Written by KEC Engineers, Katherine Farley and Layth Hussein.
With the challenge to have all new building, developments and major renovations carbon-neutral by 2030., architects are increasingly only specifying sustainable materials. The trend has made concrete and wood appealing alternatives to steel for mid-rise and high-rise buildings.
Why do more mixed-use projects mean more concrete podium slabs?
With the growing demand for mixed-use buildings and the popularity of mid-rise wood structures, the use of concrete podium slabs to properly support them has surged as well. If you’re considering building your next project with concrete podium slabs, here’s what you can expect:
Below Ground Construction
The concrete structure supporting the podium slab can extend several levels below ground to increase site capacity and create additional service floors. Underground service levels can be used as additional parking garages, storage space, maintenance and utility, etc. This is a big advantage for projects that require off-street parking in highly condensed neighborhoods and/or add to the overall resident convenience.
A higher level of quality
Concrete is stronger and stiffer than a wood base, giving your building better seismic resistance, greater fire safety, and a higher level of sound protection.
Greater design flexibility
A concrete podium slab allows the designer the freedom to use a completely different floor plan between the above and below levels. Moreover, a concrete podium slab has no restrictions to support load-bearing walls from the structure above.
Concrete podium slabs can accommodate designs to create a mixed-use space at ground level such as retail shops and restaurants.
Why is post-tensioning often the best solution?
Among all types of podium design options, post-tensioning has the largest range of financial benefits from design and construction standpoints.
Podiums are required to support several levels of steel/wood framing above. The inherent ability of PT (post-tensioning) to balance a portion of this load allows the design to work with a thinner concrete section compared to a conventional podium slab. These material savings can easily represent two or more inches of slab thickness reduction along with lighter concrete elements to support it.
The column layout to support podiums can become challenging when trying to design uninterrupted parking spaces and vehicle drive isles below. Limiting deflections in these long spans is critical. PT concrete podiums excel at this feature due to their ability to balance loads. The ability of PT to help balance a portion of the dead and live load has the effect of increasing strength and minimizing deflections. PT podium slabs outperform conventional concrete slabs significantly.
Slabs crack when tensile stresses in the slab exceed the tensile strength of the concrete. A PT concrete podium slab provides better crack control due to the pre-compression applied to the structure.
What’s involved with creating a post-tensioned concrete podium?
Now that you know the benefits of building with a post-tensioned concrete podium, you may want to know how to go about. We partner with developers and architects that run the gamut in terms of experience - from seasoned post-tensioned concrete podium slab builders to newcomers in the field. While all engineering firms have their own processes we’ve outlined our standard procedure to give you a behind-the-scenes look at how these projects typically work.
Design development stage. We understand how critical it is to the owner/architect for the ground level to remain unchanged while proposing a column layout to support the podium slab. In the case where a column layout has already been established by the owner/architect, Kline Engineering will provide preliminary design options for the given column layout and explore relocating columns with intentions of achieving a more efficient design if necessary.
Design stage. We work and coordinate closely with the architect and build team to ensure the structural design of the podium can accommodate components such as sleeves, embedment, large openings, stairs, and elevator shafts. We thrive on establishing an open line of communication between all parties during this critical stage.
Construction stage. This is when the rubber meets the road, and this is where time critical challenges can surface. We work with the construction team to resolve these challenges quickly and efficiently so that the project is a success and ultimately our clients are more successful.
Post-tensioned concrete podiums will continue outperforming conventional concrete podiums due to their improved performance and low-cost. This framing system can bring huge value to a project.
Interested in learning more about Post Tensioning? Download our Guide.
As you begin the planning process for your next building project consider this, and if you have any questions as you prepare, give us a call at 703-331-1284.