Pittsburgh Zoo Customizes Concrete Habitat for Polar Bear Return

The Pittsburgh Zoo and PPG Aquarium welcomed back the most ferocious bear species on the planet — the amazing polar bears. Having departed in 1998, the bears are back by popular demand, returning to a special new home built during the first of three construction phases at the Zoo's $14-million Water's Edge exhibit. The other two phases include a home for sea otters and a dwelling for walruses. When fully completed in April 2007, the exhibit will cover 2.8 acres and make Pittsburgh one of only four zoos in the country to feature polar bears, walruses and sea otters in its collection.

The architect, Indovina Associates of Pittsburgh, faced the complex challenge of incorporating Water's Edge into hillside terrain while accommodating special exhibit requests and maintaining a natural flow throughout the display. Quite unique in its design, the unusual project made construction a complicated endeavor.

Using vast concrete forms, a multitude of machinery and several busy crews, the entire exhibit is taking shape under the expertise of Pittsburgh, Pa.-based construction management company, Zambrano Corporation.

"The distinctive project involves many special characteristics for its construction," says Brad Smith, Zambrano's Project Manager. "This definitely isn't your typical concrete structure."

Rather unusual by today's construction standards, all walls, beams and columns in the 22,000-square-foot structure are constructed entirely of concrete without any structural steel. This cast-in-place approach was specifically required for withstanding the harsh salt water environment.

Built within a steep 60-foot embankment, the structure features an asymmetrical shape that makes concrete formwork and placement a challenge. Further adding to the task's complexity, the project specifies construction of two highly unique acrylic tunnels serving as pedestrian walkways for viewing animals overhead. In addition, the job site's location in the center of the zoo has meant working amidst hundreds of curious visitors each day.

Zambrano's professional approach to construction includes working with a select group of subcontractors who know the level of quality expected of them to make jobs run smoothly and without delays. Known and respected for its construction of parking structures and specialty projects within a five-state area, Carl Walker Construction of Pittsburgh was chosen as the concrete contractor for this unusual concrete placement job.

"The combination of terrain, footprint and location definitely proved challenging in safely and efficiently utilizing equipment and resources in this project's concrete construction," says Joe Racz, project superintendent of Carl Walker.

"The structure's irregular shape required highly customized forms that we created in the field for an exact fit," adds Racz. "Because we weren't dealing with a square shape and typical right angles, placing the formwork and pumping the concrete was obviously more complicated."

To ensure success in the intricate complexities of pumping the concrete, L&E Concrete Pumping of Pittsburgh is supplying Putzmeister boom pump models with reaches from 32 to 42 meters. It is estimated that these high-performance units will pump over 5,000 cubic yards of concrete upon the project's finalcompletion date.

"Because the exhibit is so unique, it's allowing our concrete pumps to exhibit their own unique features," says Ed Femc, co-owner of L&E.

Donna Femc, L&E's co-owner notes, "It's a juggling act to ensure we schedule the perfect model size that provides both a small setup area yet still provides enough boom reach."

Established in 1985, L&E has increased its concrete placing equipment fleet over the years to include 10 concrete pumps. The husband and wife team has established a large client base through their conscientious approach to service.

"All concrete pumps have performed flawlessly with absolutely no incidents to date," says Racz. "Plus, L&E's experienced operators have proven their invaluable skills bysetting up in very tight spots and negotiating the boom into awkward areas to place concrete."

Stone & Company of Greensburg, Pennsylvania, is responsible for dispatching two different concrete mixes on this project. One is a typical 4,000-psi mix and the other is a special 5,000-psi micro-silica mix that makes the concrete denser with fewer air pockets to withstand the long-term effects of the abrasive salt water against the concrete.

The two 12-foot-wide acrylic viewing tunnels are shaped in a horseshoe configuration for a remarkable vantage point of animals as they swim under water. The first 30-foot-long tunnel, weighing 14,000 pounds, is a seamless design demonstrating the latest fusing technology. It provides an unobstructed view of the polar bears as spectators observe the animals in the 148,000-gallon pool overhead. A second 40-foot acrylic tunnel, reputed to be the only one in the world for watching walruses, is being situated under a large 265,000-gallon pool.

"One of the most important aspects of the tunnel creation was the precise coordination required in constructing the sills to accurately match up with the huge acrylic covering," says Smith. "It had to be exact, as we only had an inch clearance on each side."

As a result, each tunnel was developed by fabricated channels, meticulously formed by hand on-site. These were specifically designed so the enormous piece of acrylic could be lifted over top and slid into deep sills. The sills were later filled with grout and sealants for a tight seal.

Another special feature of Water's Edge is the facility's huge viewing windows. Similar to the approach used on the tunnels, field-fabricated concrete forms were required to create a sizeable 14-foot-square concave window area prior to installation of the 5-inch-thick plate glass. One window is for viewing the sea otters, and the other allows visitors to peer inside the air-conditioned polar bear den.