Stage 2: The situation analysed The first step is to develop a picture (called in soft systems terminology a rich picture) that encapsulates all the elements that people think are involved in the problem. Once the rich picture has been drawn, the analyst will attempt to extract ‘issues’ and key tasks. Issues are areas of contention within the problem situation. Key tasks are the essential jobs that must be undertaken within the problem situation. 1.5 Increasing complication, complexity and risk: the underlying relationship Figure 3 showed five commonly encountered problems of effecting different types of change. These are notionally located on a spectrum of change that ranges from no change at all, to complete revolution. The relationship suggested on the figure is that as the degree of change – represented 7.2 Film properties In practice, we can hardly ever use just the fastest technique to put some material down onto the wafer. Before deciding how to deposit a particular layer, we must consider which film properties are important for the function of the device. The commonest requirements relate to uniformity, step coverage, composition, micro structure and stress. We shall consider each of these in detail. 5.15 Further investigation is possible There are still many mysteries that surround the Tay Bridge disaster, largely because so little was recorded at the time of construction. For instance, questions remain about the details of reject rates for the castings, and modifications made to the first designs of the piers and their component parts. Although enlargement of the BoT set of pictures has helped clarify the various failure modes described by Henry Law and others at the enquiry, it has also revealed yet more mysteries. Wh 5.5 Evidence of Henry Law Henry Law's report is brief and to the point, and includes a substantial appendix giving detailed calculations of the effects of wind pressure on the structure (not included in Paper 1). Further information on his inspection of the remains – the two standing piers, the twelve wrecked piers the high girders and the train within – was given during his testimony before the enquiry. Law was able to examine the extant remains in considerable detail, and noticed numerous defects in the br 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: 4.11 Model for pier failure Figure 39 shows a simple model to explain the failure of the piers. The lateral wind loading on the top of the pier bends to shear the pier from a rectangle into a parallelogram. In turn, this stretches the tie bars and also strains the bolted joints at the top and bottom of each column. 4.10 High girders and the train Divers found the high girders lying on their sides in the shallow water of the river bed a short distance away (Figure 22), within which the almost intact remains of the train itself was found. No bodies were recovered because they had all been washed away by the river or tide. Although bodies were recovered i 4.6 Photographs showing the detail: debris field The relatively clear platform of pier 3 is also visible in Figure 28. There are several pieces of shaped metal on the floor, at least one appears to be a bolt. A close-up of the floor, taken looking east, is shown in Author(s): 4.5 Photographs showing the detail: broken lugs The bases of the columns to which they were attached originally on pier 3 deserve closer inspection. Even at this scale, the two fractured lugs where the tie bars were formerly fixed are clearly visible at the right-hand and left-hand sides of Figure 28 (arrowed). The southern (left-hand) column base in 4.2 An introduction to the Board of Trade photographs It is important to bear in mind that these shots show the bridge remains in the state they were in just after the accident, and are almost exactly what the investigators would have seen when they inspected the bridge (see Input 8, linked below). Click 'View document' below to open Input 8 4.1 Condition of the bridge: an overview An investigation was put into motion by the Board of Trade (BoT) as soon as news of the catastrophe reached London. Three commissioners were appointed to consider the evidence. They proceeded at their task with haste, knowing the country looked to them for an explanation of the accident. Fifty photographs were taken of the remains of the bridge about a week after the collapse at the request of the BoT enquiry team. The photographs are vital evidence of the way the bridge piers fai 3.5 Sunday 28 December 1879 The morning of Sunday 28 December 1879 was quiet. When Captain Wright took his ferry boat, the Dundee, across the firth at 1.15 pm, he noted that the weather was good and the water was calm. The 4.15 pm crossing was just as uneventful, but the captain noted that the wind had freshened. By 5.15 pm a gale was moving in from the west and the river, in the words of the captain ‘was getting up very fast’. The local shuttle train left Newport at 5.50 pm and arrived at Dundee statio 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): 3.1 Overview The Tay Bridge disaster came towards the end of a period of intense development of the railway system in the UK. The bridge had materials that were well known. Cast iron was used for the columns and wrought iron for the trussed girders. The construction of the bridge was, at the time, the largest single engineering project in Britain, the Tay estuary being about two miles wide near Dundee, and the bridge was the longest in the world. In the shallower approaches in the estuary, con 2.4 Early disasters Many of the earliest bridges were simply a wooden trestle type of construction, an efficient and easy-to-build structure, yet providing a secure and safe passage for heavy metal trains. Although we tend to associate such structures with the United States, they were in fact widely used in Britain in the early days of steam locomotion. However, they had a limited lifetime owing to rot, so were gradually replaced by wrought iron girder bridges, often laid on brick or masonry piers. Designe 2.1 Overview Catastrophes of human origin can be just as traumatic as those of natural origin, and are studied with even greater intensity for their causes. There are several ways disasters of human origin can be classified, depending on cause or size or origin. Another way of looking at them is by the kind of human activity – perhaps mining, fishing or transportation. Equally, disasters could be classified according to the kind of event that occurred during the accident – perhaps collision, sinking, 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 Learning outcomes After studying this unit, you should be able to: understand the basic structural issues of the Forth Road Bridge; give examples of how engineers are trying to alleviate the wear and tear on the bridge. Acknowledgements The following material is Proprietary (see terms and conditions) and is used under licence Figure 7: The Royal Scottish Museum, Edinburgh Figure 8: The Royal Scottish Museum, Edinburgh Figure 20: taken from www.acmi.net.au/AIC/BLATTNER_STILLE.html Figure 13 and 25: Ampex GB Limited We also thank Nigel Bewley (British Library Sound Archive), Daniel Leech-Wilkinson (King's College, London) and Robert Philip
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