AWARD – n2 Nova Evolved, London

Built on a congested site with important water and transport assets underneath, a 17-storey commercial building forms the second phase of the Nova development in central London.

FACT FILE
Architects: Lynch Architects, Veretec
Structural engineer: Robert Bird Group
Steelwork contractor: William Hare Limited
Main contractor: Mace
Client: Landsec

Located opposite London’s Victoria railway station, on a plot directly behind the Victoria Palace Theatre, n2 Nova Evolved offers 14,800m² of office space along with terraces on the upper levels.

Built on top of major London Underground and Thames Water assets, the building is said to be an excellent example of how engineering excellence can unlock value in heavily constrained sites without compromising quality and sustainability.

Landsec Project Director Damien Bettles says: “Built on one of London’s most bustling sites, n2 Nova Evolved could only be supported on a small number of large diameter foundation piles positioned in between the subterranean assets.

“To overcome this challenge, the ground floor and first floor spaces are cleverly designed around a system of steelwork trusses, able to transfer the optimised commercial grid of the 17-storey commercial superstructure to the foundation piles. With spans of up to 45m, the use of steelwork for the truss system was key to delivering a sustainable design solution.”

As the space to install new foundations was very limited, the only option was to install a few very deep piles, with one of them as close as 1.5m from a London Underground tunnel. To achieve the required capacity, some of these piles had to be designed to reach almost 80m, which is said to make them the deepest piles in London.

To guarantee foundation optimisation, a pile test was carried out on site in order to justify a reduction in pile diameter from 2.4m to 1.8m.

Structural steelwork starts at ground level; sat atop a concrete basement substructure. In total, there are eight trusses all positioned at the lower levels of the building. They not only form bridges between the pile locations but also create column-free spaces for the ground, first and second floors.

“We worked together with the client and architect to provide the optimum superstructure grid for the scheme. However, due to the presence of the assets below ground, we needed to design a series of internal and external trusses to transfer all superstructure loads down to the foundations,” says Robert Bird Group Associate Director Alejandro Cruz.

Positioned between ground floor and level three, the trusses vary from single to double-storey height elements.

Three internal full height trusses at level two span between the core and an eastern perimeter truss. These internal trusses where integrated with the plant room that is located at level one and level two.

Probably the two most visible trusses are known as A and 6A and they form the main southern and eastern façades of the building. They both start at ground level and extend up to the underside of level two.

Truss A measures 44m-long and is 10m-high, and was brought to site in transportable sections and then erected in-situ. Typically truss A, along with all of the other trusses, is fabricated from steel plate ranging in thickness from 25mm to 75mm.

A slightly different erection procedure was needed for truss 6A, as its bottom chord needed to be installed as a complete 27m-long section.

“This bottom chord is fabricated from 150mm-thick plate as the loads on this side of the building required a more robust truss,” explains William Hare Project Director Richard Mosek.

Welding up this truss on site would have been too time consuming, so the complete 53t bottom chord was brought to site and lifted into place as one piece. Using a 450t-capacity mobile crane, the lift was completed during an overnight weekend closure of the adjacent thoroughfare.

Once in place, the remaining members of the 10m-high 6A truss – the connecting columns and the top chord – were subsequently brought to site in transportable pieces, and erected in-situ using bolted connections.

Another truss, known as 3A, is also located at ground level and also extends up to the underside of level two. Situated along the western elevation, abutting an adjacent building, this 22m-long truss will not be in view in the completed scheme.

Much of the ground floor footprint, set within the V-shaped truss columns forms public realm, with the reception area and first floor both set-back towards the western elevation.

The second floor plant level covers the structure’s entire footprint as do the office levels that extend upwards from level three. Adding some architectural interest, the uppermost office floors incorporate balconies and terraces.

A further five bridging trusses help to create the open plan column-free spaces for the lower floors, while also supporting the columns for the upper levels. The office accommodation is based around a regular 9m × 10.5m column grid pattern and so the trusses are needed to support columns that do not extend down to ground level.

Landsec are signatories to SteelZero, and the developer says it is encouraging steel producers to decarbonise steel production, and a proportion of the steel used on this scheme came from recycled sources.

“By joining SteelZero, we’ve made a commitment to transition to 100% of our steel requirement to be net zero by 2050 and to transition 50% of our steel requirement to meet the SteelZero interim criteria by 2030,” says Mr Bettles.

Summing up, the judges say a complex site with congested services, restricted building supports to just a few points, resulting in steel trusses creating a distinctive double-height feature at ground floor. Secondary transfer trusses between first and second floors house the plant, with the rest of the building free to create a unique, top-class office space.