At the University of Bristol’s flagship Sloane Robinson Building, FCB Studios and Buro Happold show that shorter spans and lower carbon don’t need to mean less flexibility. By Nick Jones
There is a tension at the heart of most new university buildings. They must be flexible, to keep up with the fast-changing world of learning, teaching, testing and researching. At the same time, universities are under pressure to reduce the embodied carbon of their estates.
Flexibility tends to translate into carbon: “loose-fit” column-free spaces need long spans and deeper slabs, supported on a chunkier frame and larger foundations. “It’s a difficult one to balance with the aspiration to limit embodied carbon,” says Ian Fiebelkorn, associate director at engineering consultancy Buro Happold. The Sloane Robinson Building, the flagship building at the University of Bristol’s new Temple Quarter Enterprise Campus, is a valiant attempt to solve the problem.
Designed by Feilden Clegg Bradley Studios, with Buro Happold providing multidisciplinary engineering services, it bears all the hallmarks of a modern, multipurpose faculty building. Across six storeys and 38,000m2, there are a range of teaching areas, research labs and workshops, all organised around two full-height atriums. There is a 300-seat lecture theatre and a huge publicly accessible entrance hall. And yet it is largely based on a modest 7.5m x 7.5m grid.
This has made a huge impact on the building’s carbon impact – reducing the structural embodied
carbon by 25% compared with the original 15m-spanning design. So how did Buro Happold achieve this without losing the looseness? It started with Covid. With the project still in its early stages and the world on hold, the structural solution suddenly came into sharp focus. Buro Happold had originally designed the building with a steel frame and hollowcore planks to maximise future flexibility. This spanned a 15m x 7.5m grid with minimal downstands, limiting potential disruption to services.
It was, however, “quite heavy on the steel”, says Fiebelkorn, while the planks were also deep: 400mm with a 75mm in-situ concrete topping. Against a changing economic backdrop, the team revisited the structural approach. “We asked whether we could make a fundamental change to create a more efficient building, and deliver significant embodied carbon savings,” says Fiebelkorn.
By this stage, the project team had a fuller understanding of the different functions of the building and how much flexibility they really needed, he explains. They worked out that by introducing an intermediate grid line and switching to a reinforced concrete frame with 300mm-deep flat slabs, they could reduce the structural embodied carbon from 487 to 354kgCO2e/m2 without affecting the majority of the building uses.
With a better understanding of the functioning of each room, they could also avoid localised strengthening in areas such as the quantum computing labs, which needed strict vibration control. “Rather than making the structure respond perfectly everywhere through expensive strengthening, we could focus key equipment in less excitable areas.”
The biggest impacts of the new grid were on the lecture theatres and the multi-use spaces for teaching very large numbers of students. “These functions want to be at ground level, so we have incorporated transfers where necessary to allow the areas above to remain on the more efficient grid.” The result does not appear grid-like or plagued by columns.
Behind the facades of glass and pale precast concrete, the spaces unfold in a sequence of visually connected public routes and 7m-wide corridors. The ground- floor reception is huge: 37m long and 6m high, with a 15m-wide avenue running the full width of the building. A bright yellow double-width staircase leads up to the main atrium, which extends through the upper five storeys.
This vast open area is framed in exposed concrete columns and slab edges, with sharp joints expressed at the intersections between the two, while a monumental fluted-concrete core rises all the way up to the roof. There are a number of larger spaces integrated into the plan: active learning areas for up to 90 students, the quantum computing lab, a ground-floor events space and workshop areas.
The centrepiece is the lecture theatre, which takes the form of a 15m-diameter circular steel drum with 360-degree screens, suspended from the concrete frame. “Originally, that space was going to be split into two more conventional lecture theatres,” says Fiebelkorn. “But when Covid hit, the university did a lot of work looking at the future of learning, and said, actually, this is a better format for us.”
TEMPLE RISING
How the university is leading Bristol’s new city-centre district
The Temple Quarter is a 130ha regeneration scheme next to Bristol Temple Meads Station. The plan is to turn a swath of loosely connected post-industrial sites, empty commercial units and car parks into a new district providing 10,000 homes and 22,000 jobs.
The Sloane Robinson Building is one of the Temple Quarter’s flagship developments, the centrepiece of a 7-acre university campus on an island site between the River Avon, a feeder canal into Bristol’s floating harbour and the railway. The site previously housed a brutalist Royal Mail sorting office, which had lain derelict for decades.
