Rising to the challenge of perfection

Concrete Construction, August, 2002 by William D. Palmer, Jr.

Corners are seldom square--there are more than 800 different corner conditions, and walls vary in thickness from 1 foot to 5 feet. Atlas Forming Systems provided the formwork support elements (walers, strong backs) and the jacking elements while as many as 60 Morley formwork carpenters cut the panels and assembled cabinet-quality forms. Other formwork was provided by Symons and EFCO. To get the required color consistency, the forms had to be watertight, like "making bathtubs out of wood," says Selna. To achieve that feat with highly fluid concrete (9-to 11-inch-slump) poured in 12-foot lifts, the carpenters had to assemble the Atlas forms with perfect corners and seal every seam. A double layer of plywood for the panels prevented pillowing, and backscrewing kept the panel faces smooth. Formsavers, threaded embedments for dowels, were used throughout to avoid putting holes into the forms.

The highly fluid concrete achieved with superplasticizers allowed sharp corners and complete consolidation at the odd corner angles and around reinforcing steel that was often very congested. To reduce the possibility of corrosion, steel on all horizontal surfaces was stainless and the minimum cover on exterior surfaces was increased to 2 1/2 inches. "Perfection is what was expected," says Atlas' Brian Quinn, "but they went way beyond what was expected. The work was so perfect that we had site visitors who thought the corners were precast."

Project superintendent Larry Sevilla refined the methods and details of pouring the walls on the conventional below-grade concrete. With 11 to 15 10-man wall crews working, every wall was numbered and, prior to pouring, every craft and the structural engineer and architect had to sign off that everything was in place--electrical, embeds, block-outs, and rebar. Morley's layout supervisor, Chay Contreras, had his surveying crew everywhere, making sure that form panels were in the proper location. "We shot over 11,000 points," he says with pride, "and because of the weird angles, the forms would want to twist out of position as the concrete was poured," requiring locating the same point two or three times.

The 70-foot-high concrete cross that seems to levitate behind the altar was one of the project's unique challenges. Weighing nearly 2 million pounds, it is supported only by the horizontal "arms"--actually a steeply sloping (9 inches/foot) wall that ties into the 17-foot-deep main concrete girders. In another example of bringing in the right player when needed, Morley hired KCJ Engineering as the sequential-element constructibility consultant. KCJ established settlement allowances and designed bracing and overturning-resistance ties for the cross; Atlas designed and supplied the shoring system. To avoid having to bear on and possibly mar the surfaces, the vertical portion of the cross was cast first, also in 12-foot full-liquid head lifts. The horizontal arms of the cross were then cast with Contreras' crew continuously checking and adjusting the shoring after every lift. "It was more like designing a bridge than a building," says structural engineer Bryan Smith, Nabih Youssef & Associates' onsite engineer.