Why the latest Colombian quake destroyed so many buildings
Building standards of earthquake-prone Colombia helps explain why this week’s event caused such devastation, researchers have said. Find out which countries have quake safety by design
READING LEVEL: ORANGE
The massive search and rescue effort continues in Colombia after the powerful earthquake that struck near San José del Palmar in Chocó on Monday local time. Major damage was observed in multiple cities, including Cali, Manizales and Pereira.
While the earthquake in Colombia and recent quakes in nearby Venezuela have created widespread destruction, there have been other quake-prone regions in the world that have been better able to withstand the violent shaking of multiple seismic* disruptions.
Let’s take a look at the way safe building practices can help to prevent earthquake damage and why construction practices in Colombia meant the country’s buildings didn’t hold up well in this week’s powerful quake.
ANOTHER POWERFUL QUAKE
The United States Geological Survey said the magnitude 7.4 earthquake in Colombia occurred mainly due to strike-slip faulting at a depth of approximately 110 kilometres. In simple terms, a strike-slip earthquake occurs when two blocks of Earth’s crust* slide horizontally past one another, rather than moving up or down.
The destructive quake comes just a month or so after twin earthquakes in Venezuela, which are estimated to have destroyed or damaged more than 58,000 buildings while claiming the lives of thousands.
BUILDING PRACTICES IN COLOMBIA
In buildings, slabs, beams and columns all provide resistance to gravity loads. But reinforced concrete walls are needed to resist lateral* loads from wind and, in rare but extreme cases, earthquakes.
But in Colombia, many buildings have thin concrete walls, typically 7-10cm thick. They only have a single layer of steel reinforcement* – commonly electrowelded* wire mesh, which is very brittle and tears quickly.
The thinness of the walls also means that “confinement*” – a reinforcing technique where hooped steel is placed at the edges of a wall to help prevent concrete crushing – is almost impossible to place during construction. In fact, it isn’t even required in building standards.
TESTING COLOMBIAN BUILDINGS
Along with colleagues from three Colombian universities, University of Newcastle structural and earthquake engineering senior lecturer Dr Ryan Hoult ran full-scale tests at the Earthquake Engineering and Structural Dynamics Laboratory at the Federal School of Technology in Lausanne, Switzerland, on concrete walls built to match common Colombian construction practice.
The team wanted to find out how these walls performed when shaken the way an earthquake shakes a building.
The researchers found the results concerning even before Monday’s earthquake.
Dr Hoult wrote in The Conversation that when an earthquake shakes a building, the ideal situation is for many small cracks to form at the base of a steel-reinforced wall. This distributes the stress.
If a single, large crack forms because of the low amount of steel, the stress is concentrated. This concentration causes the reinforcing bars to break and the wall to fail.
But the walls on the buildings in Colombia are so thin that even if there is enough steel reinforcement, they are still likely to fail during an earthquake. The researchers’ experimental tests showed there’s just not enough strength for these walls to survive significant ground shaking.
Unfortunately, this design choice has proved a standard practice across the Latin American region.
A 2018 survey of nine buildings in Cali, one of the cities hit by Monday’s earthquake, found that 90 per cent had walls with a single layer of reinforcement, and 30 per cent had walls 100mm thick or thinner.
NOT JUST SOUTH AMERICAN BUILDINGS
In 2011, a magnitude 6.3 earthquake caused widespread damage to the city of Christchurch in New Zealand, taking the lives of 185 people.
Most reinforced concrete buildings designed after the 1980s performed well. Their survival was due to the design principles introduced at the time, which required engineers to carefully think about the placement of steel to allow the structures, including the walls, to deform* and resist earthquake actions.
However, some of the collapses were in buildings designed before these principles were introduced. One such example is the Pyne Gould* building. Its collapse was likely the result of a low amount of steel used in the thin concrete core* walls, where a single crack is thought to have formed, concentrating stress.
