Continuity issue by extending a slab 1

[milkshakelake]

I'm extending a slab. Removing an old slab that's 2' higher than the rest of the floor level, and leveling it out. Do I need to worry about continuity?

I could look into alternative schemes like adding beams, but that will affect headroom. I prefer to extend the slab. But extending it means doweling pretty far in to achieve correct development length. For #4 rebar, it's like 24" doweled in. It's pretty far. I'm not confident that a hammer drill will nicely make the extremely long hole and not crack the underside/top of the slab.

In terms of continuity, the bottom rebar will be equally important, if not more important, than the top. The top will develop a column strip and some middle strip (negative moment), but if that fails or it doesn't properly develop, the bottom needs to be 100% carrying the load.

The other thing I'm worried about is shear, which will be transferred solely through the new dowels. The more I think about it, the more it seems like a bad idea. Hopefully someone can point me in the right direction.

 

[bookowski]

@MSL - Those look like Mac-Sal drawings, am I right?

I didn't read through the thread, was mostly trying to guess the original eor, so not sure if this works in your particular case. What I've often seen/done on small infills is to specify the existing slab to be cut back at a slight angle and the short drilled bars, no lap splice assumed. There's of course a limit to that, may not work here.

 

[milkshakelake]

@bookowski Yup, it's Mac-Sal. Very impressive that you guessed it. There's only one company that I can guess without looking at a title block, because they use a weird font that looks like Comic Sans. You want to take a shot?

Anyway, I didn't really understand what you mean. Why cut back at an angle, like 70 degrees? What do you mean by "no lap splice assumed"? And more importantly, do I know you? It seems like we run in the same circles.

 

[milkshakelake]

@Enable Why do Canadians mix freedom units with future units? Maybe y'all are slowly transitioning to future units. I wish USA would just cut the losses and switch already. Freedom units don't make any sense.

 

[bookowski]

Pretty sure that's GACE? Severud uses a similar font but different section tags. As everyone has moved to revit most now have the revit default of arial or arial narrow, sometimes mixed in with other fonts where they've been too lazy to update the details properly and are linking in cad. Doubt we know each other, I don't know anyone.

The cut back is to address shear by direct bearing, sort of like a manhole cover in concrete - it can't fall through. Rebar drilled and doweled minimally, no continuity assumed - the infill is simply supported sitting on an angled ledge. I doubt people are running a calc on it, so may not work out on a bigger or weird opening.

 

[milkshakelake]

Ok got it, it's kind of like a fire cut joist. That's a nice idea, I'll probably use that. And you're correct, it's GACE. Didn't know Severud uses this font as well. It's so goofy, yet charming.

 

[chris3eb]

@Enable, I had to double take when I looked at your welded splice detail because the angle is shown so much smaller than the bars, I couldn't see how it could develop the bar force (and even if it had the same cross sectional area, it would be hard to count on the entire cross section due to shear lag with only a 2" weld). But when I drew them out to scale, it looks like the directly attached portions of the legs provide at least as much area as the spliced bar, so that wouldn't really be an issue. You may want to show your angle a little bigger to please the busybodies like myself