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After the collapse of a building in the Nigerian city of Lagos, killing at least 20 people, including several school children attending a school on the top floor of the building, we look at some of the reasons why such tragedies seem to be happening. produce so often in some African countries.
Although investigations are still ongoing on the causes of this collapse, engineers have reported some common problems.
1. Foundations are too weak
Proper foundations can be expensive.
They can cost up to half the price of a building, said Anthony Ede in 2016, a professor of civil engineering at Covenant University in Ota, Nigeria.
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He said that two things should be considered when building foundations – the solidity of the soil and the heaviness of the building and its contents.
In Lagos, marshy soil requires solid foundations. Much stronger than the mainland.
But he added that developers are saving money that should be spent on foundations when building on the city's wetlands and that many buildings collapsed as a result.
Even on
The inadequacy of the foundations of a four-storey building was one of three reasons given by investigators to explain the collapse of a building in northern Rwanda in 2013, causing six deaths.
2. Building materials are not strong enough
Materials that are simply not strong enough to hold the load are sometimes used, said Hermogene Nsengimana of the African Standards Organization in 2016, while his organization was meeting in Nairobi to discuss the why so many African buildings were collapsing.
He suggested that there was a market for counterfeit materials, even going so far as to say that sometimes scrap was used instead of steel.
When a six-story building in the capital of Uganda, Kampala, collapsed in April 2016, the city's director of civic agency hinted that it had been built with counterfeit materials, reported the Ugo news site.
Mr Nsengimana said that there were even cases of counterfeiters simulating authentication certificates.
But he suggested that contractors also knowingly use the wrong materials to reduce costs.
They can therefore use concrete to support the load of a one-storey building in a four-storey building.
Mr. Ede added that it was something that regulators did not control.
3. Workers make mistakes
Even when workers have the right materials to make the concrete, they can mix them incorrectly, said Ede.
This results in a concrete whose resistance is not sufficient to support the load.
He accused developers of cutting costs by employing unskilled workers who cost less than skilled builders.
This is one of the reasons put forward by civil engineers Henry Mwanaki Alinaitwe and Stephen Ekolu to explain the destruction of a building in Uganda in 2004.
Their research showed that the workers had misunderstood the mixing proportions of the concrete.
He suggested that people use wheelbarrows instead of gauges to measure cement.
The new BBJ five-storey hotel collapsed and 11 people died.
"You find bricklayers and even technicians who call themselves engineers," warned the president of the Nigerian Institution of Structural Engineers, Oreoluwa Fadayomi, on the Nigerian news site The Punch.
For those who want to save money on professionals, he advised: "Do not save money and spend money."
4. The load is heavier than expected
Mr. Ede said that a building would collapse when the load exceeded its resistance.
He gave the example of asking a baby to carry a heavy box: "The baby will not be able to hold back the tension."
Even if the foundations and materials are strong enough for their initial construction, that can change.
So, said Mr. Ede, if a building was designed to be
He added that another reason why the load was often heavier than the original design was the fact that extra floors were added.
In March 2016, an upscale apartment building with more floors than planned collapsed in Lagos, killing 34 people, the Guardian reported.
This happened two years after the collapse of a housing unit in a church for the famous TB preacher Joshua, also said the authorities because there were more floors than there were. he could not contain it. In this
5. The force is not tested
Building resistance should be tested at all points of construction, Ede said.
"You have to be strict," he said of keeping the buildings in order.
"The law says you have to test, it is the law that is problematic," he said.
This is a big problem, he said, when at every stage of construction, there is someone who is very motivated to save money or take it.
A building can collapse for many physical reasons, but only one motivation
And for
The story does not end there.
It is not because unhealthy buildings are built that everyone must die: they can be knocked down.
And that's what happens next.
But in these situations too, things go wrong, resulting in loss of life.
6. People stay in condemned buildings
In the case of the building that collapsed on Wednesday, the building had been convicted for non-security in 2017 and intended to be demolished.
Given this, a key question asked about the tragedy is: why was there a school in the building?
The Lagos State Building Control Agency (LSBCA) stated in a statement that it was marked
It was a four-story multipurpose building with a top-floor primary school.
The engineer Felicia Nnenna Agubata, one of the reasons why the locals did not listen to the order of the Government of Lagos, was invoked.
She told the BBC's Newsday program that building inspectors were not supported by security guards able to impose evacuations.
They can therefore ask nicely, but these requests are often ignored.
Two days after the collapse of the school, the LSBCA began the demolition process of about 100 buildings whose structural integrity tests have failed.
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