Damage limitation

A trailblazing multi-disciplinary engineering research project is seeking ways to help structures and systems stand up to the stresses of earthquakes.

Governments and industries worldwide face an annual bill of many billions of pounds resulting from general mechanical failures, some caused by natural disasters such as earthquakes.

BristolUniversity has received a grant equal to 25 per cent of the UK’s annual investment in engineering higher education research to set up a centre to study various themes in performance-based engineering and find ways to reduce these losses.

The Bristol Laboratory for Advanced Dynamic Engineering (BLADE) is a new academic concept, integrating world-class expertise and analytical and experimental techniques. The lab has been set up with a £15m grant from the Higher Education Funding Council for England (HEFCE), the Office for Science and Technology (OST) and the Joint Infrastructure Fund (JIF).

Because BLADE has received the UK’s biggest single engineering grant, confidence is high that the research will yield significant applicable technology.

BLADE has six laboratories, including an earthquake and large structures lab containing a 15m strong wall and a 3m x 3m shaking table (the only one in a UK academic facility), an automatic control and test lab, and a modelling and simulation lab. The facility also houses an environmentally-controlled materials lab which provides a tightly controlled environment for materials-testing equipment. Each lab is engaged in projects of varying scale, and the integrated research often overlaps between disciplines and projects.

Prof Colin Taylor, an earthquake engineer and head of BLADE, said the facility was not just a research centre, but a way of thinking — looking at performance-based engineering and considering realistic in-service dynamic loads and the response of various systems to their non-linear failure limit.

‘Civil, aerospace, electrical and mechanical engineering — those are the core areas we have in BLADE,’ he said. ‘But we are reaching outside the faculty to physicists, chemists and so on. We found that with particular projects, we could only do it because we had the right package of people to say we can do this. That is unlikely to have happened pre-BLADE.’

BLADE’s multi-disciplinary approach has been so successful that the facility has secured projects and collaborative interest from the likes of Airbus, Rolls-Royce and BAE Systems — and could now become a model for other academic establishments.

‘I am sure other universities would be interested in what we are doing,’ said Taylor. ‘I work in the States a lot with the National Science Foundation as an independent assessor on earthquake engineering research. And while they are trying to promote this multi-disciplinary research, I would say the way we are approaching it in BLADE is more advanced than in the US because of the breadth of disciplines available to us.’

Nowhere is this better demonstrated than through an EPSRC-funded project — with industrial support from construction company KBR and Scottish and Southern Energy — on the strengthening of a dam’s reservoir intake towers with fibre-composite materials. According to Taylor, these non-seismically designed towers could be the most vulnerable part of a dam in the event of an earthquake. The fact that they are reinforced makes them brittle and likely to crack or collapse, he claimed.

BLADE’s research will involve constructing large-scale 4m-high models and subjecting them to simulated earthquake forces on the lab’s shaking table. ‘We will measure force deflection characteristics and understand how they start to crack, and develop numerical models which simulate that, and then use this model to explore the seismic dynamics of different types of tower,’ said Taylor. From the research, he will eventually be able to characterise the towers’ behaviour, model it accurately and recommend strengthening solutions.

Illustrating the way in which BLADE projects are expected to cross-fertilise, Taylor’s proposed solution draws on work carried out by a BLADE team on a separate EU-funded project looking into composite structures. That project, Less Loss, involves 43 partners across Europe, bringing together industrialists and researchers to look at performance-based engineering. BLADE is exploring two specific areas — the performance of masonry infill walls under excessive loadings, and the measures individual countries are taking to model and research the effects of earthquakes.

Taylor said that although infill walls could be built within a steel frame or concrete, they were non-structural and would collapse under earthquake pressures. Less Loss is building on research carried out by the nuclear industry several years ago on using fibre composite materials to strengthen walls.

Taylor said a lot of work was being done on wrapping bridge piers and column joints with fibres, which studies have shown can significantly increase the strength of non-seismically designed structures.

Another application of composite technology is being tested in BLADE’s heavy and light materials lab, where Dr Ian Bond is using an EPSRC advanced fellowship grant to research the use of composite dye-releasing technology to reveal faults in aircraft wings.

The second aspect of the Less Loss project — fundamental modelling — concerns the overall performance of systems and looks at the way that, for example, water and electricity supplies are affected by an earthquake. This is one area of research that needs close attention, says Taylor, bearing in mind not only the loss of human life in a disaster, but also the economic cost.

An illustration of this was the 1995 Kobe earthquake in Japan, where 5,000 people were killed but economic losses were close to $150bn (£78bn) because of a failure in basic industry infrastructure. Similarly, in the earthquake at Northridge, California, in 1994 60 people were killed but financial losses totalled $60bn (£31bn).

Taylor said these figures had to be addressed with a shift in focus in earthquake engineering. ‘We have dealt with the life safety issues — we can build buildings which may be damaged but people will not be killed — what we don’t do is build a building where functionality is retained, and that is where the performance-based concept comes in. A lot of the research now is looking at not just life safety, but business safety.’

Elsewhere at BLADE, much of the work in the heavy and light testing laboratory is focused on using fibre-reinforced composites and advanced alloys to improve the structural strength of bridges. According to Taylor, there has been a lot of interest in bridge renewal in western Europe and the US, where some structures are 150 years old. The challenge to engineers is to strengthen live systems without disruption.

The dynamics lab is carrying out research for Westland Helicopters on the dynamic interaction between the rotor blade and the rotor hub, and the dynamics of the hull. Tests on full-sized components are combined with computer simulations in a hybrid testing method known as dynamic substructuring.

The same approach will be used for a three-year multi-disciplinary project to analyse the cable allowance of cable-stayed bridges.

Taylor said this integrated approach, bringing many research skills together, was fundamental to technological progress. ‘If you look back at the history of the development of technology, the big steps have been made when all the bits and pieces come together, developed to the right level when someone realises the next big step can be made,’ he said.

So far, BLADE seems to be doing just that.