Parking Structure Options: Precast vs. Cast-in-Place

Posted by on Jul 15, 2015 in Parking | 7 Comments

The concrete solution you choose will depend on design, schedule, and priorities. Here are advantages of each approach.

Parking garages may look alike, but as you know, the structure’s construction engineering can vary dramatically. At the beginning of the design phase, and sometimes even closer to the inception of the project, I’m often asked about the differences between parking garage concrete solutions and why they matter. It’s a great question, and one I love to answer.

There are two primary ways to construct a garage: with precast or cast-in-place concrete. Here’s what makes each approach unique and advantageous — and project examples that help explain the differences.

Precast, Pre-Stressed Concrete

A precast parking structure panel is being hoisted in by a crane with the assistance of several workers.

Precast Parking Structure Hoisting

What it is:

Precast, pre-stressed concrete are formed offsite and delivered during construction. Precast, pre-stressed concrete works best for projects that require an expedited construction schedule on tight sites that do not allow for stressing of post-tension tendons. Tendons are stressed alongside the building; if there are adjacent buildings or the structure under construction is underground, the tendons must be stressed before getting onsite.

Advantages:

• Faster construction schedule. The pieces are cast in a plant and shipped to the site for erection; form decisions have to be made early.
• Construction is not as affected by the weather, because the pieces are cast indoors rather than fighting the elements outside.
• Potential for a lower initial construction cost, because early design decisions limit any formwork needed in the field.
• Architectural design can be incorporated into the exterior panels.

Example:

We used this material on the $2.5 million parking garage at The Landings in Cincinnati, Ohio. The 57,000 sq ft, 2-story structure sits on a small site beside an $18 million, 184,700 sq ft office building. During our team’s discussions with the owner, we found that schedule and budget were key. At the time, precast, pre-stressed concrete had a significantly lower construction cost versus cast-in-place, post-tensioned concrete and the owner was happy with the faster construction completion.

Cast-in-Place, Post-Tensioned Concrete

5 construction crew members pumping concrete into wooden forms.

Cast-in-Place Concrete Pour

What it is:

Cast-in-place concrete is poured into place onsite. Slabs and beams are poured together so fewer joints are produced reducing lifecycle costs. Joints require maintenance such as sealant that must be replaced regularly. Cast-in-place, post-tensioned concrete works best for projects where long-term durability and lifecycle costs are the priorities.

Advantages:

• Typically offers a more open layout, because the moment frames produced by the beams and columns cast together can resist the load without reliance on additional walls.
• Better distribution of light inside the parking structure. The beams are spaced every 20’-24’ rather than tee stems every 5’-6’ in a precast, pre-stressed concrete garage.
• Easier to customize the shape of the framing members and the overall building footprint thanks to the ability to alter the formwork onsite.

Example:

Schaefer used this material for a garage on an expanding Fortune 25 company’s Ohio headquarters. This 260,000 sq ft, cast-in-place parking structure consists of five levels and holds 800 vehicles. Added complexities included two pedestrian bridges branching off of the garage’s third level to adjacent buildings.

In discussions with the owner, our team understood that structure durability and minimal maintenance were the most important factors; all other attributes, including project schedule, fell below these. Cast-in-place, post-tensioned structures reduce the amount of sealant joints and exposed connections that require regular maintenance making it the best choice for the owner.

At Schaefer, we believe there is no one-size-fits-all solution for parking structure construction. We start the design process for every project at the same point – the beginning. It’s the best way to understand the unique needs of the final product and the best possible construction techniques required.

Nathan Walsman, one of Schaefer’s leading parking engineers, designed two award-winning parking structures. Parker Flats won the Juror’s Special Mention at the CORA Residential Design Awards and The Congress of Residential Architecture, and AIA Cincinnati recognized the project as “excellence in residential design.” Belle of Baton Rouge Parking Structure was honored by South Central Magazine with their Award of Excellence, Private Building. To see more parking examples, visit our Projects Page.

7 Comments

  1. jresquival
    March 30, 2017

    That’s cool that pre-stressed concrete is used to quickly complete projects. When materials are prepared off-site, on-site operations can focus on their tasks. I think it’s interesting how post tension is used in both cases.

    Reply
  2. Max Jones
    June 9, 2017

    I have a friend who was talking to me about precast concrete, and I thought it was really cool because I hadn’t ever heard of anything like that with cement! I like that you pointed out that precast concrete is able to allow for a faster construction schedule as well as not being as effected by bad weather. I think that if I was ever trying to construct something quickly, I would definitely look into using precast concrete! Thanks for the additional info!

    Reply
    • Schaefer
      June 16, 2017

      We’re glad you enjoyed it!

      Reply
  3. Tapan Pandey
    September 28, 2017

    Good read! Learned quite a bit about parking structures from this article. I do have one question. What is the favorite choice of material for the parapet walls on the parking lot roof? My guess would be concrete but please correct me if I am wrong.

    Reply
    • Schaefer
      October 6, 2017

      Thanks Tapan!

      I assume by the “parapet” you are referring to the vehicle barrier system above the floor line of the parking levels? This system would not typically vary from the typical floor to the roof level. In precast construction, the exterior precast spandrel beam (load bearing when supporting the double tees or non-load bearing when parallel to the double tees) would extend above the floor line to provide the vehicle barrier as well as the fall protection system along the perimeter. In cast-in-place construction, a concrete barrier wall or a cable barrier system is typically used.

      Reply
  4. dan
    October 26, 2017

    The cost of maintenance is so much higher on a Precast double tee deck. Plan on spending 100,000 or more per year after year 5 on maintenance of joints, cracks, sealant, connections etc for a 5 story parking deck. Make a reserve account now for maintenance. They are not designed to be water tight either unless there is a roof, toping slab or deck coating on the top level. Check out the life cycle costs if you plan on keeping the facility for a while. Not ideal for a deck that is 24/7 or in a mixed use environment.

    Reply
    • Schaefer
      October 30, 2017

      You are correct in that precast parking structures typically require more maintenance costs than a properly designed cast-in-place structure due to the amount of sealant joints that need replaced every 5-7 years. The exposed connections used in precast construction also require regular maintenance. However, the use of concealed connections or stainless steel connections can reduce the required maintenance, but increase the initial cost of the structure.

      Reply

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