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Saving structures across the globe

We’ve developed assessment and strengthening techniques for ageing concrete bridges and structures. Our guidance is used by consulting engineers worldwide.

Antony Darby tests the strength of a concrete beam in our structures lab.
Using carbon fibre reinforced polymer we can strengthen concrete structures and save them from unnecessary demolition, but first we need to be able to accurately measure their load capacity.
‘Our ageing infrastructure appears to be in a deteriorating state, but there’s actually plenty of life left in these older structures. Through testing and strengthening, we can continue to use them in a smart, safe and cost-efficient way.’
Antony Darby Reader in Structural Engineering

Highways England (the UK’s largest bridge owning authority) and Network Rail are responsible for maintaining around 12,000 concrete bridges, some built as far back as the 1920s. Since their construction, not only have building standards changed, but our population, private car ownership and lorry loads have hugely increased. These bridges have endured years of weathering and erosion, putting into doubt their ability to withstand these heavy loads.

Deciding the fate of our troubled bridges

Condemning vast sections of our national infrastructure would be costly, disruptive and in some circumstances, completely impractical. Highways England estimates that to close one car lane costs the UK government somewhere between £10,000 and £50,000 per day.

Despite the significant stresses these bridges are subjected to, in many cases there is no real need to scrap these older structures. They may well already meet modern building standards or can be reinforced to meet them. We just need to know how to assess their load capacity and improve this where it’s needed.

By prolonging the life of these structures, we can save the economy millions of pounds each year and use fewer resources. This means we can protect the environment without compromising our safety.

Assessing existing load capacity

At Bath, we've spent over 20 years testing how concrete structures behave under different loads and developing novel approaches to prevent them from failing.

Many bridges built before the 1970s suffer from a loss of concrete and reinforcement corrosion issues, particularly highway bridges that use prestressed reinforcement. Working with Balfour Beatty and Mott MacDonald (on behalf of Highways England) we set out to investigate how concrete deterioration affects this reinforcement in critical anchorage regions.

We found that even after severe concrete deterioration, a significant amount of strength capacity remained, which had previously been neglected in assessment standards. Once this capacity is taken into account within a structural design, in many situations, the capacity of these bridges actually meets modern building standards. In other words, these bridges were much stronger than once thought and did not need costly and disruptive strengthening works.

Strengthening with advanced composite materials

For those bridges that were found to have an inadequate load capacity, we developed different strengthening methods using an advanced composite material: carbon fibre reinforced polymer (CFRP).

CFRP is a lightweight, strong and durable composite material created by combining carbon fibres into a polymer resin. It is the same material used in Formula 1 racing cars and the Airbus A380.

We found CFRP can be used to increase the strength of columns, beams, slabs and bridge decks. It can be glued to the surface of the concrete or within slots or holes cut into the concrete to act as additional reinforcement. This allows structures to carry increased loading.

Carbon Fibre Reinforced Polymer (CFRP)

CFRP is an advanced composite material that is incredibly strong yet lightweight. Unlike steel reinforcement it does not corrode. Our research uses CFRP to strengthen bridge structures without adding weight.

After developing these strength assessment and reinforcement techniques for concrete bridges, our researchers were commissioned to write design and maintenance guidance documents.

Techniques shared across the globe

Our TR55 design guidance has been incorporated into national manuals and taken up by global design software firms like Sika AG. This means hundreds of buildings have been saved from unnecessary demolition or needlessly intrusive retrofit works.

Highways England have commissioned four major structural strengthening schemes using methodology informed by our research. Prolonging the life of these bridges has saved money and disruption. Using our CFRP reinforcement techniques has resulted in less energy and water usage than traditional steel retrofit solutions.

Sika developed a freely available software for the design of strengthening schemes, based on elements of our research such as column strengthening, near-surface mounted reinforcement and flexural strengthening. This software has been downloaded over 14,000 times across the globe. Its influence can be seen in projects such as the Rialto Bridge structural restoration in 2017 and structural strengthening of the world’s largest archaeological museum, the Grand Egyptian museum in 2019.

‘As a result of Bath’s research we’ve extended the life of many bridges. Road closures, monitoring, strengthening or replacement are only implemented when necessary. This has saved millions of pounds and minimised the associated environmental impact.’
Pierfrancesco Valerio Highways England Structures Manager

Find out more about our research activities

Architecture & civil engineering research