Inside a Transverse Airform

A panorama image inside the Transverse Airform inflated in Drummond, Oklahoma. The fabric seams arch overhead, horizontally, from one “side” of the dome to the other. This is the first Airform using the horizontal panel design for which Monolithic received a patent. (Andrew South)


Monolithic granted patent for Transverse Airform pattern

The offer for a commemorative plaque always arrives first when a patent is granted. The plaque company usually beats the patent office by a day or two. It’s an effective marketing strategy; after all, Monolithic has five of these plaques. Now there will be six. A couple of days later, the official notice from the United States Patent and Trademark office arrives. Monolithic Constructors, Inc., is granted patent number 10,400,462 for the “Transverse Span Airform Structure.”

The Transverse pattern is a new way of manufacturing an Airform membrane for building a Monolithic Dome. Instead of using triangle-like gores with seams running from the top of the membrane to the base, the Transverse design runs gently curved panels horizontally from one “side” of the dome to the other.

It is the brainchild of Dave South, son of Monolithic Dome co-inventor David B. South. Dave wrote the software for radial patterns, pioneered using CAD in membrane design, developed window/door augmentation, and expanded multiple-membrane intersections. In 2015, he and his mentor — Airform pioneer Jack Boyt — worked on a better way to pattern a dome by turning it on its side. South eventually wrote a new custom program — called Transverse — which outputs horizontal designs.

A Transverse pattern eliminates the “top” of the membrane where all the seams come together. It also eliminates the challenging final seam when making an Airform. The seaming process is more accurate because the panels curve less. It uses the maximum width of the fabric, and it requires fewer total panels than the radial design. Labor to assemble a Transverse membrane is half that of a similar radial design.

Of course, this only works for low-profile domes. For hemisphere, 3/4 sphere, or silo-shaped domes, the radial pattern is still the design to use. A hemisphere membrane would have two “ends” or “tops” if it were a horizontal pattern.

Most schools, safe rooms, gymnasiums, and other architectural domes are built on top of a stem-wall. The dome portion is generally 1/4 to 1/6 the diameter of the building. The Transverse pattern is ideal for these structures.

Using horizontal gores are not new. Prolate ellipsoids like “Eye of the Storm” use horizontal patterns. A few one-off domes needed the design as well. Each of these custom patterns required a careful, artistic touch to finish.

Why? Because a Monolithic Dome Airform membrane must inflate to a specific target diameter and height.

Air pressure pushes and stretches the fabric when an Airform is pressurized. Unfortunately, the material doesn’t stretch evenly. PVC coated fabric typically expands more across the width and less down the length. The membrane pattern must compensate for this in advance, or it will be too big when it’s at pressure.

Therefore, an un-inflated Airform is too small. It must be inflated to be the appropriate size. BUT the un-inflated membrane is also too small to fit on the circular foundation. The bottom must “flare” out to the proper size so it can be anchored to the ring beam.

With a radial design, each gore is identical to the next. The width, length, and flare compensation are symmetrical. Turning this sideways to create a horizontal pattern means constantly calculating the stretch, flare, and the intersection with the foundation or stem-wall.

Not easy.

This is why horizontal membranes are so rare. They were only used when a radial design couldn’t work.

The Transverse software written by South calculates the membrane across thousands of points. Each point compensates for stress, stretch, flare, and ring intersection. Each panel is a custom shape that is cut from fabric on an automated cutting machine.

The first Transverse Airform inflated in Drummond, Oklahoma, on June 24, 2015. Laying on the ground, the Transverse Airform didn’t look like anything made before, but it inflated beautifully. Laser measurements at pressure showed it hit the target dimensions within one-half of a percent.

The Drummond project wasn’t published at the time because the patent application was in process. The patent application was compared to and not found to violate any other air structure patents because these are different in scope and design.

The official patent issued on September 3, 2019. The full patent text for Transverse span airform structure is available at uspto.gov.

Exterior view of the inflated Transverse Airform

Sunlight glints off the Transverse panels curving down to the stem-wall. Custom software written by Dave South calculates panels individually — compensating for air pressure stress. The membrane in Drummond inflated to within one-half of a percent of the target height. (Andrew South)

Registration mark drawn at top-center

Unlike radial patterns, the Transverse seams do not meet together at the top of the dome. A registration mark was drawn on the form to help crews identify the top-center. (Dave South)

Aerial view of Drummond Gymnasium

The finished Monolithic Dome in Drummond, Oklahoma, is a gymnasium and safe-room for the school next door. (Andrew South)

Horizontal panels inside Quanah, Texas, dome

The Transverse Airform for the 91-foot diameter dome at Quanah, Texas, only needed 12 panels — instead of triple the number for a radial pattern. Calculating thousands of points at the intersection of the membrane and the stem-wall ensured a smooth, ideal dome shape. (Dave South)

Drone view of snow covered, 182-foot diameter dome in Alberta, Canada.

The largest Transverse Airform manufactured so far is 182-feet diameter by 70-feet tall — a 1:2.6 ratio dome — for a frac sand storage project in Alberta, Canada. This moonlit, winter drone shot shows the snow “following” the horizontal seams. (Andrew South)