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6.3 Tacoma Narrows suspension bridge failure

Such over-design could not be sustained for long and bridge designers gradually pared back their margins of safety. There is elegance and economy in having the lightest structure compatible with function. But history has a habit of repeating itself.

In 1940 a new suspension bridge with a central span of 2800 feet was built over the Tacoma Narrows in the United States. It was soon noticed the bridge deck was prone to oscillate in certain winds. The vertical amplitude of the oscillations
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Myths persist

Many myths still surround the Tay Bridge disaster, the most pervasive being it was brought down by wind action alone. Rothery's report (see Paper 3) should dispel that particular myth, in addition to the numerous examples shown in this unit of the way the structure had deteriorated by the time of the storm in late 1879.

Click 'View document' below to open Paper 3 (35 pages, 39 MB).

5.13 Conclusion of the BoT enquiry

The BoT enquiry issued two reports at the end of the enquiry, one authored by the chair, Mr Rothery, the other by the two other assessors. The Rothery report is Paper 3, linked below. They agreed about most of the issues in contention, as follows (Paper 3, page 47 of report).

  1. There is no evidence to show that there has been any movement or settlement in the foundations of the pier
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5.9 Mechanical tests by David Kirkaldy

In order to determine which of the several parts of the joint were weakest, and gain some idea of the scatter in strength, David Kirkaldy was employed by Henry Law to test various samples he had collected from the bases of the fallen piers. David Kirkaldy had a good reputation for accurate and rigorous mechanical testing of materials using a large tensometer he had designed and built in London (see Input 9, linked below).

Click 'View document' below to open Input 9


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Bridge oscillations

Testimony was taken from the many workers employed during construction and painting of the structure just after completion. Their evidence was more compelling, especially from painters working at the top of the high girders piers during passage of trains, as well as during windy weather. They were painting the cast iron of the piers during the summer of 1879. In the main, they reported feeling strong sideways as well as vertical motion:

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4.8 Photographs showing the detail: standing pier 28

The final part of the survey deals with the two standing piers connected to the lower girders left after the high girders section fell during the disaster. The whole of pier 28 is shown in Figure 34, and two close-ups of the columns are shown in Figures Author(s): The Open University

Bridge girders

Figures 11 and 12, below, are photographs of the bridge taken from the south and north banks of the firth.

The girders of the bridge were supported on a total of 85 piers. The first 14 piers were made from brick and masonry, built up as a solid structure. The rest were fabricated from iron on masonry platforms, and by comparison, appeared rather insubstantial (Author(s): The Open University

3.3 Description of the bridge

An outline plan of the bridge shows the main piers on which the bridge was laid (Figure 10). To allow shipping to pass up the Tay to Perth, a height of about 88 feet was required between the bridge girders and the high water mark in the middle of the firth. On the south bank, at Wormit, the land rose steeply t
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2.2 Transportation disasters

Movement of people and goods was one of the main outcomes of the industrial revolution in Britain in the late-eighteenth century, starting with canals, which were displaced gradually by railways. Industrialisation came through innovation in manufacture, especially the development of mass-produced materials such as cast-iron. While the material had been known and used since the Elizabethan period, it could only be made in small quantities by smelting iron ore with charcoal.

The Darby fam
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1.2 Earthquakes and volcanoes

The disasters that first come to mind are those where the earth itself changes in an unpredictable and sudden way:

  • earthquakes

  • volcanic eruptions

  • tidal waves

These natural phenomena are now known to be interconnected: earthquakes result from vast plates of the earth's crust meeting and moving against one another. Volcanic explosions, such as Krakatoa (1883) and Mount St Helens (1980) are also manifestations
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10 Part 2: 6 Review

In Part 2 of this unit, you have undertaken a major piece of work. In encountering the case study you were engaging with a set of events, issues, actors, stakeholders and intentions that was, by any standards, complex. In addition, you brought your own complexity to it, your own stakeholdings and understandings, your own reactions and feelings.

You used systems diagrams to structure the complexity you encountered in the case study. That then structured and clarified the situation in way
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2.5 Review

The title of this unit could have been Juggling with complexity: searching for system. This title seemed to capture something essential about the unit. Juggling is a rich metaphor and will be used explicitly in Part 3. But it also carries the idea of a skill that needs to be practised and that might seem incredibly awkward to begin with. You may find this idea helpful as you review your work in Part 1. Juggling is also a skill that, once practised, becomes second nature. This too may b
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5.14.2 Reverse osmosis

This technique, explained in Section 3.8.1, is rapidly becoming a major means of desalination, with research producing membranes with lower operating pressures (and hence lower operating costs). Originally a pressure of 14 × 106 Pa was needed to separate pure water from sea water but with newer membranes only half this pressure is required. Reverse osmosis membranes operate at ambient temperature, in contrast to multistage flash distillation, and this lower temperature minimises s
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Introduction

This unit is from our archive and it is an adapted extract from Environmental Control and Public Health (T210) 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.

With
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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 2.0 Licence.

Grateful acknowledgement is made to the following sources for permission to reproduce material within this book:

Fi
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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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3.4.5 Fretting fatigue

An additional possibility was considered. It was known that there was significant movement of the bridge during passage of traffic, because users had noticed it many times when crossing. The joints would thus have been subjected to rotary motion around the pin in order to accommodate such vibrations. Could these have caused fatigue crack growth at the bearing surfaces?

Contact between a circular and a flat plate creates so-called Hertzian stresses at the contact zone: compressive at the
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