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Global insights point to smarter, more efficient bridge design

WSP’s global review of precast bridge girders reveals design efficiencies that could cut costs, lower carbon, and speed up sustainable bridge construction in New Zealand.
In the drive for efficiency, various precast bridge components have been developed around the world. The latest research from WSP focuses on a global review of superstructure beam types - and it could reshape how bridges are designed for decades to come.

The internal research document looks at variability in prestressed concrete girders and beams used in bridge superstructures worldwide. While technical in nature, its findings have significant implications for Aotearoa New Zealand’s approach to standardised bridge design, offering opportunities to reduce both carbon and cost.

Girder types were compared across five regions - the UK, USA, Canada, Australia, and New Zealand - using a common benchmark: a 30-metre, simply supported, single-span precast prestressed concrete highway bridge with a 15-metre deck width. 

By analysing span-to-depth ratios and concrete volume per square metre of deck, the document identifies which designs deliver the greatest structural and material efficiency.
Understanding more about this subject is important, says WSP New Zealand’s Head of Bridges, Maritime and Structures, Jeremy Waldin.

 
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Jeremy Waldin
Head of Bridges, Maritime & Structures
New Zealand
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New Zealand is similar to other countries in facing growing pressure to deliver infrastructure that is both resilient, sustainable and cost effective. Bridges are a critical part of the transport network, and every design choice affects cost, carbon footprint, and long-term performance. 

“By learning from global best practice and applying those lessons locally, WSP can help set a new benchmark for efficiency, speed of construction and environmental responsibility in bridge design. A bridge built quickly is typically a cost-effective bridge, and reducing materials saves both cost and environmental impact, as well as reducing weight allowing smaller more standard lifting equipment and providing further cost and environmental savings”

Research undertaken by WSP’s Global Leadership Development Group confirms that girder and beam proportions and design approaches vary significantly between regions. 
Josh Vize, WSP’s key research lead and research document author, outlines that some countries favour deeper, heavier sections of beam, while others achieve greater efficiency with slimmer profiles.

For example, the UK commonly uses Y-beams and U-beams, Australia typically relies on Super T girders, Canada prefers I and NU girders, and New Zealand commonly uses hollow core and Super T beams. In the United States, bulb tee sections are widely adopted for their material efficiency, along with a range of other superstructure types. Of particular note to New Zealand, the UK are starting to consider their version of the bulb-tee / NU girder, based on the sections used throughout the US but optimised for Eurocode loading and durability requirements.

These differences aren’t just about shape – they reflect decades of regional practice and priorities. Understanding these variations gives New Zealand a chance to adopt the best ideas and move towards designs that balance strength, sustainability, and economy.
Jeremy says the report provides a blueprint for more efficient, smarter, greener bridge replacements in New Zealand. 

 

“This research gives us a clear view of what’s working globally and where we can improve. By standardising designs that are efficient from a cost, carbon constructability perspective, we can deliver better outcomes for clients and the environment.”

The next stage of research will look into the key drivers that are influencing the volume of concrete within standard prestressed girders, including design live load, unique aspects of the fabrication industry, constructability and other environmental factors.