Cantilever Concrete beam from Masonry Wall

[NFExp]

I was asked to provide engineering for a house very similar to the house in the attached picture.. The house in the picture is in the Bahamas and my house is in Florida. The balcony on the house wraps the corner and is supported by cantilevered concrete beams.. I told the architect that we would need to extend the concrete beams into the house to create a back span. He insists we can stop the beam at the wall. I am curious if anyone has encountered this situation. I have concerns creating a fix connection at the wall and relying on the masonry wall to resist the moment..

The loads are fairly low (260plf load + 800# point load at the end of the beam_. The span is 4' but at the corner the span is 5'-4".

Please let me know your thoughts

 

[bones206]

I'm working on a project in FL that has CMU walls with cantilevered cast-in-place concrete rain canopies over the doors. I'm designing a CIP lintel (or full length tie beam in some cases) for the torsion and applying the torsion reactions as point moments on the CMU jambs, which are pinned top and bottom. I'm paying close attention to rebar anchorage detailing, but I'm comfortable with the load path.

 

[MIStructE_IRE]

Yeah you could do it....if you want it to fall down..

Joking aside - I would be very reluctant to rely on this method of fixity. What stops it rotating? Self weight of outer leaf above, with some of the force couple resolved by wall ties, which won’t be installed correctly anyway. Even if they were, I think you would have a hard time justifying the local stresses on the outer leaf.

Balconies have a scary enough history when they do go wrong. Start off with a solid design approach and don’t let the architect bully in on this one. We would normally use a Schoeck Isokorb connector to resolve the cold bridge issue (if that’s the architects concern?).

 

[BAretired]

It would take a lot of persuasion to make me comfortable with the load path, but I suppose anything is possible.

BA

 

[masonrygeek]

I wouldn't be as alarmist as some posters here if you can resolve the forces in the CMU wall. This probably isn't a cavity wall with 2 leafs (wythes) of masonry, but a reinforced CMU wall, so there wouldn't be issues with wall ties. While a cantilever is different than a beam bearing on a block wall, there are plenty of loadbearing masonry structures that resist various torsional forces. As bones says - pay attention to the reinforcing details.

 

[bones206]

I should have clarified that the CMU walls are 12” reinforced units in my case. Another reason I’m comfortable with the design is that there are already dozens of these same canopies at this facility that have been there for decades and gone through hurricanes. But again, these are just canopies and not balconies. Similar concept though.

 

[hokie66]

Not on my watch. Perhaps if you have a 12" CMU wall, heavily reinforced and fully filled. Otherwise, stand you ground for the backspans.

 

[NFExp]

Thank you for all the responses. I’m going with the back spans. It’s a funny looking beam. The beam will be 16” in the floor and drops 10” at the balcony so that it is below the balcony framing. Luckily the first level is a garage and I don’t have to worry about ducts

 

[XR250]

The door below (if it exists on your project) would be a problem if you do not go the back-span route. You would have to resolve the torsion in the header - somehow.