Composite Girders Raise the Tone in Bridge Construction

Added traffic, heavier truck loads and more extreme weather variations make it harder to design safe and enduring road bridges for Australian sites.

Structural engineers know that steel-concrete composite structures benefit from the positive features of each element. For decades they have been trying to improve the way these elements interact in challenging local conditions and produce the safest outcomes.

 

The latest European methodology uses modern, computer-programmed, continuous flame cutting to create steel dowels for the composite action. It has been widely trialled on international bridge projects with great success.

 

The new Tone River Bridge in the South West region of Western Australia became the first Australian project to incorporate this state-of-the-art approach and demonstrate its considerable long-term financial and safety benefits.

 

Overcoming Unique Challenges

The 90-year-old single-lane timber bridge crossed the Tone River on the beautiful undulating Boyup Brook Cranbrook Road – a tourist route between Bunbury and Albany that passed the Tone-Perup Nature Reserve. Every day around 400 vehicles used the bridge, a high proportion of them heavy freight trucks, road trains, and caravans.

 

Unnerving numbers of near-miss heavy vehicle collisions on the single-lane timber bridge made its replacement a priority for Main Roads Western Australia (MRWA). But, transporting large precast concrete beams normally used on a bridge site like this, would have been a big challenge.

 

WSP’s Technical Executive Wolfram Schwarz and his team adjusted the new two-lane Tone Bridge design and proposed the alternative solution of a composite dowel bridge girder based on a Technical Approval from the German Institute for Construction Techniques. This form of steel concrete composite dowel has not been tried in Australia before which propels WSP’s solution of cutting an intended shape from steel I-girders to form a steel dowel in steel-concrete composite girders to a true novelty.

 

“Due to its load capacity and favourable fatigue strength, one composite dowel is able to replace a group of shear studs which adds economic advantages to the constructability and structural benefits,” said Mr Schwarz.

 

The value engineering and safety-in-design approach replaced the traditional shear studs; used reduced-weight beams that allowed improved span to depth ratio bridge superstructures; needed less material; reduced transportation limitations and costs; avoided construction works within the river; and minimised changes to the road’s vertical alignment.

 

The innovations didn’t stop there. The team’s design also incorporated strain gauges that measure how materials are coping under the pressure of real-life forces to prepare the structure for ‘live’ lifetime structure monitoring. And they used low-maintenance, long-life modified polymer plug expansion joints. The combined innovations improved load ratings, maximised the remaining working-life forecast, and has the potential to adjust MRWA’s maintenance intervals.

 

Rita Saffioti MLA, WA Minister for Transport, Planning and Lands, was thrilled with the outcome. As she said at the June 2018 opening, “Sometimes as Minister when you hear innovation or leading edge, you get a bit scared. But obviously this one is really state-of-the-art and the first time it’s been used in Australia. I congratulate all those involved – WSP, Fulton Hogan, Main Roads, all the shires and all those that have contributed.”

 

Wolfram Schwarz is a WSP transport technical executive. He joins other WSP speakers at the Adelaide Convention Centre for the Australasian Structural Engineering Conference, 25 – 28 September 2018. Wolfram’s session: ‘Steel Concrete Composite Bridge with Dowel Strip Replacing Shear Studs’ is at 11.00am on Thursday 27 September 2018.

 

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