Design changes to Old Oak Common station will result in a £7m saving
Engineers at WSP have reduced the amount of structural steel required to build the station roof at HS2’s Old Oak Common station by 27%, after a series of value engineering reviews.
WSP, with SME Expedition Engineering and architects Wilkinson Eyre, used results from wind tunnel tests and a snow load review, to conclude that structural thicknesses and profiles in the station roof could be modified to reduce the amount of steel needed by 1,000 tonnes.
The changes will result in a cost saving of £7m, as well as a 2,700 tonne reduction in embodied carbon.
Adrian Tooth, project director at WSP, said: “Taking the benefits from wind tunnel testing and snow modelling, we have been able to make small incremental changes and reductions in material thicknesses of the roof resulting in a significant saving in the cost of the station”.
“Further applying the benefits from these techniques, we were able to harness savings and due to the reduction in material tonnage, realise the logistical benefits of reduced crane sizes.”
Matthew Botelle, HS2 programme director added: “By challenging the standard design approach, the WSP-Expedition design team have realised savings in the roof steelwork tonnage that has significantly reduced cost, construction complexity and embodied carbon.”
Dr. Pete Winslow, associate structural engineer at Expedition, said: “As the roof shape is not fully represented in the wind and snow loading design codes, testing was carried out together with specialists RWDI to establish more representative loads; proving them to be less than the code suggests.
“The WSP-Expedition team has then refined and validated the structural design all whilst maintaining Wilkinson Eyre’s architectural vision for the station”.
The roof at Old Oak Common comprises a series of tapered vaults with glazed rooflights to provide ventilation and daylight for the station. Spanning up to 65m, the vaults are formed from fabricated steel box section arches and are supported on box section primary beams founded on tapered steel columns.
Fabricated using weathering steel, the visible parts of the roof steelwork will be painted for aesthetic reasons.
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WSP seem to have done a good job but as an industry, we need to be careful about banding the Value Engineering tag around.
If the party who initially went along with a worst-case, over-design of the elements they are responsible for, knowingly or otherwise, later refines the design to find the optimum solution, isn’t that just “Engineering”?
As a Client, I would be more than disappointed to be told this was something beyond a normal service. Worse still, I would be horrified if I had not been told the potential for the significant saving was there when given the initial input. We don’t know if this happened here but sadly, Value Engineering tends to be used to describe refinement that nearly got missed. If a refinement nearly got overlooked, It immediately begs the question as to whether there may be other items slipping through the net of proper design.
£7M saved for 1000 T of steel. Why is the steelwork costing £7,000 per tonne in the first place?