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Introduction

This unit is from our archive and it is an adapted extract from Systems thinking: principles and practice (T205) which is no longer in presentation. If you wish to study formally at the Open University, you may wish to explore the courses we offer in this curriculum area.

This unit has been written because it is al
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Acknowledgements

The content acknowledged below is Proprietary (see terms and conditions) and is used under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 Licence.

Course image: drpavloff in Flickr ma
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3.7 Aftermath

In the immediate aftermath of the disaster, it was vital to prevent any further collapses, especially on bridges of similar design. Two other bridges were built to a design similar to that of the Silver Bridge, one upstream at St Mary's, West Virginia and the other in Brazil at Florianopolis. The bridge upstream on the Ohio river, at St Mary's, was the focus of concern, and it was closed to traffic immediately after the disaster. The eye-bar design was actually quite widespread in other bridg
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3.6 Failure sequence

Following the discovery of the broken eye bar near the top of the northern suspension chain on the Ohio side of the bridge (Figure 36), it was possible to reconstruct the sequence of events during the collapse.

When the side chain separated, the entire structure was destabilised, simply b
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3.5 Design of the bridge

The design of the original structure was governed by applicable standards in 1926. The official inquiry found that the design and build fell within those limits, the most important being the allowable stress in the eye-bar chain of 345 MPa. The steel was to be made with a maximum elastic limit of 520 MPa, with a safety factor on the strength of the steel of 2.75. It was argued at the time that over 70 per cent of the load was from the self-weight of the structure. Other suspension bridges of
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3.4.6 Residual stress

One factor that can cause serious problems in any material is the presence of residual tensile stress. The problem often arises as a direct result of manufacturing, when hot material is shaped and then allowed to cool to ambient temperatures. For large castings like those needed to make the eye bars, such residual stress would be modified by the subsequent heat treatment to strengthen the steel, but had to be studied as part of the research effort into the catastrophic failure of the bridge.<
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3.4.4 Stress concentration at joint

Although it is known that a round hole in a flat sample will theoretically produce a stress concentration of about 3, the issue was decided experimentally. A tensile test at 25 °C was undertaken on an intact eye-bar-pin assembly from the bridge, being some 8 m long and from a lower part of the chain. It yielded at about 7 MN, and fractured in the shank at a stress of about 770 MPa. The yield stress in the shank was about 520 MPa, and the failed eye bar showed ductile behaviour with a reducti
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3.4.3 Simulated environmental tests

The investigators wanted to know about the fatigue properties of the component, to find a feasible explanation of why it took 39 years for the eye bar to break. They needed information on the several stress corrosion mechanisms that were possible in the material, including hydrogen embrittlement, the effects of sulphur compounds such as H2S (hydrogen sulphide) and the effects of moisture and salt. Notched eye-bar material was loaded to failure in various environments.

In fact
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3.3.2 Planning the investigation

A plan was needed to determine the chain of events leading up to and during the collapse. That sequence would necessarily depend on which parts had broken first, and a fault tree would enable a plan of action in isolating the cause (or causes) of the disaster. Such a systematic approach is known as fault-tree analysis or FTA, and is part of the armoury of methods used by accident investigators. With large-scale and devastating accidents, all possibilities, however remote, need evaluation in t
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2.4 Corrosion processes: galvanic corrosion

When two dissimilar metals are in contact, or in close proximity with a conducting fluid in between, an electrochemical cell can be formed that leads to the more reactive metal becoming an anode and the less reactive metal a cathode.

This kind of corrosion is known as galvanic corrosion. It is not uncommon, since metals are often coated with others of different E0, and different metals are often in close contact with a common electrolyte.

One of the earlie
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Introduction

Structural integrity is the study of the safe design and assessment of components and structures under load, and has become increasingly important in engineering design. It integrates aspects of stress analysis, materials behaviour and the mechanics of failure into the engineering design process.

This unit is an adapted extract from the Open University course Author(s): The Open University

Philosophy and the Human Situation
Philosophy and philosophical enquiries are relevant in some shape or form to many aspects of everyday life, for example our treatment of the environment, the rapidity of today's technological progress, whether animals should have rights and if so how they should compare to ours. Philosophy also encompasses questions about the existence of God, how life is sustained on earth, and even at what point should the Government intrude on a person's freedom. This album introduces the study of philosophy
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Writing family history
This album contains extracts from interviews with a wide range of people talking about family history. Some history is recalled in oral form, some in photographic and some in written form, as biographical or autobiographical evidence. Many aspects of this approach to writing are discussed in illuminating and perceptive depth, giving wide-ranging yet informative coverage of the topic. This material forms part of the course A173 Start writing family history.Author(s): The iTunes U team

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Social housing and working class heritage
Would you consider a dilapidated seventies tower block as heritage? In England, some social housing developments have already been given listed status, a level of protection usually associated with castles, monasteries and stately homes. Others are considered as a failed experiment by an outmoded welfare state, fit only for demolition. In this album, we see working class residents of one such estate fighting for its survival. By doing so, they may be challenging some of our fundamental assumptio
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Carnival and the performance of heritage
There's a lot more to Notting Hill Carnival than a great street party. This album gives you a true insider guide, by some of the people who have made the Carnival what it is today. Its story reaches back to the darkest recesses of European tradition, through Colonialism and slavery, to racist Britain of the 1950’s and 60’s. It merges contemporary ideas with art forms reaching back via the Caribbean slave plantations to tribal Africa. And its setting in West London brings out a history of th
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Museums in contemporary society
What are museums for? In this album we look behind the displays to reveal the conflicting roles, power struggles and ethical dilemmas that affect museums today. Once the undisputed sources of authority on the objects in their care, museums now have to justify their decisions to the government, to their audiences, sometimes even to vociferous pagans. The challenge is to reach out to new audiences and devise new ways of communicating with them. The rewards are many: to maintain status and respect,
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Changing approaches to heritage
If you could save one thing for posterity, what would it be? Your answer is likely to depend on the things you value. But the things that society values are changing all the time. The tracks on this album explore four different heritage stories. In the feature on the Lake District, we hear how the values of Wordsworth sometimes have to give way to the values of farmers. In two features on archaeology, we shine the spotlight on a discipline where there is increasing emphasis on the ordinary over
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Exploring the classical world
Exploring the classical world introduces texts by Homer, Horace, Juvenal and others, placing them in their social and political context and assessing their value as historical sources. Readings in the original Latin or Greek and in translation illustrate the metric structures used and the challenges of effectively recreating these works in modern English. The material is drawn from The Open University course A219 Exploring the classical worldAuthor(s): The iTunes U team

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Imperial Rome and Ostia
The splendidly evocative ruins of ancient Rome have long been a challenge to historians and archaeologists in reconstructing how it looked and functioned. It became the largest city in the western world during the imperial period, so how was the city constructed, and what were the materials used? How was it defended, supplied with food and water, and how were the people housed and entertained, and above all, how did it function? These video tracks use various famous sites such as the Baths of Ca
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Greek Theatre
What was it like to go to the theatre nearly 2500 years ago? Greek theatre has survived through the ages as a powerful and influential art form. This album introduces what early Greek theatres looked like and the kind of audience they attracted. Using the Theatre of Dionysus as a starting point, experts discuss the significance of attending the theatre as a civic occasion, associated with the political and cultural achievements of Athens. Through archaeology and analysis of contemporary art form
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