The project has also included wider landscaping of the pedestrian campus, a new £23m eastern entrance to the station and connections to river walkways into the city.
Throughout the interiors, as-struck concrete exudes permanence while an overlay of exposed services suggest more of a plug-and-play approach. Lighting and ductwork are suspended from the soffits, again clearly expressing the idea of the building as layers that can be renewed in different cycles. Apart from the toilets, there are no suspended ceilings anywhere in the building.
Despite the expanses of visual concrete, few special finishes were specified. The only exceptions were the soffits and entrance walls in the public reception area, for which FCB Studios designed the plywood board layouts, and the atrium’s feature core, which was cast using a flexible formliner to give definition to the fluted surface.
“Bristol were very open to having characterful concrete,” says David McLeod, contract manager at frame contractor Toureen Group. As part of the early engagement, Toureen produced a large sample panel to test tie hole arrangements, board layouts and different shutter types – a joint decision was taken to use timber rather than steel, due to its less shiny finish.
Lower-carbon concretes have been used throughout. Again, the Covid lockdowns enabled a change of approach to specification. “Usually it’s quite a linear process,” says Fiebelkorn. “The engineers specify their requirements, and that gets passed to a contractor who adds their requirements for early stage design, and that then gets passed to a supplier.
A CERTAIN RATIO
How Toureen fine-tuned the concrete for long pours and fluted cores
One of the biggest challenges facing concrete contractor Toureen Group was the double-height ground floor – the main public route – which FCB Studios wanted to convey a strong civic quality. Contracts manager David McLeod took the ambitious decision to cast the vertical elements in a single 7.2m-high pour to avoid horizontal joints and emphasise the sense of scale.
Toureen’s intention had been to increase the GGBS in the concrete from 35% to 40% in these areas, in line with its own carbon-reduction commitments. However, initial tests showed some evidence of water bleed during the high-pressure double-height pours. McLeod suggests that this may have been due to the local limestone aggregates, which don’t offer the same cohesion as gravels used elsewhere in the UK (although they did seem to improve early strength gain in the high GGBS mixes).
The concrete design for the ground floor was adjusted to increase the cement content from 300 to 370kg/m3 – the minimum deemed necessary to avoid bleeds. The GGBS was reduced to 36% and the water-cement ratio lowered from 0.55 to 0.45. Superplasticisers were added to keep the mix workable.
The concrete team were nervous that the smoothness of the flexible formliner used on the fluted feature core might still cause water to rise to the top of the pour, leading to further bleeds. Although embodied carbon was the priority with most of the concrete, the surface quality of the core was paramount.
The decision was therefore taken to also use the redesigned mix on the 3.6m lifts for the upper levels of the ribbed feature core. “There was a lot of pressure to achieve the crispness of the joints because it’s a real visual centrepiece,” says McLeod. “It does dominate the space, and it looks fantastic.”
Instead, we held a series of workshops where we talked about the practical limitations. So rather than us as engineers saying, just take as much carbon out as possible, we were taking on board everyone’s drivers and coming up with a compromise position, and actually getting to the most efficient practical solution.” With high levels of GGBS available locally at the time from the Port Talbot steelworks, the specification included 75% for the foundations, 50% for the columns, ground-floor slab and retaining walls, and 35% for the superstructure slabs.
All proposed concrete mixes were assessed against the Lower Carbon Concrete Group (LCCG) market Benchmark, and all materials were monitored on site by main contractor Sir Robert McAlpine using a proprietary tracking system. Of more than 35,000m3 of concrete poured, 93.7% was B-rated or better, aligning with ConcreteZero’s definition of “low embodied carbon concrete”.
On top of the carbon savings made during the design process, the specification of A- and B-rated concretes reduced the total structural embodied carbon to 268kgCO2e/m2, almost half the original long-span steel frame and close to the LETI 2030 target of 228kgCO2e/m2.
A lot of this was down to asking the right questions of the right people at the right stage of the process, which led to a more efficient structure, more achievable concrete mixes and a far clearer idea of what the client meant by flexibility. It seems that loose fit might be going out of fashion: the future lies with clever tailoring. Watch Ian Fiebelkorn talk about the Sloane Robinson Building on the Concrete in Practice webinar.