Timber balcony 3

[greznik91]

Im designing timber balcony. It looks pretty simple but I havent done it before, so Im just looking for some confirmation...
Is my model alright? I did it based on photo below.
I will desing bolts on shear + tension (interaction) and check for pull-out force.
Also, do you think there should be more bolts, different locations?

 

[greznik91]

Triangled - yes, the center support is attached to a 3 story column unsupported in perpendicular to wall direction- So the load path will go through horizontal ties to side walls.

 

[greznik91]

I also have an option to make steel supports. I was thinking about RHS profiles (hollow box profiles) that are welded together.

I was looking at some photos on internet. Im not really sure why they make it with vertical profile between horizontal and diagonal profle? Is a force to the wall distrubited along a vertical element?

 

[greznik91]

This is my final model...
I have 4 tension bolts per support (very conservative - 3x bigger tension capacity /pull out force than calculation requiered). Bolts are 15 cm in the RC tie (drilled in concrete). I was also thinking about adding a steel plate at the end of the bolts but that would mean that the bolts has to be installed before concrete - RC ties are even poured.
I added a steel beam at the end so the guard rail can be placed.
All steel members are welded together.
I added X bracings in horizontal plane based on horizontal wind force on railing.

 

[ProgrammingPE]

If you consider the effect the brace will have on your wall reactions, you'll actually end up with all the shear reaction at the bottom connection since the load on each side of the brace is balanced like a seesaw (depending on dimensions) (see sketch).

By adding a vertical member at the wall, you can argue that the shear reaction would be shared between your top and bottom connections, which also gives you a little more redundancy.

It may also have been added for architectural or fabrication reasons.

http://www.structuralcentral.com

 

[LittleInch]

I would still install the vertical wall plate as it reduces / eliminates the shear force on the bottom bracket.


Also prevents accidental overstress of the knee joint where the bracing meets the horizontal support.

Welding all those joints looks like a much better idea.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[ProgrammingPE]

If you're going with X bracing then where your members intersect you either have to cut one in half and make a connection or they have to pass over each other which may be possible with steel angles. You could also use V bracing which is fewer pieces as long as the members can work in compression.

http://www.structuralcentral.com

 

[greznik91]

ProgrammingPE thank you for your elaboration. You helped a lot!
Im more comfortable with X bracing. They will pass over each other.

 

[mats12]

Is X bracing in horizontal plane of the balcony even needed since all joints are welded and there is a horizontal beam at the edge? Couldnt this work as a horizontal moment frame for small loads like in this case(wind on safe guard)?

 

[molibden]

There is another load case that is often overlooked in practice and also in codes. Horizontal forces induced by occupants. On decks that is often worse than wind and seismic. I will try to find an article based on experiments. I think that Eurocode doesn't cover this. So yes, you need the bracing or some kind of diaphragm.

 

[kipfoot]

I think the primary issue with this is the connection to the existing wall. Assuming you've determined that the wall can carry the loading, I'd also suggest:

1) using a vertical piece along the face of the wall as your first diagrams suggest. This may help give you flexibility when they're finding places to anchor to the wall. If they're drilling and encounter a reinforcing bar, does your system have the flexibility to avoid it?

2) consider using anchors that go through the wall and are anchored to a plate on the inside.

3) If circumstances push you to use wedge or epoxy anchors, consider having some testing performed to establish the capacity in your case. Some manufacturers will send out a representative to do this prior to installation. Perhaps also include inspection of the holes or training by the anchor rep to be sure the hole preparation is correct.

4) Since your connection to the wall is concealed, consider the durability of the materials you're using. Specify stainless anchors? A galvanized vertical plate?

5) be sure to consider how the capacity of the anchors is affected by the anchor spacing.

 

[LittleInch]

Also be sure to fix a plate on the balcony saying "No more than X people on the balcony at any one time". X being your calculated number for the load ( assume the people weigh a LOT and are all leaning on the balcony guard rail). It won't stay there I bet, but will help you if the thing falls off the wall at any point in the next 10 years or so.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[oldestguy]

Signs are for people that obey them. Drunks having a fun time ain't about to read any sign.

 

[KootK]

well there are timber boards on top of those frames. So they act as diaphragm/sheating. I dont think thats an issue.

I'm inclined to agree. One of the unique features of a system like this is that the bracing/diaphragm is not required to provide stability for gravity loads. If the support frames racked sideways, the loads would move no closer to the earth and, therefore, system potential energy would remain unchanged. Consequently, the frames are neutrally stable and the gravity load induced stability demand on the diaphragm is nominal.

The balcony will see some minor, direct lateral loads as described by others above (wind, EQ, occupancy). There's a marked difference between diaphragm demands of that nature and demands associated with the stability of gravity loads however. So long as you get two fasteners into each deck board to frame connection, the deck boards will act like little moment frame beams and all should be well.

Im not really sure why they make it with vertical profile between horizontal and diagonal profle?

It hearkens back classic timber frame connections. In the absence of shiny Simpson connectors, it made for an aesthetic and efficient means of dragging the vertical strut force into the wall fasteners which would often only be installed along the vertical leg of the bracket.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[delagina]

@kootk, so hor bracing is not necessary in this case?

 

[KootK]

@kootk, so hor bracing is not necessary in this case?

There's clearly a diversity of opinion on that. I certainly think that there's a reasonable theoretical case to be made for omitting the bracing. I like the aesthetic better without the bracing. Particularly if it ends up as painted - soon to be corroded - A36 steel.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[BAretired]

The compression force does not necessarily occur at the lower bolt as shown in the sketches above. It occurs where the centroids of the diagonal and vertical members intersect. This results in a smaller lever arm when calculating the tensile force in the upper bolt. If the vertical member is stiff in bending, the location of the compressive force may be considered lower, but it is not related to the location of the lower bolt.

BA