American Air Museum, including 'Counting the Cost' war memorial

American Air Museum

Museum exhibition hall built in 1995-1997 to designs by Sir Norman Foster and Partners, with Ove Arup and Partners as consulting engineers and John Sisk and Son as main contractor. The building stands on a north-west to south-east axis and takes the form of a giant concrete shell, a half-ellipse on plan, partly buried within a raised landscape. It rises from a narrow north-west end, where a low entrance is cut into the grassed, earthen bank, to a tall glazed curtain wall that cuts off the ellipse just before its mid-point.

The roof is a composite system consisting of two precast concrete shells, each 100mm thick and spaced 900mm apart, adopting the geometry of a torus. It comprises a total of 924 precast panels: a lower shell of 274 curved panels with inverted T-shaped cross-sections (10m long by 2m wide), supporting 650 curved rectangular panels (3m long by 1.9m wide) forming the top section. The curved roof spans 90m. Forces from the roof are collected into an in-situ curved upper concrete ring beam and are then passed through an aluminium-framed clerestory, which varies in width from 500mm at the front (south-east) to 3000mm at the rear (north-west), via 34 steel arms spaced at 4m intervals to a lower in-situ concrete ring beam at abutment level, then to the concrete abutment walls and foundations. The roof is covered with a waterproof membrane, while a grassed, earthen bank covers the retaining walls up to clerestory level.

At the south-east façade, the arched opening is closed by a glazed curtain wall with a circular sector of 63m radius, 90m width and 18m maximum height. The glazing is supported by a series of steel-plate twin mullions 25mm thick and 40mm apart (clamped together with studs), spaced at 3m intervals. Each mullion is of a different height and shape to match the bending diagram, with curved profile; the taller mullions being deeper and the shorter mullions shallower. The glass consists of 19mm sheets (with ultraviolet film applied in the early 21st century), the largest measuring 3m wide by 5.5m high. The façade is stabilised out-of-plane by the roof and is otherwise self-supporting. To ensure overall stability of the façade in its own plane, the mullions are linked into vierendeel frames, each with two mullions and one set of transoms. Double-leaf glazed doors are positioned at the centre and at each end of the façade.

At the narrow north-west end is the main entrance, placed below the clerestory, comprising plate glass doors with sidelights flanked by reinforced-concrete wing walls.

The main entrance leads directly onto a mezzanine floor overlooking the ground-floor display area, with recesses to its left and right-hand side accommodating a café and a small exhibition space respectively. From the mezzanine, two cantilevered ramped walkways lit from above by the clerestory descend to the ground-floor display area. The walkways have tempered glass balustrades embedded at the base and surmounted by a stainless steel tubular handrail on the display area side, while the opposing side has a double-line stainless steel tubular handrail fixed to the perimeter walls (angled at 30 degrees from vertical) by projecting steel brackets.

At the rear of the ground floor, immediately below the entrance, is a small exhibition room known as the Georgia Frontiere Gallery (named after one of the major US Appeal Board members). Flanking the left- and right-hand side of the entrance to this gallery, at around the quarter-way point from the rear, are recessed doorways with double-leaf wooden fire doors through which toilets, plant rooms and storage rooms are accessed.

To the underside of the roof, formed by the underside of the inverted T-units of the lower shell, each panel has two aircraft suspension points of cast-in steel sockets. The floors are of reinforced concrete with an epoxy-resin finish. Several contemporary concrete benches are dispersed throughout the display area.

A contemporary glass war memorial sculpture entitled 'Counting the Cost' by artist Renato Niemis lines the raised walkway leading to the museum's main entrance. It comprises 52 glass panels engraved, in 1:240 scale, with plan-view silhouettes of the 7,031 Eighth and Ninth Air Forces and US Navy aircraft lost while operating from British bases during the Second World War. Each panel bears the outlines of the exact number and type of aircraft lost by specific USAAF groups and US Navy squadrons. Stainless steel inscription panels read: COUNTING / THE / COST // DEDICATED / TO ALL THE / AIRMEN / WHO FLEW / IN THE / SECOND / WORLD WAR // US AIRCRAFT / LOST / FLYING FROM / UK BASES // USAAF / 8TH AF / 6346 / 9th AF / 692 // US NAVY / 24 // Supported / Henry Moore / Foundation // Friends of the / Imperial War // Simon Gibson // artist / Renato / Niemis.