Design Awards: 2004

Selfridges Structural Frame, The Bullring, Birmingham

Selfridges Structural Frame, The Bullring, Birmingham

Architect

Future Systems

Structural Engineer

Arup

Steelwork Contractor

Severfield-Reeve Structures Ltd

Main Contractor

Sir Robert McAlpine Ltd

Client

The Birmingham Alliance

The structural frame of the Selfridges Building in Birmingham is like most other multi-storey building frames in many respects. It is designed to resist vertical and lateral loading (which in this case included reactions from the attached cable-stayed bridge) and to ensure acceptable dynamic performance and movements. However, there are two specific design criteria which differentiate this building from most conventional frames and which lead to an unusual and ambitious design. The first of these was the need to define the curved building shape and support the freeform sprayed-concrete facade system. Secondly was the desire to create retail floor-plates with minimum vertical structure and of maximum height. To achieve these goals the design takes advantage of CAD/CAM technology and mass customisation to allow the economic fabrication of an irregular framework. It also achieves a high degree of integration with services feeding the retail floors to maximise floor to ceiling heights. Neither of these strategies are ground-breaking in isolation, but in combination they create a truly holistic solution, an economic synergy of architecture and building engineering which could not have been achieved with a more conventional solution.

The starting point for the frame design was to derive a suitable column layout. The super-position of a standard cartesian column grid on the irregular plan shapes of the building seemed inappropriate and incompatible with the architectural layout. The chosen approach was to locate a string of columns around the building perimeter spaced approximately 12m apart and a separate necklace around the two internal atria at the same spacing. A handful of extra columns were required to limit primary and secondary beam spans to 12m and 16m respectively, the maximum spans that were considered as economically feasible. Again these additional columns were individually and strategically placed to suit both the structural and architectural requirements.

The plan shape of the building changes from floor to floor to match the curvature of the envelope in section. This requires secondary beams to cantilever from the perimeter column line by different distances around the slab edge and at each level. At the ‘waist’ of the building the columns sit tight against the inside face of the facade, where as at the ‘hips’ and ‘shoulders’ the floor cantilevers up to 4.5m deemed as a maximum practical limit, thus controlling the vertical curvature of the building. It was these relatively long spans and lack of regular grid resulting from this minimum column approach that drove the design towards a steel solution.

A desire for maximum floor to ceiling heights in retail areas lead the integration of structure and building services within the same 1500mm deep zone. This coordination exercise required a balance of practicality and flexibility, allowing the potential for future rearrangement and refitting of retail departments. The chosen strategy provides fixed routes for primary ductwork through standard notches at beam ends, with secondary ducts and pipe-work running through 650mm diameter holes in beam webs. These holes are not located specifically for the current services arrangement (indeed this arrangement was unknown until after the completion of the frame erection), rather they are designed to ensure that a reasonable level of variation in layout is possible. This standardisation of notch and hole sizes/spacing simplified the fabrication requirements and allowed a certain amount of repetition despite the large number of different beam lengths. The coordinated structure/services strategy also steered the structural design towards a deep but light beam solution with good stiffness characteristics and hence good dynamic performance. Asymmetric plate girders of a standard depth were chosen for the majority of beam sections working compositely with the 150mm deep concrete floor slab. The use of plate girders allowed greater control over the distribution of material than a solution using equivalent depth rolled sections, resulting in much lighter beams and less fabrication waste.

It became clear during design that the secondary floor beams made up over two-thirds of the total frame tonnage, and that small improvements in the design of these beam types would yield significant overall savings of weight and cost. The optimisation/rationalisation process was complicated by the large number of different beam lengths and support conditions resulting in a vast matrix of different demands. The resulting designs and number of different beam types are a balance of performance and practicality.

The choice of corrosion and particularly fire protection systems also formed an important part of the frame design and the potential for exposing the floor structure and services as a ‘technical ceiling’ was recognised early in the design process. A fire engineering study was carried out which resulted in a reduction of the fire resistance requirement of floor structure from two hours to 60 minutes, thus allowing the economic use of a site applied intumescent paint system. The result is a clean soffit appearance that has been left exposed in several areas of the current fit-out.

Traditionally the emphasis in multi-storey steel framed construction has been on regularity and repetition to create function and economy. In recent years the possibility for accurate fabrication of highly irregular frames has been demonstrated and such frames have been constructed, typically for the sole purpose of creating unusual architectural form. The Selfridges building is proof that these desires need not be mutually exclusive. As such Selfridges should not be considered as a ‘one-off’, and this ability to marry the requirements of function, economy and form helps to unleash the potential for a new generation of steel framed buildings.

