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?

 

[MotorCity]

"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

 

[JStructsteel]

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

 

[greznik91]

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..

 

[Leftwow]

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.

 

[JAE]

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.?

Check out Eng-Tips Forum's Policies here:
faq731-376

 

[greznik91]

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).

 

[jayrod12]

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.

 

[JAE]

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.



Check out Eng-Tips Forum's Policies here:
faq731-376

 

[dhengr]

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.

 

[atrizzy]

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.

 

[LittleInch]

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.

 

[oldestguy]

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

 

[greznik91]

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.

 

[JAE]

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.

Check out Eng-Tips Forum's Policies here:
faq731-376

 

[atrizzy]

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!

 

[oldestguy]

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.

 

[ProgrammingPE]

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.

 

[oldestguy]

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.

 

[Triangled]

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?