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Timber balcony
3

Timber balcony

Timber balcony

(OP)
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?







RE: Timber balcony

"Is my model alright?"......"do you think there should be more bolts".....these questions would not inspire confidence in users of a balcony. While it may seem like a simple structure, there are many things that need to be checked beyond what is shown in your model. Consider lateral resistance of the balcony in the long direction. Consider checking the capacity of the wall to support the balcony. Consider corrosion of the deck and fasteners, consider roof load being supported by the balcony as shown in the photos......and yes, use more than 2 bolts

RE: Timber balcony

Seems legit. I would add a X brace under the decking to stop it from racking if possible.

RE: Timber balcony

(OP)
Consider lateral resistance of the balcony in the long direction

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

consider roof load being supported by the balcony as shown in the photos

There is no roof above - no timber post at the end of frame - photo is just for an example..

RE: Timber balcony

I am not experienced in Timber design, but I would have to add horizontal bracing to reduce any deflections in the horizontal axis. Instinctively I wouldn't want to rely on the decking connections to resist any bending moments at the base.

RE: Timber balcony

Can the exterior wall take the moment that is applied to it from the balcony?

Is the interior floor properly secured to the wall?

Uplift forces on the deck from wind?

Agree with the concern over long term deterioration of the anchors.

Will the anchors have adequate strength against pull out, etc.?

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RE: Timber balcony

(OP)
Well I have a masonry wall reinforced with RC ties as shown below.
The only problem I see is the middle balcony support (truss) because it doesnt have horizontal bracing - there is no RC slab right there because of staircase opening). Corner supports are OK since there is a wall perpendicular to wall of balcony fixation.

hmmm Im sort of surprised that you think that timber boards/beams on top of balcony truss supports arent working as bracing/sheating...

I was thinking designing middle vertical RC tie and horizontal RC ties to this balcony load (moments form balcony truss supports).

RE: Timber balcony

Quote (Greznik91)

hmmm Im sort of surprised that you think that timber boards/beams on top of balcony truss supports arent working as bracing/sheating...

They will act as LTB bracing for the frames themselves. But if they are not connected into the building adequately then all 3 support frames could realistically buckle the same direction.

RE: Timber balcony

The decking on top, if it is well fastened to the frames, could create some amount of lateral stiffness against movement where it would somewhat prohibit all three of the frames moving together and rotating in a horizontal plane....buckling sideways as jayrod12 suggests. Even if not connected to the building, if the decking created a rigid diaphragm which resisted a parallelogram distortion then the system might be OK.

The problem is, you don't know what that stiffness is. All the deck boards would be acting individually, not as a larger flat diaphragm.
The stiffness would be dependent on the fasteners and how much loose slip would develop over time.

We've had other posts here where we've discussed the fact that even thicker glue-laminated timber decking (tongue and groove) nailed together and to the supports has a somewhat limited knowledge base of diaphragm capacity or stiffness.

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RE: Timber balcony

Greznik91:
If the balcony support frames are o.k., why are you asking here? You asked for some advice, but nobody is forcing you to read btwn. the lines and think a little bit, and take that advice. Here’s 12 ozs. of confirmation, but that’s a little short of a pound.

RE: Timber balcony

Ensure the top horizontal beam can transfer the horizontal force to the vertical beam.
If you have gaps between the decking it can still rack to the side. I'd add a few horizontal braces.

RE: Timber balcony

i'm no real structural engineer, but there are big issues with balconies as numerous failure will testify.

1) Loading is not uniform. People have this nasty tendency to gather at the outside edge leaning on the guard rail. This causes uneven loading and by the look of it vertical and horizontal loading on that horizontal member where it meets the wall. That joint looks to be crucial, but will be difficult to inspect / rot with time secure to the wall beam

2) that brace looks way too short to me on your last sketch.

3) One bolt in tension doesn't look to have enough FOS to me.

4) calculate the loads in one of the beams fails - will it cause catastrophic collapse?

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

RE: Timber balcony

The photos show a roof. The model doesn't.

RE: Timber balcony

(OP)
Its not the same project. A photo is just for an example of similar project.

I thought about what you guys wrote. I agree there should be horizontal bracing below timber boards.

RE: Timber balcony

I would add to the other comments that any of your tension connections should be very, very conservative - double or triple the capacity since a balcony like this has NO redundancy. If you use one tension anchor and it isn't adequate, the whole thing comes down.

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RE: Timber balcony

Are you going to tension connect the braces at the intersections and at the ends? If not, just have one per side in a V format where one side is in compression and the other inactive.

Have you given thought to the tension connections? Not just the bolt but also the top beam to connection to the vertical?

It seems like you're trying to rush this without having thought through the entire load path. Be careful!

RE: Timber balcony

Is this balcony exposed to weather? If so, I'd use treated lumber for all. The contacts between pieces of deck and the braces otherwise may tend to rot. Painting does not always take care of these things. I have a step son-in-law who put a non-treated deck around 3/4 of his cabin. Now 20 years later most had to be torn down due to rot.

RE: Timber balcony

It is possible to consider Horizontal Lumber Sheathing as a diaphragm per 4.2.7.4 and Table 4.2D of AWC's Special Design Provisions for Wind and Seismic. The problem, though, is that you don't have a boundary element on two sides since you do not have members going between the frames. This would mean that AWC's tables are inapplicable since your nail spacing is infinite at the diaphragm boundaries since those members do not exist. I would either provide these members and fasten the horizontal lumber to them or rely on diagonal bracing in a V shape (see image below) with an edge member connecting the frames.

I would also verify that your horizontal lumber can span that distance. A 2x begins to fail deflection at a 5ft span, so you may be better off using joists between the frames.

How are you planning on on attaching a guardrail? Typically, there would be a member along the entire edge that this is fastened to. That edge member also does not have the capacity to resist the torsion created from a lateral load at the top of the guardrail so unless the edge member is a girder with members framing into it, blocking to the adjacent member is required.

You're right that the middle frame will require additional reinforcing to transfer the load into the building's diaphragm. The compression and tension in the wall must be transferred vertically to a member spanning horizontally between the end walls (or possibly just to the concrete slab depending on how elevations work out). Just check the entire load path. You may be able to just provide additional reinforcing in the masonry, but if that's not enough, then switch to concrete.

RE: Timber balcony

OG again. I question the situation of attaching to wall studs, unless they are well checked out after this gets attached. Any drilling for bolts weakens them. Is there any redundancy in case one fails? Bringing all wall studs to play likely will help on redundancy aspect, perhaps with horizontal planks at both top and bottom where bolts are located, secured to every stud.

RE: Timber balcony

very much agree with cautions above, plus a question on one of your diagrams: are there 2 balconies, one at 2nd floor and one at 3rd floor, and are the center supports attacked to a 3 story column unsupported in perpendicular to wall direction?

RE: Timber balcony

(OP)
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.

RE: Timber balcony

(OP)
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?

RE: Timber balcony

(OP)
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.


RE: Timber balcony

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.

www.structuralcentral.com

RE: Timber balcony

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.

RE: Timber balcony

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.

www.structuralcentral.com

RE: Timber balcony

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

RE: Timber balcony

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)?

RE: Timber balcony

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.

RE: Timber balcony

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.

RE: Timber balcony

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.

RE: Timber balcony

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

RE: Timber balcony

Quote (OP)

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.

Quote (OP)

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.

RE: Timber balcony

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

RE: Timber balcony

Quote (op)

@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.

RE: Timber balcony



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

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