steel construction for balconies - profiles and connections 3

[mats12]

Hi, Id like to design a new steel construction for balconies next to existing house.

My experiences with steel constructions/connections are limited so I have few questions.

1. main frame (marked red) has to be a moment frame, but side frames dont have to be, right?
2. stability of construction is provided by a house in Y directions and by a moment frame and bracing in X direction
3. bracing in balcony plane is mandatory, right?
4. supports has to be fixed?
5. what do you guys think about my connections, are they alright? something more simple, cheaper?

I would like to get a design/model right from the start. Calculating connections would not be a problem for me, but to choose the right/best ones is an issue for me.
I was trying to use RHS profiles but Im not confident about connections. I think its better and easier to choose H profiles?

I really hope you guys will help me out with some suggestions and pictures of connections.

tnx in advance

'column - column' moment connection

 

[BigInch]

Don't understand why you think you need anything more than something like this,
Moment connections resist sidesway.
Why do you want each beam pinned into the house wall.
All you need is 2 per floor. Then you could make the balcony floors in the shop.
Take them out to the field and bolt them to the moment resisting frame and the building wall.

Reaction to change doesn't stop it

 

[klaus.]

well... a balcony is made for people....old an young and kids also
You should leave this job to an expert ( structural engineer)
there is a lot that can go wrong....
This is my advice !



best regards
Klaus

 

[XR250]

For something of this size, probably just fully welding some tube steel members together would suffice.

 

[KootK]

1. main frame (marked red) has to be a moment frame, but side frames dont have to be, right?

Right, as long as the existing structure can stabilize the decks perpendicular to the moment frame.

2. stability of construction is provided by a house in Y directions and by a moment frame and bracing in X direction

Agreed. With a floor diaphragm of some sort (bracing/sheathing) at each deck, you might even be able to get by without the moment frame. It depends what you're able to grab on to within the existing house. That said, there's certainly nothing wrong with your moment frame concept.

3. bracing in balcony plane is mandatory, right?

I don't believe that it is mandatory so long as you've got that moment frame.

4. supports has to be fixed?

They don't have to be. That's an engineering judgement that you, as the designer, are at liberty to make.

5. what do you guys think about my connections, are they alright? something more simple, cheaper?

Is wood construction and option here? In my neck of the woods, we'd do this with timber posts, a deck diaphragm, and no moment frame.

What is the existing house constructed out of? Wood? Concrete?





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.

 

[mats12]

Existing house is a masonry building (standard in Europe).

Timber as material... interesting, but that means that all connections are pinned so we dont have a moment frame which means a diaphragm in balcony plan in very important, otherwise its a labile structure.

 

[jayrod12]

Timber is common becuase generally the wall construction in our areas is timber as well. You can make a reasonable tie into the floor diaphragm and just make the balcony an extension of it. But in your case that may not be an option.

 

[KootK]

Timber as material... interesting, but that means that all connections are pinned so we dont have a moment frame which means a diaphragm in balcony plan in very important,

Exactly. I'll leave it to you with regard to what jives with expectations in your market place. However, if you have any diaphragm stiffness at all, which you almost certainly do, then the reality is that you're moment frames won't really be working at all. They'll just go along for the ride with the stiffer main building and never actually develop the anticipated forces etc. It's certainly nice to have the moment frames as a fail safe, backup system though. So maybe they make sense simply for that reason.

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.

 

[OzStruct]

Your moment frame will do what you want it to do but it is a heavy design and probably more than is required. My concern is your connection D. I would only bolt back to the existing house like this if you knew that the wall you were fixing to was reinforced masonry or concrete etc. There isn't much load here I know, but its not really good practise, especially if it is non-structural brick veneer. If the deck floor can diaphram brace back into the house then I think you can really reduce the moment frame.

 

[BigInch]

Reducing the moment frame strength would simply tend to put more load into the wall.
No free lunches.