Judges’ Comment

s:

A big retail name for Birmingham’s city centre, this is an architecturally challenging and exciting building, but with a common sense approach to its structural framing strategy. The rationalisation of steel sizes in the highly irregular multi-storey frame provides a sense of balance between the required flexibility of function and the practicalities demanded for construction

The Swansea Sail Bridge, River Tawe, Swansea

The Swansea Sail Bridge, River Tawe, Swansea

Architect

Wilkinson Eyre Architects

Structural Engineer

Flint and Neill Partnership

Steelwork Contractor

Rowecord Engineering Ltd

Main Contractor

Balfour Beatty Civil Engineering Ltd

Client

Welsh Development Agency

This project is part of a larger scheme comprising two bridges across the River Tawe with an additional opening span and associated Quayside walkways. The bridges connect the city centre with a publicly funded redevelopment project currently under construction to the east of the city on the site of the Swansea Docks. The requirement for units in the redevelopment to be pre-let at an early date, with necessary infrastructure visibly in place, resulted in an unusually compressed programme – from design inception through to constructed completion in less than 15 months.

The 140m north bridge, named the “Sail Bridge” by the WDA, is an iconic design explicitly required by the Client and City Council to form an emblem for the regeneration of the Port of Swansea. Though the structure of the North Bridge adopts a classic symmetric cable-stayed configuration, in cross section the deck is held along only one edge. The simplicity of the overall form is augmented by the apparent delicacy of the asymmetrically suspended walkway.

The 42m high mast, of varying cross section, is fabricated from a series of flat and rolled steel plates of decreasing thicknesses from base to tip. The cross section migrates from a filleted square at the base through to a kite shape at mid height, culminating in a triangular configuration at the tip. This developing form is achieved without the use of warped planes [all faces are ‘flat’] and yet the final form is visually complex. The plate thicknesses in the mast vary from a maximum of 45mm at the base to 10mm at the tip. The final craneage weight of the mast was 78 tonnes from an initial material procurement tonnage of 93 tonnes, and the mast was lifted in one piece using a 1200 ton crane on the west bank.

The project was procured using the NEC Target Cost Form with the specialist steelwork fabricator, Rowecord Engineering Ltd, appointed early on in the process. Very close co-operation between the design team and the specialist sub-contractor meant the highly modelled nature of the mast and the simplicity of the overall structural solution was retained through the design development to deliver an end product that is incredibly faithful to the original scheme design.

Furthermore, in terms of detailing, Rowecord were able to advise fabrication methodologies that surpassed the design team’s expectations in terms of formal clarity and final surface finish. One good example of this is the sharp arris on the back of the mast from mid height to apex. Because of the extremely acute angle between the side plates, the design team had envisaged a shadow gap detail at the junction between the plates to lessen the visual impact of the welding. Rowecord suggested an alternative detail where a kite shaped bead of solid steel, running the full height of the intersection, formed the junction between the two plates. This allowed for a sharp edge as plates met and greatly simplified the welding details.

Steel is also used for the deck box sections and the cantilever ribs supporting the pedestrian walkway. The deck is suspended on one side by 70mm diameter spiral strand stay cables connected to the mast. As a result of the eccentric cable support, the deck is a closed steel box in order to provide the necessary torsional stiffness. The 20mm deck plate is stiffened longitudinally, but the 15mm webs and 20-30mm thick bottom flange are unstiffened to simplify fabrication and box assembly. The stay anchorages are formed from simple intersecting tubes designed to facilitate proper alignment because of the complex 3-dimensional geometry. The whole bridge was modelled by Rowecord as a 3-dimensional plate model to ensure correct geometry and control of tolerances, with the result that there were very few problems in the alignment and assembly of the units. Following the installation of the mast, the deck was lifted into position in nine individual lifts of approximately 20 tonnes each. This allowed for off site fabrication of individual deck units, transportation by road and rapid erection onto temporary piled supports in the river using craneage from both banks. This method enabled the correct geometry to be achieved prior to welding up the splices and stressing the stays to lift the deck off its temporary supports.

The bridge parapets differ between the vertical parapet to the cycleway and the inclined tension wire downstream parapet. This counterpoint between sides of the curved deck is accentuated by the more visually solid parapet infill panels and bespoke lighting units on the upstream side, which provide effective functional lighting for bridge users as well as subtle coloured lighting elements to viewers further upstream. The bridge mast is uplit to enhance the night-time visual impact.

