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Plastic beam takes heavy load

MATERIALS - Cutting Edge

US DESIGNERS have developed a plastic composite box bridge beam for highspeed railways.

Under a study funded by the Transportation Research Board in Washington, USA, scientists developed a lightweight structural beam that meets strength and durability requirements for rail and highway bridges.

Built using fibre-reinforced plastic, the box beam has three main components: a FRP outer shell; a profiled conduit that houses mass concrete and acts as compression reinforcement and tension reinforcement in the bottom of the beam.

Lead engineer on the project John Hillman, from designers Teng & Associates, used the Hardwire carbon, glass and steel fibre reinforcement system anchored in the compression reinforcement to strengthen the beam against tension loading.

He said the steel fibre mat was easier to use than glass fibre and boosted structural performance.

He said: 'It was easier to control tolerances than the glass.The structural properties made the Hardwire the logical choice for the tension component.'

Mr Hillman and his team built and tested a 5.5 m-long prototype beam that would withstand typical loading from ballasted track and live loads using hydraulic actuators.

The loads were applied both asymmetrically and symmetrically to imitate a fullscale track and the beam was eventually loaded to destruction with a final failure load of more than 3.5 times the design service load.