How earthquake engineering saves buildings and lives

Amid the rubble of broken door frames, window shards, and concrete columns in Gaziantep, a Turkish city known for its Byzantine fortresses and fortresses, social media users posted images of one building in particular that had been standing still for the past month. The surviving structure that made the social media rounds is a sturdy office that, despite two consecutive earthquakes measuring 7.8 and 7.7 on the Richter scale, doesn’t seem to have shattered even glass.

The building was designed by the Union of Chambers of Turkish Engineers and Architects, which years ago warned the national government and local officials that earthquakes do not kill people, but poorly constructed buildings do. It turned out later that their warnings were prescient. The February 6 earthquake and its aftershocks caused the collapse or severe damage to more than 160,000 buildings in Turkey and Syria. And many of those buildings were apartments, where a large part of the population lived, resulting in the deaths of more than 40,000 people.

The destruction of some buildings but not others drew attention to the importance of earthquake-safe architecture and building codes in both countries. Popular Science spoke with structural engineers who study how buildings can withstand earthquakes to understand what makes certain designs more life-saving.

How to engineer buildings for earthquakes

The most important factor when building a building that can withstand an earthquake, says Mehrdad Sasani, a professor of engineering at Northeastern University in Massachusetts, is to make it strong and deformable, meaning it is durable but can also bend and swing with the ground without collapsing. , which investigates earthquake resistance models of buildings.

At the granular level, this means that buildings built of concrete, stone, brick, and similar materials need reinforcing iron bars to make them strong. To make buildings deformable, engineers need to carefully design and build the beams and columns of the building, and place the steel bars in a certain way. This strategy is called seismic detailing, and it focuses on areas where the building may experience greater impact from severe tremors. The metal bars have multiple joints to help stabilize the poles, but also allow them to wobble and absorb stress. When the building is finished, the metal bars are hidden inside the columns and beams, usually behind the apartment walls.

[Related: A humble seismograph beneath the Great Smoky Mountains could be one of the best in the world]

Before engineers build columns and add anchors, they must consider a number of factors, including the ground beneath the building itself. They design buildings based on how intense the ground is shaking, rather than a specific strength or earthquake number on the Richter scale. “The harder the ground shakes, the greater the damage. This is not directly related to the size, but the size definitely affects it,” says Sassani.

“The point is, when the ground starts to shake, the buildings start to move. And if that movement is too much for the buildings to handle, they can collapse. And that shaking is what we’re designed for.”

When building codes save lives

Engineering is only half the challenge in making housing safer during earthquakes. It is possible that the main reason why the Gaziantep earthquake was so deadly is that some developers did not follow Turkish building codes, which Sasani says is sufficient. Completed in 2019, three apartment buildings, reviewed by the BBC, presumably amount to Turkish symbols, were still collapsed during the disaster. As many as 75,000 buildings in southern Turkey have been granted construction amnesties, where property owners can pay fees to absolve them of construction violations, according to Pelin Pinar Geritlioglu, head of the Federation of Chambers of Turkish Engineers in Istanbul.

We cannot design buildings to be earthquake resistant. We make it earthquake resistant. “Even if you follow the standards and rules, there is always a possibility of failure and collapse, but that possibility is small,” says Sasani. If buildings are designed based on code, will some of them collapse? Yes. is this too much [buildings] Collapsed in Türkiye and Syria? The answer is no. “

An engineer from Istanbul Municipality inspects a pillar of an apartment on March 10, 2023 in Istanbul, Turkey. Since the 7.8-magnitude earthquake on February 6, the municipality has received more than 140,000 applications from residents wishing to test the structural integrity of their buildings. OZAN ​​KOSE/AFP via Getty Images

Syria first included earthquake safety measures in its building codes in 1995, and updated them again in 2013. But the country is in the midst of a 12-year civil war, and bombing by the Assad regime has likely made buildings more vulnerable to collapse. during the war period. The earthquake, says Bilal Hamad, professor of engineering at the American University of Beirut and former mayor of Beirut. By way of comparison, some of his students studied how the port of Beirut exploded in 2020, when large quantities of ammonium nitrate that had been suspended for several years in the port suddenly burned, compared to the strength of the earthquake.

“The bombing triggered an explosion on a building,” Hamad says. “They found similarities, because [chemical] The explosion is almost like an earthquake. It is even worse, because the explosion of earthquake energy is located underground. Get wet with soil. But the [chemical] The explosion is above ground level, and there is nothing to dampen it.”

A way forward for countries that lack resources

When planning for earthquakes, engineers consider two types of buildings: old and new buildings. The way an “old” building is defined is if it was built before engineers applied seismology to the most common rules of construction. In the United States, Sassani says, most of the codes, which are determined locally, have been updated with recent research on seismic forces and construction techniques in the 1970s. Anything built before that time is considered an ancient building.

The majority of countries use US building codes, Sassani says, but it takes a while for the rules to travel across land and sea, which means the date they actually adopted the code may be way back in the 1970s. For example, Hamad says Lebanon did not require any earthquake safety in the building until 2005. It took another seven years, until 2012, for the government to require builders to hire technical offices to ensure buildings were constructed according to codes. In the aftermath of the earthquake, the Turkish president claimed that 98 percent of the collapsed buildings were built before 1999, though experts have questioned the statistic, saying it was used to deflect blame from the construction amnesty policy.

Thus, old structures are likely to need rehabilitation, especially if they include masonry and are built of brick, stone or other similar material, according to Sassani. He says that bricks and the like are connected to mortar, which makes them more vulnerable to earthquakes. Masonry structures are more common in the Global South, where buildings are older, while the United States has more structures built of wood and is less susceptible to earthquake damage.

These old buildings can be rehabilitated through mechanisms such as adding the so-called shear wall in engineering to make the building more solid. But rehabilitation is expensive. Sometimes it is cheaper to demolish a building and start a new one. “If you don’t have the resources, you think about your most important priorities,” says Sasani. “If you haven’t had an earthquake in many decades, don’t think of it as a priority.” (The last time Turkey and Syria suffered heavy losses from an earthquake was in the 1990s.)

So what should countries that lack resources do? Sassani says building inspections aren’t very expensive — they can get started. “The least developed countries can do is have codes and standards that are implemented,” he says. “This would reduce the possibility of such events occurring in the future.”

[Related: Disaster prep can save lives, but isn’t as accessible to those most at risk]

As Karim Najjar, a professor of architecture at the American University of Beirut who researches climate-responsive design strategies, explains, it doesn’t cost much to make future buildings earthquake-safe either. He says adding additional beams and columns to strengthen a building’s infrastructure is usually only a small part of the overall design. “These measures make for 5 to 10 percent of the costs of structures,” Najjar wrote in an email to PopSci. “Cement in concrete is often reduced to maximize profits,” which can make the building less robust and, therefore, less resistant to earthquakes.

Instead, Hamad estimates the cost of the building structure to be around 20 percent of the total project. If the building is designed to withstand earthquakes, that 20 percent goes up by only 3 to 5 percent. “There will be sheer walls, more reinforcement, beams, columns and foundations,” he says. “Why not? Safety comes before changing the bathroom.”

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