Design Awards: 2001: Commendation

Wessex Water New Operations Centre, Bath

Wessex Water New Operations Centre, Bath

Architects

Bennetts Associates Architects

Structural Engineer

Buro Happold

Steelwork Contractor

Wescol Glosford plc

Constructor Manager

Mace

Client

Wessex Water

Situated on a brownfield site just outside Bath, the £23M bespoke headquarters building overlooks an area of outstanding natural beauty. It incorporates a host of environmental features such as greywater recycling and passive climate control.

Placing sustainability at the heart of the design concept provided impetus for fresh thinking and approaches to the problem of finely-detailed exposed structure.

The office spaces have been designed to facilitate natural cross-ventilation and passive cooling. They feature a soffit formed of exposed sculpted precast concrete coffer units on slender steel beams. The exposed structure provides thermal mass to control temperatures within the spaces. A subtly curved rib is a feature of each coffer, providing strength as well as increasing the surface area available for heat exchange.

The steel frame has enabled a very light appearance. Only the bottom flanges of the secondary beams are visible, as slender dove-grey strips supporting the precast coffer units.

To express the lightness of the structure through the façade, a study was performed with the architect to establish the optimum column spacings.

Whilst the central columns are at 6m centres along each wing, reducing the edge column centres to 3m (one for every secondary beam) meant that the edge beam functions purely as a tie. A small PFC section sits below the edge coffer unit, framing the BMS-operated high-level windows which provide night-time cooling. The shape of the coffer is expressed externally through the glazing.

The primary “spine” beam was designed as a box-section, perforated to maintain the flow of natural cross-ventilation below the soffit.

The internal faces of the spine beam can be seen from the office space. It was decided to fabricate the beam from a pair of PFCs toe-to-toe, to allow shop application of paint to these faces.

Particular attention has been paid to the detailing of exposed steelwork connections. Machined pins are used to provide interest where the spine-beam-to-column connection is expressed.

It was recommended that the steelwork, precast units and painting to both should be procured as one package, under the leadership of a steelwork contractor.

Fire engineering studies carried out by Buro Happold FEDRA demonstrated that the secondary beams did not require applied fire protection, and that only the external faces of the primary beams required intumescent paint.

Whilst undoubtedly not the cheapest structural solution in capital cost terms (steel, precast floors and topping, painting and erection together cost around £220/m² in a typical bay), the system offered numerous holistic cost and environmental advantages:

  • The optimal integration of the natural ventilation solution considerably reduces the amount of area required for mechanical plant, saving an estimated £50/m². It removes the cost and programme implications of supplying and installing ductwork (estimated saving £20/m²) as well as yielding a saving in running costs (estimated saving £50K per year).
  • Saving in materials embodied energy: used half as much concrete as a coffered concrete naturally-ventilated design (or a third as much as a flat slab), with the same total weight of steel.
  • In providing a first-quality exposed soffit with attractive details, the cost of a suspended ceiling was removed.
  • The coffers integrate the lighting within the structural zone and maximise the sense of height and space within the storey height.
  • The excellent quality of the working environment, developed around the integrated structure/M+E/architecture solution, offers potentially significant benefits in terms of increased staff productivity, and reduced absenteeism and staff turnover.

Judges’ Comment

Carefully engineered modular design, creating a high quality office environment with a simple, but well crafted, frame solution. Thermal mass of this steel-framed structure is successfully utilised for internal climate control. A significant step towards the development of fully integrated building design, with good environmental credentials.

Shanks Millennium Bridge, Near Peterborough

Shanks Millennium Bridge, near Peterborough

Structural Engineer

Whitby Bird & Partners

Steelwork Contractor

Fairfield-Mabey Ltd

Main Contractor

May Gurney

Commissioner

Peterborough Environment City Trust

The Shanks Millennium Bridge forms part of the Peterborough Environment City Trust Project funded by the Millennium Commission. It provides a new equine/pedestrian footbridge across the River Nene, and is sited at an ancient forded crossing. Following the construction of nearby sluice gates, the river became non tidal and the forded crossing impassable. The Shanks Millennium Bridge recreates a crossing at this location and links the north and south banks of the River Nene.

The structure is located 2.5km from the eastern edge of Peterborough. At this point the River Nene is contained by raised flood defence embankments, known as the North and South banks, and is above the general level of the surrounding drained farmland. It is open to a range of river traffic and contains a designated navigation channel.

The architect-designed bridge comprises a five span structure, approximately 120m long. It consists of a curved, slender steel box section, to which is bolted a cantilever walkway and handrail. The northern half of the bridge turns through approximately 90° in plan. The bridge deck comprises segregated footpath and bridle path areas at two levels. The footpath at the higher level is surfaced with hardwood. The lower bridge path deck consists of non-structural reinforced concrete. The parapets were constructed using a steel frame with hardwood slats set into the frame. This gives the horse and rider more space and, should any horses be startled, will prevent them climbing the parapet.

