Parking Garage 1

[chencfp]

I will design a building using roof as parking garage. The roof span will be 60-ft. could someone here tell me the following questions:
1. What type materials (steel truss, steel beam or prestress concrete) will be the best fit 60-ft span?
2. What is live load for parking garage?

Thanks.

 

[lkjh345]

If you are in the US, see IBC 2006, Table 1607.1 and section 1607.6 for garage live load requirements.

As for what type of material is best, that depends on a lot of factors. Local availability of material, contractor experience with one system or another, owner's desire for economy upfront versus long term maintainance issues, etc.

We have done garages in precast concrete, CIP Post-tensioned concrete and steel beam/concrete deck. Each individual project has certain parameters and constraints that make one choice better in some situations, and another choice better in others.

 

[jike]

You did not say where in the world this is located in.....so my response is quite general.

Considerations for construction materials depend upon many factors:

What is available locally?
What is most economical?
What material can be received to meet the desired schedule?
Does it best meet fire rating and load requirements?

Live load will be determine by the local building code.

 

[frv]

In many parts of the US, PT is a good option.

But as the previous two posters mentioned, depends on a lot of factors.

 

[jike]

There may also be considerations of environment.

 

[ronster]

Loading and member size will depend greatly on weather or not you allow trucks on the parking deck. For cars only the 2006 IBC uses 40PSF or a 3000 pound wheel load. I would add a flat roof snow load to this if you are in area subject to snow. If the deck is designed for cars only then you need to construct a barrier at each entrance preventing trucks from getting on the deck.

You are going to need a water proofing system. Decide if you will use a exposed traffic bearing system or a topping slab over a membrane as the topping slab will add additional weight. Since the structure will be protected from water and deicing salts then I would probably use a concrete slab on metal deck over steel beams but this may not be the best system in all areas.

 

[chencfp]

Thank you all for replying my question.
The project will be in North of New York State. The building will be used for performing art stage and the roof will be used as parking deck (for cars only). We are now going to choose one material between prestressing concrete and Smartbeam system (standard WF beam, which is cut in half longitudinally. The two halves are separated, staggered and welded together). We did not known well about Smartbeam system for vibration, sound proof, waterproof, etc. since underneath the deck is a stage. It will be great someone here can give me opinions on this material. Thanks.

 

[Teguci]

I would suggest that, since your occupancy under the deck is a stage, a plaza system should be used for waterproofing the roof deck. A hot applied asphalt layer is added above the structural slab, then a drainage layer and then a wear slab. Any other waterproofing system will get worn and need to be maintained every three years or so.

You will probably also need to look at fire separation between occupancies.

As for sound proofing, I suggest this be accomplished with a system below the structure. Vibration should be reduced with deeper members and a heavier system.

Never done castellated beams before but they seem simple enough.

PT is the most expensive option, but may allow you to get away without a waterproofing system. I have done a precast deck with 60 ft DoubleTees-2 hour fire rating with a plaza system over office space.

 

[chencfp]

Teguci, Thank you very much. could you please explain more about "Plaza System"?

 

[hokie66]

A 60 ft span for a rooftop carpark is not really a long span structure. I have used castellated beams in the past, but never for spans under 100 ft. A rolled steel beam of the appropriate size is probably more economical.

Steel or precast double tees could be used, but your system should be selected as a whole, including the lateral support system. If you use steel, you could use steel columns and portal action, but that option would not work with pretensioned roof members.

As others have said, since this is both a floor and a roof, waterproofing is all important. What Teguci means by "plaza system" is that the waterproofing membrane is protected by a wearing surface. Architects are meant to be responsible for waterproofing specifications and details, but few these days are any good at it.

 

[Teguci]

I wouldn't leave the detailing of waterproofing to an architect unless I run out of time on a project.

Plaza system, from botom to top:
structural system - Precast, PT, Steel & slab
Waterproofing membrane - Hot applied asphalt or, if you feel lucky cold applied
Drainage Board - Geotextile that allows water to flow to the drains (everything is sloped to drain)
Slip layer - tough, thick plastic film that forms the bottom of your wear slab and allows some movement between your wear slab and the structure below (think of VQ/Ib between slabs)
Wear slab - 3 or 4" thick concrete that the cars park on.

 

[ronster]

In agreement with Teguci except for:
PT will never replace the need for waterproofing over a dry interior space
Membrane is usually a liquid applied rubber membrane rather than asphalt
Slip layer not required as drainage board and membrane will give you a break between the slabs
Detailing of the waterproofing system assumes risk. Leave it to the architect who is responsable for it. If you detail and specify it then you take the liability for it. Offer the the architect guidance and info but make sure it is shown on their drawings.

By north of New York do you mean Canada or upstate New York?

 

[chencfp]

Thank you very much. We were also looking into the standard W-shape steel with joist truss and concrete slab. But we concrened the deflection limit. We also thought that the camber might be required for about 60-ft span (The exact span for our project is 55-ft and 47-ft, and one Beam/Girder span needs to be 60-ft). Does W-shape beam require to be cambered for the above span lengths? Our building shape is rectangle. All four sides are reinforced concrete wall with columns. The roof steel beams are seated on top of concrete wall. It will be great if standard W-shape is good for the above spans. The stage has some light system and equipment loading.

 

[msquared48]

Teguci:

How do you handle the tendency of the 3 to 4" wear slab to move in a seismic event? Is there enough inherent friction to prevent movement other than temperature related movements? I can envision a solution, but do not want to re-invent the wheel here...

Mike McCann
MMC Engineering

 

[Teguci]

Mike,
The wear slab is cast in tight to the existing walls. Since the code doesn't allow for friction to resist seismic, I guess we're stuck with putting the full lateral on the exterior walls which shouldn't be a problem. Good question. Thanks

Also of note - small tubes should be provided around the perimeter to prevent a vacuum when water tries to drain in the drainage layer.