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Straw bales may aid in rebuilding Iranian town

| 04 February 2004

 

bales

Straw bales held in place by steel bars form the core of the Spar and Membrane System being used to construct the Rancho Arroyo Grande winery near San Simeon, not far from the recent damaging quake that struck Paso Robles.
William Robertson photo

Berkeley architecture professor Gary Black says he has a safe, simple, and affordable solution to rebuilding the city of Bam, Iran, where 41,000 people died after a magnitude-6.7 temblor earlier this year.

His answer: the Spar and Membrane System (SMS), a construction system of straw bales and prefabricated steel bars encased in thin membranes of concrete. It’s an ideal fit for low-rise buildings in California, Iran, and other seismically unsettled regions that share similar geological conditions, he says, particularly because “the main materials — an agricultural by-product and concrete — are readily available worldwide, and the construction is relatively low-tech.”

For the past decade, Black has been testing and perfecting the system, producing aesthetically appealing small and large buildings. It’s been used in a church meeting hall in Kansas, a small winery in the Sierra foothills, and a 7,000-square-foot villa in Sonoma. The latter building survived, without any damage, a quake in 2000 that measured 5.2 on the Richter scale and was centered just eight miles away.

The system — copyrighted by the Berkeley-based Integrated Structures, Inc. (ISI) firm that is headed by Black — also is the cornerstone of the 100,000-square-foot Rancho Arroyo Grande winery complex being constructed not far from San Simeon, near where a magnitude-6.5 earthquake in December left buildings in Paso Robles in shambles and two people dead. The SMS system has reduced the cost of the 100,000-square-foot facility by approximately 20 percent and will reduce the cost of operation by 15 percent annually, said project manager William Robertson. He calls Black “an amazing oracle of creative and technical solutions.”

Black also has strong support from his UC Berkeley colleague Abolhassan Astaneh, an Iranian-American professor of engineering. “The SMS system would be a very good system in Iran,” said Astaneh. “It is relatively light, yet strong, and ductile enough to withstand the ground shaking.”

The main reason for the high death toll in the Bam quake was the collapse of the relatively heavy and brittle mud and brick houses, noted Astaneh, who continued: “If you want to survive earthquakes, you need to make your structure light, sufficiently strong, and stiff, and tie it together in a ductile way so it bends but doesn’t break or fall apart. Systems like [SMS] do all that well.”

Straw building construction has been a staple in Europe for the past 400 years. It is popping up in the United States largely in response to a desire for environmentally friendly building techniques, and in response to a growing need to conserve energy.

Black said his system is green, energy efficient, and good for withstanding fire as well as earthquakes. Design calculations indicate the geothermal walls constructed with SMS can withstand fire for at least two hours. A preliminary analysis shows that resistance may last five hours or more.

The system uses products such as wheat or rice straw, an agricultural by-product available in virtually unlimited supply. Rice straw, which is typically burned or buried in landfills, works with the concrete’s thermodynamics to make buildings easier to heat in cool weather and easier to cool in hot weather. SMS has an insulation rating of about R-50, or three times the level required for buildings in California.

A real breakthrough in simplifying the system, Black said, came with refinement of a technique to stabilize the bales with the spar assembly, thus eliminating the costly and more time-consuming use of wood bracing to erect the walls.

And his use of steel-wire reinforcement to create the lightweight concrete walls that are one-fourth to one-fifth the weight of standard mud or adobe of the same thickness makes the SMS building particularly resistant to the damage caused by the shaking of powerful earthquakes. The lighter weight, Black said, “is so significant, it’s incredible.” Because of a one-to-one relationship between weight and force levels, he added, halving a wall’s weight essentially doubles its ability to resist earthquake forces.

In answer to a plea for solutions to build safe, affordable housing for the thousands left homeless in Bam, Black hopes ultimately to gain the required clearances to build several prototype buildings there and exhibit his construction system’s merits.

“From the construction point of view, it needs very little technological know-how and can be constructed by anyone with a small amount of training and practice,” said Astaneh. “That is exactly what is needed for Iran. Black’s system is exactly what they have been doing for more than 3,000 years [there], but this has the most modern seismic-resistance concepts in it. What Iranians have now is a ‘mud coffin’ that buries them as soon as a moderate earthquake hits.”

The only high-tech aspect of the SMS, Black said, is the application of concrete with a strong pressure gun, which is in common usage in the United States. But it would be possible for the concrete to be hand-applied, much like swimming pools once were built in the United States, as long as the walls aren’t over two stories tall.

It takes about two weeks to build and complete the walls for a 3,600-square-foot, two-story SMS home, said Black, and the walls don’t require insulation, sheet rock, siding, stucco or trim — thus considerably reducing the time and cost. In the United States, the typical construction cost is about $80 per square foot, but Black said costs would be even lower in Iran, which lacks the extensive uniform building code requirements of the United States.