The bridge was opened to the public for the inaugural ‘Great West Wales Triathlon’ in June 2003, and has already received warm public acclaim, becoming a popular icon for the region and destination in its own right as well as an essential link between the new Port Tawe Innovation Village and the City Centre.

Judges’ Comment

s:

This bridge, providing an essential link in the regeneration of Swansea, is a culmination of collaborative expertise and teamwork. Its architectural form, design and fabrication have all paid great attention to detail, to give the people of Swansea an exciting, simplistic, but visually complex structure to use and look at.

More London Plot 1, Tower Bridge, London

More London Plot 1, Tower Bridge, London

Architect

Foster and Partners

Structural Engineer

Arup

Steelwork Contractor

Severfield-Reeve Structures Ltd

Main Contractor

McAlpine-Mace JV

Client

More London Development Ltd

More London Plot 1 is an £85M office development on the south bank of the River Thames in London adjacent to HMS Belfast, to the west of Tower Bridge. It consists of three 10-storey buildings with car parking, loading bays and some lettable space in a basement covering the entire site. Plantrooms are located on the roof, set back from the building perimeter and enclosed by a louvred screen. Two of the buildings, Plot 1A, are linked by a full height atrium with bridge links at every level. The third building, Plot 1B, is completely separate.

The superstructure consists of concrete/steel metal decking floors supported by a steel frame consisting of Fabsec beams spanning up to 22.5m and UC columns. Lateral stability for each building of Plot 1A is provided by a concrete box core located about mid-way along the length. Lateral stability of Plot 1B is provided by two concrete cores. The atrium structure consists of a glazed wall facing the river views and a glazed roof supported by a steel hollow section structure.

The scheme for Plot 1A was originally based on an 11.5m grid across the building with a central column on grid. During development of the scheme design the client asked what the consequences would be of eliminating the columns within the office floor plate, thus creating a 22.5m span, whilst maintaining the same overall floor depth. The benefits were added flexibility in the planning of the internal space, which would give the building an edge in the office letting market. The additional cost due to the increase in steel weight was evaluated and accepted by the client and the building was pre-let. This was crucial to the viability of the project in an over-supplied market.

Although the revised design met the brief upper limits for pedestrian-induced floor vibrations (Response Factor (RF) = 8) the client was advised that there was recent evidence of increased office worker sensitivity to floor vibrations. The introduction of flat computer screens mounted on arms projecting from office furniture had resulted in complaints from users who were experiencing difficulties reading text displayed on their screens. The problem was attributed to floor vibrations. In cases investigated by Arup the level of floor vibration was around RF=8, which is the generally accepted upper limit for normal offices.

It was decided to investigate the possibility of a cost-effective method of significantly reducing floor vibrations by providing additional damping. The idea of using a bituminous damping layer sandwiched between steel and concrete had been developed and used successfully on the long span spiral ramp structure in the atrium of the neighbouring City Hall building completed in 2002. In the case of City Hall the concrete was a non-structural topping covering the entire ramp and the damping layer similarly occupied the entire width. For More London Plot 1A the width of the damping layer is restricted to the width of the steel beams. A thin layer of bituminous material is sandwiched between two metal plates and placed between the top flange of the steel beam and the metal decking towards the ends of the beam. Composite action is maintained by providing shear studs over the central portion where the damping layer is absent. To test the effectiveness of the system, computer models of the concrete slab, shear studs, steel beam and damping layer, characterised by a ‘loss factor’, were analysed using the advanced finite element package NASTRAN and subject to transient dynamic loading. The results obtained were compared to similar analyses where the damping layer was omitted. The results showed that significant improvements in damping were feasible. Using this system a 22.5m span floor can achieve RF=6 or less without the need to increase depth or mass beyond that required for strength design. The idea was presented to the client and received favourably.

The solution adopted for the long spans is a 720mm deep Fabsec beam with 400mm diameter web holes, supporting a 130mm deep concrete floor slab. The 850 deep structure occupies the entire depth between the raised floor and false ceiling with the air-conditioning ductwork passing through the web holes.

Floor vibrations were assessed by calculating the vibration modes of the floor structure using a computer model consisting of steel beams offset vertically from a finite element model of the concrete floor. Response was then assessed by calculating the walking pace that would cause resonance for a particular vibration mode and then combining the response of all the vibration modes that could be excited by a person walking at this pace. Typically the lower frequency modes, around 3Hz, are excited by the first harmonic of the walking input, whilst the higher harmonics excite higher frequency modes.

