“Fastrak enabled us to visualise a very complex structure in a 3D environment and then provided us with all the tools to deliver what we needed.”

Jonathan Svikis, Structural Engineer at Mott MacDonald

Fact file

Name: Mott MacDonald

Location: Croydon, UK

Incorporated: 1976

Key details: Forge Valley – delivered for

Sheffield City Council – is an environmentally

and socially sustainable, £25m community

school that includes a five-storey learning

hub and two-storey sports centre, and can

accommodate 1500 pupils.

CSC products:Fastrak

Key benefits of Fastrak:Mott MacDonald designed a complex

structure and reacted quickly to project

changes using Fastrak, reducing project

down time and increasing efficiency.

The challenge

Forge Valley Community School is the flagship project of the Sheffield BSF programme comprising 12,000m2 of accommodation for 1,500 pupils in the form of a five-storey learning hub and two-storey sports centre. The design required a structural solution that complemented the concept of an environmentally and socially sustainable, flexible building able to support a variety of activities undertaken by the wider community outside of school hours. This concept has driven the design away from standard classroom modules towards a series of exciting, open-plan, multi-functional spaces. Structural efficiency, sustainability, buildability and value for money were essential requirements. Procured via a D&B contract, the £25m scheme was designed by consulting engineers Mott MacDonald with VINCI Construction UK as the main contractor, and was handed over to Sheffield City Council in September 2011 following an 18 month construction programme. The final structural design played a significant role in achieving BREEAM Very Good and DfA 60% carbon reduction targets.

The solution

The engineering challengeThe design of Forge Valley Community School was complex and the architect’s exciting form threw up a number of interesting engineering challenges.

These included:• Framing of a five-storey, 25m x 40m column-free central atrium and undulating feature roof

• Requirement for transfer structures supporting inset storeys and plant loading within tight deflection limits above a multi-use performance hall

• 20m clear-span feature entrance canopy

• Curved plan geometry around central atrium requiring a complex stability strategy

• Steeply sloping site requiring over 100m of retaining structures supporting columns carrying significant, varying loads

As is often the case, the more complex the structure, the more beneficial software becomes, and by taking advantage of the integrated building design approach with CSC’s Fastrak software, Mott MacDonald was able to handle the challenges accurately, quickly and with confidence.

A complex designThe architect provided 2D drawings which were hard to visualise as the building was geometrically complex. After importing the drawings into Fastrak and creating a 3D model, Mott MacDonald was better able to understand what the architect was trying to achieve. The 3D model provided a frame of reference for the project team and enabled Mott MacDonald to identify potential issues early in the design process.

“With Fastrak we could alter the geometry, changing levels and grid arrangements with ease. This reduced project down time and increased our productivity.”Jonathan Svikis, Structural Engineer at Mott MacDonald

Discover the benefits of Fastrak for yourselfVisit: www.cscworld.com

Contrary to the typical design of schools, which often comprise a number of structurally independent blocks, the architect’s vision was to have a single multi-purpose structure all sharing the same footprint. The design therefore incorporated a diverse range of structural elements encompassing trusses, composite construction, precast planks, supporting purlins, simple roof beams and Westok beams to name a few. Rather than using a range of elemental design packages, Mott MacDonald was able to design all the different structural elements within Fastrak, understanding how all the elements interconnected, rather than reviewing each member in isolation. Mott MacDonald also found Fastrak invaluable when considering the structural stability system which included moment frames, braced frames and shear walls. Using Fastrak, Mott MacDonald was able to quickly identify the most cost effective solution.

Atrium and roof landscapeThe focal point of the design was the 25m x 40m column-free central atrium. The architect specified the atrium as column-free, hence the design combined long span trusses and cantilevered beams with hidden columns to accommodate the library, lecture theatre, corridors and breakout dining space. This in itself presented engineering challenges which Fastrak helped Mott MacDonald overcome.

Architectural steel roof trusses spanning up to 28m were adopted to provide a cost-effective, high-quality solution in favour of a more expensive glulam option. Mott MacDonald used the truss design functionality within Fastrak to trial different geometries, member arrangements and depths for the long span trusses, in order to optimise the design.

The trusses ranged between 2.5m and 4m deep and integrated seamlessly within the north-lights, geometrically defined as part of the team’s sustainable energy strategy to flood the atrium with daylight. A visually dramatic saw-tooth roof expressed both

internally and externally was created by cranked steel beams spanning 10m between trusses, which reduce in height to mirror the surrounding landscape.

The beams skew by varying angles to accommodate a change in geometry of 45 degrees on plan. A lecture theatre at the base of the atrium supported an open plan learning centre above. Westok beams and composite slabs provided the required large, clear spans and optimum services distribution within.

Steel beams cantilevering from concealed columns around two sides of the atrium perimeter provided impressive floating circulation routes. A feature steel stair, comprising an unrestrained 13.5m tall central column, supporting a series of 3m wide cantilevered flights and landings created a striking focal point within the space.

The overall structural solution to the atrium employed simplistic load paths and connection details which minimised costs and maximised buildability. The use of long span trusses and cantilevered floor plates eliminated internal columns to the 40m x 25m space, providing an adaptable, socially sustainable environment suitable for a multitude of activities.

Multi-functional performance spaceA spacious 35m x 15m column-free performance space was provided at lower ground floor level. Two 5m high, 15m long movable acoustic walls suspended from the first floor structure, as well as two inset storeys above and high plant loading at roof level, presented a significant challenge. This was overcome by the efficient use of 1.8m deep steel transfer trusses spanning 15m within the ceiling void. To ensure reliable performance of the movable walls, imposed load deflections to the supporting trusses are limited to span/1000.

Faced with an awkward footprint and many transfer levels, Fastrak was invaluable in helping quickly predict load paths and accurate foundation forces.

In order to supply the separate piling designer with data, Mott MacDonald extracted reactions and pile loads quickly using Fastrak’s design focused output.

Due to the critical nature of the transfer structures, key element design was undertaken for the supporting columns. Catenary ties between adjacent trusses were also designed-in to provide additional load paths and robustness. The ground floor slab was designed to accommodate loads from retractable tiered seating creating a large flexible space.

The result

Jonathan Svikis, Structural Engineer at Mott MacDonald, said: “Fastrak enabled us to visualise a very complex structure in a 3D environment and it then provided us with all the tools to deliver what we needed. We encountered many project changes, but with Fastrak we could alter the geometry, changing levels and grid arrangements, with ease. This reduced project down time and increased our productivity.

Fastrak gave massive efficiencies when generating code compliant documentation for issue to the local authority for building regulations approval, including detailed calculations for all elements. This was a major change from using an analysis package which would have simply provided member forces. The level of detail required can easily be controlled to produce a very clear and consistent set of calculations that are easy to review. This integrated approach saves an enormous amount of time and reduced the risk of documentation mistakes.”

Discover the benefits of Fastrak for yourselfVisit: www.cscworld.com