huangyhg

partial rebar development
i have a situation where the stair guy is attaching a stringer to a bent plate at edge of slab where the slab is cantilevered out past the beam 1'-6".
this was not the intent of the original design and the slab isn't poured yet. i am detailing some rebar in the top of the slab(attached to the bent plate at edge of slab) to take this moment back into the slab.
i can't get a fillet weld around a #4 bar to develop the bar unless it is like a 1/2" weld (that's not going to work). i ended up counting on the length i have from edge of bent plate to centerline of beam (1'-6") to partially develop the rebar and am only counting on the weld to the bent plate for the remaining portion.
does anyone see any problem with this?
why can't you weld all around the #4 bar? you should only need a 5/16 weld around to develop it, at grade 60.
why not hook the top bar?
if the load is in the stringer, then in the bent plate, all of it would need to go into the rebar, not a portion of it.
jmeic-
i could hook the top bar, but the load needs a way to get into the slab. the stringer is attached to the bent plate, not the slab itself and there are no studs from bent plate into slab.
ucfse-
how do you get 5/16"? a #4 = 0.2 in^2 * 60ksi = 12k. the length of fillet weld will be pi*d = 3.14*0.5 = 1.37". a fillet weld (using lrfd) is good for 1.392k/in/16th in.
i take 12k/(1.37*1.392) and get a required fillet weld of 6.3 16ths --> 7/16" fillet weld.
am i doing that wrong?
i am welding the rebar all the way around, but given what i showed above, i couldn't get it to work with the weld only.
nutte-
i know all of the load has to go into the rebar, not a portion of it. i don't have to take all of it into the rebar at the weld, though, do i?
it needs to be developed at point of max moment, not at the end of the cantilever.
oh, missed that part. ok, so why not anchor bolt the bent plate to the slab?
what exactly do you mean by anchor bolt the bent plate to the slab?
if it is what i am imagining (bolting through the bent plate and having a nut on the end of the bolt into the slab), it seems like it would need to be a relatively long bolt to develop the rebar. also, i don't think the architect wants to see a nut on the outside of this bent plate as it is exposed below.
i thought about just adding studs on the bent plate, but i have the same problem with developing that into the rebar if it is just hooked.
can you just use a #5 or #6 bar to get enough diameter to use a 5/16" weld and then only count on the bar as if it was a #4?
i think the anchor, stud or bolt, only needs to carry the force into the concrete (appendix d), not develop the strength of the rebar. by the way, i think your length of fillet weld is 1.57".
just get the thing ground to a cone and butt welded to the plate - end of story.

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