Technology and Innovation spotlight: building bridges

We’ve all had that sinking feeling you get when you realise the train journey you’ve just planned for the long-awaited weekend break is going to take hours longer because of engineering works; or your sat-nav is re-routing you off the motorway through rural parts of the UK. Well, our engineers have developed a solution that will make that occurrence rarer.

We’ve developed an approach to delivering bridges that will save weeks off a programme. Not only that, but our solution requires less resource, and it will produce a smaller carbon footprint.

The approach that is underpinned by a digital bridge configurator and an engineered kit of parts has been developed, tested and refined by our technology and innovation team, working in collaboration with industry and academic partners. Our methods have already successfully delivered multiple solutions for major UK clients like High Speed 2, Network Rail and National Highways.

Being part of a team that pushes the boundaries of what’s possible, to come up with a solution that will benefit society is a privilege. Knowing that you’re coming into work each day with the aim of delivering better ways to deliver infrastructure by changing the way we build bridges is exciting and what engineering is all about. Here’s the technical outline of how we’re doing it.

Bridge product set and digital configuration

Laing O’Rourke’s award winning modular bridge system consists of a standard range of precast products that can be readily configured to form high assurance solutions for modular single-span integral bridges with precast prestressed concrete beams, and associated wingwalls, as shown in the figure below.

The use of the modular bridge system adopts 'product-led design' where the bridge design takes account of the characteristics of the products, rather than attempting to retrospectively fit a set of precast products to an outline design. This demands an understanding of detailing and engineering constraints associated with the products and bridge solutions, to ensure that a preliminary design is capable of development to detailed design. This approach is automated in our digital bridge configurator in what we call a digitally enabled and assured workflow.

Delivering benefits across current infrastructure projects

The kit of parts is also readily applicable to steel beam solutions, (as used on our M42 bridge for HS2); bridges with bearings (as used at Oxford on our East West Rail project); multi-span bridges (M25); standalone elements in larger schemes such as piers (Bletchley Flyover replacement piers); retaining walls (HS2 Sublot 8); and box-structure sections (Bletchley). These solutions are being developed into the configurator to expand the reach of our digitally enabled and assured configuration process.

The current kit of parts includes families of shell units, variable height L-walls, products to form stub walls to support the vehicle restraint system behind the abutment, stringcourse units, and precast infills between the deck beams.

Precast gallery units for bearings (M42), precast parapets (HS2 Birmingham Interchange Station), precast deck planks (M42/M25) have also been successfully manufactured and combined with the kit of parts and are being standardised for deployment on future projects.

Enabling better programme, productivity and sustainability. Unlocking opportunity and driving inclusion

Programme 

Using the modular bridge kit of parts, the construction and assembly of the 35m span HS2 trace bridges resulted in a programme saving of 18 weeks, reducing the original programme from 37 weeks for traditional construction to 19 weeks. This 50% programme reduction is typical for bridges constructed utilising the modular approach and is primarily enabled due to the rapid construction of the abutments and wingwalls.

These savings on individual structures, when considered across a wider programme of works, can offer major benefits in reducing the overall duration of larger schemes and as such offering significant savings associated with prelims.

Reduced construction durations also allow local roads to be handed back sooner, shortening the length of time that traffic management is required to be in place, minimising disruption to the local community while again offering commercial benefits.

Productivity of resource 

Offsite manufacturing of the kit of parts creates the opportunity for a dramatic reduction in on site labour, and as such offers a solution as to how major infrastructure can continue to be delivered at pace amidst the current skills shortage within the construction sector. The construction of the modular abutments and wingwalls of the HS2 trace overbridges, each measuring approx. 400m2 on elevation, was completed in just three weeks with a team of six people on site. For comparison, if constructed traditionally using in-situ reinforced concrete this activity would have needed a team of ten people on site for at least 11 weeks, equating to an 84% reduction in on site labour.

Sustainability – reducing carbon

A detailed carbon study of the modular bridge system was completed using the single span integral bridges we built over the HS2 trace. To enable a fair comparison with traditional in-situ construction design consultant Ramboll fully redesigned the HS2 North overbridge as an in-situ reinforced concrete structure with zero offsite construction. Using the redesign, the original Expanded project team prepared a fully detailed project delivery plan including temporary works designs and craneage etc. The study concluded that the modular approach reduces embodied carbon by 8% in the abutments, compared to an equivalent, traditionally designed in-situ reinforced concrete abutment.

Using the shell abutment system creates the potential to use low carbon in-situ concrete mixes for the shell cores as the pressure to strip and cycle formwork is eliminated. Low carbon mixes which may need more time to gain equivalent strength can be used without impacting the critical path of site operations.

Unlocking opportunities 

Constructing bridge foundations and substructures is often dictated by the earthwork seasons. The modular abutment system, with its speed to assemble and designed capability, allows back-filling to commence as soon as possible without needing the bridge deck in place. This can help accelerate earthworks, unlocking the opportunity to do more in a single earthworks season. This can instantly save months of time and even allow follow-on activities such as utilities/services installation and road surfacing to commence ahead of programme.

The rapid construction of the new bridges across the scheme also offers the opportunity to reduce or remove the need for temporary bridges, while creating the opportunity to utilise the bridges as construction/logistics routes, opening new work fronts earlier than would have been possible.

Safety, quality, and inclusion 

Product led modular bridge solutions support a transition from ‘trades to technicians’. Teams of multi skilled technicians are deployed on site, responsible for carrying out well defined and repeatable assembly processes, rather than inherently larger teams of specialist trades with multiple interfaces and hand overs. This results in fewer people on site, for less time, in a safer working environment and drastically reduces the opportunities for mistakes.

By moving work into a factory this provides a warm and dry environment in which the workforce can carry out their roles safely. This provides consistent and continuous employment opportunities for the local community and provides job security to the workforce. It also reduces the number of people required to work on site in conditions that can be difficult and dangerous when exposed to changing weather conditions and minimises the need for scaffold access systems.

By creating a more desirable place of work, with technically challenging and digitally enabled roles, we hope to encourage greater diversity within the workforce and create new roles which provide opportunities for people who previously may not have considered construction an achievable career path.

Where next? Flexible abutments 

Flexible abutments are the next step on our journey as we develop industry leading precast modular bridge solutions. With them, we aim to broaden our reach and deliver more bridges using our DfMA approach and the developments we've made to our kit of parts. We are aiming to be 50% faster than conventional flexible abutment construction and our physical trial has shown promising results.

To find out more, or to discuss our bridge solutions please get in touch.