Time was short since construction of the foundations and basement had commenced. A potential manufacturer of the product, Richard Lees Steel Decking (RLSD), was approached and registered enthusiastic interest. Two test panels, each consisting of two 12m long simply supported steel edge beams supporting a 3m width of concrete slab on metal decking were constructed by RLSD; one with the damping layer and one without. Vibration testing, carried out by Arup, consisted of attaching an accelerometer to the middle of the beams and measuring the natural frequency and damping due to a heel-drop at midspan, and the acceleration response due to a person walking along the middle of the slab, from end to end, parallel to the beams, at a walking pace chosen to excite the lowest natural frequency of the beams. The walker carried a hand-held metronome set to the desired pace. The results confirmed the analytical findings.

Following the testing and analysis of the results the decision was made to incorporate the damping system into the Plot 1A buildings. Safe erection methods for the decking in the absence of studs and the damping layer sandwich were developed with the decking supplier and main contractor and incorporated into the erection method statement.

Post-construction, further testing was carried out by attaching an accelerometer to the middle of the critical areas of the floor and measuring the real natural frequency and damping due to a heel-drop at the same location.The building is now fully occupied and favourable comments on the feel of the floors have been received. The cost of significantly reducing floor vibrations was approximately £2/m2 of floor area. The damping layer is now an RLSD product called “Resotec”.

Judges’ Comment

s:

As can be expected with this team, the development pushes the design process to the limit in meeting the client’s brief for large open office space that is essentially column-free and environmentally efficient and controlled, whilst taking full advantage of the superb views of its riverside location.It has achieved a simple, clear design that is logical in its master-planning, sophisticated in its detailing and uncompromising in its execution. The result is a classic of its type.

VT Shipbuilding Facility, Portsmouth

VT Shipbuilding Facility, Portsmouth

Architect

AMEC Design and Management Ltd

Structural Engineer

Watson Steel Structures Ltd

Steelwork Contractor

Watson Steel Structures Ltd

Main Contractor

AMEC Capital Projects Ltd

Client

VT Shipbuilding Ltd

This large industrial structure encompasses all that is good in modern structural design. The 60m span roof trusses at 14m centres make use of the largest cold formed purlins and rails available and provide a structure that is light, well-proportioned and with the minimum number of pieces. In addition the structure accommodates four large EOT cranes up to 200 tonnes capacity. The 3000 tonne plus facility is located within the Naval Base at HMNB Portsmouth and forms part of a £40M development. The contract was awarded on a design and build basis with WSSL being responsible for the complete design, construction and final finishing of the superstructure.

The Client’s requirements were contained in a number of specifications. The following list identifies some fundamental requirements.

  • Buildings to have a design life of 25 years with 10 years to first maintenance
  • Buildings to incorporate two tier crane systems – largest capacity 200te
  • Structure to be two integrated buildings/bays
  • Various Doors to be provided – including two adjacent 23m x 30m doors which when used together must provide a maximum opening of 46m x 30m
  • Various openings to be provided – generally allow transfer of units between bays of dimensions 13m x 12m weighing up to 40te, plus maximum opening of 25m x 18m between bays
  • Clear openings between members to be maintained
  • Working platforms at various levels to allow access for working on different types of ship/modules/units
  • Platforms to provide support for services and portacabin accommodation
  • Platform widths to be sufficient to allow movement of personnel along the structure and past services/portacabins

The structural form consists of columns supporting crane beams and lattice roof trusses. A key decision to be made in the design process was the spacing of the main frames. Due to the height of the building and the requirement to carry large crane loads, the most economical solution was found to be the adoption of the maximum possible spacing of frames. This was dictated by the maximum available span of the cold-formed purlins and rails, which was assessed as 14.5m. The bays share a central column at the junction of the two bays. Bay A1 has permanent gable columns to the North and South ends of the building. Bay B1 has permanent gable columns at the South end, albeit in temporary positions to allow for future extension, and two independent 30m x 23m vertically operating fabric doors at the North end. The doors share a removable central post which is raised/lowered using a series of winches to provide a maximum opening of 30m x 46.7m.

Lateral stability against wind and crane surge loads is achieved by frame action and fixed bases across both bays. Roof bracings at top and bottom boom levels of the trusses transfer longitudinal wind loads to two panels of vertical bracing on each gridline. Longitudinal crane surge loads are transferred from the crane beams to the two panels of vertical bracing on each gridline. All gable columns have slotted connections to the roof trusses to prevent transfer of vertical load.

