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Dr Al-Mahaidi has come up with a high-tech material to strengthen bridges

Bits & pieces

Carbon fibre is used extensively in the aerospace industry because of its light weight and exceptional strength. Its usefulness in aircraft construction has encouraged the development of more advanced carbon fibre composites, and the civil aerospace industry is still the biggest consumer of these materials

Carbon fibre composites have found a strong niche in the sporting world: Formula One race cars, high-end racing bicycles and even fishing rods use carbon fibre composites

Besides its light weight and high strength, carbon fibre's superior stiffness makes it excellent at dampening vibration, a feature that has led to its use in tennis and squash racquets.

Carbon fibres strengthen sagging bridges

What does Melbourne's Westgate Bridge have in common with F1 race cars, passenger jets and squash racquets? Answer: the latest in ultra-light, ultra-strong carbon-fibre reinforced polymers. Monash Uni engineers are giving over-age and under-strength bridges a revamp with this high-tech material.

Many Aussie bridges were built decades ago and are carrying loads their designers never intended. Add the effects of time to daily wear and tear, and it's no surprise that even the toughest traffic bridges eventually need reinforcement to keep them sturdy.

Old-school methods of reinforcement use steel plating to boost the strength of concrete and steel structural elements. And while steel is an excellent material, it also has some serious drawbacks.

heaviness, adding extra weight the bridge has to support, and making it difficult and expensive to install
rigidity and fixed shape, which make it great for reinforcing straight surfaces but less useful on curved or unusually shaped bridge elements
vulnerability, over time, to corrosion and decay that might compromise the integrity of the reinforcements.

To counter these problems, engineers at Monash University have been working on better ways of reinforcing ageing structures using Fibre Reinforced Polymers, or FRPs.

FRPs consist of a layer or layers of carbon fibre embedded in a matrix of epoxy resin, creating a light, strong, durable material that is ideal for many applications where strength without weight is required.

Monash Freeway bridge in Melbourne

Dr Riadh Al-Mahaidi, head of structures group in the university's Civil Engineering Department, has been conducting research into the use of FRPs for reinforcing bridges and other structures.

"It's lightweight, it's non-corrosive, it has a very high tensile strength, and it's available in different forms - either sheets, like wallpaper, or solid strips just like steel plates," said Riadh.

FRPs can be bonded to concrete or steel using powerful epoxy adhesives. Their light weight makes them easier and less expensive to install than heavy steel reinforcements, and their versatility makes them perfect for many applications where traditional methods aren't suitable.

Flexible FRP sheets are uniquely suitable for reinforcing structural elements against being twisted by the loads they carry, a process known as torsional strengthening. This application has particularly interested Riadh and his team, because traditional reinforcement methods are not ideal for this application and little research has been done internationally on using carbon fibre for torsional strengthening.


Working in the lab

"Torsional strengthening is an area that has been neglected, that has not been given attention overseas and this is something we have been working on here for the last three years" said Riadh. "We consider that we have pioneered this particular area of strengthening."

VicRoads, the Victorian road and transport authority, has been using the FRP technology in collaboration with Riadh and his team to reinforce bridges in Melbourne. Recent examples include the Westgate Bridge and the bridge spanning the intersection of Monash Freeway and Warrigal Road in Chadstone.

The ease of installation that the lighter, more flexible material offers is a serious drawcard for VicRoads, eliminating the need for heavy lifting and reducing traffic disruption on the bridge.

"Not only is it an efficient way of doing things, but it minimises the impact on traffic. You require less traffic management because it's quicker - you go in and go out" said Mr Fred Andrews-Phaedonos, Principal Technical Consultant for GeoPave, the materials arm of VicRoads.

"We've found it to be an efficient and effective way of doing things, and I'm pretty sure we'll do a lot more jobs as funding is provided and jobs are identified" said Fred.