Addition of a story to an existing 2 story RC building 3

[hoshang]

Hi all,
If the foundation and RC columns permit, how a story can be added to a 2-story RC building when 2nd floor column lap bars are cut? i.e., how new story RC column bars are planted into 2nd floor RC columns of the existing RC building? Is it permitted to plant these bars?

 

[Lomarandil]

If there is sufficient stub column length remaining, replacement lap bars might be drilled and epoxied into the stub column. The details of this fix would also depend on the ductility required (based on seismic potential).

If there is only a short stub column, or none, this is usually not feasible because of congestion in the beam/column joint.

Some of my colleagues just had to tell a client that it wasn't feasible to add a story for this exact reason. The bars had been cut to let the stub columns serve as makeshift seating on the rooftop. Those became expensive seats.



----
just call me Lo.

 

[hoshang]

Hi Lomarandil,
Please find the attached file.
Could welding lap bar to the angle be appropriate to add the story above?

 

[Lomarandil]

That might be a solution, depending on a few questions:

-Does the lateral stability of the added story need a fixed base, or is a pinned base acceptable?

-Is the depth and width of the beam sufficient to develop and anchor the embedded bars?

-Is the beam able to handle the local effects in addition to the original design load?

-Can the connection be made with the proper amount of stiffness (avoiding prying but also providing any ductility needed)?

----
just call me Lo.

 

[MSUK90]

Would be interested to know the solution for this as I have also come across the same situation recently.
I have sent the client to discuss the connection issue with Hilti(if they can work out a moment connection between the new and existing columns).
Yet to receive their review though!

 

[MIStructE_IRE]

Also watch if the increase in height changes your consequence class/vertical tie requirements etc.

You’re probably ok though if it’s an RC frame anyway.

 

[hoshang]

-Does the lateral stability of the added story need a fixed base, or is a pinned base acceptable?

Sorry, but I can't catch this.

-Can the connection be made with the proper amount of stiffness (avoiding prying but also providing any ductility needed)?

Sorry, this also can't be caught (at least for me)

Also watch if the increase in height changes your consequence class/vertical tie requirements etc.

Any explanation would be appreciated.

 

[MIStructE_IRE]

This table of course differs depending on what part of the world you’re in. But adding a storey can change your consequence class, which can change your robustness tie requirements.

If you’re in a seismic zone then you may have further requirements to meet.

 

[HTURKAK]

Pls provide more info. regarding applicable code , use of bldg structure, seismicity etc..What is the reason for new storey with RC columns? Why not steel frames with columns nominally pinned supports ?

How the longitudinal column rebars ended? If bended ( most probably ) you may chip and make straight the existing column rebars and new rebars could be splice welded.

But i will suggest steel frame with nominally pinned columns.

 

[dik]

In some jurisdictions if you have 3 occupied floors, you require an elevator... a matter of first checking the use and occupancy parts of the code. Adding another story, I'd be looking at the existing roof to see if the load capacity was OK and then I'd be adding a lightweight steel roof and deck over. Easy to attach with current epoxy anchors... lateral or changes in the code may be another issue.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[BAretired]

Dik raises a good point. Is the existing roof capable of resisting floor loading?

BA

 

[phamENG]

What about switching to steel for the new floor? I've seen this done successfully. No need to worry about lapping bars, etc. as long as you can get a good spot to anchor your columns. It's also lighter weight so, if the original design hadn't considered a third floor, it has less of an impact on your structural systems on the lower floors.

 

[thereitcomestoday]

you can complete a push-over analysis in order to assess the behaviour of the existing building prior the addition.

 

[stripez]

hoshang, Is the edge beam right in the property line to the next building? If so, don't forget about the Firewall requirements of 6 hour fire rating. The engineering designer of a building I'm handling now forgot about this years ago.

They put baseplate and I-beam on top of column but it's very difficult to mix I-beam with concrete wall. You can't put them align because the steel i-beam is exposed to fire and has torsion problem if you just use thin metal roof and no diaphragm action. If you put the I-beam inside like the following, how do you support or brace the wall at the 3 meter height (with about 1.4 meter) parapet above it (the 0.4 meter is the I-beam web size plus the C-purlin above). Photo here.

[image]

https://imagizer.imageshack.com/img924/671/IpKyH7.jpg

[/image]

Other structural designers in my country can't solve it. It may be one of the most difficult engineering feat in our modern society.

So we are close to just condemning the floor and declare it as Unoccupied.

Don't repeat our mistakes. Something nearly unsolvable now. The strength criteria must be it having same strength as I-beam directly over wall that can last 50 or 70 years (just like normal RC structures).

 

[Harbringer]

It may be one of the most difficult engineering feat in our modern society.

Please don't hijack another thread with this...

 

[stripez]

Please don't hijack another thread with this...

It's not hijacking. Just warning that if it required a firewall. Better to use RC beams, because it's extremely difficult to mix exposed steel I-beam and concrete firewall.

Now we have to remove all the baseplates, I-Beams, Rafters, Roof, everything and starts chipping column to put RC Beams. Losing about $30,000 in the process or more. Don't want OP to have same mistakes.

 

[hoshang]

Hi all,
Besides my post on 6 Mar 21 10:10, what other options are available for planting a new RC column?
Any considerations regarding this solution?

 

[hoshang]

Hi all,
Any thoughts would be highly appreciated.

 

[JLNJ]

My thoughts?

- You have already been offered good free advice here - advice you have chosen to ignore or not respond to.

- A project like this has a host of serious complications. You should seek the in-person advice of a skilled and experienced structural engineer. You can’t design such a complicated project via a search on Google or eng-tips.com.