There are positions where the Client’s requirements precluded using the two span frame at 14.5m spacings. In two positions in bay A1, 15m x 16m doors are incorporated and result in the lattice columns splitting 29m into an 18.5m bay and a 10.5m bay. The roof trusses remained at 14.5m spacing necessitating the use of an eaves level truss to span the 18.5m bay to transfer the roof load.

The requirement to provide a 25m x 18m clear opening between bays also precluded using a lattice column on shared gridline 2 on grid B. As a result the crane beams were designed to span 29m resulting in a maximum I-beam plate girder size of 3160mm x 800mm weighing over 50te.

The main 23m x 30m launch doors take up the majority of the North gable of bay B1. There are clad areas to each side of the launch doors and cladding above the door up to roof. The door framework consists of two box section outer posts, a clad lattice framed central removable post, and two composite door header beams. The composite door header beams carry the weight of the door and also span horizontally between centre and outer door posts to resist wind loading. The composite beams are also restrained via braces up to the roof level bracing system. When the central post is in position and the doors closed, wind load is transferred to the top and bottom of each post. Loads are resisted at the foot of each post by the base connections that incorporate shear keys. Loads at the top of the outer door posts were transferred directly back to main roof bracing system.

The environment for the steelwork was classed as marine aggressive and the life to first maintenance was to achieve 10 years. The corrosion protection system used for the majority of the steel was 240 microns of an Epoxy Zinc Phosphate primer/MIO build coat in a dark grey shade. Kick flats and stair stringers to the walkways and platforms were the exception having 175 microns of the primer/MIO plus 50 microns of an acrylic urethane gloss in yellow. Both systems gave a minimum life to first maintenance of 15 years.

The erection was carried out using a combination of 200te crawler cranes for the elevations and roof, 100te crawlers for assembly and general erection and 50te mobiles for miscellaneous erection and assembly of walkways. Erection proceeded at the rate of one week per bay for buildings A1 and B1 giving a total of approximately 18 weeks to erect 3055te.

Whilst the building is generally unheated, the roof cladding is insulated to minimise condensation. The wall cladding however was retained as single skin since the effects of condensation were considered less severe than on the underside of the roof.

Judges’ Comment

An important maritime manufacturing facility located in this historic naval dockyard. This is an industrial building on an impressive scale, housing two tiers of heavy-duty overhead cranes. It is the marriage of traditional steel structural forms, scaled-up to optimise the use of secondary framing components that has produced this most efficient structural design solution.

Intech Science and Technology Centre, Winchester

Intech Science and Technology Centre, Winchester

Architect

Hampshire CC Architecture and Design Services

Structural Engineer

Gifford

Steelwork Contractor

Tubecon

Main Contractor

Trant

Client

Hampshire Technology Centre Trust Ltd

Intech is a new 3,500sq m educational interactive science centre commissioned by the Hampshire Technology Trust Ltd. Hampshire Technology Trust Ltd is a local charity set up because of concerns about the quality of scientific training in schools and the lack of interest that school children had in science and technology. An exhibition centre was created with the vision to set up a hands-on science experience to help local schools in their teaching of science and technology in an inspirational way. The success of the centre meant that expansion was needed if the quality of the service that Intech provided was to improve.

The client’s brief for the new Intech building was to provide a large exhibition hall and café with associated administrative and teaching spaces and a 200 seat lecture theatre that had the potential for future conversion into a planetarium within a limited budget of £5M. To complement the scientific use of the building the architect’s design was based on simple geometric forms cut into the chalk hillside. The lecture theatre was designed as a domed building linked to the main pyramidal exhibition hall via a two-storey glazed link corridor.

The client wanted a building that would not only achieve the spatial requirements but would also allow visitors to understand the form and function of the building. Thus the vision was for the building to have the potential to be used as a learning tool, hence the building form needed to be simple to understand in both terms of structural form and building services strategy.

The architect’s initial concept for the exhibition hall roof was to have four plates leaning together supported on concrete buttresses to form the pyramid shape. The space needed to be column free so the roof had to be capable of spanning the 50m width of the building. To achieve the concept of a plate it was proposed that a form of grillage structure was used.

To minimize the member sizes, and hence the tonnage, a series of bowstring supports was introduced. A hierarchy of supports was introduced, the first larger tie bars were provided to prop the main roof plates, with the secondary series of tie bars being introduced to support the smaller panels between the main props. The tie bars need to be post-tensioned to resist wind uplift.

