Can You Predict the Future? Of Course Not.
Only engineers can.
Engineers want to predict the future. It doesn’t matter if you are an electrical, civil, industrial, aeronautical, software or any of many other specialties. Your design task is to combine facts and knowledge to predict the future behavior of an object. There’s a saying that goes like this: “With enough money, infinite time, and perfect knowledge, an engineer can create anything.” And that includes predicting the future.
From predicting the behavior of a high-frequency signal in its passage through a transmission line to that of a bridge with hundreds of cars on it, the engineer who designs needs to predict the future to know if what’s to be built will work. Not only once but always. And not only for a short time but for a long time. And under many environmental conditions. And especially without anyone getting hurt, or dying.
It ain’t easy. The saying I mentioned earlier is a warning. There has never been or will be a situation without limits. The designer’s achievement is to create safe systems despite having limitations in money, time, and knowledge. As our growing civilization demands services — water, electricity, transportation, housing, food — it also increases the burden on engineers who want to predict the behavior of increasingly complex systems.
The past reveals the future. This is never truer, in any profession, than when we learn from our mistakes. It happens to us every day. But only if we recognize our responsibility and are open to learning. Edison couldn’t predict the material to use in an incandescent bulb until he tried 1,000 times in different ways. That past allowed his engineers to predict future bulbs.
The past reveals the future, also extends to the collective level. It’s an indispensable mental model for engineers and their organizations who have the lives of human beings in their hands. Today, nobody designs complex systems on their own, especially when other people’s lives are in danger. The current history of engineering in situations like this is of project managers, groups of engineers, committees, inspections, professional associations, and good practices. If you think about it, it’s not very different from medical and surgical procedures on which our lives depend when it comes to a novel remedy.
But, what happens when the vision of future use falls short ?.
Or, what happens when the power of decision and design is in the hands of a single person?
The Silver Bridge
“Now I know what it is to drown. I expected to die”, Bill Needham said from his bed at the Pleasant Valley Hospital. Trapped inside the cab of the truck he was driving, “I was out of breath when I noticed a small crack in the window and finally forced it down. I managed to grab a box and float”.
Bill, a 27-year-old truck driver from Kernersville, North Carolina, survived the tragedy of the Silver Bridge with a broken back. His driving partner didn’t have the fortune to escape. “He was in the bunk at the back of the cabin”, Needham continued. “I think he had tied himself up, for security. He had no chance. The cabin reached the bottom of the river”, Bill told reporter Sandra Grant of the Charleston Gazette newspaper in 1967.
2,235 feet (681 m) long and crossing 80 feet above the Ohio River, it was called the Silver Bridge because it was the first bridge in the United States painted aluminum. Built in 1928 by the American Bridge Company using a new high-strength steel in the eye-rod chains, it collapsed on December 15, 1967, at the busiest hour. 46 people died and two bodies were never recovered.
Many people, their cars loaded with Christmas shopping, heard the sound. “The sound of the collapse was like a shotgun.” Those who saw it said: “It seemed that the bridge fell like a deck of cards”. Horror captured the area and hundreds of lives changed forever.
Charlene Wood witnessed not only the tragedy but also a personal miracle. She had started the approach from West Virginia when the bridge began to collapse. She described it to the reporters.
“I felt a jolt on the bridge. I wasn’t crossing yet, so I threw my car in reverse. The tremor was so severe that my car died, but kept receding due to the inclination. As I watched in horror, the bridge fell right in front of my eyes. It was as if someone had lined up dominoes in a row, and had given them a push, and they all fell and there was a big splash of water. I could see the lights on the cars as they fell into the water. The car in front of me fell. Then there was silence “, she said.
The old saying “A chain is as strong as its weakest link” turned out to be a fact in the collapse of the Silver Bridge.
