While many school districts in large Texas cities attempt to keep pace with their swelling student populations by constructing huge, multi-million-dollar high school campuses, smaller towns with less money to spend must be more creative.

The rural communities of Italy and Avalon, located approximately 50 miles south of Dallas, were able to stretch their relatively meager budgets into a pair of unusual gymnasium projects. Each school district constructed a monolithic dome.

Simply put, a monolithic dome is a super-insulated, steel-reinforced concrete structure originally designed for bulk storage facilities. Neither district had to go very far to find a construction manager for the projects; Monolithic Construction Management is headquartered in Italy.

Each of the structures now resembles a miniature of the Houston Astrodome, a Texas landmark since the 1960s. But the smaller domes are much more than simple sports venues. According to project manager Alden Porter, tight budget parameters and energy efficiency set them apart from steel-framed structures.

"Once you get over 100 ft. in diameter, domes are more economical than free-span steel buildings are," Porter said. At the cost of about $85 per sq. ft., the $1.2 million dome in Avalon came in about $50,000 under budget. The cost per sq. ft. was the same for the $2 million multipurpose facility in Italy.

"Not only do you save money in up front construction costs," Porter added, "but perhaps the most important aspect as far as a school district is concerned is that the domes are so economical to operate as far as energy costs are concerned. The dome has an effective R-value of 60, which allows you to use approximately half of the air-conditioning costs that you would have on a steel or metal building."

Safety is another important reason why more school districts and small towns are entertaining the idea of building domes. Each is built to meet or exceed the Federal Emergency Management Agency guidelines for structures that can provide what the agency calls near-absolute protection during severe storms. According to FEMA, "Near-absolute protection means that, based on our knowledge of tornadoes and hurricanes, the occupants of a shelter built according to this guidance will be protected from injury or death."

Avalon ISD superintendent David Del Bosque said, "We looked at the cost of a traditional structure versus a dome and were really impressed with what the long-term savings would be in utilities, maintenance and those kinds of things.

"Also, I personally was concerned about safety for students and the stability of the building in case of a storm. But this is the safest structure anywhere here and we plan to contact the Red Cross, get it certified and use it also as a community storm shelter."

Unusual Beginnings

While most conventional structures begin with a foundation, monolithic domes begin with construction of a ring beam.

"Because all of the weight and structure of the dome comes down to the ground at the edges, we build a steel-reinforced concrete ring beam based upon the structural engineering of the dome itself," Porter said.

For example, the 148-ft. diameter dome in Italy was 36 in. wide by about 2 ft. deep.

Once the ring beam is placed, a stemwall of 2-in.-thick reinforced concrete is erected outside the ring beam and a specially designed airform of the dome is attached. Stemwalls vary in size according to the dome's size. For example, Italy's facility features seating for 1,400 and was constructed on a 16-ft. stemwall. The dome at Avalon is smaller with a dome diameter of 124 ft.; it seats approximately 700 and was built on a stemwall of 12 ft.

Once the airform is in place, it is inflated with fluctuations in pressure to allow it to retain its shape. From grade to the top of the stemwall, 3 in. of polyurethane foam insulation is installed at a thickness of about a half-inch at a time. Halfway through the process, crews place rebar hangers into the walls. Each is a 6-in. piece of wire that sticks out through the foam that will eventually hold reinforcing steel, which is later placed in a horizontal/vertical checkerboard pattern along the wall.

"Obviously, the size and end use of the dome may play a factor," Porter said, "but normally we use No. 4 rebar tied 12 in. on center for the pattern."

After completion of the insulation installation, additional rebar is installed at the top of the stemwall where it meets the roof, which prevents the wall from pushing out sideways.

Once the checkerboard pattern of reinforcing steel is completed, construction continues with shotcrete being sprayed on the walls at 150 psi of pressure. The rate is approximately one-half inch per application. Initial shotcrete mixtures include 3/8-in. pea gravel and sand while final applications eliminate the gravel to give the exterior a more even texture.

"Once the concrete covers the rebar, the dome is structurally sound," Porter said. Additional smoothing techniques of the shotcrete may be utilized and decorative patterns can be added to the outside of the structure. The exterior of the stemwall is typically finished with a coat of protective elastomeric (acrylic) product.

"When it is finished, we typically have about 4 to 6 in. of concrete from top to bottom plus 3 in. of insulation plus 2 in. of stemwall," Porter said. "That makes for a wall thickness of about 9 in. at the top to about 11 in. at the bottom. You begin to see why these structures are so safe and energy efficient."

The airform remains in place overhead to serve as a single-ply roof membrane. The 3-in. layer of polyurethane foam acts as insulation for the roof as it did for the stemwall and it is topped by another 4 in. of sprayed shotcrete.

Slab Goes Last

Only when the dome structure is complete does underground utility work begin. Plumbing and electrical lines are placed before a 4-in. concrete slab is poured inside the dome.

"Because it is inside and protected from the weather, you don't have the cracks in your slab that you might normally see," Porter said. "The slab is able to cure without being subjected to temperature fluctuations or sudden weather changes. Then once the slab is complete, you can proceed with the interior finish as you would any other building."

The domes are structurally strong enough to hold approximately 1 ton of material for every 6 ft. of vertical wall. "Hanging such things as drop-in ceilings, catwalks or air conditioning ducts is not an issue," Porter said. "You simply go up there, attach them with wedge anchors and move on to your next project."

The foundation of the building is also one of its strengths. "You no longer have to worry about having structural supports in the floor below, so there is no need for cross beams or anything like that," Porter added.

In addition to its state-of-the-art gymnasium floor - a maple, parquet floor installed by the same company that installed the famous parquet floor in the old Boston Gardens - Italy's facility contains locker rooms, a concession stand and ticket booth.

Avalon also has four locker rooms in its facility and anticipates using the dome long after basketball season has ended.

"In our opinion, there's no use having a beautiful building like this and only using it for athletics," Del Bosque said. "I'm hoping to have a summer recreation program that will use the dome. You know how our summers are so hot.

"This dome is air-conditioned, so we can have an optional, extended-year program that will run from 8 a.m. to 12:30 p.m. We'll coordinate that with a federal free lunch program from 12:30 to 1 p.m. and then we'll open the gym from 1 to 4. So, we'll have a full day of activities for the kids in the community. I think it will be terrific."