The roof is designed to be two-way spanning thus moment connections were required at all joints. It was decided to fabricate the roof panels in longitudinal ladder frames and to minimize site welding the joints were designed to be contained within the profile of the SHS members.

The auditorium structure was designed with UB curved ribs expressed below CHS purlins curved to form full circles, each circle being of a different radius. The UB ribs are built off a reinforced concrete retaining wall that supports the earth banking which is mounded around the base of the auditorium. There are simple bolted connections between the CHS purlins and the UB rafters that are hidden above the top flange of the ribs.

Judges’ Comment

s:

Intended to house exhibits to inspire children towards science, engineering and technology, the structure itself intentionally demonstrates structural form and strategy. Its striking pyramidical form triggers the inquisitiveness and appreciation of both children and adults, even if not wholly understanding the full extent of engineering achievement involved.

West Stand, Kingston Communications Stadium, Hull

West Stand, Kingston Communications Stadium, Hull

Architects

The Miller Partnership

Structural Engineer

Anthony Hunt Associates Ltd

Steelwork Contractor

Watson Steel Structures Ltd

Main Contractor

Birse Stadia Ltd

Client

Kinston-upon-Hull City Council

The Kingston Communications Stadium is unique in a number of ways. Firstly, it is thought to be the only stadium to be constructed in an ‘asymmetric bowl’ form. This gives the flexibility of combining single and double tier stands, whilst an effortless transition between the single and double tier stands maintains the impression of one continuous building structure.

This continuity is enhanced by the adoption of an internal public concourse that runs the full perimeter of the stadium. Unusually, this concourse is at first floor level, thereby freeing up commercially valuable space at ground floor level.

Further, it is the first stadium to be built entirely within an existing public park. However, rather than destroying the park environment the stadium ‘respects’ the park, and will in fact introduce new visitors to it.

The West Stand roof is arguably the most interesting aspect of the stadium. Due to the significant overhang of the West Stand roof and the presence of the upper tier, the cantilever solution used for the other stands was not appropriate here. Consequently, a stayed rafter solution was adopted, using relatively slender 406mm diameter CHS stays to support box section rafters which are fabricated out of steel plate, and range from 1350mm deep at their supports, down to 600mm at the tip.

The CHS stays are up to 40m long, and rise gently in pairs up to the rear of the roof, where they meet six CHS section ‘A-frames’ which transfer the significant vertical and overturning forces down the stand, via terracing raker beams and diagonal bracing hidden within partition walls between hospitality boxes. To overcome potential problems associated with self-weight deflection and bending moments, the CHS stays were cranked at third points so that the deflected form approximated to a straight line.

The main sections of the roof, the ‘A-frames’, were assembled and welded at the rear of the West Stand and lifted into place as complete frames using crawler cranes sat on the outside of the structure. This resulted in lifts of up to 110 tonnes. In order to minimise out of balance forces, the ‘A-frames’ were erected in a symmetric manner from the centre outwards. Hence, the two central ‘A-frames’ were erected first, and then joined together by erecting RHS infill purlins between them. This process was subsequently repeated for the two central and the two outer ‘A-frames’, after which the roof decking could be laid. The west side of the pitch is lit from a dedicated lighting gantry slung off the underside of the West Stand roof.

The total build cost of £27.5M equates to £1,100 per seat, which is not significantly higher than for a more conventional stadium.

The first ‘sod’ was dug in October 2001, whilst the first match was played only 14 months later in December 2002. Further, the production of construction information commenced just two months before the start on site date.

Judges’ Comment

s:

An asymmetric bowl form, possibly unique at this time, creates a spectacular roof for this 25,000 seat community stadium set in beautiful parkland. In meeting the brief this enables a combination of a single and double tier stand to be accommodated under one continuous building structure. A simple solution has been produced that is elegant in its design, rational in its engineering technology and economic in its means of implementation.
The development gives the community a facility that is great value for money – Hull can be proud of this multi-purpose stadium.

Festival Place, Basingstoke

Festival Place, Basingstoke

Architect

Lyons + Sleeman + Hoare

Structural Engineer

whitbybird

Steelwork Contractor

Severfield-Reeve Structures Ltd

Main Contractor

Laing O’Rourke

Client

Grosvenor

The Festival Place Shopping Centre provides over 93,000 m2 of retail and leisure space and 3,000 car parking spaces. The development comprises a complex assembly of new build and refurbishment.