Reaction to change doesn't stop it

 

[mats12]

tnx for answers guys.

one more thing id like to make it clear. What about column to column moment connection? is it OK?
Since column most likely would not be in one piece I was thinking about connecting it like this (picture) where bending moments are almost or close to zero.

ps
what do you guys think about RHS profiles for structure like this?

 

[BigInch]

That's really more of a pinned connection, however if there is no or little moment, you don't need a moment connection.

Reaction to change doesn't stop it

 

[KootK]

What about column to column moment connection? is it OK?
Since column most likely would not be in one piece I was thinking about connecting it like this (picture) where bending moments are almost or close to zero.

I don't love it. If it's aesthetically tolerable, I'd prefer to see some bolted flange plates. If you're placing the splices at low moment locations, that probably means around mid-height between floors. And that's right about where you'd really like to have some flexural stiffness in your column to prevent it from buckling. You could design the fame to accommodate a pinned connection at the splice but that's pretty unconventional. And there are other things that could be done to create a stiffer connection while still keeping it inboard of the flanges.

what do you guys think about RHS profiles for structure like this?

I don't see any issues other than, perhaps, the need for field welding. It's probably more of an aesthetic choice.

One thing to watch is that your moment frame beams are pretty long and that single bolt connection to the joists won't do much to prevent lateral torsional buckling of the beams. I'd try for at least a two bold connection. Using an RHS beam would also help as closed sections are inherently stiff torsionally.


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.

 

[klaus.]

You need to watch for corrosion protection
Hollow sections ( like RHS ) are difficult to protect inside the section
one option is to make the air tide...like welded end plate on both ends

but since this looks like a private project.... corrosion might not be such a big issue



best regards
Klaus

 

[Leftwow]

No offense but you will find that a lot of engineers are reluctant to design your structure for you. The forum is basically here to discuss concepts and share information on specific topics, but not here for giving away the integrity of our profession. They can tell when someone is attempting to design something out of their field of competency, which is unethical.

 

[mats12]

discuss concepts... thats all Im asking for...

 

[jdgengineer]

I skimmed most of the thread so I will apologize if I am saying things that are already stated.

If it were me, I would look at trying to cantilever the balcony laterally from the main building diaphragm. I think you will find the forces to be relatively manageable. You will need to find a way to tie the balcony to the main diaphragm through the masonry wall. I'm not as familiar with this construction as it is not commonplace in my area, but I suspect it should be possible. Waterproofing at the interface (especially at building penetrations) needs to be reviewed closely.

If you decide to go with the steel moment frame option you may be limited on your options depending on your seismic design requirements. I'm not sure if you have high seismic forces or not, but if you do in the US you would be limited in detailing provisions. I believe you would need to design this a special moment frame due to the # of stories. Although potentially you could argue the first level is not really a story as it is so close to the ground. In US code, your column splices would need to meet requirements of D2.5 which require minimum strength requirements at the splice regardless of your demands to ensure ductile behavior. These can be problematic at times to meet. You will have similar requirements at the column bases.

As far as I know, in the US the AISC requires (or at least highly suggests) a minimum of 2 bolts at connections. I would not use a single bolt personally even if allowed by the code due to lack of redundancy.

In the US, regardless of the lateral system at the deck, the US Residential Code would require hold-down tension devices at not less than 2 locations per deck. This is more intended for wood framing, but the thought should be carried to steel framing as well to provide a tie between the deck and the main residence.

I'm not sure of the exact building code requirements in your area, but I suspect they would have similar provisions. If you decide to tie cantilever the deck from the main building, I wouldn't be against putting in steel columns at the corner to act as a redundant system if you are especially nervous, but I would say in general that is probably unusual.

If you are not in high seismic, you likely have less detailing restrictions and can have at it. But in an area that has low seismic forces, I would question the need for the moment frame for lateral resistance.

 

[kingnero]

Why would you splice the columns as you can buy them in easily available lengths upto 12m (and longer on request)?

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