When the CEO of the Vogel Alcove, Karen Hughes, told the Leadership Dallas Class of 2015 that she needed shade to cover her kids’ blacktop recreation space from the Texas heat, the challenge was on. For 10 months, the Leadership Dallas class worked to define and create a vision for their community service project that would impact the North Texas region in the most meaningful way. Little did they know that the team’s resources would literally be stretched and ultimately lean on a creative structural solution to a complex yet playful architectural vision.
For 28 years, Vogel Alcove has provided free, quality child development services for Dallas’ youngest victims of poverty — homeless children six weeks to 12 years old. Vogel Alcove is the only comprehensive early childhood education program in the city of Dallas, whose primary focus is to provide free childcare and case management for homeless children and their families. These kids have an amazing, newly renovated building, but the outdoor space was left useless in the summer months as the extreme 100°F-plus temperatures kept the basketball court’s blacktop sizzling and the kids inside.
The initial schematic designs to shade the outdoor basketball court stemmed from an idea once used by the author to keep bombs from entering mechanical spaces on United States Military installations. But, when Halff Associates’ Derek Downs came to the table with a crisscrossing tensioned cable catenary system that integrated tensioned square and triangular shade fabrics, the stability of the structure became the challenge and the star of the show.
JQ’s engineers designed cantilevered steel masts on two sides of the rectangular space to keep steel aircraft cables tight in the primary direction (see Figure 1). Perpendicular cables were checker boarded to allow gripping points for the shade fabrics and reverse curvature tension lines were installed on each end of the rectangle to tension the cables in the opposite end since there was no place to space columns on all four sides of the court. Compression struts were utilized to offset the tension forces in the cables.
Vogel Alcove is located in the Trinity River basin where only 20 feet below grade level the underlying clayey sands were holding water. Concrete drilled shafts were installed to 25- to 30-foot depths through temporary steel casings using slurry displacement methods to keep a constant concrete head. Due to the limited space available for placing the column supports for the shade structure and wanting to maximum usable playing surface on the court, the cables were brought straight down to the tops of the piers, removing any chance at angling down to a lateral restraint; like what you would see on street electric poles. The concrete piers were designed as both gravity and lateral forces members to resist the forces imposed by the cables.
This portion of the project included a new structure that provides 5,000 square feet of shade using 125 cubic yards of concrete, 18,000 pounds of reinforcing steel, 50,000 pounds of structural steel, and 3,500 feet of steel cables; all donated. For all the projects completed by the Leadership Dallas Class of 2015, close to $250,000 was raised for this effort.
In the fall of 2015, the group received the Thelma Vogel award from Vogel Alcove for vision and collaborative efforts and for advancing the services for homeless children and families.
Barry K. Krieger, P.E., MLE, senior project manager, is a principal at JQ (www.jqeng.com).