The shopping centre is split into a series of independent structures with malls, in between, forming a route through the complex. The glazed roof of the malls are elegantly designed and detailed using a combination of hollow section trusses and columns with plated steel struts. These are designed as independent structures adhering to the movement joint philosophy between the buildings. In the main mall tree style hollow section columns support bowstring trusses and frame the glazing. The bowstring trusses incorporate yacht technology in the design of the rod; a tension member pivoted about a single point and evenly stressed throughout its entire length. This provides an almost transparent element spanning the 10m mall.

Vertical bowstring trusses are also used at the glazed south entrance to the shopping centre, these are approximately 15m high and are supported by the portals at first floor level and the roof structure above. Each individual bowstring truss varies in height suiting the curved profile of the entrance.

Porchester Square – the interface between the old shopping centre and the new complex – is a 36m x 25m glazed space framed by a truss structure standing 12m above ground level. Two 25m high masts and a series of high strength tension rods support the frame, which is then laterally restrained. The support condition was governed by the aspirations for a column free space and the retention of existing swimming pool complex beneath the square’s ground floor slab.

The Wote Street entrance is a circular steel glass block clad tower. The 20m high tower was designed as a fully rigid/moment framed structure. The tower is supported by two stiff UCs double cantilevering over the existing RC perimeter retaining wall below. A prop at a high level within the existing roof stabilises the structure.

The Leisure and Cineplex structure is a series of ‘boxes within boxes’. Each individual auditorium is designed to prevent structure-borne vibrations being transmitted to adjacent structures. The Cineplex roof is supported by a grid arrangement of deep trusses, which spans up to 22m in length creating large column free zones necessary for the Cineplex.

Each building of Festival Place incorporates its own service/loading bay, requiring large areas of column free zones. This was achieved by using 2m deep pre-cambered steel fabricated beam sections, which transfer the column loads from the car park and shopping mall areas above.

To link the east side of the centre to Churchill Plaza a lightweight bridge was required. The bridge is a space frame in section and as a truss in elevation providing an acceptable aesthetic solution to an exposed structure, whilst keeping the overall weight to a minimum.

Judges’ Comment

s:

This enormous shopping mall, which has transformed Basingstoke as a retail centre, has relied heavily on the use of steel to meet successfully the demands of budget, schedule and fitness for purpose. The elegantly light bowstring roofing structure is particularly noteworthy.

Whittle Arch and Glass Bridge, Coventry

Whittle Arch and Glass Bridge, Coventry

Architect

MacCormac Jamieson Prichard

Structural Engineer

whitbybird

Steelwork Contractor (Glass Bridge)

Rowecord Engineering Ltd

Steelwork Contractor (Whittle Arch)

Westbury Structures Ltd

Main Contractor

Butterley Construction

Client

Coventry City Council

The Phoenix Initiative is Coventry City Council’s most extensive city centre regeneration project to date. The £20M scheme, jointly funded by the Millennium Commission and Coventry City Council, has created an attractive journey from the Cathedral Quarter down the Museum of British Road Transport, tracing the city’s thousand year history along the way.

The City Council, with its architects, has drawn up designs for the city that have created new spaces that are both imaginative and functional. Priory Place, set to give Coventry something to rival Birmingham’s Brindley Place with café bars and new city centre housing, and Millennium Place, a fantastic new open plaza capable of hosting all kinds of outdoor entertainment, are the two civic spaces.

The Millennium Place incorporates two structural steelwork features, designed by architects MacCormac Jamieson Prichard with engineers whitbybird that are unique. The Place is overlooked by the twin arch structure of the Whittle Arch, and the spectacular glass bridge that spirals out of Millennium Place and provides an impressive new view of the city.

Whittle Arch

The twin arches each span 60m. They lean toward each other, and mutually support each other through a single connection point at the crown. The clear height to the crown is approximately 15m. The arches are fabricated from standard CHS’s spanning between the regular plate diaphragms. One family of tubes travel directly between the diaphragms to carry the axial thrusts and bending moments, another forms a series of spirals between the diaphragms and these carry the shear forces and torsions that exist under the different loadcases. The structure is clad with stainless steel sheet, perforated so that the sinuous organic nature of the structure remains visible. The diaphragms are in fact annular, again to enhance light flow through the structure and to enable it to be lit at night.

The arch follows the tradition of Frank Whittle by pushing the use of technology. The arch geometry was initially set up in the 3D computer drafting package X-Steel. It was then directly transferred into the finite element package LUSAS. The deflections were calculated and these were directly transferred back into the X-steel package so the pre-set, or pre-cambered, form of the structure was directly available to the steelwork contractor.

