Addition of Balcony While Constructing a Floor On Existing Ground Floor

Find a local structural engineer to look at the drawings of the existing structure, look at it as-built, and then design something to achieve what you want.

Thanks .I intend to do that shortly but the discussion is for exploring different ideas.

I should have attached some sketches,but I didnt know how.Lemme try

Could you provide plans or drawing detail of proposed structure?

Thanks for the messages in response.I need different feasible ideas from others.I will attach a sketch shortly.

For Balcony A (coloured)

At column 14 it may be possible to take the cantilever back into the room above the existing roof slab because there is goining to be a wall between col 14 and col 13

At col 17 there is no way to take the cantilever back beyond the column.The rein forcements cannot also be taken down into the column that is existing as part of ground floor.I dont know how clear I have made it out.Please ask if doubts arise.

For Balconies B and C ( coloured ) I think the cantilevers can be taken into the rooms embedded in walls. these have not been shown in the 2nd sketch.

The problem solution is regarding detailing of reinforcement at the junction of col 17

Suggestions on the detailing of the balcony slab -Option A) with slab to in flush with room floor

Option B) balcony floor top stepped up.

Anything I post here is "in principle" and not necessarily practical.

It is possible to cantilever off the bottom of the upper column, C17 but the cantilever needs full depth contact with the column to make the moment connection. you have it shown as overlapping the existing slab. You will have to drill in some means of shear transfer at the base of the column.

If I was doing this, I would expect to demolish the slab and top of existing column C17, careful to not damage the reinforcing, so that I could splice it to new bars for the upper section.

You need a structural engineer to agree on the arrangement and run the numbers to see whether this is practical or not. An engineer, on the spot, can give you better ideas and limitations, and probably save you money. I find when a client has done what you are doing that I waste many manhours finding ways to gently tell them why their ideas won't work, or are unnecessarily expensive.

• Why does it have to cantilever? Why can't it launch off the ground on new columns?
• Why concrete and not something lighter, like timber?

I have some observations about this proposal, but unfortunately I don't have much time to devote to looking into this in great detail.

Where are you located? It's sort of odd to use a mix of English and Metric measurements. Was the original building structural elements designed by a Structural Engineer? Who built this building, and was there construction inspection provided throughout the construction period? Was the concrete tested as well?

Like Passingtongreen, I feel you must discuss your proposal with a registered Structural Engineer before proceeding any further.

I have some concerns about cantilevering a heavy RCC balcony off the columns or interior slabs. Of course we don't have any clue regarding steel reinforcement installed in the columns, slabs, and spandrel beams and what loads they're capable of supporting as well as complying with the local building codes (if any). I have great concerns about the columns being able to structural resist any large amount of applied bending moment and gravity reaction resulting from an "add-on" cantilevered balcony, especially if it is RCC; the columns may not be large enough nor reinforced enough. Add on a RCC balcony like you've proposed could possible result in a catastrophic structural failure (no warning signs).

The easiest and most economical way to add a balcony would be to install outboard corner columns (on individual square column footings). They could be either RCC or structural steel. Steel columns would be more economical. You could install a structural steel wide flange between the two columns, that would support a thin reinforced concrete slab laid down atop a galvanized corrugated steel floor deck spanning between the building face and the new outboard beam. the deck could be supported by a structural steel angle secured to the existing concrete spandrel beam with structural expansion anchors. You would need to lateral support the two corner columns with a wide flange beam or channel secured to the existing RCC columns with a pair of clip angles (at the beam web) and structural anchor bolts.

Another less intrusive construction would be to construct 3 new masonry walls (Concrete Masonry Units....CMU's), together with new reinforced concrete footings and foundation walls to support the heavy weight of a RCC balcony.

Yes, I am a NYS Licensed and Registered Professional Engineer.....

