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it's almost like a family.

Khoa, 2nd Year

Professor Chris Burgoyne

Chris Burgoyne shows that Structural Engineers do much more than just building bridges.

Most laymen would think of Structural Engineering in terms of the design of bridges or buildings, and indeed these are an important part of what we do.  But Structural Engineering crops up in many different places, and at many different scales.  I recently attended a series of lectures in the Engineering Department: one speaker was applying Structural Mechanics to the folding of DNA, and was measuring dimensions in nanometres; the next speaker was talking about the construction of a bridge with a main span of 1 kilometre, a difference of twelve orders of magnitude.  Yet they were using the same principles.

My own background is as a designer of prestressed concrete bridges, but that has led into new and innovative fields.  The steel tendons normally used to make these structures are the most highly-stressed structural elements around, but they potentially suffer problems caused by corrosion.  So it makes them ideal candidates to be replaced by high strength fibres such as carbon or the aramids.  These remarkable materials have significant potential for engineers; they are almost ten times as strong as mild steel, have similar stiffness, a fifth of the weight and above all do not rust.  But they cost 4 times as much (per unit force) so have to be used to their full potential to be economic.  They were originally developed for use in bullet-proof vests and rocket nozzles, so very little was known about their long-term properties; my research group has spent a lot of time measuring these properties and working out how we can safely extrapolate our results to design lives of 100 years.

These advanced fibres are often used in the form of fibre-reinforced plates that are glued onto the sides of existing structures to strengthen them, but they can fail by peeling away from the underlying concrete.  Conventional analysis to determine the stresses doesn't work because it relies on knowledge of the detailed structure of the materials at the interface, and this can never be known beforehand.  We have thus been studying how this failure occurs and trying to devise methods of predicting it so that designers can take it into account, using a technique called fracture mechanics.  We are in the process of producing design guidelines for use by industry.

My work on fibres has recently taken me in an unexpected direction because of the potential need to control the Earth's climate.  Governments have committed to bringing down our use of CO2, but it is quite likely that they will fail.  So we must consider what to do if the temperature does start to rise to the extent that it causes catastrophic change, such as melting the Greenland Ice Sheet or releasing methane hydrates from the permafrost.  One option is to shield incoming solar radiation by injecting particles into the stratosphere, (which is what happens in large volcanic eruptions), and the cheapest way of doing that is from a tethered balloon at a height of about 20 km, with the particles being pumped up a pipe within the tether.  It doesn't sound difficult, but how do you make such a tether?  Most materials will not support 20 km of themselves, let alone have sufficient reserve of strength to support a pipe.  The only option is to go to the sort of high-strength, light weight materials, such as the ones we have been studying for a completely different purpose.

I still do work on conventional structures, and was involved with the investigations into Hammersmith Flyover, and we are currently doing a review of the prestressing systems in Coventry Cathedral.  But structural engineering can be much broader.

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