The ‘Glass Bridge and Ramp’

The bridge snakes out of the Millennium Place through a 360 degree spiral ramp and takes pedestrians 3m over a medieval city wall and the restored Lady Herbert Garden before making a gentle landing in the garden of International Friendship.

The bridge and ramp take their name from the glass fins which envelope the parapets but the structure is very much in steel. The main spine of the ramp and bridge is a large diameter tube that was pre-bent to the various radii needed to form the profile of the bridge. The main engineering feature of the structure is the very large unsupported spiral that forms the ramp. This spiral would be very prone to excitation by vandals and as a result within the tube are three tuned mass dampers, sized to deal with the first principal mode of vibration. Again the finite element package LUSAS was used to analyse the structure and its modes of vibration.

Judges’ Comment

s:

This exciting project shows high quality steelwork as sculpture and structure on a civic scale. The arch is formed of a pair of aerofoil section tubular lattices with perforated stainless steel sheathing, which are internally lit to provide a glittering shape in the night sky, while the bridge, with its unsupported spiral lower ramp formed of a tubular spine and coloured glass fins, is a fine example of a complex torsion structure which makes a strong visual statement.

Beaufort Court, Lillie Road, London

Beaufort Court, Lillie Road, London

Architect

Feilden Clegg Bradley Architects LLP

Structural Engineer

Michael Barclay Partnership

Steelwork Contractor

Littlehampton Welding Ltd

Main Contractor

Llewelyn Rok

Client

Peabody Trust

From the outset this project aimed to follow best practice in sustainable development, introduce innovative construction and a high level of prefabrication.

Beaufort Court is a high-density urban development with mixed tenure including provision for the socially excluded. It is situated adjacent to an existing estate of 19th Century buildings and provides 65 units of housing, a tenant’s meeting room shared with the existing estate’s tenants, and an underground car park for 44 vehicles.

The development consists of three blocks forming the north, south and east boundaries to a protected enclosure. The external façade of the buildings consists of a pattern of full height glazing, stack bonded terracotta blocks, terracotta rainscreen cladding and coloured render. The elevation is punctuated with visually expressed steel columns, beams and balconies, continuing the rhythm of the existing adjacent Peabody buildings. The roofs of the lower blocks are planted with sedum, reinforcing the green landscape strategy. Steel was chosen after a comparative analysis of the alternatives. The aim was to devise a high quality, safe, cost-effective solution in the context of sustainable construction. The structure devised is a prefabricated steel system incorporating large light gauge steel panels for floors and walls, three dimensional modules for the bathrooms and hot rolled steel for balconies and other “visually expressed” steel components. This form of construction was chosen because of the following advantages:

  • The hybrid arrangement allows bespoke construction giving considerable flexibility in architectural form – important because of the mix of accommodation types needed and the planning constraints.
  • The ease of integrating services with the structure.
  • Low U values leading to low energy consumption.
  • Excellent sound performance that exceeds Building Regulation requirements.
  • Environmental benefits – reducing waste, minimising pollution by carrying out the work under controlled conditions, recyclability, lower environmental costs of transportation.
  • Safe construction: pre-decked floor cassettes provide safe working platforms during erection; off-site construction in a controlled environment reduces risk.
  • Economies in foundations and transfer structures through exceptionally light weight construction.
  • The use of light gauge steel panels reduces transportation and eases site access and storage.
  • Fully fitted bathroom pods reduce on site construction time and secure quality of high value components.
  • The site work is predominantly dry and clean – dry floor construction; dry-lining to the walls, much of the cladding is clipped in place and factory-made bathrooms. The result is high quality of construction and minimum wastage of materials.
  • The form of construction was shown to be comparable in cost to traditional construction; but superior in the other respects identified above. The construction was built to budget and within a week of the programme.

In order to maximise structural efficiency, load paths are made as direct as possible by avoiding transfer structures and by ensuring that wall studs and floor joists are aligned at every junction. This is an important factor in the design process and requires a significant co-ordination effort. To put it in context at Beaufort Court, there are some 1,000 panels of 400 different types in the six-storey block. Such a high degree of non-standard panels is only viable because of the extensive use of computer aided design.

Judges’ Comment

s:

Once again the Peabody Trust has shown how steel can be used so effectively to provide high quality social housing using a prefabricated steel system incorporating light gauge steel panels, modular bathrooms and exposed hot rolled steel construction.