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Structuring a business Thames Court uses its river views to best advantage with a light structure that draws the visitor in JANE WERNICK, JANE WERNICK ASSOCIATES. PHOTOGRAPHS H G ESCH

steel design

Thames Court is a 30,000m2 new speculative building in the City of London. It sits between the noisy and unfriendly Upper Thames Street and the comparatively quiet and tranquil River Thames, next to Queenhithe Dock, just west of Southwark Bridge. The brief was to provide accommodation for both banking and a corporate headquarters. The plan of the site, approximately 45m x 100m, allows for a mixture of very deep floor plans suitable as dealer floors, and 18m-wide bands of corporate office accommodation around the atrium. There is a basement, a lower ground floor, and five storeys of superstructure. The plan arrangement of the top floor has to some extent been dictated by the strategic views of St. Paul's.

The building may be approached from either direction along Upper Thames Street. The architect, Kohn Pedersen Fox, has considered both the view from the car and the view presented to pedestrians in its design of the front facade. The face of the building is set up as a huge stone-clad portal, four storeys high and the full width of the building. This portal, or proscenium arch, almost frames the facade which has a gentle curve on plan. It consists of a series of steel columns from which is hung a glass wall, and behind which lies the entrance foyer. These columns form a sort of palisade which appears dense as one drives past the building, but which opens up as you approach, to reveal the space behind.

Creating spaces

This somewhat theatrical facade reveals a building that comprises an intriguing mix of private spaces, linked by a sequence of public routes that cut through the building horizontally and vertically. In section the building has been designed with a front atrium - the entrance foyer - and a stepped atrium which starts as the escalator lobby and is linked by the lift lobby to the main top atrium.

The deep-plan floors at the lower levels are approached from the front of the building via the lower entrance foyer. This area acts as a buffer zone between the noisy city environment and the quiet office spaces behind. Light is let in through the full-height glazed front wall, and through slots in the ground floor.

From the entrance foyer one is drawn through the security zone, which with its low ceiling and glass floor becomes the threshold. Then you are taken up through a three-storey-high hall on escalators, the walls clad in Purbeck Spangle, to the main lift lobby at the first floor level. The main atrium is in the middle of the building and starts at the second level. It connects with the rooflights over the lift lobby, giving a feeling of increasing openness and daylight as one passes up and through the building from north to south. In effect the atrium has been stepped to allow light to penetrate to the ground floor. The horizontal links across and around the lifts provide a sense of continuity between the separate spaces. These landings also use glass floors which let through some light and give a clear differentiation between the public spaces and the private areas - which all have different floor coverings, Purbeck Cap in the entrance and Swaledale in the escalator lobby.

Opening up views

Generally a 9m x 9m grid is used, except at the south end of the building, overlooking the river, where this is opened up to 9m x 12m. Storey- height steel trusses, spanning 27m, are placed on either side of the atrium at the roof level to allow the second and third floors to be hung so that a large column-free dealer space can be provided on the first floor.

At the south end, which faces the river, the two corners of the building are cantilevered out over the public walkway along the river wall, increasing the floor plate at the higher levels and providing great views.

Structural steelwork is used throughout the building as an expressive material, both for the main frame and for the facades, stairs, lifts, and landings. Although the building is below Section 20 height limits, it has been provided with full sprinkler protection. The fire period in the superstructure was 60 minutes for main elements, and 30 minutes elsewhere. This allowed the use of relatively thin intumescent coatings, which gave the architect considerable freedom for the expression of the structure.

For the main frame the building uses a conventional structural steel, and stability is provided by exposed cross-bracing behind the lift cores and staircases. The lift cores are clad in glass to reveal the structure. Concrete is used for the slabs and walls, and concrete-encased steelwork for the columns. This choice of structural material allowed a short construction time - the majority of the base building was completed within a year. As the site is rich in archaeology the weight of the building was a major factor. Minimising loads enabled the reuse of some of the existing basement structures and kept the pile sizes to a minimum.

Structural expression

The main structural expression is made with the two trusses that support the upper floors around the atrium. The booms and the diagonals are fabricated using I-sections. Circular hollow sections are used for the verticals, which reflect the circular sections of the exposed hangers below. The nodes are detailed in a robust, straightforward way reinforcing the nature of the loads being carried.

Steel hangers are used on the south end to support the cantilevered corners as diagonals, which are tied back to the main columns, and they are expressed as part of the facade. At the north end of the building the front edges of the floors are stepped back from the main grid to make a front atrium behind the glass wall that is half a bay wide at the ground level narrowing to just a slot at roof height. These edges are also supported by steel hangers from the beams at the fourth floor level.

The columns that form the front wall of the building are made of channels and plates welded together. They are set outside the glazing and are propped against the building at the roof of the front atrium. Wind loads on the facade are carried by the columns spanning the ground and the roof. The glazing is point-attached single glazing, the internally glazed office spaces are further protected by the buffer zone. The steel castings supporting the glass were developed by the glazing contractor, and use spherical bearings in the plane of the glass to allow for the eccentricity of the glass load without putting bending into the glass at that point. As with the main truss nodes, their design is clear and unfussy.

Another set of castings was developed for the project's glass landings. Long, rather bone-like, shapes are used as inclined struts under a fabricated steel frame that supports the glass to form a shallow vaulted filigree above each of the landings.

Air and light

The way sunlight and air enter the building has been treated in a variety of ways. The majority of the building is glazed to allow as much daylight as possible into the deep-plan offices. Along the south facade motorised blinds and deep, high level brise-soleil are used. Motorised rotating louvres are provided on the south-west to combat low sun. The windows open all along Queenhithe, except for the first 20 metres from Upper Thames Street, where the pollution level is high. Around the atrium spaces there are openable windows and the atrium also acts as an extract plenum for the office spaces.

The light levels in the main atrium are controlled by a fabric shading device. This specially designed system comprises a set of louvres - that can be rotated to either block or let through the direct sunlight - and a set of diagonal fabric shades that change automatically three times a day in reaction to differing daylight conditions. The steel beams that span the atrium support the shades and the glazing, casting interesting shadows on the fabric.

This building is largely about the use of steel, but a great deal of attention has been given to the use of other materials. Glass gives light and translucency to the building through use in the walls and doors. The architect also provided a contrast between the permanent private finishes, and the more flexible finishes that each tenant may want. A fossil-rich Jurassic limestone from Somerset was used for paving and wall cladding in the entrance areas, the size of stones increasing closer to the street. The limestone gives a gentle reminder of the archeological heritage of the site.

The impression is of comparative calm after the hectic and hostile main street. The building draws the visitor up and into its heart around the escalator and lift halls and then, inevitably, to the spectacular views of the river and Queenhithe dock in the foreground to the west. Different scales of robustly-expressed steelwork reinforce a sense of the history of the site and reflect times when the river was more intensively used.

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