FitzGerald Principal Presents Precast Concrete Residential Design to Illinois Institute of Technology Students

Chicago, Ill. (February 13, 2009) - On February 13, 2009 FitzGerald Associates Principal Mike De Rouin, AIA, CSI, CCCA, presented Precast Concrete Residential Design in landmark Crown Hall at the Illinois Institute of Technology.  Taught by Thomas Brock and Steve Kibler, the P3 Graduate Studio’s semester project is to design a multifamily mid-rise building combining parking, residential and commercial uses. 

Mike’s presentation started with questions to be considered at the beginning of a project about the appropriate use of pre-cast concrete, a brief overview of typical precast concrete components, and a lesson about the need to master how to use these components to create good architecture.  Precast structures fall into one of three types: total precast concrete, steel frames with precast concrete floor planks and concrete masonry unit (CMU) bearing walls with precast concrete floor planks.  The use of the building, occupancy requirements and total building height influence which system is the most appropriate solution.  Also, of great importance, are the reasons to select pre-cast concrete as a buildings structural system.  Can longer spans be taken advantage of to reduce building foundations?  Will erection speed allow earlier occupancy?  Reduced construction costs?  Does the site have sufficient space for a large crane?  Trucks to deliver the pre-cast concrete pieces?  What about lateral structural resistance, pre-cast concrete has poor resistance to wind loads because it is literally “a house of cards”? 

Typical pre-cast concrete column shapes are rectangular because of the need for haunches to support beam connections.  Beams are typically, L or inverted T shaped to provide a bearing ledge for floor planks.  These L or inverted T beams are typically 20-24 inches deep.  Large beams, known as bridge girders, are very deep, 4 feet or more and required for large spans.  Slabs are created from planks or double-tees depending on the span requirements.  Planks typically have hollow cores to reduce dead loads and range from 6 to 12 inches thick.  Hollow core planks are extruded from a machine, whereas solid cast
planks are “wet cast” in a form bed and used in special conditions such as exterior balconies.  Most planks are 4 feet wide and can span up to 36 feet.  Double tees are used for very large spans that are typically found in parking garages.  These slab components are also 4 feet wide, 32-36 inches deep and span over 60 feet.

Mike presented three projects that FitzGerald has designed using pre-cast concrete.  University Village Mid-Rises are two total precast concrete structures that took advantage of pre-cast concrete’s spanning ability to eliminate an entire row of columns.  This meant that 9 fewer caissons were needed and shortened the foundation construction time by 3 days.  A 2004 PCI Design Award winner, these 9 story buildings each have 115 loft and traditional condominiums and requisite parking.  FitzGerald worked with Spancrete to design an effective balcony that didn’t utilize hollow core plans projecting to the exterior because of the known concerns about water infiltration and thermal bridging of the structure.  Instead we combined the perimeter beam with the balcony which was “wet cast” or solid.  The beam was also L shaped on the interior face to provide bearing for the interior floor planks.  This provided us with the best solution because the top surface of the balcony was pitched to drain water away from the building and provided a break in the structure to impede thermal bridging. 
The buildings at University Village were constructed in phases from east to west.  During construction of the first building the crane was positioned on the street in front of the building because it was private property.  This structure was erected one complete floor at a time.  Construction of the street to complete the townhomes north of the building prevented the crane from erecting the west building in the same way.  For the second building, the crane was placed in the west end of the building footprint to erect the complete east half of the building before being located on the street to the west of the building to complete the structure.

A link was created between the buildings to provide shared outdoor space that has views towards Chicago’s skyline and the green boulevards of University Village.  This link required spanning an abandoned street right-of-way that has many active utilities buried below the surface.  These utilities include such vital services as a 4 foot diameter water main that serves the Pilsen neighborhood to the South, electrical transmission lines that provide power to the Loop and fiber optic communication lines.  Needless to say, we needed to be very careful in designing the link structure so that these utilities can be serviced in the future.  Our solution was to clear span the right-of-way and construct as few foundations as necessary in the former parkway/sidewalk area of the right-of-way which avoids the below grade utilities.  This 59 foot span is crossed by 34 inch deep double-tees supported by 20 x 48 girder beams that span up to 32 feet.  The top of the link deck is landscaped with a lawn and generous planting beds along each building.  The focal point of the deck is a large trellis and brick paver patio with patio chairs and tables.  This space is very tranquil and provides a sunny place to view the greenway vista north through University Village.

The second project Mike presented was 2510 West Irving Park Road.  A four story steel frame building with 8 inch hollow core that span 24 feet across W14 steel beams.  This design was employed to provide high acoustical separation between the floors.  The floor plans at this building are unique because the units are accessed from an outdoor walkway and terrace area that is made of solid cast precast concrete for its durability.

Lastly, Mike presented The Grove at Oakwood Shores which is a new building to be sold as part of the second phase of the CHA’s HOPE VI transformation of the Madden-Darrow-Wells homes on the near south side of Chicago.  This building located near 39th and Drexel Boulevard is a six story total precast concrete building.  The challenge of designing a total precast concrete structure that contains a commercial use ground floor with residential units above is how to maximize the wall panel at grade for retail exposure while minimizing the windows in the residents for privacy.  The result was the use of a transfer panel in the high volume space of the first floor to distribute the wall loads from the punched window panels above into the columns at grade. 

Providing outdoor space for the residents without hanging balconies out over the sidewalk was another challenge that required some thorough study of how the load paths of the pre-cast concrete wall panels were taken down to grade.  Our simple solution was to align these return walls of the balconies with the potential entries for the retail space creating entry vestibules with the columns at the first floor.
Design of the exterior wall panels required a coordinated effort with the Owner and the selected pre-cast concrete manufacturer because the range of possibilities is nearly infinite.  The use of different aggregates, color in the mix, form liners, thin-brick or stone inserts and finishing require study, evaluation and refinement until the desired solution is achieved. 

Mike’s presentation concluded with a round of questions from the students and professors that stimulated some good discussions about the benefits of pre-cast concrete, best practices and thoughts about how much thought, planning and coordination is required during the design process to effectively use pre-cast concrete.  Mike may return later in the spring to review the students’ final designs.