Book Review — Why Buildings Fall Down by Matthys Levy & Mario Salvadori
This morning, I finished Why Buildings Fall Down: How Structures Fail by Matthys Levy and Mario Salvadori. Levy is a Swiss master structural designer and a professor of Civil Engineering at Columbia University. He was named a Structural Engineering Legend in Design by Structural Engineering Magazine in 2003. Salvadori, his co-author, was an American structural engineer and professor of both civil engineering and architecture at Columbia University. The book was written in 1987.
Salvadori decided to embark on this project after writing his well-received book, Why Buildings Stand Up. He had given a copy of the book to his mother-in-law, who, upon receiving it on her ninety-second birthday, said matter-of-factly: “This is nice, but I would be much more interested in reading why they fall down.” My kind of person!
Using easy-to-understand language but still far below what a non-Engineering-inclined mind would find attractive, the authors examined buildings of all kinds, from ancient domes like Istanbul’s Hagia Sophia to the state-of-the-art Hartford Civic Arena. They dissected why they failed to continue to stand.
I liked their description of what comprises a building in the opening pages. A building is conceived when designed, born when built, alive while standing, dead from old age or an unexpected accident. It breathes through the mouth of its windows and the lungs of its air-conditioning system. It circulates fluids through the veins and arteries of its pipes and sends messages to all parts of its body through the nervous system of its electric wires. A building reacts to changes in its outer or inner conditions through its brain of feedback systems, is protected by the skin of its facade, supported by the skeleton of its columns, beams, and slabs, and rests on the feet of its foundations. Like most human bodies, most buildings have full lives and then die.
In other words, just like humans, buildings are designed to die. Their duration of existence depends on different factors, some of which may not be the designers’ fault. But any accidental death of a building is always due to the failure of its skeleton, the structure.
For instance, why did the pyramid at Meidum in Egypt shed 250,000 tons of limestone outer casings when the other pyramids did not? Why is the shape of the pyramids like that? These and many other questions are answered in the first chapter.
#WILT Do you know that the pyramids were filled with the most precious possessions in the belief that the dead had to be surrounded by all the conveniences of life to be happy? Even when the pyramids were enclosed with ingenious stone doors to prevent thievery, thieves, smarter than the police, still looted the treasures in droves throughout the thirty Egyptian dynasties.
Some other bits of knowledge jump at you as you read the book. Those who watch movies about Egyptian Mummies would remember the name, Imhotep. This name belongs to the greatest mathematician and engineer in Egyptian history. His design of the Great Pyramid at Gizeh in the Fourth Dynasty was imitated in all technical details in all later pyramids. He was so good that he was made a god and venerated by the Egyptians for three thousand years.
A book about structural failures can be expected to be filled with the analysis of assorted structural failures. The dome collapse at the C.W. Post College of Long Island University is an intriguing illustration of how a dome could still fall while meeting and exceeding code standards due to a failure to account for natural factors. The assumption behind the design was that snow would fall uniformly, just as we often have with rain. In the same building, rain falling on one part of the building is expected to be uniform with the other parts. But that was not what happened with this building. During the storm that collapsed the roof, an east wind blew snow in huge drifts on one side of the dome, stressing it beyond design limits. That, coupled with the natural lifting effect caused by wind passing over the top of a dome, caused the structural members to fail. So even though the total snow load was one-quarter the maximum, it was concentrated on less than one-third of the dome’s structure, bringing it down.
The building of domes is an impressive work of engineering. I learnt of Dante Bini, who is undoubtedly the builder of the largest number of domes in history, more than fifteen hundred in twenty-three countries, from Italy to Australia and from Japan to Israel. Curiously, none were built in the United States for specific reasons. Want to know? Read the book.
Domes are stable and permanent due to their continuous, curving shape. Unlike arches, which need substantial buttresses, the dome distributes the load among all its elements. They can withstand heavy weights thanks to their extraordinary strength. Do you want to know how strong a dome is? Try to squash an egg by pressing its ends towards the middle. It’s incredibly difficult. Eggs are really just two domes glued together. The ratio of an eggshell’s span to thickness is about 30. That of a conservatively designed dome is usually at least 300, or about ten times stronger. However, the rigidity of domes makes them vulnerable to quakes and soil subsidence. More domes would have been built except that Christian liturgical requirements, including the need to have the shape of the cross on buildings, posed great difficulties for medieval builders who wished to incorporate the dome into religious structures.