Until recently, this type of design practice – thin walls with typically a light amount of reinforcing steel – was also allowed under the Australian Standards for Concrete Structures.
After the Christchurch earthquake, this design practice became a concern for the structural and earthquake engineering community, and Australian standards were revised in 2018 to help prevent this type of structural failure in future designs.
However, there could still be lightly reinforced, thin concrete walls across many Australian buildings that were built before this revision. Testing on walls built to this same practice, including some conducted here in Australia, has shown they perform just as poorly as their Colombian counterparts under earthquake loading.
While strong earthquakes are rare in Australia, the country is not immune.
A 5.6 magnitude quake hit the NSW city of Newcastle in 1989, damaging 50,000 buildings.
QUAKE-PRONE REGIONS WITH BETTER BUILDING PRACTICES
Several cities and countries around the world have reformed building practices to ensure their buildings are better protected from earthquakes. These include:
- Christchurch, New Zealand – The devastating 2011 earthquake led to a series of reforms around the types of foundations that were allowed to be used nationally, as well as a shift to better earthquake resistant material such as structural steel.
- Chile – A series of earthquakes led to several reforms that strengthened building practices in the South American country. Chile has suffered through the most powerful earthquake in recorded history – the 9.5 magnitude Valdivia quake in 1960 – as well as the 8.8 Maule earthquake in 2010. While there was widespread destruction from the 2010 quake, most of the modern buildings constructed after building practices were improved in the 1980s remained intact.
- Japan – Renowned for its earthquakes, Japan has also become well-known for its ability to engineer modern structures that can withstand seismic shaking. Its Building Standard Act is regularly updated to ensure all buildings are constructed to withstand earthquakes.
The majority of this article was authored by University of Newcastle Structural and Earthquake Engineering Senior Lecturer Dr Ryan Hoult. The original version was published by The Conversation and the Kids News edited version is republished with permission.
POLL
GLOSSARY
- seismic: relating to an earthquake or movements of the earth
- crust: the outer layer of the earth
- lateral: sideways movement
- reinforcement: strengthening
- electrowelded: metal pieces joined together using the heat of an electrical current
- confinement: reinforcing concrete using steel ties or spirals to prevent the concrete from cracking
- deform: change shape or position
- Pyne Gould: a five storey, reinforced concrete building that collapsed during the 2011 Christchurch earthquake, claiming the lives of 18 people
- core: thick, reinforced concrete walls built in the centre of high rise buildings that are like the backbones of a tower, providing strength against earthquakes and strong winds
EXTRA READING
What is a double earthquake?
Why some buildings fall in quakes
Aussies shaken by three quakes
QUICK QUIZ
1. What was the size of the earthquake that hit Colombia?
2. Which nearby country also recently experienced a destructive earthquake?
3. What factors in the construction of walls in Colombia meant the buildings there were not earthquake-proof?
4. What are two countries that improved building standards to protect against the risk of destruction from quakes?
5. How strong was the most powerful earthquake in recorded history?
LISTEN TO THIS STORY
CLASSROOM ACTIVITIES
1. Why not?
What are some of the barriers that stop people from using building methods that are safer in earthquake zones? Write a list of as many barriers (or reasons why they don’t or can’t do this) as you can think of.
Time: Spend at least 20 minutes on this activity
Curriculum Links: English, Science, Personal and Social Capability
2. Extension
Do you know what makes parts of the earth’s crust move in different directions, and does this always cause earthquakes? Brainstorm as many ideas as you can to answer these questions. Then, use your research skills to check your ideas. Use the information that you now have to create an infographic or poster that will help other kids understand the most important information that you have learned.
Time: Spend at least 60 minutes on this activity
Curriculum Links: English, Science
VCOP ACTIVITY
BAB it!
Show you have read and understood the article by writing three sentences using the connectives “because’’, “and”, and “but” (BAB). Your sentences can share different facts or opinions, or the same ones but written about in different ways.