The modus operandi was clear. Design a dumbbell-shaped 2 million-sq.-ft. mall in the Dallas suburb of Frisco that entices shoppers to both ends while blending with the high-tech appearance of the surrounding region. It was the first time that Berkeley, Calif.-based architect ELS had created such a large project that combined trusses of varying lengths. Says Ed Nolan, lead designer, 'Because the overall layout of the shopping center was pretty much just straight, we wanted to add some interest by making the roof structure vary in shape and size. Basically, each truss is a different length, although you could say that because the building is symmetrical, half of them are the same as the other half.' The trusses range from approximately 50 to 90 feet in length.
The curves help break up the roof visually. The middle section, which is about twice as long as the two end sections, orients with the clerestory to the north. The two end sections and the clerestory orient to the south. 'So you get this nice sort of flipflop as you're walking along the mall,' says Nolan. 'The quality of light is totally different and you may have the sun shining in on one side but the other side not. It makes what appears to be just a long straight mall a little different. You're experiencing different things as you walk along because of that.'
Challenges for Dallas-based structural engineer L.A. Fuess Partners Inc. included controlling the movement of the glazed area of the building, says project engineer Ann Piazza. A computerized 3-D model allowed the engineers to visualize real deflection of the glass.
The orientation of the skylights and clerestories affects heating, ventilating and air-conditioning requirements. 'If all of the skylights face south or west, it would overheat, so the bulk of the skylights face north,' says Nolan. During the day, air heats and rises to the top, but the ceiling is so high that the heat doesn't affect people inside.
Skylights and space frames help create a directional pattern. 'It's a very big mall and so it seems to me you need a very simple organizational idea. Otherwise, you may tend to get people lost. It may be hard to find your way through it. The fact that we've twisted and turned the skylight gives you some way to orient yourself,' says David Petta, principal in charge.
The designers specified a sloped clerestory, which created challenges from a glazing point of view. Glass appears to curve with the structure, while it is actually segmented and follows the structure, says Nolan.
To fit in with nearby Plano, known as the Silicon Valley of Texas, designers exposed the structural system, the graphics on brackets, the handrail connection, the light fixtures and much of the ductwork. The structural engineers became creators of the aesthetics as well.
'All the steel that's a part of the skylights is exposed to view,' Piazza says. 'We knew that we couldn't always go with the straightforward structural solution because maybe it wouldn't provide architecturally what ELS wanted to see. It was really just being conscious that everything we did would be exposed to view.'