "S+". S+ is not in the diagram, so I think it is just additional straight bars. I just can't tell if it goes in the top or the bottom. Can anyone shed some light?






RE: 1927 Concrete Building
RE: 1927 Concrete Building
I would thin that your 703 bar is what we would call a "crank" bar or a "truss" bar....where its left portion is up high (a top bar) - it transitions down diagonally to a bottom bar in the middle, then transitions up to a top bar on the right.
So at the bottom of your slab/beam, you have a straight bar plus a bent bar for your +As. On the left, you'd have the bent bar from your particular span, plus the bent bars from the adjacent left span for your left side -As. Similar for your right side -As.
RE: 1927 Concrete Building
Anyhow, without knowing the original use of the building, I have to assume office live load at best. That's what I'll tell the client, unless I find overwhelming evidence otherwise.
RE: 1927 Concrete Building
In any case, most of these older beams will generally be controlled by their shear capacity. Low f'c values and minimal stirrups. When you try to back-calculate an allowable live load, the shear controls most always over the positive and negative moment capacities.
RE: 1927 Concrete Building
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the sizes and spacing was provided on the plan, but nothing indicating location in the slab as either top or bottom straight bars. a schedule provided the lengths of the bent bar. I do not recall if the straight bars were designated "St".
my thoughts were that the bottom bars were straight bars, not top bars as my partner thought they might be. he checked the slab two ways, with the bars as top and bottom bars. the slab checked out with the straight bars as bottom bars but not with them as top bars.
RE: 1927 Concrete Building
RE: 1927 Concrete Building
My father always referred to the zig-zag rebar described above as "galloping steel" - Contractors hated it since it was very difficult to keep in proper position before concrete placement.
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