Moment Applied to End of Cantilever (Reinf Concrete)

[bpiermat]

If I have a concentrated moment applied to the end of a cantilever slab and lets say the moment is applied as a horizontal shear to the concrete surface (both top and bottom). Lets assume the bars are fully developed in the back span of the slab.
My question is: Is the moment capacity limited by the development of the bars between the applied moment and the cantilevers free edge? And if so, if I hook the bar around a longitudinal bar does it solve this issue?

 

[KootK]

My question is: Is the moment capacity limited by the development of the bars between the applied moment and the cantilevers free edge?

Probably.

And if so, if I hook the bar around a longitudinal bar does it solve this issue?

Certainly, that is the minimum that I would do unless anchorage of the thing inducing the moment could be handled using anchorage based on concrete tension alone. And, even then, I'd still hook the top bars. None of these things guarantees that it works though even though I'll admit that this is probably the end of what most of us would do for design checking. To evaluate this more rigorously, we'd need more information.

1) What's causing the moment? Balcony guard rail? Concrete parapet?

2) How thick is your slab?

3) How close to the end is your moment applied?

 

[bpiermat]

Thanks! This is what I typically assume as well.

In this case, I can't provide a edge bar and hook the bars around it. (This is often how I get around this calculation)
However, in this case the load is applied to the end via a direct rebar connection, so all is good, but to verify my results I created a table of bar development away from the free edge and everything seems to be fine in this case.
But the reviewer did question my logic as the bars are considered fully developed in the back span...

1. In this case, it is actually a vertical wall with a precast coping on top with overturning loads applied to the precast
2. 5.5 inches
3. It is applied via reinforcing connection at the very end. But often times I run it to this exact same problem with no such reinforced connection.

THANKS!!

 

[bpiermat]

Oh and yes the load cannot be handled by unreinforced concrete alone (I check that first)

 

[bpiermat]

Has anybody got a photo of this type of failure mode?

 

[KootK]

This is a comprehensive thread on opening and closing joints in concrete: Link.

By the book, I very much doubt that this can be made to work in a 5.5" unless your moments are very small. I'd probably do whatever it takes to make your reviewer happy lest it land on the desk of someone who forces you to do something even less practical. I've seen standard details for this kind of thing from numerous top tier firms. It's always central wall verticals hooked into the slab. Nothing terrible ever seems to result. Whatever you're up to is surely more robust than this.

 

[bpiermat]

The demands are small..but large enough to be just greater than the capacity of plain concrete.

In this case the connection is at the top of the wall..I saw that thread, it is somewhat similar, but there is no clamping force.