[USSGahagan]

Most new mid-rise condo towers (18 stories or so) in Southern California include several levels of parking (maybe 6 levels) between the ground floor retail and the first residential floorplate. My friends are currently paying $30,000/underground parking space & $22,000 - $25,000/above grade space, so I am wondering if buying an existing parking garage for which to add 12 stories is feasible from an engineering standpoint and if it could be potentially cost saving (granted you buy it at its market value) comparedto the alternative of building ground up. I understand the layout challenges this would produce, but I'm curious about the feasibility of the concept. Would the structure be strong enough to only need minor reinforcing? What engineering challenges would have to be overcome? Thanks!

[vid]

I would think that it would need a lot of reinforcing, if it is possible. Unless the parking garage was built with the expectation that more floors would go on top, it probably wouldn't be possible. Why not just raze the parking garage and build a new tower with a garage? I think that would be a bit cheaper.

[Kelvin]

Two problems surface immediately, but are not insurmountable.

One the columns (at least at the ground level) will see their basic loads increase in approximate proportion to the number of levels added. These members may or may not have sufficient existing capacity. If they do not, they can be improved. One of my favourites is to encase a concrete column with a steel box slightly larger than the old section and grout the gap. If it is a steel frame, one can easily slap reinforcing plates on the old section. The existing floors plates see no new load, so they are likely good to go.

The other problem is the substructure and knowing what capacity you can derive from the foundation and the soil system. If you are on any kind of semi-reliable rock, you will be in better shape than if you are on wet clays, etc. Again, we can improve substructure capacities in many ways, but they are not always cheap.

If you can get a grip on those to aspects then adding floors is a snap! Make sure you have enough room to get men and materials onto the site without disturbing adjacent properties (including any excavations and back-slopes).

Unless the structure becomes significantly taller, then I doubt that you will encounter any dramatic problems with overall structure behaviour. The biggest question mark might be the particular soil-structure interaction for your given local seismic characteristics.

[Nowhereman1280]

I know of at least one Parking Ramp in Chicago that was specifically built to support up to a 30 or story addition on top. The air rights have been bought and sold a few times for the area above the ramp, so it is possible that we may actually see a mid, or possibly high, rise built on a preexisting (1960/early70's) ramp.

Other than that, like the guys above said, it depends on how the ramp was built.

[USSGahagan]

Thank you gentlemen. Excellent feedback.

[GeorgeLV]

One example in Las Vegas is Venezia hotel tower (Venetian Las Vegas addition) which was built on-top of the existing parking garage after some reinforcement work.

http://www.skyscraperpage.com/cities/?buildingID=25461

[USSGahagan]

If I wanted to bring someone in from a construction company to assess the cost and scope of work needed to build on a particular parking structure, who within the construction company should I ask to speak with? Bidding? Engineering?

[Kelvin]

The engineering department would definitely give you a better view of complications present at the site. Smaller construction firms may not have sufficient resources to render an opinion. If that is the case, then local structural consultants can give you varying levels of recommendations depending on your budget.

They could give you anything from a walk around inspection and some ballpark construction budgets to a refined pre-engineering report (meaning they would cost out a viable project based on your needs & budget). If you are working with one contractor (who doesn't have in-house engineering), they may pay the consultant cost in order to secure the work from you when you do decide to build.