Designers created a unique trolley turn at the intersection of two key city streets in Dallas, Texas. Cityplace Uptown Station became an area landmark with its almost whimsical combination of precast concrete structure, glass, and wood.
Precast concrete was chosen for the structural supports due to its integral natural beauty, plasticity, durability, and structural efficiency. The columns taper in two directions, which would have been difficult to achieve with other materials. The repetitive nature of the components also played to precast concrete’s strengths.
The precast concrete columns are freestanding, with all other elements tying into them. Producing the high quality needed for the columns, which can be approached on all four sides by the public, required a special casting process. Four-foot (1.2-m) vertical forms were created, into which was poured a flowing concrete mixture that minimized entrapped air. The mixture had to flow around a variety of obstacles in the form, including canopy tubes, conduit, pipes, and reinforcement.
Only 12 pieces were required, and they were given a medium- to heavy acid-etched finish to promote both strength and aesthetics. Each column, about 3 × 30 ft (0.9 × 9 m) and weighing 24,000 lb (11 tonnes), was designed to lean out of plumb away from the center by 14 degrees, creating erection challenges. A hollow steel bracket was fabricated and bolted to each footing to keep the columns from pulling away from their designated position at the base while maintaining their angle.
The columns then were lowered into the bracket and welded in alternating sequences to avoid excessive heat on the concrete. Erection of the pieces took just under one month to complete.