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Sustainability and Resiliency: Key Components in Rebuilding After the Mexico City Earthquake

Allison Preston • DATE: September 29, 2017

Categories:  engineering and Environmental Sustainability Research

While one building swayed, another fell into a crumbling heap. What makes some buildings resilient to earthquakes like the powerful 8.1 and 7.1 magnitude quakes that rocked Mexico City in September?

According to Kevin Walsh, director of the resiliency and sustainability of engineering systems minor, it relies on structural design and a little luck.

“Generally speaking, there are rules and numerical figures we are fitting our designs to,” says Walsh. But when it comes to earthquakes and other natural disasters, we’re actually just playing the odds.”

There are some tactics that can be implemented to put the odds in a building’s favor. Some of these changes were put into practice after a powerful 8.1 magnitude earthquake struck Mexico City in 1985. According to the National Oceanic and Atmospheric Administration (NOAA), roughly 10,000 people were killed and over 800 buildings were destroyed. The majority of these structures were tall buildings between six and fifteen stories.

However, the epicenter of that earthquake was located over 200 miles away, so why was the city so badly damaged?

The answer lies in Mexico City’s soil.

Mexico City was originally built on an island in a basin formed by volcanic activity. Eventually, the lake surrounding the island was drained in an effort to expand the city, but the soil below was soft.

“What happens with an earthquake that is far away and then has its vibrations pass

Walsh, Kevin
Kevin Walsh, director of the minor of resiliency and sustainability of engineering systems
through soft soil is that you filter out a lot of the quick back-and-forth motions and you tend to have the longer motions and heavy swaying. Then you hit resonance,” says Walsh.

At that point, smaller buildings still experience shaking but taller buildings experience heavy swaying, larger displacement, and higher force demands. Some may withstand the movement, but several tend to collapse, as seen in the aftermath of the 1985 quake.

During this time, most buildings in developed nations were designed to withstand heavy loads. Yet, this failed to allow the building to sway along with the moving ground. As part of the rebuilding efforts, design changes were implemented for ductility, allowing solid materials to stretch under stress.

“We started designing reinforced concrete columns which is a very popular form of construction in Mexico,” says Walsh.

To do this, steel is put inside the concrete to reinforce it. The soft soil also makes it necessary for structures to have deep foundations that serve as an anchor when earthquakes strike. If a building were to fall, the deep foundation would prevent the building from toppling over. Instead, it would collapse straight down.

As the city prepares to reconstruct, engineers, architects, and builders will be analyzing the structural integrity of buildings created after the 1985 earthquake. Specifically, they hope to understand if a focus on ductility led structures to be more resilient to earthquakes.

“It’s hard to compare one earthquake to another because there are different locations, magnitudes, and frequencies,” says Walsh. “But about 10,000 people were killed in 1985 and so far, roughly 300 have been killed. Putting the tragedy aside, you could see that as an improvement from the past 32 years.”

Resiliency is just one of the buzzwords being used in the discussion of rebuilding efforts. With that comes an interest in designing sustainable structures. 

The two are also the main components of the new Civil and Environmental Engineering and Earth Sciences (CEEES) minor being offered to students, Resiliency and Sustainability of Engineering Systems. As the director of the minor, Walsh is using case studies and risk assessments as part of the classroom discussion.

“A system cannot be sustainable no matter how well it was designed or how energy efficient it is if it gets knocked out by a hurricane next week,” says Walsh. “So the students have been learning about how resiliency needs to precede sustainability.”

The minor also provides an opportunity for crossover between the CEEES Department and the Keough School of Global Affairs. Walsh, along with Dr. Tracy Kijewski-Correa, have collaborated on a project students in the minor will complete.

“The students are actually going to be seeking out demographic data for areas recently hit by natural disasters, including Houston, Miami, and the U.S. Virgin Islands,” says Walsh.

The information will be used to help predict how resilient these communities are to natural disasters.

“As a student, when you get to do something that is actually going to be applied in the real world, your motivation goes through the roof.”

The minor consists of 16 credit hours that introduces students to themes such as global change, sustainable energy, environmental policies, and energy technology.

As the past month has shown, the key components of the minor are certainly timely, and the problems students are seeking to solve will have relevance well beyond their education at Notre Dame.