Balcony brackets...connection design??

[tjacorn]

Our architect wants get away from cantilevering joists when building balconies due to water problems (joist rot) over time. So instead he wants to use brackets to support the balcony.

My analysis shows that this creates a bending moment in the wall, which I will counter with a 4x4 or 6x6 column in the wall. This, however, will create a lateral force on the diaphragm that will be picked up by shear walls. So far I’ve been able to design the shear wall and diaphragm but I’m hung up on the connections between the top of the column and the diaphragm. The bracket (which is placing a 1000 ft-lb factored load on the column) will be bolted both to the Rim-board and to the column.

Questions:
1) How should I go about designing the connection so that the rim board won’t be ripped out of the diaphragm?
2) Is this the proper approach for designing with brackets? In the past, the architect placed a steel column in the wall embedded in the concrete below to resist the induced moment. Surely there’s a better way…

 

[RARWOOD]

Are you able to run some sort of Simpson strap from the top of your diaphragm to the top of your horizontal bracket member?

If you are concerned about the column pulling away from the diaphragm you might look at using a josist hanger installed horizontal. That would allow for the column reaction to be taken out in bearing with the hanger flanges transfering the load in to the horizontal framing. You might look at something like the Simpson THAI hangers.

One thing I think you need to remind the architect about is that without proper detailing you may end up with a decay problem where the brackets frame into the wall.

 

[apetr26542]

I've done something similar with an exterior balcony, the developer did not want to drill the corner piers for the columns, instead the posts were angled in to the foundations, the horizontal reaction was developed with strapping to the interior.

Your connection is a bit harder as it is a full moment, I would also be concerned about deflection and there may be an inherent bounciness. If the balcony member is not snug tight to the rim joist, it may sag when loaded.

Can you run your 4x4 or 6x6 post to the second floor and lap your balcony joists on each side and through bolt it?

 

[kxa]

How big is the balcony and howmany brackets are you placing under it. I would spread out the loads over the wall and the rim joist, if possible. You can use Simpson-StrongTie holdowns (check the web site) on the inside of the floor joists the the rim joist is connected to. If you look at the catalog of Simpson you will se what I mean. The long leg is attached to the floor joist and the short leg to the to the bracket thru the rim joist. This way the horizontal load is carried by the joists and the floor diaphragm. Of course, you need shear walls to support the floor.

 

[tjacorn]

Thanks for the helpful posts.

I'll be leaving tomorrow for the Home Builders Show in Orlando so I'll have to wait to post again.

apetr26542, what do you mean by "lapping the balcony joists on each side of the post?" How does this help? Maybe I've misunderstood you...

 

[archeng59]

RARSWC, you make an excellent comment regarding corrosion of the brackets. also, fastener corrosion attaching the bracket to the wall will be a problem to resolve. The architect doesn't realize the water problem will still exist, just in a different form.

 

[apetr26542]

tjacorn, yes, essentially this would requre the brackets be let into the wall, just what is trying to be avoided.