Structural Engineers at Stanford: Enough of Flat Slab Construction
This is after they discovered that many of the building collapses in the recent Mexico City earthquake use such construction method.
Other than scientific principles, engineers do their jobs according to codes and regulations. With discoveries in engineering and development in various technologies, these codes and regulations evolve through time, changing how systems and techniques are performed.
Like civil engineers who use construction methods. Some of these methods are already obsolete because they are proven to be a cause of disasters. And it is disheartening that it has to involve the death of hundreds to get the point across that there should be construction styles already left in the 1980s. A team of structural engineers at Stanford University calls for the ban of a building technique called flat slab wherein floors are supported only by concrete columns. This is after the team discovered that this was the style used in 61% of the building collapses in September’s magnitude 7.1 quake in Mexico City. The disaster killed 369 people and left many others wounded and homeless.
Mexico City after the September 2017 quake. Photo by AP via Wired
Eduardo Miranda, a professor of civil and environmental engineering at Stanford and global expert on earthquake-resistant design, is disappointed on the matter. He said that this type of construction could have been forbidden or building codes could have been toughened after the 1985 8.1 earthquake which hit Mexico’s capital.
The 8.1-magnitude earthquake in Mexico City in 1985 which had thousands of casualties.Photo via Wikimedia
“We have known for 30 years that this system killed lots of people, so why are we still using it?” asked Miranda. “The right decision after ‘85 would have been to completely ban this kind of construction. We could have saved lives,” he added.
Efforts to strengthen Mexico’s City seismic codes after the 1985 earthquake by academics, building officials, and engineers were in place. But the ban on flat slab construction was opposed by many architects and builders. “There were lots of builders and owners who were not going to be happy that you just stopped their construction,” said Miranda, who later served on Mexico’s code committee in the 1990s. “These things start as technical conversations but then you run into policy and politics.” Until the parties got into a resolve. Flat slab construction was allowed, granting that the building design should be seismically stronger than structures with beams or concrete walls. Miranda said that authorities did pay enough attention to evaluating if existing flat slab structures needed a seismic retrofit. But the new codes provided an opportunity for developers to hire private engineers and let them submit structural plans to authorities. And in this process, unfortunately, there is a bigger room for corruption. “Corruption can come in many forms, from the moment someone accepts a bribe to when someone falsifies documents, or fails to present the right structural plans to borough authorities,” said Renato Berron, head of the Institute for the Security of Constructions of Mexico City, a city agency. This resulted to buildings with poor seismic provisions, consequently the tragic collapses last month.
Photo via Independent UK
Roberto Meli, a renowned structural engineer who served on the code committee in 1985, weighed in. “It would have been better to have insisted very much about not using flat slab,” he said.
He added that he and the committee will seek to strengthen retrofitting standards first, and by early next year may reexamine flat slab, although he is not convinced prohibiting the method outright would have worked. The flat slab construction method is now forbidden in seismic hotspots in the United States, Chile, and New Zealand. Hopefully, Mexico will soon follow with a conviction.