The shaped deck and the intermediate piers were constructed from weathering steel to reduce whole life maintenance costs and provide an architectural feature. Concrete abutments tie the bridge into the existing ground levels at the north and south ends. Two abutments were constructed on either bank of the River, and two intermediate piers located on the flood meadows.

Close working relationships that developed between all parties involved permitted drawings to be completed and approved in sufficient time to allow fabrication of the structure to proceed with minimal delay. The use of CAD/CAM provided a 3-D model, which gave virtual views of the bridge at every elevation and linked directly into automated fabrication facilities, including plate profiling and plate marking for assembly, minimising cost. The complex structure meant that all the steelwork was hand welded either in the steelwork contractor’s workshop or on site. The weathering steel was blasted at the works during the fabrication process prior to delivery to site.

Due to the complexity of the geometry, partial trial erection of box joints of the box sections was carried out at the steelwork contractor’s works.

The five span box girder sections were delivered to site in 12 individual box lengths. Each box section was supported by trestle towers and butt welded in the air to the adjacent box section. A crane was positioned on the flood plane adjacent to the River to enable the three box girders above the River to be erected. Closure of the River Nene was required during erection. Ancillary steelwork was then fixed to the bridge and then the decking and surfacing was added.

The complex design and the use of weathering steel has resulted in a bridge which is simple in its purpose to accommodate bridle path users and pedestrians whilst remaining aesthetically pleasing and architecturally challenging.

Judges’ Comment

This is a most beautifully designed curved box girder bridge in weathering steel that fits the Fens landscape as if it were a natural part of it. It is a pity that land restrictions necessitated stepping of the decking on the approach to the south bank.

The Lowry, Salford Quays, Manchester

The Lowry, Salford Quays, Manchester

Architect

Michael Wilford & Partners Ltd

Structural Engineer

Buro Happold

Steelwork Contractor

William Hare Ltd

Main Contractor

Bovis Lend Lease

Client

The Lowrie Centre Trust

The Lowry project on Salford Quays has been designated the Nation’s Landmark Millennium Project for the Arts. The Lowry consists of two theatres, two galleries and various facilities for conferences and general hospitality.

In the Lyric Theatre two rows of columns based approximately 3m apart set out on an oval grid as defined by sight lines and linked back to shear walls by curved steel beams were used to provide the transverse stability. These columns were used to support cantilevered trusses which in turn supported the seating. The central core columns and beams were painted with intumescent paint to satisfy the one-hour fire rating requirements.

Set on the outside perimeter of the leaning concrete wall, the Lyric Foyer provides access from the theatre entrances to the galleries and exits. The roof beam consists of a plated 610 deep beam cut to suit the architect’s requirements. The difficulty of connecting this to the cruciform column which was made up from a 356 UC with Ts welded to the web was overcome by means of a tubular insert welded to the top of the column.

This Adaptable Foyer comprises four cruciform columns made from four 120 x 120 SHS welded together. These in turn support a tree top configuration made from tapered beams out of 610 UCs. The tapered beams supported 165 UC purlins which in turn supported the metal decking roof. A curved 152 RSC formed the edge support.

The two Galleries comprise longitudinal trusses supported on 322 x 25 CHS columns with the bottom boom supporting first floor cell beams and the top boom supporting similar transverse roof trusses. The connections had to be kept as clean as possible to satisfy the architect’s requirements for clear uncomplicated lines as the steelwork is visible both internally and externally.

The Diagrid Tower is used to house the artwork when not in use the architect required this to be the highest visible feature using symmetrical steel beams to form a cylindrical shape with no connections visible on the perimeter. Four beams connected together formed a facetted diamond shape and this pattern was repeated around the cylinder and from bottom to top.

Set at the entrance to the Lowry, the Canopy was designed as an imposing architectural feature as well as a functional structural item. Supported on two sets of A-frame legs with six smaller CHS supports the structure consists of a central toblerone shaped truss on which are supported frames with a sloping top boom and curved bottom boom to give the architect’s required shape. This structure was covered in perforated cladding.

Why Steel? The design team recognised from the outset that the structure had to satisfy both structural and architectural requirements. The geometry of the structure with its various leaning walls, cylindrical shapes and large spans meant that for the majority of the structural framing, steel was the only logical choice.

Despite its complex nature the engineers could design the structure confident that the steelwork would achieve their requirements within the tolerances required.

From an installation perspective steelwork was the only logical choice due to the limited nature of the space available on site. Vast areas of space were not required for temporary support/propping during installation as the steel frame was designed to be stable within its own right and installed in a manner to minimise any temporary bracing required. The speed of erection also confirmed steel as the correct material for the structural framing.

Judges’ Comment

:

A prestigious project of great complexity, incorporating two theatres, galleries and support services. The exposed structural steelwork in many areas has been innovatively fire engineered. The combination of steelwork and stainless steel cladding is very effective.
The public already shows great enthusiasm and appreciation for this building, which displays steelwork to good effect.