Vertical phasing of projects

[Mike K.]

For vertical phasing potential, must the foundation of an existing building be greatly altered even for a small percentage of the total height/massing of a project being added?

Say, would a 5-storey office building, with a foundation suitable for such a building, be able to squeeze an extra two or three storeys atop the 5th floor without having to perform significant alterations to the foundation or other major (and costly!) structural elements?

I'm simply wondering whether or not it would be economical for the owner of an office building to vertically phase the project several storeys and whether that would be an economical option if only a small vertical addition is added.

[Kelvin]

Every foundation is going to have a certain "capacity" based on the dimensions of the elements involved and the condition of the soil/rock. There is no real relationship between the size of a given building and what it's foundation may actually permit. It is fair to say though that foundations do have the largest saftey factors only because it is so difficult to accurately define the relevant characteristics of any given soil.

So unless a foundation was designed for some specific amount which was then not utililised, there is likely little expansion capacity in the foundation. The same is also true for the lower levels of the building (columns, etc.).

By far the easiest thing to do is to add new foundations and beef-up the existing structure for the new loads.

Keep in mind that it is not only the ultimate condition that needs to be addressed (ultimate -> load failure condition), but also the day-today servicability of the structure as well. Servicability refers to how it performs or functions as a building: level floors, no cracks, no settlement, etc.

[Mike K.]

Wow...thanks for the quick response, Kelvin!

[Gahrok]

There are methods by which existing foundations can be upgraded for increased loading, such as underpinning and micro piling. Similarly load transferring members such as beams and columns can be strengthened.

These methods are often used in renovation works on old and historically important buildings subject to preservation orders to arrest and repair, for instance, subsidence damage. Such technigues are however, by their labour intensive nature, very expensive to use.

Whilst technically there is no reason why the scenario you describe, adding floors to an existing structure, cannot be contemplated, working on and within existing structures, is a costly business and it is hard to imagine any circumstances that would make it a financially viable proposition.

You should also consider the more obscure and less obvious considerations of such a proposition such as extending the capacity of existing services, electric, water, drainage, HVAC etc, replacement of lifts or elevators to service the extra floors. The increase in occupancy levels, +60% in your example, would impart all sorts of additional fire and safety issues to be addressed.

As I think you surmise, I would say, no, adding additional floors to an existing building would not be economically viable.
Good question though.

[LMich]

Maybe slightly off topic, but does anyone know exactly how the Mid-Continent Tower in Tulsa was expanded vertically from it's original 16-stories constructed in 1918?

http://www.emporis.com/en/wm/bu/?id=122952

http://www.midcontinenttower.com/

[The Cheat]

Maybe not existing office or residential buildings, but some parking garages were originally built with the capacity for another building to be built on top.



The Drexel Law expansion is one example. Another is the Hilton Garden Inn Philadelphia Center City, which is built on top of a parking garage that also spans a street. The garage was built in 1984, but the hotel addition was made in the late 1990s.

The Gallery Mall in Philadelphia was similarly designed to have an office tower built on top, but that has not happened yet. You can see the massive columns if you visit the Gallery mall.

[LMich]

Plenty of buildings have expanded upward, albeit, maybe not entire towers ontop of smaller buildings. The Mutual Building was originally built as a 3-story structure, and added two more stories a few years later.



In fact, though cancelled, last year a developer planned to convert the building to residential usage, and add another floor to the top of penthouses.

[plinko]

Originally Posted by LMich

Maybe slightly off topic, but does anyone know exactly how the Mid-Continent Tower in Tulsa was expanded vertically from it's original 16-stories constructed in 1918?

http://www.emporis.com/en/wm/bu/?id=122952

http://www.midcontinenttower.com/

Lilton,

My uncle was a civil engineer on that project. Basically they doubled the size of the base 16 stories, shared some of the existing building's gravity load on a new joint foundation (requiring huge transfer beams underground) and then built the new tower on top. The new tower portion actually cantilevers out over the old section, transferring all of its vertical loads into the columns of the new base building. There was also some substantial retrofitting in the existing base building (new columns and beams at certain locations).

[snappingturtle]

32 stories; designed to be capable of carrying 24 more!!!

[jmyap1]

Does anybody know where I can get materials to study vertical phasing in detail? some published literature of projects that were done would be great.

[alps]

Look closely and you can see where they added 7 stories to this building a while back:



No idea how they did/planned it, sorry.

[Kelvin]

Originally Posted by jmyap1

Does anybody know where I can get materials to study vertical phasing in detail? some published literature of projects that were done would be great.

Every building situation is so unique that I suspect that you will not find a "textbook" on the topic. Each project has to be looked at on a case by case basis as to what members and elements need to be strengthened and which foundations need to be modified. Suffice it to say, that the structural and/or geotechnical engineer(s) will look at any reasonable method to achieve the end-result.

[SFUVancouver]

Phase 1


Phase 2 under construction

In Vancouver the Bentall 5 office tower was built out in two or actually 3 phases. The initial phase was a seven storey underground parking lot that was completed in 1994. Phase 1 of the build out was 22 floors and 340,000 square feet and completed in 2002. Phase 2 of the build out is now almost complete and has added an additional 12 floors and 210,000 square feet. The total height of the tower is 141 meters/463 feet.

[Steely Dan]

many buildings thoughout the history of chicago have had floors added on to them. the biggest previous example of this is the Roanoke Building which was originally built as as a 16 story office block in 1915, then in 1922 5 more floors were added, bringing it to 21 floors, and then in 1927, a 16 story tower section was added on top of the block bringing the total height of the building to 37 floors/452' tall.

now, another significant vertical addition is set to start up in chicago, surpassing the vertical growth of the roanoke building. the BCBS building was originally built as a 32 story/411 ft. building in 1996. now, 11 years after its completion, an additional 25 stories are to be added to the tower, briging its total height to 743'. the BCBS building was planned from the very beginning for this kind of vertical growth with beefed up caissons and other structural members and atriums that ran the full height of the tower that will now be filled in with new elevator banks to serve the added floors.


BCBS existing:


image courtesy of NewcitySkyline




BCBS proposed:


image courtesy of NewcitySkyline

[i_am_hydrogen]

^And you can't forget about Union Station's proposed vertical expansion up to a height of 26 stories.