The bridge had been designed at the time of the Ford Model T car and for trucks no larger than nine tons. In 1967 the cars weighed four times a model T and the trucks authorized to cross had increased to 27 tons. Eye rod # 330 fractured due to a microscopic defect that time, corrosion, and excess weight widened. Engineers in 1928 relied too much on their eye bar’s steel strength predictions and didn’t incorporate enough redundancy to distribute the weight in case a bar failed. Nor did they have a correct view of the vehicle load over the years. The weight of the bridge, together with the weight of the dozens of cars and trucks that were almost stopped due to the slow traffic, caused excessive pressure. A bar broke. The steel frame of the bridge bent and fell along with all the vehicles above it to the depths of the Ohio River.
The collapse of the Silver Bridge frightened the entire nation. Many bridges of similar design closed. The Silver Bridge tragedy was the impetus for the National Bridge Inspection Standards in the United States. These guidelines, still in use today, require that all public bridges that contain a stretch of 20 feet or more be examined every two years. If it’s determined that they are a high-risk bridge, examinations should continue with a monthly frequency or less, until repaired.
Engineers are now more informed about corrosion fatigue which allows designing — that is, predicting — with increased certainty.
During the lifespan of the bridge, the only way to detect the fracture would have been to dismantle it. The technology used for the inspection at that time was not able to detect such cracks. An example of imperfect knowledge.
The engineering historian Henry Petroski considers it “a cautionary tale for engineers of all kinds. Precisely and indisputably the cause of the disaster was a design that inadvertently made inspection almost impossible and the failure almost inevitable. If a design was ever blamed for a flaw, this was it”.
The San Francisco Dam
“We were all asleep in our wooden house in the little canyon just above the powerhouse. I heard a roar like a cyclone. The water was so high that we could not get out through the front door. The house disintegrated. In the darkness I got entangled in an oak, I freed myself and swam to the surface. I was wrapped in electric cables and I held on to the only pole in the canyon. I grabbed the roof of another house, jumping as it floated towards the hillside. I was without clothes, but I climbed up the side of a mountain. There was no moon and it was overcast with a spooky fog — very cold”, Ray Rising said.
Ray, an employee of the BP & L company who ran hydroelectric power plant # 2, lost his wife and three children in the flood caused by the sudden breakdown of the San Francisco dam.
At 11:57 p.m. on March 12, 1928, the dam failed catastrophically, and the resulting flood claimed the lives of some 431 people. The collapse is considered one of the worst civil engineering disasters in the United States in the twentieth century and remains the second largest loss of life in the history of California, only after the San Francisco earthquake of 1906. The subsequent investigation painted the disaster with numbers: 12.4 billion gallons of water that enclosed between the walls of the canyon went up to 140 feet. Once out, it was a 2-mile-wide and six-foot-high tsunami that swept through three towns, carrying bodies and houses to the Pacific Ocean 54 miles away.
In the weeks prior to the disaster, as the water level in the dam increased, water leaks had been detected. Twelve hours before the disaster, Chief Engineer Mulholland and his assistant had inspected the dam when alerted of a leak. Like previous leaks, it was classified as “normal”, leaving instructions on how to divert the water until a future maintenance.
The story of the San Francisco Dam is also the story of William Mulholland.
http://www.scvhistory.com/scvhistory/lw2054.htm
Hired in 1878 as a zanjero — digging ditches to divert water from the Los Angeles River to the city of the same name — the Irish-American William Mulholland proved to be a brilliant employee who after his day job studied textbooks on mathematics, hydraulics, and geology, and taught himself engineering. Mulholland quickly rose to the ranks of the Water Company and was promoted to Superintendent in 1886, followed by Chief Engineer in 1911.
Mulholland achieved great recognition among members of the engineering community when he oversaw the design and construction of the Los Angeles Aqueduct, which at that time was the longest aqueduct in the world using gravity to carry the water 233 miles (375 km) ) from the Owens Valley to Los Angeles. The project finished in 1913 and is still in operation today. So much was his prestige at that time that he was considered as a candidate for mayor. When asked, however, he replied: “I’d rather give birth to a porcupine backward.” An example of an engineer more concerned about reality than appearances.
One of his associates described Mulholland thus:
“A man with a mind remarkable for its breadth and brilliant wit. A man who can build an aqueduct, and a man who can also, while grilling trout on a mountain fire, give a profound discourse on structural geology. A man whose life has been given to public service for the benefit of the people in the country of his adoption. Remarkable for his originality of thought and analysis, but equally active in the practical application of his ideas. Original in the minute details of the construction, but brave to conceive a limit and take on the responsibilities of the largest projects”.