An engineering mind would enjoy the chapter on dynamic dampers in large buildings. All tall buildings oscillate because of the pressure of the wind. While not always dangerous for the structure, although it can be, this movement can make the occupants of the building queasy. On top of the structure is a sizable tuned concrete block placed there to match the frequency of the building’s oscillations. Huge steel springs and shock absorbers hold it to the exterior walls. Due to its high inertia, the damper tends to remain in place when the building oscillates, allowing the structure to slide beneath it on the oil layer. The building is pulled back into shape by the longer springs on one side of the damper. The springs on the opposing side force it back to its starting position.
The context the authors gave for many of the engineering decisions helped. There is the revelation that a stadium rooftop was re-designed partly because flaws in the city sewer system prevented the efficient disposition of significant rainfall. The fact that the rainfall could not be evacuated on time led to the collapse of the structure, which would have killed up to 14,000 people had the collapse happened at night. Only hours before, tens of thousands of people were gathered under that roof. That narration was indeed good. If more of the book was like that some of those who abandoned the book with me as I read would have tarried a while longer.
For some structures, the question is not really why they fail; the right question is why they survived for as long as they did. There was a structure, by post-collapse analysis, that should have failed 6 years earlier. It stood partly because of a term known as progressive collapse. Progressive collapse can start as the result of even a minor deficiency unless redundancy is introduced as a matter of structural insurance.
Redundancy is a quality that we should hope is embedded in all of the structures we find ourselves stepping in. Redundancy ensures that even when a part of the building cannot bear the load imposed on the structure, the other parts of the building can receive the load from that part and distribute it among one another. In more technical terms, redundancy implies that a structure can carry loads by more than one mechanism- that the forces on it can follow alternate paths to the ground. It guarantees that loads can still be carried by other mechanisms if one mechanism fails. Many structures have collapsed because the design and development did not build into them enough redundancy. There was the case of a structure where the introduction of less than 50 reinforcement bars (what you call iron) would have prevented the fall of a multi-million-dollar structure.
Sometimes, the reader learns that even though ancient structures may have stood for thousands of years, scientific calculations can make us build more efficient ones. For instance, earthen dams built by the Romans centuries ago survived thousands of years because, according to them, their bases were three to four times the width of the dam’s height. However, engineering calculations by a Scottish engineer in the 19th century showed that the base width need be no more than the height. The beauty of modern technology.
As a public affairs analyst of the Nigerian space, several times, I shook my head reading the investigation results. There were cases where building collapse led to the reevaluation of building regulations worldwide in terms of both safety and unusual loads. How many times have buildings collapsed in Nigeria, experts were called to make recommendations, and the recommendations set aside only for the same kind of failure to occur again, sometimes within the same region of the previous ones?
There was the case wherein a startling afterword to a disaster revealed evidence of incredibly shoddy workmanship as the tower was demolished. Upon this revelation, hundreds of similarly built apartment towers were deemed unsafe and demolished. There were no ifs and buts.
As someone who studied engineering and still practices, the book was definitely worthwhile. It would be if you’re interested in learning how a small and subtle design flaw or change can cause a building to fail. Consider the walkway collapse caused by the builders changing the configuration of a certain nut/washer such that it had to carry twice the design weight. The walkway collapsed, and several people died. It causes you to appreciate effective government regulation. The book is structured so that the authors give each chapter a subject and bring examples to make their points.
Because the book was written in 1987, you will not see any analysis of the building collapses that have captured our imagination in recent times, such as the Twin Towers in the USA, the Sampoong Department Store in South Korea and the three High-Rise Office Buildings in Brazil. I would have loved to see the analysis of the failure of Lotus Riverside Compound in China. This case was fascinating because one of eleven 13-story apartment buildings in Shanghai toppled over, completely intact, as if a huge tree was uprooted by a giant. I would love to see the revised version of this book someday covering more recent cases. But I wonder how that would happen with one of the authors dead.
I learnt this is a required book in some schools for construction degrees. I would recommend it to be read by every structural engineer in Nigeria.
