Ledge in a masonry block wall 3

[Robbiee]

Hello,
Like they used to do with cantilevering brick to create a ledge, do you do/have you done something like this?
if not what is the issues with doing it?
All inputs are appreciated.

 

[JLNJ]

If I could stay under the allowable for the shear in an unreinforced section, then I would consider it. I would probably use the depth of the grouted section only and neglect the bottom masonry shell.

I don't think your rebar does much for you here since the bar development space is so limited.

 

[phamENG]

You're going to need to "form" the bottom anyway to keep the grout/concrete from running out, so you might as well dispense with the 12" block and form a corbel designed per ACI 318 or equivalent standard (not familiar with Canadian standards). I'd feel a lot better about the performance, though it may cost a day or two in construction to let it set up before continuing with the masonry.

 

[dold]

I've seen this detail a couple of times out on the west coast. Seems like you'd have a tendancy for the block to rotate and jack up/split the courses due to applied moment out of plane. And i've only seen it where they use two courses of 12" block.

But you can see how the mason used a #3 bar to create the mortar joint at the stepout.

 

[Robbiee]

Thanks for the input.
I was thinking of using a bond beam to avoid forming. Cut holes for the rebars at the bottom and use 8" or 16" deep bond beam that will be fully grouted.

 

[phamENG]

By bond beam do you mean a U-shaped lintel block? That seems a bit dubious to me - the hole would have to be cut really well to ensure grout flow and maintain continuity. And continuity is everything here.

Why not go with a steel angle bolted to the wall? Your sketch makes it look like either a slab or simple wood/cfs joist system. A toe-down ledger angle would be quick and easy to install, and the connections to the floor system would be pretty straightforward, too.

 

[BAretired]

One problem with the proposed detail is that the floor is not connected to the wall which means the wall is not laterally braced at floor level. The sketch does not indicate whether the floor is cast in place concrete, precast concrete or something else.

BA

 

[Robbiee]

Thanks all. Will not do this detail.

 

[masonrygeek]

Did you look into corbel block? These concrete block are 8" on the bottom and 12" on the top. Here is an example:

Not all block manufacturers can make this unit so check with your local block manufacturer to see if its available.

Also, you should check the empirical corbelling requirements in TMS 402 (ACI 530). It is for solid units, but you can make these solid units by fully grouting them (knowing the comments above about grouting). And instead of corbelling out the block all in one course, could you step out the units over 2 or 3 courses?

 

[phamENG]

masonrygeek - that's pretty nifty. I've seen several unique block designs, but that's a new one for me.