Abstract
Experts tell that the twentieth century was the century of brutal man-made natural and environmental disasters. Often, we hear reports about falling missiles, planes, explosions on environmentally hazardous industrial objects, about the collapse of buildings. The main reasons of these tragedies are design errors related to insufficient knowledge of the laws of mechanics with the incorrect use of mathematical models. To prevent new disasters, we just need to look into the past and draw conclusions on the basis of the occurred accidents.
Tacoma Washington Bridge Disaster (1940)
Suspension bridges have a number of advantages in comparison with the construction of bridges of other types. However, it has long been observed that suspension bridges are very unreliable during a strong wind. One of the largest disasters in the history of bridge construction was the collapse of the bridge over the river Tacoma on November, 7 in 1940. The construction of this bridge was completed in the summer of 1940. Its span – third longest in the world was 934 yards. Huge traffic was not expected so the bridge was designed very narrow - only 13 yards. The roadway could accommodate two rows of cars. The roadway was suspended by two steel cables with 77.3 yards sag.
Right after the construction was over, the bridge showed a large sensitivity to the action of wind − amplitude (magnitude) of the oscillations of the bridge reached 1.6 yards. There were made several attempts to resolve these large fluctuations by installing additional connectors and hydraulic dampers (shock absorbers) on the pylons. Unfortunately, this did not prevent the disaster. On November, 7 very strong vertical multinodal (in the form of several waves) flexural vibrations were observed. When the spin reached its maximum, the roadway was inclined to the horizon at an angle of 45°. The bridge was withstaanding these oscillations for about an hour, before the large part of the carriageway broke off and fell into the water. The whole process was filmed, so it became a valuable material for the study of the causes of the collapse. The disaster attracted researcher’s attention. Two weeks after this, famous engineer Theodore von Kármán gave an explanation of the causes of the disaster and even indicated the wind speed at which this might happen. The destruction occurred when the wind speed was about 18 − 19 m/s.
The catastrophe that took no human lives was a shock for the whole engineering community in its turn had a great impact on bridge building industry in United States. A new bridge with a very conservative design was built in 1950 (2006).
What conclusions can engineers make? Now, there is another bridge across the river Tacoma. Its width was increased in more than 1.5 times and is 19,7 yards. Also, the cross section of the roadway was changed. In addition, continuous beams were replaced with truss, which greatly reduces the force of wind pressure. Modern suspension bridges are lightweight constructions, suspended on steel ropes, which are called shrouds. They can withstand large winds and other loads and function normally for years. It is known that such catastrophe, which happened with the Tacoma bridge cannot repeat here. Othmar Ammann (1941) a bridge designer member of the Federal Works Agency Commission which was investigating the collapse of the Tacoma Narrows Bridge wrote the following:
The Tacoma Narrows bridge failure has given us invaluable informationIt has shown [that] every new structure [that] projects into new fields of magnitude involves new problems for the solution of which neither theory nor practical experience furnish an adequate guide. It is then that we must rely largely on judgment and if, as a result, errors, or failures occur, we must accept them as a price for human progress. (p.2)
Chernobyl disaster (1986)
The accident at the fourth unit of the Chernobyl nuclear power plant on April 26, 1986 is definitely regarded throughout the world as one of the most severe accident in the history of nuclear energy. It was accompanied by the release of radioactive substances into the environment, which led to adverse environmental impact, loss of human lives and serious economic damage and concerns of world community.On April 26, 1986 at 1:23 am there was an explosion of the reactor and the partial destruction of the reactor building, the roof of the turbine hall in the fourth block of the station. The fire in the reactor hall engulfed the entire space of the building. A lot of solids from the reactor core were thrown out through the gaps in the building. The air ignited the hot graphite and started a graphite fire (1990). The reactor explosion and the fire resulted in a complete failure of all its systems, including system control and protection. The reactor ceased to exist as a controlled system. The high temperature of the melt and its great weight caused the continuous evaporation and sublimation of radioactive substances from the surface. Thus, the destroyed reactor turned into a permanent source of evaporation of radioactive substances into the atmosphere. From 1986 to 2000, 350,400 people were evacuated and resettled from the most severely contaminated areas of Belarus, Russia, and Ukraine (2002).
The lessons learned from the accident at the Chernobyl NPP and other nuclear and non-nuclear facilities in the USSR and abroad consist primarily in the fact that inventions in the field of scientific and technological revolution, new sophisticated machinery and technologies require special attitude to the safety and reliability, do not forgive being careless and unskilled.The question of optimization of relations between man and machine is relevant to all modern technologies. The Chernobyl accident has exacerbated its understanding.The accident has caused the rise of social movements against nuclear power development in many countries. The Chernobyl reactor is now enclosed in a large concrete sarcophagus, which was built quickly to allow continuing operation of the other reactors at the plant (1988).
Shuttle Challenger(1986)
On January 28, 1986. The Famous Cape Canaveral. Shuttle Challenger makes his tenth start. And here is the 73rd second of the flight. Explosion. One of the accelerators tears off and gets struck in the fuel tank.The explosion of the Challenger became the first man-made disaster, which was broadcasted live. All seven crew members were killed in front of their relatives, friends and millions of television viewers. Shock. Someone even applauded – they probably thought that all is as it should be, like, just the accelerator got disconnected.Flight preparation has been widely publicized in America. For the first time, amateur astronaut got onboard of the shuttle. President Ronald Reagan initiated a nationwide competition for the right to fly into space. The Commission found that this disaster was not accidental. It was the result of NASA management culture and the specifics of the program of creation of the shuttles. This program was developed over 30 years ago, and the first space Shuttle (Columbia) made its maiden flight in April, 1981. Initially, it was thought that the shuttles will run almost on demand, and within a year they will make a lot of flights. In fact, it turned out that the launch of such a vehicle is an extremely complex event, and their maintenance requires a significant investment of time and money. The Commission concluded that NASA did not pay sufficient attention to the safety of shuttle flights and did not ensure their timely and proper maintenance (2011). Number of measures to ensure safety were adopted after the death of space shuttle Challenger. However, the funding of the Space Shuttle program was reduced in the 90-ies. The number of staff responsible for the execution of the program has also been lowered. The Commission drew attention to the fact that many of the shuttle’s devices have been designed to work for ten years, and operated for 22 years without repair. It failed in the goal of achieving reliable access to space, partly due to multi-year interruptions in launches following Shuttle failures (2008).
References
The Engineer (2006). Tacoma Bridge. Retrieved from
http://www.engineering.com/Library/ArticlesPage/tabid/85/ArticleID/171/Tacoma-Bridge.aspx
Othmar H. Ammann, Theodore von Kármán and Glenn B. Woodruff. (1941) The Failure of the Tacoma Narrows Bridge, a report to the administrator. Report to the Federal Works Agency, Washington
Medvedev, Zhores A. (1990). The Legacy of Chernobyl (Paperback. First American edition published in 1990 ed.). W. W. Norton & Company. ISBN 978-0-393-30814-3.
UNDP and UNICEF (2002). Table 2.2 Number of people affected by the Chernobyl accident (to December 2000) The Human Consequences of the Chernobyl Nuclear Accident.
David R. Marples (1988). The Social Impact of the Chernobyl Disaster, p. 166, ISBN 0-333-48198-4
Axelrod, Alan (2008). Profiles in Folly: History's Worst Decisions and Why They Went Wrong. Sterling Publishing Company. pp. 62–63. ISBN 978-1-4027-4768-7.
Outer Space Universe. "Remembering the Challenger Shuttle Explosion: A Disaster 25 Years Ago". Retrieved January 28, 2011.
