| Project name: | Enclave Apartments |
| Location: | Philadelphia, Pennsylvania, US |
| Keller company: | Suncoast and Hayward Baker |
| Client: | Lindy Property Management Company |
| Techniques used: | Post-tensioned structural slab supported on Vibro Concrete Columns (VCCs) |
| Project date: | [tba] |
Suncoast post-tensioned slab proves to be an economic solution for this Philadelphia condominium project The Enclave Apartment Complex Project is a three-level multi-unit condominium project in Philadelphia constructed by Concrete Artisans LLC for Lindy Property Management Company. Three levels of wood framing were to be built on concrete slabs-on-grade. Due to poor sub-soil conditions, an alternative method of supporting the super-structure was needed. A post-tensioned structural slab supported on Vibro Concrete Columns (VCCs) was selected as the solution. The Option: The geotechnical investigation of the job site revealed ground water at 18- to 23-foot depth with weak soil conditions. Hence, the options of Geopiers or VCCs were initially considered with VCCs being the selected solution. Hayward Baker designed and constructed the 24-inch diameter, 95kip capacity VCCs. The structural slab, designed by Suncoast, was value-engineered from being a 9-inch or 12-inch conventionally reinforced slab to a 7-inch post-tensioned slab. The Design: The project started with the construction of the VCCs spaced at 15- to 16-foot grids. The VCCs’ depth varied from 25- to 33-feet. A 2-inch structural mud slab was placed over the project footprint after the VCCs were constructed in order to facilitate and expedite the placement of the post-tensioning and rebar reinforcements at the correct height from the bottom elevation of the slab. A few dowels from the VCCs were bent into the 7-inch slab after the placement of the mud slab. The foundation slab was designed as an elevated flat plate supported by columns, assuming a hinge connection between the column and the slab. By using this approach, the slab was kept independent from the soil bearing pressure under it. The Advantages: The Enclave project was initially planned as 9-inch and 12-inch conventional structural concrete slabs with pier caps, for punching shear, which would have required more concrete and reinforcement quantities. Using a 7-inch post-tensioned slab proved to be more economical and better suited for this application because of the compression provided in both directions by the post-tensioning. |
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