Seele structural shells
King’s Cross Station redevelopment, London
Simon Jenks, project director, Vinci Construction UK
The King’s Cross scheme is a £500m project to restore the grade I listed station designed by Lewis Cubitt in 1852, as well as designing a new concourse to feed it.
The new steel concourse roof, designed by architect John McAslan & Partners and engineer Arup, is essentially a semi-circle of 16 steel beams connected to a funnel of steel columns radiating out from the front of the old ticket hall in the grade I listed building. Roof loads are transferred to the ground by 16 “trees” around the perimeter.
Vinci decided that Seele, having worked on Munich’s Allianz Stadium, as well as on Westfield at White City, demonstrated the capability to manage major projects as well as giving us the best value for money. Their integrated solution is a steel diagrid supporting an aluminium cladding and glazing frame at node points. This diagrid provides lateral support to the primary steel members. It is self-supporting, but tied back to the original station’s west facade.
Being a public station, the main structure had to be welded rather than bolted, to meet the strict criteria for blast resistance. This was delivered in the largest sections possible — a logistical issue that involved abnormal loads and night-time delivery.
To construct it, Seele needed to build a special birdcage scaffold that remained in place until the steel was self-supporting and the roof cladding was on. When it was removed, it was thought deflections would be in the order of 120mm, but in the end, they were nearly half that.
The roof was started in April 2010 and was completed in July. The weight of the steel structure is about 1,200 tonnes, but it is covering a total area of 9,000m2.
It might not compete on scale with the neighbouring St Pancras station, but in terms of “wow” factor, it’s a fantastic new terminus space for London.
Product news
timber frame housebuilders that are fed up with having to store uPVC windows on site to fit later will be pleased that window and door manufacturer Sidey has a solution that kills two birds with one stone. Its KitFix system enables timber frame kit manufacturers to install finished windows into its panels as part of their factory production, which it says results in faster construction times, simpler supply chains and reduced costs. Not only that, it also addresses problems with theft and health and safety concerns with on-site fitting.
The steel frame of the new Forsyth Barr Stadium in New Zealand, designed by architect Populous and the setting for some of this year’s Rugby World Cup Games, has been honed to some fine diameters despite its 105m span, thanks to Vector Foiltec’s Texlon ETFE membrane. This cut the loads to a tenth of those normally associated with the use of glass. It not only allows the light in, creating a perfect environment for growing the pitch’s natural turf, but it is strong enough to keep the South Island’s winter snows out.
Architect timothy Hatton put the hard-setting fabric Concrete Canvas through its paces at the London Design Festival this year by forming structural columns and trusses from the concrete-impregnated material. The 7m x 8m x 2.4m high “Pavilion” derives all its structural strength purely by casting the flat material in primitive three dimensional moulds. Strong, durable and fast to deploy, it looks like Concrete Canvas can be used for aesthetic as well as emergency applications.
Tips of the Trade
Cross-laminated timber (CLT) frames in multi-storey construction
| 01 The modular form of CLT lends itself to cellular forms of construction, providing early stability through construction. There is no need for formwork, with panels being fabricated under factory conditions to incorporate perforations for glazing, services, or door openings. |
| 02 Don’t be limited in scale. Buildings as high as 17 storeys have been built in Europe using cross-laminated timber construction. CLT members, although essentially massive panels, need not only be thought of as walling and decking members, as whole structures can be built using CLT, including the stability cores. |
| 03 Jointing of CLT panels is critical in terms of both structural performance and thermal performance. Concerns exist over the interconnection of panels, particularly in multi-storey construction, both on an elemental level, and also when considering the overall stability of large-scale structures in terms of progressive collapse. |
| 04 Careful attention to detail is paramount, as well as high level of construction management to ensure that buildings of this form are inherently safe once constructed. In terms of disproportionate collapse, buildings of substantial height are covered in Approved Document A to the BuiIding Regulations. |
| 05 Take build time into consideration. Apartment blocks of average footprint can be erected at the rate of a new floor every two days. Rapid erection produces savings on site preliminaries, but careful timetabling is necessary to ensure follow-on trades are planned appropriately. |
By Alan Murray, technical author at the British Standards Institute
