29 novembro 2023

Article_After Morocco Quake, Earthen Buildings Come Under Scrutiny_Bloomberg

After Morocco Quake, Earthen Buildings Come Under Scrutiny

By María Paula Mijares Torres
'Recent disasters have raised questions about the seismic vulnerability of mud-brick and rammed earth construction. Can this traditional building style be made safer?

Mud-walled buildings lie in ruins in Ouirgane, Morocco, on Sept 11. Photographer: Nathan Laine/Bloomberg

The 6.8 magnitude earthquake that struck Morocco on Sept. 8 — the strongest in the country in 120 years — was centered in the High Atlas Mountains, one of the nation’s poorest regions. In remote villages, thousands of homes and buildings collapsed during the quake and its aftermath, with devastating results: More than 2,900 deaths have been confirmed, and 300,000 people have been made homeless.
Many of these buildings were made of unfired mud bricks and rammed earth, a traditional building technique that’s been used for millennia. Newer buildings crumbled alongside historic ones, some of which have stood for several hundreds of years. Among the structures that appear to have been damaged are the Kutubiyya Mosque and parts of the Jewish quarter in the Old City of Marrakech, as well as the Tinmel Mosque and the Aït Benhaddou fortified city — centuries-old complexes that are partially or entirely made with earthen materials.
This building style is common across Africa, as well as parts of Europe, Asia and the Americas: One in 10 of Unesco’s World Heritage sites employ the technique. But earthen buildings have a reputation for seismic vulnerability. In the 2003 quake that struck Bam, Iran — home of the 2,000-year old mud-brick Bam Citadel, as well as many other ancient buildings — up to 90% of the city’s urban fabric was destroyed or severely damaged.
The heavily damaged minaret of a mosque in Moulay Brahim, Morocco.Photo By Fernando Sanchez/Europa Press via Getty Images
But experts in the history of earthen buildings, like Huma Gupta, the Aga Khan professor in Islamic architecture at the Massachusetts Institute of Technology, say that in many ways this time-tested technique has been unfairly maligned. “I have been seeing a lot of reportage whenever there is an earthquake that affects a city or a town with a majority of earth architecture,” Gupta said. “There’s a sort of attribution of structural collapse to the material, but I want to make the distinction that it has very much to do with the fact that these earthen buildings have not been retrofitted for earthquakes.”
Indeed, modern concrete construction without proper seismic reinforcement can also fail during quakes, as seen in recent disasters in Turkey and Syria. And the sustainability benefits of earthen construction are considerable. “I just want to make sure that we don’t demonize earth architecture as being inherently bad in the face of natural disasters like earthquakes,” Gupta said.
Experts have pointed to other factors in widespread building failures, including inadequate maintenance and modern repairs made with incompatible materials and techniques. Mehrdad Sasani, professor of structural engineering at Northeastern University and expert in building collapse and building resilience, points to the general poverty of the High Atlas region. “The most important reason for that area being so drastically affected by the earthquake is the lack of socioeconomic resources,” he said. “If you don’t have those resources, you think first about what to eat, having a roof over your head and how to provide. There is no time to think about whether my building is earthquake resistant.”
Crumbled buildings line a road in Tinmel, Morocco.Photographer: Matias Chiofalo/Getty ImagesEurope

Many buildings in this region are the product of informal construction, built without codes or standards and erratically maintained or inspected, Sasani said. Non-reinforced dwellings are also known for being particularly deadly after a collapse, because they crumble into a dense pile of rubble without leaving air pockets, as concrete-and-steel structures typically do. “When this kind of building breaks, it becomes practically soil,” said Sasani. “It would be hard to survive in a building like that — it’s like a ton of soil had fallen on top of you and it pretty much uses up all the spaces to breathe.”
Seismic reinforcement can dramatically improve the performance of existing earthen buildings. At the Getty Conservation Institute, the Earthen Architecture Initiative has studied how to retrofit historic churches and other earthen buildings in Peru, working with the Peruvian Ministry of Culture and two local universities. “The methods that we’re testing range everything from walls that are covered with a geomesh, to timber reinforcements, to certain roof structures, all different kinds of methods to improve the performance of earth buildings,” said Benjamin Marcus, project specialist at the buildings and sites department at the Getty Conservation Institute.

Built of rammed earth and mud bricks, the Kasbah of Taourirt is among the best-preserved examples of Berber architecture. Photo: Scott S. Warren/Getty Conservation Institute

A key goal of seismic reinforcement is to strengthen the walls of a building to create a stable “box structure,” so that walls don’t separate from each other, leading to floor and roof collapse. That’s what brings down many unreinforced buildings — regardless of the material they’re built in.
Marcus and his team are familiar with Moroccan building styles: The Getty group recently undertook a conservation and rehabilitation plan for the Kasbah of Taourirt in the city of Ouarzazate.
Earthen buildings can also be engineered to be seismically resilient during the construction phase. At the University of California at Berkeley, architecture professor Ronald Rael has been experimenting with ways to use 3D printing to create earthen buildings embedded with fibers that make the structure more stable.
“It’s really a lot like reinforcement steel and concrete,” Rael said. “You see those metal cages that are inside the concrete, so imagine a fabric cage inside of earth.”
Like Gupta, Rael cautions against villainizing earthen architecture, an environmentally friendly technique that has been the focus of much interest in the green building industry. He cites the work of Burkina Faso architect Diébédo Francis Kéré, which relies heavily on the idea of using local materials like unfired clay rather than more energy-intensive steel and concrete. “If one of the most recent winners of what is basically the Nobel Prize of Architecture, the Pritzker Architecture Prize, can make buildings out of mud, why are we still seeing it as a bad thing?” he said. '


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