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Topic outline

 

  • Time: 20 hours
    Level: Advanced

 
 

Introduction

  • Introduction Resource
  • 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...
 

1 Engineering for purpose

  • 1.1 Safe design Resource
  • This unit is about the concepts and theories that underpin the field of engineering known as Structural integrity – that is, the safe design and assessment of load-bearing structures in their entirety,...
  • 1.2 Component failure Resource
  • We have all experienced component failures in one form or another. In many cases this is because something has reached the end of its working life due to a slow-acting failure mechanism: car tyres wear...
  • 1.3 Environmental factors Resource
  • I indicated earlier that many failures occur after a product has been in service for some time: such as the wear of a car tyre, or corrosion of the car body itself. It is also possible for components to...
 

2 Environmental deterioration

  • 2.1 Introduction Resource
  • Structures are not always doomed to fail, but they do usually have a limited useful life. Exceptions include many of the monuments that have survived from the ancient world, such as the Great Pyramid in...
  • 2.2 Degradation, dissolution and corrosion Resource
  • A variety of common terms are used to describe the ways in which structural materials can be attacked by environments and although they do have specific connotations, they are frequently used as blanket...
  • 2.3 Corrosion processes Resource
  • For many materials, degradation processes are simply one or a series of chemical reactions that act to erode or deteriorate the material. The deterioration of metals is a little more complex than that...
  • 2.4 Corrosion processes: galvanic corrosion Resource
  • 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...
  • 2.5 Corrosion processes: galvanic series Resource
  • A similar concept to the electrochemical series that has been used by engineers for many years is the galvanic series (one example of which is shown in Table 2: here the list should be read down the columns...
  • 2.6 Corrosion in stressed products – stress corrosion cracking (SCC) Resource
  • If a stress exists in a product exposed to a corrosive environment, the rate of corrosion can then increase and be extremely localised, such as at the tip of a growing crack. Furthermore, some specific...
 

3 Case study: The Silver Bridge

  • 3.1 Background information Resource
  • Stress corrosion cracking can produce devastating damage in large structures, as the examples of swimming-pool ceilings and roofs in Section 2 showed. But even larger structures can also be attacked, as...
  • 3.2 The disaster Resource
  • The 39-year-old Silver Bridge collapsed suddenly at about 5 p.m. on 15 December 1967 when the roadway was filled with rush-hour traffic – 37 vehicles were trapped on the roadway.
  • 3.3 The investigation Resource
  • The investigation took three years to complete, although critical evidence emerged within weeks of the accident.
  • 3.4 Analysis of eye bar 330 Resource
  • One particular broken part was recognised quickly as part of an eye bar. There were 146 eye bars in the original bridge, and they were safety-critical because if broken the main chains could be threatened....
  • 3.5 Design of the bridge Resource
  • 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...
  • 3.6 Failure sequence Resource
  • 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...
  • 3.7 Aftermath Resource
  • 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...
 

References and Acknowledgements

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