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Concrete: The rock solid case for precast

It has become almost almost a cliché, but is still true, that the construction industry can learn lessons from manufacturing to streamline and improve the way projects are run.

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Pre-assembly, factory production conditions and standardised components are all elements of removing uncertainty and risk from site works and increasing the safety of projects.

To this end, Irish firm Banagher Precast Concrete sees the use of premade concrete elements as an increasingly important part of infrastructure provision in the future.

The use of 3D models and building information modelling (BIM) design technology has also helped integrate the use of premade and precast components into schemes, and their use has grown considerably, particularly for building. Heavy civil engineering has been catching up with the commercial and office sectors too, though perhaps more slowly.

“Of course, there will always be a place for in situ concreting,” says Eammon Shortall contracts director of Banagher, currently one of biggest suppliers to the British civil engineering sector.

“Nuclear power stations with slabs and reactor walls 2m thick, structures with complex foundations, and the many one-off requirements that are found in complex civil projects are all best done with on-site casting,” he says. But for many works, particularly in road bridges and the railway work currently taking place, there is major scope for the use of precast.”

These components can be on a massive scale; some of the largest bridge beams the company makes have come in at 135t in weight and much of its output is in very large units, such as complete railway underbridge sections weighing 120t, large portal tunnel sections, arch units for tunnel construction and heavy sea defence units. The spectrum of components also includes carpark units, water treatment channels, stadium elements and tunnel segment work.

“We do not really do smaller precast elements,” says Shortall. “Our output is for large scale civil engineering.”

The production yard sited in the middle of Ireland at, unsurprisingly, Banagher in County Offaly, is on a scale commensurate with the industry. The facility, with both indoor casting space and external curing and storage yards, covers 20ha and has a total of over 70 gantry cranes for moving elements.

Some 60,000m3 of concrete is poured for precast units each year in controlled conditions. Capacity at peak can allow for 2km of bridge beams to be turned out every week, though the current market conditions mean output is below that right now.

“We are a long way off that at present,” concedes Shortall, though he hopes that the planned railway work in the UK and a ramping up of roads work will create demand.

The company has been in production for 50 years and made components early on for the M1-A1 link in the UK, and in the 1990s was a significant supplier to High Speed 1. It expanded substantially during the 1990s and early 2000s Irish construction boom and the large scale development of the motorway network there with major bridges, as well as tunnels - notably the Dublin Port Tunnel - and other schemes.

“The company has been heavily involved in nearly all the design and build infrastructure undertaken in Ireland over the last decade,” says Shortall. “Now we are focusing on bringing this expertise to the UK.”

A large proportion of the components it made over the years were standard bridge beams, U-beams, Y-beams and other types of prestressed beam, culvert box elements, and parapet units. But the company has also developed its own variant, the wider section W-beam.

“This design emerged from our hands-on approach to value engineering in design and build contracts,” explains Shortall, “and as a result our own in-house design department developed the W-beam. It allows for greater span ranges than previous beam types.”

The largest of this type were the 45m long bridge beams developed and delivered for the Limerick Tunnel.

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“The W-beam can be also placed at larger centres which reduces the quantity of beams required,” adds Shortall. That reduces the number of deliveries required, crane lifts, overall deck weight and therefore cost.

Banagher has also produced a portal frame design for rail bridge replacement work which comes as a portal section and two side pieces with cantilevered footings as an alternative to standard side walls and beams.

Its factory controlled technology is fairly sophisticated; for example it no longer relies on concrete cube testing alone but a system of embedded thermocouple temperature monitoring of the concrete cure known as the maturity method.

With the possibility to position abutments further apart there is major scope for reductions in other site work. “Piling of piers and abutments is a major expense,” says Shortall, “which can be reduced by longer spans.” The long beams are also in demand for motorway widening projects, which mean four or even five lane spans are more frequently required.

Banagher works with designers and contractors to refine designs for structures, Shortall says, and with its specialist understanding of prestressed units, is able to suggest options for tailoring the elements. It has an experienced in house team of design engineers and draughtsmen and also uses a consultancy in South Africa for design work.

Quite often by refining the design requirements of an initial order, it is possible to reduce thicknesses of sections, Shortall says, even by as much as half on occasion.

Investing in training and updating design packages for Eurocodes has reaped rewards in terms of being ahead of the curve when it comes to design and detailing.

The reductions cut material requirements and the size and weight of the units when it comes to delivery.

Shortall says that it can be useful for designers to consult the company early on to see what the options are “because later on into a project it may be more difficult to modify things to take advantage of the possibilities.

“With involvement at the early stages of a contract we can work with the contractor to propose economical solutions to those provided by the more traditional beam types.”

But the company works equally with prespecified design as well as more open ended requirements.

A recent development which Shortall thinks will facilitate design integration is the company’s adoption of BIM technology. “We have recently begun using the Autodesk Revit structural software, which seemed like a natural progression from the AutoCAD 3D draughting we were doing,” says Shortall. The 3D model is useful for visualising and discussing production of precast units with customers for specific projects, and will fit into their 3D models.

A critical aspect of larger precast units is obviously the capacity to deliver them, and Banagher works with a local logistics company to move and transport the beams and other components. Getting the items from central Ireland to the UK is usually done by road transport and poses little problem for large elements.

Craneage has advanced considerably over the years, says Shortall, and lifting capacity of up to 120-130t is not difficult to find; larger lifts to around 250t are also more commonplace, although they might require longer lead times for hiring equipment.

Some major elements have recently been installed in South Wales for road works on the A477 St Clears to Red Roses project. Both Y-beams and the 120t W-type beams up to 43m long were delivered. In Scotland the company is supplying precast beams for the approaches on the Forth road bridge replacement crossing.

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Bridging the gap: Bridge beams form a large part of Banagher’s precast output

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