Driving digital forward on the A453
Digital Engineering is helping to drive significant programme efficiencies on the project to widen the A453 in Nottinghamshire
Scheduled for completion in April 2015, the Highways Agency (HA) scheme will widen an 11.5km stretch of the A453 between M1 Junction 24 and the A52 Nottingham Ring Road – a major link serving Nottingham, the M1 and East Midlands Airport.
The project includes changing an existing at-grade junction to one that is grade separated, upgrading an existing junction, the construction of eight new under-bridges and two widened over-bridges, and the incorporation of nine existing under-bridges. It also involves diverting publicly owned services, associated landscaping and environmental works, and provision for pedestrians and cyclists.
When the scheme was halted in 2010, as part of the incoming coalition’s freeze on capital schemes expenditure, the preliminary design was substantially complete with detailed design practically finished on two structures. On remobilisation of the project in late 2011, the HA set initial tasks which included value engineering the scheme to achieve a 20 per cent cost reduction on the target cost value.
To achieve this, Laing O’Rourke re-evaluated the proposed construction methodologies and identified that concurrent construction of the new structures could take several months off the completion date.
The HA was sceptical. Aware of legacy issues with 1960s and 70s offsite construction techniques, its structures specialists robustly challenged Laing O’Rourke’s initial Design for Manufacture and Assembly (DfMA) proposals.
Undeterred, Laing O’Rourke demonstrated how DfMA could generate a significant saving by enabling the construction of a bridge abutment in one week, as opposed to the four weeks associated with more traditional arrangements.
"We used the HA Lean methodology to evaluate the impact of the DfMA approach and considered the logistics and temporary works requirements for each structure to reduce resource and time through the systematic adoption of DfMA," explains Senior Design Manager for Laing O’Rourke Infrastructure, Richard Wood, "and in July 2012 we issued a structures cost and programme paper to the HA which identified a six-month reduction in programme and significant cost savings".
Perhaps most surprising of all though was the validation of anticipated resource savings through the application of robust DfMA principles to each structure’s design. The combination of a shortened programme, a 30 per cent reduction in onsite labour, and a 10 per cent reduction in the cost of structures, gave the HA the confidence to accept the DfMA strategy for the project.
This underpinned the realisation of the targeted 20 per cent efficiency savings and in October 2012, a much reduced target cost, including further value engineering challenges for the scheme, was agreed. What followed was a three-month period in which Laing O’Rourke reviewed all design packages in collaboration with the HA technical assurance team, to identify the processes, design and engineering resources needed to remove every ounce of fat from the details.
The opportunity cost of the time spent going back over design elements in a bid to achieve BIM (Building Information Modelling) Level 2 on all aspects of the scheme resulted in an anticipated negative impact of three months on the design programme. To mitigate this, Laing O’Rourke undertook a further DE opportunity review, focusing on the scope of works most benefiting from 3D modelling, the client’s requirements for BIM Level 2 information in the health and safety file, and its capacity and resource availability to realise DE outputs to challenging programme milestones.
"We identified that the HA’s asset databases were unable to accept BIM Level 2 data and that the health and safety file had drawings in CAD and PDF format," Wood explains.
"Turning our focus to the civil engineering elements of the works, we noted that the MX model was well progressed and provided excellent setting out of digital output for our land surveyors and earthworks and pavements subcontractors. The balance of the civil engineering elements were designed on a multitude of design software platforms, all requiring one or more stages of translation in achieving BIM Level 2 output, each with the risk of introducing errors," he says.
This confirmed that the opportunity cost of introducing a BIM Level 2 benchmark for the civils elements at this stage was too great. For structures however, BIM Level 2 was achievable, Wood adds. "All that remained was for us to train our design teams in the Explore Manufacturing digital engineering protocols needed to achieve IFC file outputs capable of being imported into the manufacturing software suite. We knew that this would reduce significantly the traditional lead in times Explore was constrained to offer when in receipt of traditional 2D output, adding to the benefits of the DfMA strategy for structures."
In late January 2013, Laing O’Rourke issued the first structures design packages for interdisciplinary review as published drawings and fully coordinated digital models, including drawn and modelled contributions of detailed reinforced precast concrete elements from Explore Manufacturing. "By September 2013, we were in a position to test our abutment proposals on structure S4, achieving installation of the east abutment in just three days, which elicited astonishment from interested parties," says Wood.
"This was closely followed," he adds, "by the equally impressive precast column and crosshead arrangements on structure S5, for which laser-cut stainless steel templates were made from the digital manufacturing model produced by Explore Manufacturing. The HA commented it felt more like an assembly area than a construction site," says Wood, and soon after his team installed its first braced pairs of fabricated steel girders, complete with permanent formwork, over the Midlands Main Line.
Laing O’Rourke approached the designers and supply chain to source suitable alternative products to loose laid bar and identified wire-tied carpet reinforcement for use on bridge decks.
Having carried out cost and programme impact studies using site achieved rates, the team confirmed that the use of wire-tied carpet reinforcement (compared with loose laid bar) would generate a reduction in bridge deck construction labour hours by approximately 30 per cent, a corresponding reduction in programme, and savings of around 5 per cent on cost.
A review by the HA structures specialists deemed wire-tied carpet reinforcement acceptable and it was adopted where practical, across the entire structures scope.
The team believed that an onsite peer review by the Engineering Excellence Group (EnEx.G) would be an ideal opportunity to share accumulated knowledge and changes to the original DfMA strategy, and in October 2013, invited an EnEx.G team, led by Sarah Williamson, to the site.
We reviewed, with the EnEx.G team, the application of DE and DfMA experiences on the project from a ‘gap analysis’ perspective, and focused our attention on what could be achieved with their support, within the available design and construction programme constraints, to bring about further improvements.
This included the production of a detailed 3D design model of the construction issue reinforcement for structure S12. Alongside this, the team trialled a combined total station and laser scanner, with the EnEx.G, to identify software to support progressive validation of the structure’s as-built position against the detailed design model.
In November 2013 the EnEx.G provided a full reinforcement model that had identified and proposed resolution to clashes. This was positively received and the construction issue design was updated to reflect the changes.
The following month, Laing O’Rourke held onsite workshops with the EnEx.G to review the available outputs from the model and agreed on content that met the requirements of both the HA and the Laing O’Rourke team. In early January 2014, the EnEx.G provided a full construction issue pack of reinforcement detailed design for structure S12 generated from the Tekla model.
Armed with this, the team trialled the use of the combined total station and point cloud scanner to set out and progressively validate the construction of the reinforcement on the structure S12 base slab, with the objective of preventing clashes and associated disruption to progress.
The combined expertise of Laing O’Rourke’s manufacturing, project delivery and engineering specialists enabled it to prove, to a once sceptical client, the benefits of DfMA and DE.
The challenge for the next scheme and indeed wider infrastructure sector will be to extend these solutions to the balance of the constructed asset and align the digital hardware onsite to maximise the benefit achieved.
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