Industrial revolution

Ed Shearer from Arup reports on how a residential project has transformed Victorian gasholders in London to provide surprising luxury while embracing heritage

The Victorian era left a long architectural legacy in London, with many examples of architecture and industrial heritage providing lasting widely-recognised symbols of the city. The boldness and ingenuity of Victorian engineers is still visible across the capital, and 21st century engineers are adopting modern analysis and digital tools – combined with ingenious structural engineering – to revive and re-imagine these historic structures. The Gasholders London project exemplifies this marriage between contemporary urbanism and Victorian industrial heritage.

In King’s Cross, a group of iconic Victorian gasholder guide frames emerge from the landscape of canalside docks and warehouses. Three of these, aptly nicknamed the ‘Triplet’, stand boldly on the north bank of Regent’s Canal. Fully restored and re-erected, these frames have been given a new lease of life by the project to create a luxury residential offering.

Adaptive re-use of industrial structures

The Gasholders London project, which was structurally engineered by Arup and designed by architects Wilkinson Eyre, re-imagined these structures by repurposing them for an entirely different function, and thus avoided them falling into disuse.

The project is a stunning example of adaptive reuse of industrial structures, which would otherwise remain unused. In a time of increasing urbanisation, such projects are essential to land conservation, and the reduction of urban sprawl.

Arup has played a critical role in the re-rejuvenation of the capital’s Victorian landmarks, including King’s Cross Station and the recently opened Exhibition Road Quarter, V&A. It has also been involved in the restoration and reuse of other listed structures as part of the King’s Cross Central redevelopment vision, such as Midlands Goods Shed and Gasholder Park, a beautifully landscaped urban park nestling inside guide frames. Gasholders London brings back to life and celebrates the charming appeal of iconic industrial structures, while providing luxury residences to an existing King’s Cross site.

Close collaboration

Arup has worked closely with developer Argent on its vision to regenerate the former industrial site north of King’s Cross since the partnership took ownership of the land in 2000. From early feasibility studies informing the masterplan, through to delivery of many of the buildings, Arup has provided integrated and holistic multidisciplinary advice throughout this complex development. Retention of the rich industrial heritage at King’s Cross is central to the story of Argent’s vision. And the repurposing of the gasworks infrastructure, so quintessential to the area, is a thrilling starting point for much of the new public and private space.

Working with Grade II listed frames

The project presented unique engineering challenges, both in the restoration of the Victorian gasholder guide frames, and in the design of the new residential blocks in collaboration with architect Wilkinson Eyre.

The Grade II listed guide frames were built in 1879 to house new, enlarged storage drums for gasholders 10, 11 & 12, which remained in active use until 2001 when they were dismantled to make way for the construction of the new Channel Tunnel Rail Link from St Pancras International.

The frames, comprising cast iron columns and wrought iron lattice beams, were stored temporarily at the east edge of what was once the gasworks site. A series of studies by specialists at Arup defined a strategy for restoring and repairing the guide frames, such that these could safely be reassembled and remain as a popular feature of the local landscape.

A new location on the north bank of Regent’s Canal was identified for the frames and, in a competition announced by Argent, Wilkinson Eyre won the commission to design residential apartments based on its concept of three cylindrical blocks set within the guide frames. With a strategy for their reuse in place, as defined by Arup, the frames were relocated to Barnsley for refur- bishment by Shepley Engineering and structural engineer, Craddy, and design of the new residential blocks began.

Arup provided consulting advice on structural, civil, geotechnical, facade and wind, and Hoare Lea led on building services.

The structural engineering challenge

The geometry of the guide frames posed a significant constraint to the design of the new buildings, and successful delivery of high-spec residential units within required careful integration of design goals

from the start. Taking design decisions early was key. Detailed early studies of the floor plates justified ambitious

minimum structural depths, set storey heights, and enabled early apprehension of an efficient yet flexible structural diagram. These allowed Wilkinson Eyre to proceed with extensive massing studies to achieve the right unit mix. The result: three lean concrete frames, optimised for maximum internal space, on a grid accommodating a large variety of non-stacking apartment layouts and basement parking, without resorting to transfer structures.

Drawing opportunity from constraints

Non-linear analyses of the slabs justified efficient and simple reinforcement detailing for ease of construction. A unitised cladding system was proposed by Arup’s facade engineers whereby cladding and balconies, assembled offsite, could be lifted into place and installed without external access, with minimal impact on the re-erection of the restored gasholder frames two metres from the building envelope.

In the centre of the three circular blocks, a fourth ‘extruded’ circle provides an open courtyard where the intersection of the three Victorian gasholder frames is revealed. Floating at the top of the courtyard, circular steel bridges provide graceful links between the three residential blocks.

Making use of the geometric stability of a closed ring, the bridge decks are supported from the buildings on a single row of diagonal props without the need for horizontal tie-back elements. This pared-down structural diagram not only provides a sense of lightness, it also releases restraint forces generated by thermal movements in the decks and sway in connecting buildings.

Specialised shutters

A key feature of Gasholders London project are the motorised sliding, folding shutters over which residents have individual control, as can be seen above. At 4 metres high, the shutters are unusually tall and with four panels each operating concurrently around a faceted curve, these presented a challenge. Their reliability and operation was paramount to the facade’s success. Arup’s facade engineers defined a full test programme, which included life-cycling of the system, impact and simulated wind loads. This gave everyone confidence that the shutters could withstand even gale force winds in any open position.

A fusion of historic and contemporary design

The design of Gasholders London is an exciting exchange where contemporary architecture responds to Victorian infrastructure; and state-of-the-art engineering re-unites with its industrial past. Gasholders London exudes the symbiotic relationship between the art and science of engineering.

The fusion of historic and modern design for Gasholders London now completed is a joy to behold; the slender steel bridges sharply contrast, and complement the Victorian ironwork of the guide frames, providing an eloquent counterpoint. This meeting of history and modernism is a consistent theme across the wider King’s Cross Central vision. Brick, iron, concrete and steel all meld perfectly, underpinning complex design and engineering solutions.

Gasholders London was a rewarding project to be part of, born out of intense and creative collaboration between developer, architect, engineer and contractor, and the result is truly striking.

Ed Shearer is a structural engineer at Arup