Thanks a lot. I appreciate all 3 comments.I stepped on the document below. Can it give some ideas? I would like to have a few more.

www.bd.gov.hk/english/documents/pnap/APP/APP068.pdf

The location is Chennai India.All the columns have their reinforcements ( 4 of 12 mm RTS steel upward of the groubd floor roof slab for some three feet or 1 metre which can be lapped with extensions.

I think the balconies from C18,C 19, and C20 are possible as they have anchoring beams into the new walls for 1.5 times cantilever length.( please refer the plan)

I have strong doubts that any of those columns will be able to safely resist bending moments and axial loadings induced by a cantilevered RCC slab of the size you have proposed.

The first thing that I noticed is that the columns are under-reinforced by American standards (re: ACI 318 Standard). Minimum acceptable reinforcing steel-to-concrete ratio for columns, pursuant to ACI 318 is 1.00%. You have 0.581%, based on the ratio of steel area-to-concrete column area, therefore there's avery strong possibility that the column will not fail in the ductile mode (ie. slowly, with some advance warning), but rather in a catastrophic matter. That's not to say that even a column with 1.00% steel-to-concrete ratio would be sufficient and safe: IMHO, most likely it would be insufficient. [It's no wonder that there are massive structural failures around the world with this sort of substandard design....]

The presence of "anchoring beams" is of little conscience. If you construct a RCC cantilevered balcony oppositehand of these beams most likely you will be inducing negative bending moments through the columns and into the ends of the beams, thus they will most likely fail because they we're designed for large negative end moments. anyhow, the weak link is the inability of the columns to safely support the proposed constructs. Same can be said of the RCC sprandrel beams: you would be introducing torsional moments (twisting) into a beam that wasn't designed for that sort of loading/action.....no doubt in my mind that you will rip it apart.

I have no clue why you posted that link (from Hong Kong?????), nor what it's relevancy is to the matter at hand.

For the safety of any future occupants of this building hire a structural engineer who knows what the hell he's doing. Changing the building in mid-stride is not a good idea if the original designer didn't take such loadings into account as those that would be produced by the proposed balconies. Change one thing and it affects other structural components.

Is there something you are not telling us, such as: the presence of a street, road or ally below that prevents you from supporting a balcony with new outboard columns or a new exterior masonry wall? Why the dire need to "cantilever" any balcony?

RC buildings are the norm in most of urban Asia.

These sorts of alterations are routine.

What you want is totally doable.

Talk to a civil engineer in your locale for details.

I don't know anything of local building regulations, but why does the balcony have to be reinforced concrete? A minimum weight balcony constructed from RHS SS with say glass balustrades and a hollow aluminium plank/GRP decking could be supported from the sill and lugs set into the extension columns, The columns would have to be reinforced to take the additional side loading but at the design stage this should not create a problem.

Reinforced concrete is the cheapest and strongest construction material in these parts. The labor and skills pool is well versed in RC construction so the implementation costs are very low.

Using non standard methods (albeit desirable) without proper supervision or experienced crews is fraught with unpredictability. One deviates from standard local practice only when absolutely necessary and then with trepidation.

Guru Wall is very much right.In this parts RCC is widely used and such improvisations are routine . I am sure that a workable idea will emerge when we open our thinking further.Of course the thing will be got checked by a qualified Civil engineer.I will post here some solutions suggested by local engineers too when I get them.Thanks again for all contributions. More ideas are welcome please.This site is really nice !

How are you getting on with your cantilever balcony design?

I have a similar technical issue on a renovation project requiring RC staircase landings to be cantilevered. Columns are neither desirable or practical in my instance.

I am proposing to my CE the use of chemical setting anchorage for the rebar "developments" (I think that's the right term) using Hilti's HIT-RE 500 product in accord with their post installed rebar connection system.

The normal/traditional practice in these parts is to is break open existing RC elements to engage the rebar for the additional elements and then cast in. This method seems to result in sound structures but subjects the existing structure to considerable trauma, is very time consuming, noisy, messy, and very very disruptive if the original structure needs to maintain its utility at areas beyond the immediate works.

