Removing the insides of an existing structure +underground car parking

[mikesg]

Hallo to all,

I am currently working on a project in which we have an existing reinforced concrete building (moment frame) which must be changed entirely from the inside. It is a five-storey two-bay (10m+5m) frame in the short direction (15m) repeated at 4-5m intervals to get a rectangular building of approximately 70x15m.

The task is to entirely remove the internal row of columns, slabs and beams (except for the roof). And in addition to that - make an excavation about 10m under the existing footings in order to have place for parking.
In fact only the facade must remain unchanged due to building status, otherwise it would have been easier to destroy and rebuild everything.

There is not too much space around the building, because it is in a central location and is surrounded by streets.
I would highly appreciate if you can give me some ideas that will give some direction for finding an appropriate solution.
I believe some of you has worked on similar projects and will share your experience. But this is a good place for finding engineers with good ideas, even without having worked on exactly the same things.

To get an idea about the scheme please see the attached PDF.

Many thanks!
Mike

 

[rowingengineer]

Maybe a stupid question but can you remove the façade in whole, and then reattach once the building is complete?

Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it

 

[mikesg]

Thanks for the quick reply. Unfortunately no, we cannot touch the facade due to administrative regulations - we tried to talk the architects into this option without success. The building has a cultural heritage status.

Some of our thoughts at this stage are:
-to install temporary piles to support a heavy girder at ground level to carry the structure while digging around those piles until the substructure is ready. This will be done in the plane of every frame bilaterally to the frame.

-excavate to the level of the foundations, unite the bottom part of the columns with a new thick R/C wall around the perimeter of the building and then dig in sections relying on the wall acting as a girder with point loads from the columns while we dig under them.

Thanks again and I await your comments

Mike

 

[SkiisAndBikes]

Mikesg,

Sounds like a complex project, more complex than most topics discussed here to get any detailed info. Look up information on the Christ Church Cathedrale in Montreal (or Promenades de la Cathedrale). A great example of caissons and post tension beams supporting a massive stone cathedrale while an approx. 4 storey mall was constructed underneath. The work was done in the late 80's and won all sorts of awards. Caissons were sunk just outside of the footprint of the building, then post tension beams cast across the width of the church below the footings prior to excavation.

Facade retention projects likely involve a significant amount of braced steel framing attached to the facade where the floors are removed. The steel framing can sometimes be incorporated into the final structure, however, often is temporary until the final structure is in place.

 

[RacingAZ]

I've done a similar building configuration before but it's all new construction so it's a bit easier though still a complex design task.

It looks to me this is a major project endeavor so why not hire a sub-consultant to help you out if no one within your company has the expertise.

Relying on ideas from this forum is kind of risky as we won't have all the facts. Though this forum is a great source of info, I think what you're after is way beyond what this forum is about. Also, if I'm the building owner, I would not want to know that my engineer got his proposed solution from a website.

 

[paddingtongreen]

I imagine that the floors have to go so that you can squeeze in nearly twice as many. That, and removing the interior columns will increase the load on the exterior columns unless you plan to introduce an entirely new structure inside. Whether new structure or beefed up columns are used, they will still exercise some control over the rest of the work. This is evident when you think of supporting the roof without an interior column.

Assuming a new framing inside the shell, the roof could still go on the old columns. To pick up the interior column load, minimizing deflection would need a steel beam, cambered up, jacked into place at the supports.



Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[MultiVar]

Though only peripherally involved in the Civ. Eng. field, I can see this is a JUICY project, on several levels--no pun intended.

1) The budget is the moon, or higher, lol.

2) High-profile project, and your firm's name is on the construction fence (and in local newspapers) for a long time.

3) You get to dig into the less frequently used portions of the engineering "toolbox".

4) Large "horizon" for creativity, incl. crafty ways to incorporate the "temporary" supports/scaffolding into the permanent final product.

5) The chance to make dozens of architects and historic preservation types VERY nervous... on-site: "stand back, dangerous jacking in progress..." back-at-office: "keep your distance, differential equations being solved..." ;')


PS: Can we know the name & location of this project, so we can follow along? Congrats on winning this job, hope it's a plum.

 

[cvg]

I have been in project "brainstorming" workshops which were successful in formulating ideas and alternatives and narrowing those down to come up with recommended solutions. Gather all the experts plus the owner plus any approving agencies in one room. Provide all the data possible, photos, reports, etc. Provide a facilitator and start generating ideas. Every idea may be considered. Go through them all from every standpoint. Cost, risk, aesthetics, etc. Narrow the list down to the most promising ideas. After the workshop, do an engineering / fatal flaw analysis to see if the method will work and if the cost will be acceptable without high risk.

 

[mikesg]

Wow! So many replies, I am impressed by your will to offer support, thank you!
A thankful response for each of you:

>SkiisAndBikes, thanks, I followed your advice and checked some information about this project, maybe post-tensioning is indeed a good idea to make sure that no additional deflection will be introduced in order to get the new structure working.

>RacingAZ - we already use exterior expertise, and this forum thread is yet another source for idea gathering, we will not accept and implement a solution unless supported by sound reasoning, calculations and detailed check of all steps needed. But what this forum can propose are ideas, even in a simple short sentence, that if understood and adapted can save a lot of risk and budget. Thanks for the remark, of course

>paddingtongreen - we will introduce a doubling structure, no way that the existing one can support the new loads, and besides it is built to an old code that has no provisions for seismic design. We will explore the idea about girders you propose.

>MultiVar - sorry, can't do that

>cvg - that's what I want to achieve, hope we will find a good facilitator, though, because it can eaily become very messy with lots of conflicts.


Once again, thanks. Even without specifics your answers are useful to me because they broaden the range of ideas and can be used to support my position.

Mike

 

[cvg]

there are consultants that do this and make a nice living doing it. Most often done for value engineering, risk assessments and partnering workshops. Best if the facilitator is not part of the project team but an independant consultant with very good diplomatic skills.

 

[hokie66]

As the existing floors have to be removed, rather than supporting the existing, I would want to do the demolition prior to the underpinning and footing work. That will require a lot of temporary bracing of the side walls, but will remove most of the mass and give better access for the work below.

 

[Ron]

You are going 10m below existing floor level. I'm not sure what kind of foundation system you have, but that will require some significant consideration of the geotechnical aspects (undermining, lateral pressures, protection of adjacent structures, protection of existing perimiter bearing walls,etc. Such excavation within an existing building is difficult at the least and ludicrous at worst...the cost will be phenomenal.

While the project is challenging from an engineering standpoint, I cannot imagine its benefit to cost being greater than 1.