How to Add Cantilever Slab to Existing Slab

When I poured new slabs to exsisting slabs, we would drill into exsiting slab 12" to 16" and epoxy rebar into the holes. We then tied the new slabs reinforcment to these bars. The epoxy we used had a compressive strength of 12,000 psi, stronger than the concrete itself. This might be an option you can use.

The anchor epoxy we used is manufactured by Hilti.

http://www.us.hilti.com/holus/page/module/product/prca_catnavigation.jsf;jsessionid=1BCE5FBD67FDBD15521A97D826196F25.node4?lang=en&nodeId=-58688

Have you considered prayer?

Perhaps a civil engineer might be delivered to you by divine intervention.

Just curious. Where are you, what country?

How do you FORGET to pour a section of concrete that big?????? I think the forum deserves to hear that lame excuse explanation.

Happened in Qatar! And forgot from the start! I mean there was no form work , no reinforcement! Why it happened? Lack of proper supervision! I came at the time of concrete, just checked lap lengths, heights, covers etc! Now can we get back to the topic! A solution came in my mind! Let me share it with you! What if we do 20cm chipping/cutting on two sides! Then drill up to 20/30 CM inside the HB! And apply strong bonding agent between old & new concrete, P.S we try Light weight high grade concrete? & give a 20x30 beam at the stairs side?

Yikes!

What is the consequence of failure?

I have a suspicion that you should remove and replace the incorrectly cast concrete that was designed to be monolithic. I have a suspicion that is your suspicion as well.

It is an error, the bell has been rung. Sometimes it is not possible to unring a bell.

Engineer?

What makes you thing that an engineer was ever involved here?

I have no doubt that the design drawing included the reinforcing, it must be on a drawing because the OP gives the size and type numbers, the size appears to be #10s (1¼"dia.) but no spacing and no bar bending schedule shown.

Sounds like a typic engineering design from here in AZ. Constantly have to field fix engineering problems. Thank goodness for field experienced personal fixing desk experienced PEs. LOL.

You beat me to it. I was thinking of the same thing but was not going to post it because it wasn't really that funny a joke in this context.

<cringe>

Best you talk with the engineering consultancy company that produced the original design and get them to sign-off on a suitable fix that wont endanger the public. A design change to an existing site of this magnitude MUST be made and signed off by professionals.

What you need to do is draw-up your solution in as thorough a detail as possible,

and then redraw the (situation) in an appropriately isometric sketch to provide as much clarity and completeness as possible,

and then, as soon as possible, convey all such relevant information to the structural engineer(s) for this project,

and then, get them to resolve the relevant issue(s) because they are the ones who get paid to solve such problems as they may have created,

and then, wait for their answer(s), preferably, on their premises...

You're right, it is sort of confusing...

Maybe a stair from ground level to lower level, arrow indicates down the steps? Arrow not identified as up or down. 25 risers, so about 14 foot elevation change. Good catch, though.

He did state GF to FF. This is another reason not to use acronyms. Say what you mean. By that I took the arrow to be going up. Could be the landing on the first floor and arrow is going down. Then the missing slab is not at ground level.

I just wonder how many floors have this gap in the landings?

I noticed it too was on the ground floor only, but with too many unknowns regarding the site, foundations, etc I prefer to err on the side of caution.

If the slab sinks (for example) it may not cause a safety issue but is still going to be a major problem for the contractor to fix at a later stage.

I think you missed the title. Some how this missing slab is a cantilever. It should be supported only at one end. Tension and compression forces will be happening.

Even if this was on the ground, not just at a ground floor, I would expect any ground material can and will move from the effects of local conditions. I'll admit that in Qatar frost heaving will never be a concern but I'll just bet that day to night heat loads will move things a little bit. Don't forget the possibility of plant and animal life might under mine this ground, too.

Another good reason to contact the engineer is that this maybe precisely what was planned for. Assuming that this is a mistake maybe the actual mistake.

As you know concrete only has considerable compression strength. No tensile strength of any practical use. You should analyze the forces working on your construction with maximal load and determine the place and direction of the reinforcement steel. (always covering the tension - you'll calculate with the steel instead of the concrete in this case)

Keep compression in mind on all the existing structures. If tension has to be distributed you will need to tie into the existing rebar or it will crack down in time.

Check for positive, but also for negative reinforcement.

He cannot do what you recommended! he is not the Engineer (or an Engineer...). He is asking for an advice/solution from an Engineer.

common problem. best would be a steel frame appendage butt jointed with existing canti slab edge, one short end of frame resting on short steel post on stair tread, the other end fixed to beam this side.

Top off with conc fill on thin decking or just plain chequered plate.

There are many unknowns to be able to give any precise design as a solution.

What is the existing slab thickness? Reinforcements? etc.

What this Cantilever is expected to carry as load?

Your type of solution: Will the original Owner/Designer accept it (appearance, aesthetics...)?

Frankly, I'm NOT going there. Not enough information is provided. The OP needs to provide several cross-sections through that missing landing, to show us what the heck is going on. Also, he needs to tells us exactly what is under the horizontal beam and the missing landing slab. Is there soil there, or is it air?

Also, which stair is going up and which is going downwards? Somehow I think this missing landing slab is suspended is stairs are going down on one side.

Additionally, are those masonry bearing walls at each end of the horizontal 30cm x 90 cm concrete beam?

A few pictures of the actually field conditions would go a long long way.....

You really need a local Structural Engineer, who is registered in Qatar, to sort this mess out. We don't provide FREE engineering services in this Forum. We can make suggestions, not a remedial design thousands of miles away.

Qatar, eh? My son, who is in the U.S. Air Force, will be deploying to the massive airbase there in 3 weeks!

I have a suggestion that needs vetting by the experts since I'm not, but if it makes sense and passes... (maybe with tweaks?)

OP: Can you give up on casting the entire slab-addition, and cast only the portion needed to access/connect to the stairs?

If so, bolt two steel beams to the underside of the stairs and the existing slab, so that each spans from the stairs to the slab - one on each side. Lay a corrugated galvanized-steel deck (eg: http://www.metaldeck.com/floor_deck.htm) and rebar on top, and cast the concrete.

OK guys, go at it!

rude? perhaps but take a step back and look again. other than a simplistic drawing and zero supporting data on soil condition and preparation how is anyone here expected to know code and standards in your location ? did your plans call for 3500 psi concrete or 5000? were you using 5/8 re bar or was any or all of the slab under tension? what is the total expected weight of the upper floor(s).....the complete lack of information is staggering, but yet you'd like a group of strangers to bail you out for free? trust me when I tell you to expect some good matured fun at your expense if this is how weak your presentation is to a group who can see just how far down the rat hole your project is at this point. to be honest I think your term "blunder" is a massive understatement. the list of things that should have been in place before your pour is quite significant and you provided us with almost nothing. if this were a project on American soil two groups would already be working on your project......a demo crew to level your mess and prepare the site for a new foundation/slab. and of course a legal team to sue to restore damages for Mickey Mouse construction that wasted time and money.

I think you need to buy Moosie a 6 pack an see if he can save you.......get out the check book

It will take more than a 6-pack of brews and a "bouncing" check to fix this clusterfuk: ***Gaaaa-boing, your serve Pal....***

10 cases of Scotch of my choosing + a big fat CERTIFIED BANK check + airfare for Mrs. Moosie and myself, to and from any destination that we desire....hmmmmm Bora Bora sounds inviting this time of the year.