Drilling holes and gluing in rebar starts to look very attractive, though not cheap.

Are there any members here who have experience (direct or otherwise) with this post installed rebar system? .

Yes Wall, I do have experience with epoxy anchorage bolts and rebar.

I must warn you to select an epoxy (or other chemical adhesive) that does NOT exhibit creep under load. Especially under TENSILE LOAD. Independent laboratory testing is mandatory if the concrete installation may pose a life-safety issue in the future, be it short term or long term.

Look at the problems that occurred with the precast concrete ceiling panels in the Boston tunnel project ("The Big Dig"), where the anchor bolts used to support the panels exhibited alarming amounts of creep in a very short time period that they were in place. A young woman was driving through that tunnel when one of the concrete panels dislodged and squashed her like a bug. An investigation of the remaining ceiling panels revealed that most anchors were failing. All panels were subsequently removed and never replaced.

About 13 years ago I myself had driven through a completed section of the "tunnel" that was between Logan Airport and downtown Boston/ I-95 Interstate. Looking back in hindsight, I was damned lucky one of those ceiling panels didn't come down on me and my Aussie GF who i had just picked up at the airport! SQUASH!!! **IICCKK**

Frankly, I'm entirely in favor of doing it the old fashioned way by embedding the deformed rebar, as required, pursuant to the ACI 318 Code provisions. I just don't trust manufacturer's chemical compound claims regarding set and creep issues. Never had, never will. The track record is way too short. From what I've read, they keep changing the chemical formulations all of the time (for economical reasons?), but I ask, do they keep up with the independent lab testing as well? So far, I haven't seen too much documentation regarding that issue!!!!!

Call me conservative on this issue....but, it's for multitude of reasons!

Thanks Moosie. Got me reading some more.

Apparently that particular adhesive that failed was not approved/qualified for creep.

Others, including the product I'm planning on using, are "creep ok" qualified.

Wal, good luck with the product that you have chosen.

For me, I will stay away from specifying such products....their "track records" are just not long enough for my liking.

Short track record....20+ years is long enoughfor my application. If I can get 10 years I'll be happy, by that time the next renovation will be due.

Next renovation will most likely be done with a wrecking ball and a bulldozer! (Phnom Penh is growing/redeveloping fast and my house is near the palace, an inner city locale, constantly appreciating land values, have to keep/make the land pay more)

I really appreciated your opinion and value your trepidation..

I stayed up quite late reading up on chemset creep issues. Installation quality was a major issue especially with overhead setting where adhesive voiding was more likely if injection is not properly implemented and monitored. My application is all horizontal.

Remove "all" dust and make sure there are no voids....just like the manufacturer spells out in their application notes. I've had a play with it at some less critical connections to see and feel how the product behaves. Drilling at busy nodes was a challenge to get between the rebar looped ends... nothing that some careful measuring, observation and persistence didn't overcome. Part of the instructions also specifies that the extant mating face is hollowed out to provide shear keying, easy enough with an air chisel. Once the cover is broken through the existing rebar locations become quite clearly visible.

The trials went a little like this....

Chisel, drill, cuss, drill, sweat, cuss, cuss, cuss some more, drill, drill, cuss, get sun burned, sweat even more, cuss, drill, blow out and brush dust from anchor holes, cough, sneeze, cough, cuss, repeat clean, repeat clean, inject adhesive, poke bars totally into holes, support bars during initial cure time, leave them alone for a few hours, drink cold beer. You can tell when it's curing because the adhesive that dripped on your feet gets really hot...another cussing opportunity.

Cheers.

Ahhh, there's nothing like a lot of hot hot weather & extremely high humidity that's usually found Thailand!

Now, I can really understand the need for lots of cussing, usually to the X-max, when dealing with concrete demo work!

Now, the ice cold beer is the best part of any project....

Good luck with that chemical anchorage system! I sure hope that you found one that meets your needs!!!!