High Speed 2 and East West Rail are sharing knowledge to help develop modular bridges in a unique collaboration.

A  kit of parts approach that enables greater efficiency in bridge design and construction is taking the industry by storm. 

Laing O’Rourke is using its pioneering design for manufacture and assembly (DfMA) strategy to make a range of bridge elements for major projects at its Centre of Excellence for Modern Construction in Nottinghamshire.

Interchangeable components are being manufactured, giving the flexibility to assemble them in different ways depending on the demands of a project.

Laing O’Rourke civil engineering leader Phil Robinson explains: “With the kit of parts, we can put components together in any way we see fit to create the geometry we want.” 

A key output of the Nottinghamshire factory are precast modular blocks which have been used to form bridge abutments for High Speed 2 (HS2) and East West Rail (EWR).

It is an approach that enabled the rapid installation of a 45m long HS2 bridge over the A446 in Solihull in 2020. A total of 80 precast concrete modular abutment blocks were made at the factory, and structural engineer Cleveland Bridge manufactured and supplied 220t of steel girders for the bridge.

HS2 is using precast prestressed beams for some bridges

After assembling the modular abutment sections, the final part of the process involved using a 128 wheel hydraulic platform to move the bridge span 150m, where it was lowered onto the DfMA abutment shells. 

Laing O’Rourke operations leader Mitchell Pretious says the whole process works a bit like a set of Lego.

“You have a set of components that are like your Lego pieces and you can build anything you want out of it.” 

Laing O’Rourke has also created its own digital configuration tool for bridge products in partnership with National Highways, using the road operator’s research funding. This has enabled the development of a standard library of parts.

“We’re on a journey of expanding the capability of that tool to be able to deliver 80% of the bridges in the market,” Robinson says.

Overall, the approach enables clients and consultants to optioneer bridges quickly while providing a better understanding of programme, cost and engineering.

Work on the bridges for HS2 has informed bridge designs for EWR and vice versa.

Meetings between representatives of HS2 Ltd and EWR were held to explore ways to create components that would work on both projects. Attending those meetings were members of Laing O’Rourke’s precast concrete manufacturing team, HS2 designers DJV – a joint venture between Ramboll and WSP – and Atkins which is the design consultant for EWR Alliance. EWR Alliance is delivering phase two of EWR and comprises Atkins, Laing O’Rourke, Network Rail and VolkerRail.

“It’s the only project I’ve worked on where we’ve had two different clients with two sets of consultants for each project all coming together to work on the innovation of a set of products to be used on both projects,” says Robinson.

“To bring the two teams together and say we’re going to have one approach and deploy it to both projects was really quite special.” 

For EWR, the team has built five new road over rail overbridges, four of which use the precast modular abutment solution developed for HS2. Structural works for all five are now substantially complete and two are open to road traffic. 

Another key part of the project was the partial rebuild of the 605m long Bletchley flyover which takes the EWR across the West Coast Main Line. This used the same modular solution deployed on HS2. The flyover comprises 37 spans and 36 piers. As part of the project, the team removed and replaced 15 of the 300t spans and nine of the piers. 

A modular bridge abutment component is lifted into place

Work on the flyover also included construction of a new 90m long “box bridge” in the section passing over the West Coast Main Line. In total, 138 precast shell abutment pieces manufactured at the offsite factory were used to build the box bridge structure. The team also installed 103 precast concrete beams.

There is now a set of components that works for HS2 and EWR and that can be used with National Highways’ network and the local road network.

In comparison to traditional methods, the kit of parts approach provides a standard methodology which provides better quality assurance in a controlled factory environment. It also reduces construction times – constructing a traditional abutment would take around seven weeks, compared to around one week based on the HS2 work.

Going forward, Laing O’Rourke is talking to clients about starting to lift the pile cap foundation for bridges out of the ground. The contractor hopes to use the approach this year. 

The new approach means the pile cap is built at ground level to avoid digging a hole around the tops of the piles. As such teams can effectively “hide” it inside precast concrete fascia panels, which are non-structural but blend in with the structure to look like an abutment. As a result, the pile cap is formed above ground which reduces or removes the need for earthwork support or open excavation.

“This [new approach] is valuable to clients who want to build a bridge next to the motorway as it reduces the impact on road users,” Pretious explains.

In addition, the team has been refining its abutment designs for greater flexibility, with a trial at the Nottingham factory scheduled after nine months in development as this issue of NCE went to press.

With the kit of parts, we can put components together in any way we see fit to create the geometry we want

In a fully integral bridge, where the bridge deck is rigidly connected to the abutment, cycles of thermal expansion and contraction of the deck have a stiffening effect on the soil behind the abutment, making it difficult for the bridge to expand.

This means the stresses on the bridge increase, with Robinson explaining that the “longer the bridge is, the higher those stresses can get”. 

He adds: “Traditionally you wouldn’t take that form of bridge longer than 60m – that’s where you have to let some of that expansion go by putting bearings in.”

This is where the flexible abutments come in. They separate the bridge support from the retaining wall, which means the support can move independently, allowing the bridge to expand and contract freely, without imparting stresses on the soil and avoiding the build-up of stress within the bridge itself.

As a result no bearings are needed – an advantage because it removes maintenance requirements. 

Laing O’Rourke is currently considering how to modularise this approach, which would be suitable for clients like National Highways who might be trying to avoid using components in bridges that need maintenance.

It seems the modular approach has wide-ranging benefits – from design to installation and, finally, maintenance.

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Tagged with: Modular Construction Structures

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