A safer fabric membrane ceiling
A new fabric membrane ceiling provides a prudent replacement for a Tokyo museum.
Specialty Fabrics Review | October 2011
By Kikuko Tagawa
Due to the earthquake in Japan in March 2011, some panels of the ceiling boards of the National Museum of Emerging Science and Innovation (Miraikan) in Tokyo, Japan, collapsed. Three months after the earthquake, it reopened with a new ceiling made of a membrane material which is about 1/40 the weight of the original ceiling. Under the guidance of Dr. Ken’ichi Kawaguchi, a professor at the University of Tokyo, a new design concept created “a ceiling that will never lead to a serious accident, even if it collapses.”
A near catastrophe
On Christmas day in 2010, Dr. Kawaguchi was enjoying a visit to Miraikan with his daughter. They were celebrating a family event, as it was her birthday the next day. When he and his daughter left the exhibit hall upstairs, the six-story-high ceiling at the entrance hall, built in a conventional manner, seemed to appear in front of them, as several leaf-shaped objects were hanging from it, with a single wire for each. He immediately thought, “This is dangerous!” and took several pictures of it.
A few months later his concern unfortunately became reality. At 2:46 p.m. on March 11, 2011, the huge earthquake struck in eastern Japan. The uniquely shaped museum, built in 2001, shook terribly, but the structure withstood it; however, some boards of the 28-meter-high ceiling collapsed at the first aftershock, 30 minutes after the main shock. Museum staff led everyone to safety outside, and there were no casualties, but there could have been a much more serious situation if people had been underneath that part of the ceiling when it happened.
Many buildings had ceilings collapse in the earthquake, including the Ibaraki airport, Kudan kaikan auditorium in Tokyo and numerous others. Ceilings installed using conventional methods have a great possibility of collapse due to an earthquake or other factors, Dr. Kawaguchi says. “There are, in fact, many reports of collapsed ceilings in large-span buildings, such as gymnasiums and other buildings with an open public space.”
Determining the danger
From his structural engineering vantage point, Dr. Kawaguchi conducted a study in 1995 that investigated 117 large-span structures immediately after the Kobe earthquake that year. “To my surprise I found few structures were damaged, or with small damage, even though the earthquake was a magnitude 7.3, and it was directly under the city,” Dr. Kawaguchi says. However, about 20 percent of the facilities’ ceilings collapsed due to the tremble.
Since a ceiling is a nonstructural member, there is no particular seismic criterion to be applied to them. “People are saying much about the earthquake strengthening of large-span, steel-frame structures, but we should be more concerned about interior materials, lighting fixtures or other things high above people’s heads,” Dr. Kawaguchi says. “There have been many people injured by ceiling collapses due to the earthquake, but unfortunately safety measures have not been taken seriously.“
Buildings with large public spaces often have high and large-span ceilings. “Not only is the collapse of a ceiling very dangerous, but then those buildings cannot be used as refugee shelters in an emergency,” Dr. Kawaguchi says. “This is one of the important functions of these facilities.”
The decision to use fabric
Miraikan’s director, Dr. Mamoru Mohri, is an astronaut and scientist who was on the space shuttle Endeavour twice, in September 1992 and February 2000. He was relieved to know that no one was injured in the Miraikan incident and agreed with Dr. Kawaguchi that the best design for a new ceiling would be one that would be safer even if it collapsed. “I believe that could save a lot of people’s lives in the long run,” Dr. Mohri says.
The decision was made to install a new 535-square-meter ceiling made in part of PVC-coated, glass-fiber fabric that is just 0.3 mm thick, .38 kg per square meter and flame-retardant certified. The gypsum board used before the renovation was about 15 kg per square meter with its sub-frame.
Dr. Kawaguchi emphasizes that other factors can cause a ceiling to fall. With leaks, dew condensation and moisture from any source, gypsum boards or similar materials can deteriorate easily, causing it to collapse even without an earthquake—and it could happen all of a sudden. Earthquake-strengthening treatment to gypsum board would not necessarily prevent a ceiling collapse, Dr. Kawaguchi says. That fact, the high and large ceiling, and the large numbers of people who gather in these spaces all contribute to serious accident risks.
The danger associated with height depends on the material, he says. The fall of a light material would not cause serious injury. Dr. Kawaguchi’s team of researchers has been doing experiments to establish an evaluation system on the height and the material. “If an ordinary gypsum board ceiling is higher than four to five meters, there is a great risk of skull fracture when the ceiling collapses,” he says.
Regulations and cost
Because a ceiling is an interior application, the material used in public buildings is required by law to be noncombustible. Glass fiber fabric is certified as noncombustible, but gypsum board is often used because it is the cheapest noncombustible material.
Dr. Kawaguchi questions the nature of the specific regulations, however. “If the ceiling is higher than a certain height, the fire will not reach it,” he says. “If we think of safety, it is safer to use light material in a higher ceiling, rather than a heavy ceiling that could fall down. I believe there should be some kind of deregulation of the restriction of the interior material according to the height so that a soft PVC or mesh material ceiling could be possible.”
Regarding the cost, he says, PVC-coated glass fiber material is about 1.5–2 times more than traditional gypsum board. However, if the framing for a gypsum board ceiling is seismic-reinforced, the cost is almost the same. According to Dr. Kawaguchi, the choice is simply whether to use a potentially dangerous ceiling with seismic reinforcement or to use membrane at the same cost. Also, if membrane ceilings become more popular, it is expected that the cost will go down.
Not only is a membrane ceiling lightweight, but it is also flexible, so it can actually prevent a residual risk associated with a collapse. For example, if speakers suspended from the roof were to fall down, the membrane ceiling underneath could function just like a safety net.
When Dr. Kawaguchi visited Berlin in 2005, he saw the fabric mesh ceiling of the Olympiastadion Berlin first hand, which also has a safety net. “The mesh ceiling of the stadium is beautifully designed with lighting during nighttime, softly hides equipment in the daytime, and yet it acts as a safety net,” he says.
A serious choice
If we are to avoid the collapse of a ceiling, the best choice may be to have no ceiling at all, says Dr. Kawaguchi. The Ibaraki airport chose this option after its ceiling collapsed in the March 2011 earthquake. In some circumstances, however, a ceiling is necessary to hide cords, ducts and pipes, absorb sound and provide thermal insulation.
“Membrane ceiling is one of the options for a safe ceiling,” he says. “I am not thinking this is the only choice.” At this time, a membrane ceiling does not function well for acoustic absorption, for example, because it requires a certain mass. “For this purpose, we should rather think how we use heavy materials safely,” he says. “For thermal insulation we may put glass wool, or micro beads onto it, but it is still in the development stage.”
Because a ceiling is not a structural element, the material does not require tension, so there are limitless possibilities in design. Several fabric membranes have already been used in ceilings. The Kushiro Airport, whose ceiling collapsed in the 2003 Tokachioki earthquake, has a membrane ceiling of catenaries, and the Shizuoka swimming pool replaced its ceiling with a retractable membrane ceiling following its collapse in a 2009 earthquake.
Printing is even possible with a new PTFE glass fiber material, recently introduced by Chukoh Chemical Industries, and there is the potential for image projection under indirect lighting, which opens up a range of design opportunities.
The membrane ceiling is a new concept for offering a safer environment in many buildings that has other advantages, too—and it could be a promising new market for fabric membrane.