The gorillas at the Cleveland Metroparks Zoo needed more room to roam. Two gorillas joined the resident male in 2017, and another was welcomed last year. So the zoo modified its gorilla habitat to support the growth, dividing the space into two main sections that are joined by an elevated GFRP bridge at the rear of the exhibit.

The enclosed passageway is approximately 40 feet long, 8 feet tall and 8 feet wide. The bridge’s GFRP skeletal structure and flooring are connected to stainless steel wire mesh, which allows the gorillas a view of their entire habitat as they roam the area and permits visitors to see the animals as they move from place to place.

Though the initial design called for the bridge to be constructed entirely from stainless steel, the zoo’s designers soon began considering composite materials. They asked Advantic LLC, a design/build structural solutions firm in Dayton, Ohio, to compare the cost and benefits of a steel structure to that of an enclosure made from pultruded GFRP.

“The zoo’s design team had read about composites as an alternate material,” says Brad Doudican, a managing partner with Advantic. “Zoos and aquariums tend to be pretty aggressive on steel. Because water and urine can degrade the material, it has a high cost of maintenance. If steel is used it’s often an alloy, like stainless steel, which is better for corrosion than traditional carbon steel but often significantly more expensive and difficult to install.”

Once the designers learned about composites, they were won over for several reasons: It met all structural requirements, was corrosion resistant and the lightweight composite bridge components could be carried by hand to the gorilla area and constructed onsite. This reduced the need for rigging, lifts and cranes to install heavy steel components. Space was tight at the gorilla enclosure, and designers and builders weren’t able to determine how cranes could access the area. The only access was through two personnel doors where zookeepers enter the habitat.

The bridge was constructed with Strongwell’s EXTREN® structural shapes, including wide-flange beams, angles, plates, I-beams and channels. EXTREN features polyester or vinyl ester resin reinforced with either continuous strand mat fiberglass or continuous strand roving, depending on the application. The shapes include a surface veil that protects against corrosion and deterioration from ultraviolet light. The GFRP structural shapes are stronger than structural steel on a pound-for-pound basis and weigh 80 percent less than steel, according to Strongwell.