Ipswich Town Football Club's new North Stand at its Portman Road ground seats more than 7,000 fans - 4,000 more than its predecessor - with vastly improved facilities including a club superstore, bar, WCs, lifts and staircases to provide easy access for all, including wheelchair users.
Since the publication of the Taylor Report on ground safety following the Hillsborough tragedy, many new football stands have been built, mostly with steel structural frames.
Ipswich's North Stand is different. The lower tier and main frame are of precast concrete;
the frame supports the upper tiers, concourse and roof in a truly hybrid concrete structure.
Precast concrete was chosen as the only material that could realise the design within the physical constraints of the site and the very short construction time available.
The site was a critical factor:
like many football grounds set in built-up areas, it is hemmed in by an existing infrastructure of roads and buildings - there was absolutely no space to extend. A basement was not an option - the site is on low-lying ground with a high water table.
The football season was another factor. 'We started detail design at the end of January , ' explains Mike Crook of architect HOK Sport, 'and we had to move on to site at the end of May so that the lower tier would be ready early in the next season.' (The club was in the Premiership at the time and the stand needed to be filled to capacity for every game).
Change of tactics To achieve this, it was clear that the team would have to re-assess design and procurement procedures radically. Precast concrete offered the advantages of shorter erection time, as the number of components is minimised; use of off-site fabrication; use of applied finishes; inherent structural fire resistance; and ease of erection.
The new stand comprises two tiers sheltered by a projecting steel roof structure and 'bookended' at each side by a three-storey tower of bar and ancillary accommodation.
Instead of the more usual tier structure - a steel frame supporting interlocking concrete terrace units - the lower tier is formed of a series of structural stepped precast concrete 'staircase' units - like a series of staircases set side by side. They combine the functions of the conventional steel frame/precast terrace unit to form a slim concrete slab without downstand beams, with self-finished and fire-resisting precast soffits. This approach maximised a critical dimension: the floor-toceiling height of the lower concourse, which ran below the tier (the position of the groundfloor slab was predetermined - it had to lie above notional flood level).
The lower precast concrete tier units rise to rest at their ends on beams spanning between a series of 14 massive precastconcrete shear walls at the rear of the stand. The shear walls - a dominant element on the rear facade where the main entrance is located - were the solution to the problem of how to increase seating capacity within the confines of the existing road layout.
Each shear wall is 3m wide, more than 11m high and is generally spaced at 7.6m centres.
The shear walls support the upper concourse - a steel and hollow-core precast floor plank structure - which extends beyond them on both sides, including a 3.6m cantilever over the adjacent road. Above the upper concourse, the shear walls are sloped at the tops to support the steel raker beams of the upper tier;
they also provide stiffness to the upper tier against overturning forces, allowing it to cantilever nearly 4m out over the road at its highest point.
The road layout was so critical that the shear walls had to be notched back from ground to first-floor level to stand at the edge of the public pavement.
Precast-concrete access staircases are set between pairs of shear walls, rising to give access to the upper concourse and to both lower and upper tiers.
'Open-book' success For HOK Sport and structural engineer Jan Bobrowski and Partners, quality of manufacture and tolerance control were critical to achieving the fast construction programme. It was decided that supply and erection of the entire structure should form one contractor package.
This was ultimately awarded to ABC Structures, with Trent Concrete as the precast-concrete supplier. The package was negotiated on an 'open-book' basis to allow the earliest possible specialist input into the design process.
This gave great flexibility - client and architect could select concrete types and finishes while the price was being negotiated.
The result: every precast unit fitted on site perfectly and the lower tier was completed in time for all the big matches.