It was during the construction process of the Los Angeles Aqueduct that Mulholland considered the San Francisquito Canyon as a potential dam site in a natural narrowing below a large reservoir area.
Mulholland used his free time to familiarize himself with the geological characteristics of the area. He ordered the excavation of exploratory tunnels and wells. He also performed water percolation tests. The results convinced him that the site would be satisfactory for a dam in case the need arose, although noting the dangerous nature of the shale rock formation on the eastern side of the canyon.
The population of Los Angeles was increasing. The pressure on Mulholland and his department to provide an adequate water service to the growing population led him to build seven small reservoirs. But the need for a larger reservoir was clear. It was considered in an area on the northeast portion of the San Fernando Valley, but the high value of ranches and private lands, in Mulholland’s opinion, made it economically difficult. Forgetting or ignoring his previous recognition of geological problems in the San Francisquito Canyon, he renewed his interest in the area he had explored twelve years earlier as it was of federal ownership and less expensive.
The construction of the San Francisco dam began in August 1924, its concrete design similar to one that the Office of Water Works and Supply had started a year earlier for the first time. Something remarkable that was discovered later was that the chief engineer in the construction of the dam reported an increase of 10 feet above the original design in the height of the dam. The decision, motivated by an increase in water holding capacity, was not reviewed by other engineers or Mullholland.
The jury in the forensic investigation that preceded the disaster determined that one of the causative factors was in what they called “an error in engineering judgment in determining the base at the site of the San Francisco dam and deciding the best type to build there” and that “the responsibility for the engineering judgment rests with the Office of Works and Water Supply and its Chief Engineer”, although without criminal culpability. They also recommended that “the construction and operation of a large dam should never be left to the exclusive judgment of a man, no matter how eminent”.
The California legislature created a dam safety program and eliminated the exemption that municipalities with engineering departments had to design and build dams without state oversight. In addition, the newly created Dam Safety Division was authorized to review all non-federal dams over 25 feet high or with reservoirs of 50 acre-feet of water or more.
Mulholland retired in March 1929 from his position, one year after the disaster. He worked for a while as a consultant, in a life of semi-isolation. He died in 1935, at the age of 79 years.
During the investigation, Mulholland said: “This investigation is very painful for me, but it’s because it’s a painful occasion. The only ones I envy are those who are dead”. In a later testimony, after answering a question, he added: “Either good or bad, don’t blame anyone else, just me. If there was an error in human judgment, I was the human. I don’t try to blame someone else”.
The impossibility of a perfect prediction
Herald-Dispatch.com
For thirty-nine years the Silver Bridge remained, allowing passage through the Ohio River. Nobody conceived that the structure could collapse and fall to the river bed. However, on that fateful afternoon of December 15, 1967, in a matter of seconds, it did so, killing and injuring many people.
Nobody blames the designers of the bridge, who were not aware of later knowledge in corrosion, metallurgy, and future vehicles. Neither was it considered a good practice to design taking maintenance into account. Studies of this disaster point to the future instead. “If there is something positive about the failure of the Silver Bridge, its legacy is to remind engineers to always proceed with the utmost caution, always aware of the possible existence of unknown unknowns and the potential consequences of small design decisions”.
The San Francisco Dam disaster continued to be studied over the years, refining the causes with advances in technology and experience. Prominent engineers and scientists added details that will serve as a lesson to future predictions. J. David Rogers, Ph.D. in geology, investigated the failure and published an extensive scenario. He attributed it to three main factors: the instability of the material on which the dam was built, the lack of compensation in the design for the additional height added when building the dam, and the design and construction supervised by a single person.
As a civil society, we often act as if there is a perfect prediction in engineering works. We don’t maintain it or it’s not enough. Amazed at what we can do with time, money, and knowledge of the past, we ironically impose limits on them. We forget that what was built was by necessity based on an imperfect prediction of the future.
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