A stunning new public park has opened at Gasholder No 8 in the old industrial lands north of Kings Cross station in London. Arup’s engineers share how the project came about.

Arup’s involvement in the wider regeneration of the King’s Cross area continues to evolve. Working in close collaboration with the King’s Cross Central Limited Partnership, led by developer Argent, Arup engineers have influenced the designs of a stunning new public park and striking visual marker, Gasholder Park, in the former industrial heartland.

Ensconced amongst contemporary residential apartments and nestled closely to Regent’s Canal, Argent continues to set the pace with investment in high quality public realm, comfortably bringing together modernity with Victorian industrial heritage.

“As a child of the Meccano generation, when it was red and green, who could resist the opportunity to help engineer the dismantling, refurbishment and re-construction of a large structure, which happened to be one of the few remaining examples of the Victorian mastery of iron work" - Richard Henley, lead structural engineer 

Designing the elegant canopy is part of the wider project which involved dismantling and re-erecting a Victorian gasholder. The project inside the frame once known as Gasholder No.8 opened to the public earlier this month and has been designed with Bell Phillips Architects.

To tell the story we have to start with the gasholder guide frames, which can almost be seen as a sequential development of the art and sciences of iron (cast iron to wrought iron to steel) and the associated opportunities that stronger and more reliable materials that led to larger gas holders.

The gasholders at King's Cross Station were built from 1860-67 for the storage of town gas. The gas was manufactured on site from coal by Imperial Gas, Light and Coke Company and formed part of one of the largest gas works in London.

The highly decorative frames were built with two tiers of hollow cylindrical columns and wrought iron riveted lattice girders, and were still in use at King's Cross until 2001. Strange as it may seem today, the Victorian gas industry was similar to the IT sector of the last three decades or so. These magnificent structures created a considerable utility infrastructure to the benefit of industry and society; attracting high levels of investment and consequently appealed to the finest engineering and technological minds.

Gasholder No.8 is a very refined example of the ironmasters’ engineering and craft skills, comprising cast iron tubular columns with wrought iron lattice beams with no cross bracing. This was witnessed by Arup engineers during the dismantling and refurbishment process.

During the masterplanning stages for the King’s Cross development it proved impossible to retain the gasholder in-situ without considerable loss of presence to the surrounding landscape, which had prevailed for many decades, despite the removal of the gas works and closing down of the railway yards. The gasholder silhouetted the skyline and had become an important feature for the local community, and those passengers arriving and departing from King’s Cross Station.

It was agreed that Gasholder No.8 would be refurbished and relocated on a site north of and adjacent to Regent’s Canal to create a free standing enclosure to public space.

Structural assessment as an activity is different to design. The fundamental questions posed were “Is the structure adequately safe now and will it remain so in the future”? In the case of the gasholder, Arup engineers had to make the assessment on the basis that the structure could be dismantled and refurbished; thus ensuring the legacy of our industrial heritage would remain part of the landscape in the 21st Century.

“Walking around King’s Cross really shows how the quality of the public realm is key to creating destination spaces that are a pleasure to inhabit" - Simon Bateman, structural engineer

“As a child of the Meccano generation, when it was red and green, who could resist the opportunity to help engineer the dismantling, refurbishment and re-construction of a large structure, which happened to be one of the few remaining examples, of its type, of the Victorian mastery of iron work and making it accessible for public enjoyment,” says associate director and lead structural engineer Richard Henley.

“It was by no means a journey of pure nostalgia as to bring this gasholder into public use without the need for overtly modern intrusions required a fairly sophisticated fusion of historic inquiry and the exploitation; of how our understanding of materials and structures has evolved since its original manufacture. In its new life Gasholder No.8 is simultaneously a celebration of the past and presents the wonders of engineering and manufacturing that radiate from its physical presence”.

To complement the surrounding landscape the aspiration was for a new canopy to increase in openness as the elegant structure met the canal to the south west. This was realised by having a gradation in structural density from one side to the other, with a solid roof supported by closely spaced columns to the north east. A heavily perforated roof and sparse column spacing was designed for the opposite side. This effect was further magnified by the orientation of the columns, which appear larger when moving around the canopy from the canal than when moving towards it. The entire canopy is fabricated from mirror- polished stainless steel.

“Experimentation and exploration have remained at the heart of this project for Argent. The quality of the engineering designs of the new canopy had to match that of the historic gasholder guide frame" - Ed Clark, project director

Arup’s engineers used parametric modelling software (Grasshopper) to help the architect quickly explore a number of possible column layouts. Different mathematical rules and parameters were used to set out locations of the columns. The canopy roof would be made from a slender stainless steel plate with relatively flexible joints between panels.

It was important to check that the plate would not deflect so much under its own weight and detract from its crisp and flat appearance. By testing potential column layouts in the analysis software engineers were able to provide the architect with 3D models to help visualise this distortion. Arup suggested adjustments to the column layout to ensure these provided optimum support to the roof plate.

“Experimentation and exploration have remained at the heart of this project for Argent. The quality of the engineering designs of the new canopy had to match that of the historic gasholder guide frame" - Ed Clark, project director

Once the column layout was fixed, parametric modelling skills were used once again to assist with generating the layout of perforations through the roof plate. The perforations are parallelogram-shaped and, although at first glance appear random, are laid out on a grid which is closely related to the orientation of the columns.

As well as the architectural aspiration of increasing porosity of the canopy, the team was keen for the perforation density to respond to the structural behaviour of the plate. To achieve this, engineers developed an algorithm, incorporating a stress plot from a structural analysis of the canopy, to generate “random” sizes and dispositions of perforations. The openings are most frequent, and largest, at the southern end of the canopy, and in areas of low stress. Perforations are least frequent and smallest at the northern end, and also where stresses are highest.

Simon Bateman, structural engineer leading on the parametric modelling commented, “Everybody on the project wanted the canopy to be as good as it could be and was willing to go a little further to add as much to the end result as possible. We worked extensively with the architect in exploring different ways of bringing together the architectural and engineering requirements for the canopy, using software which let us experiment with dozens of potential designs for the perforated roof in just a few minutes. 

"The team also collaborated at length with the fabricator in developing joint details which were outside of the usual catalogue, yet still buildable, in order to suit the architectural ambition. This was a fun project to work on, to create a new landmark for King's Cross”.

As well as this work in a virtual environment, a physical mock-up was fabricated to test both the visual quality and the buildability of the proposals. This exercise also served to shape the final form of the canopy, and moved the team away from a fully welded solution which would have not delivered the design intent. Arup also worked with the fabricator to develop a testing regime that would enable engineers to validate some of the more bespoke connections and to tune the analysis model to be more representative of its physical behaviour.

“Walking around King’s Cross really shows how the quality of the public realm is key to creating destination spaces that are a pleasure to inhabit. Playing a pivotal role in creating the features of the stand-out open space has been fantastically exciting, and seeing people enjoy the park and understanding the concept is the most rewarding part of all,” says associate director Simon Lindop.

The Arup team has been fundamental in every component on this stunning centrepiece, to the historic frame, and its subtle elegance is a testament to our skills and commitment to this project”.

Arup also designed the civil engineering elements associated with achieving the landscaping requirements of the site, comprising significant numbers of retaining walls and ancillary foundations to support further elements such as the rollers.

Ed Clark, Project Director concludes:  “Experimentation and exploration have remained at the heart of this project for Argent. The quality of the engineering designs of the new canopy had to match that of the historic gasholder guide frame. The use of 21st Century design tools, materials, details and fabrication techniques have allowed Arup to create a delicate and elegant response to this wonderful Victorian backdrop.”