Design Awards: 2009: Commendation

New Academic Building London School Of Economics & Political Scene

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Architect

GRIMSHAW

Structural Engineer

ALAN BAXTER & ASSOCIATES

Steelwork Contractor

BOURNE STEEL LTD

Main Contractor

OSBORNE

Client

LONDON SCHOOL OF ECONOMICS & POLITICAL SCIENCE

The LSE’s New Academic Building is an extensive remodelling of an Edwardian government office block. A range of strategies was employed to help achieve the aim of an ‘Excellent’ BREEAM rating, with over half the building’s original fabric being reused.

The atrium is the central hub and contains the main circulation cores. Its timber floor folds down to provide access to the lower ground floor before sweeping three storeys upwards to the roof, framing the two cantilevered mezzanine gallery levels.

There are eight storeys above ground and two below. Teaching and larger social spaces are centred round the atrium circulation toward the lower levels of the building. Departmental space is arranged in a U-shape around the central lightwell on the upper levels.

The most dramatic feature of the new structure is the suspended floor system. This was key to providing extensive column free spaces and opening up the core of the building. All major teaching and social spaces are located on the lower floors providing a clear division between teaching and departmental space. To achieve this, all floors above ground level are suspended from continuous steel hangers connected to an 18m long storey-deep truss which forms the backdrop to the rooftop pavilion. Separate hangers suspend the second and first floors which are stepped back from the atrium to allow more daylight to enter. To support the 15 tonne truss two 600mm diameter CHS columns were erected on new piled foundations. These extend through the atrium and straddle the lecture theatre beneath.

The 10-storey high columns were installed in three sections and restrained at each floor level from third upwards via an edge beam. Primary structure and condeck were installed to provide work decks on levels 1-3. By not pouring the slabs to these floors their weight was kept down so the level 1 and 2 hangers could be used as temporary props. The roof truss was installed to the top of the columns using a 700 tonne crane. The exposed hangers to levels 3-8, each made up of two 100mm x 50mm solid steel bars, were also craned into site in 16m lengths. The floor plates were then progressively completed up the building.

Another 18m long 6 tonne truss was installed at ground level to provide support for eight 18m long sculpted pre-cast concrete ribs. These ribs form the lecture theatre roof and express the curvature of the atrium floor above. The installation of these major prefabricated elements presented one of the biggest challenges of the project. The operation’s scale required the work to be scheduled over the weekend, with road closures arranged in advance.

The project benefitted from the use of Corus’ Bi-Steel core system for two of the lift shafts. These were completed twice as quickly as an equivalent concrete jump-formed version providing major programme benefits.

These structural interventions have provided the LSE with a 400 seat lecture theatre and an expansive atrium at its centre. The atrium is capped by a glazed roof with delicate bowstring trusses spanning 13m, allowing maximum light to enter.

This impressive 12,700m2 building meets all the client’s aspirations and was completed to programme and within budget.

Judges’ Comment

s:

Steel and glass skilfully combined to transform an Edwardian office block into light, airy accommodation. To provide column-free spaces in the old cellular offices, the elegant solution is to suspend the new floor system from a deep roof-level truss.

An excellent example of updating an existing building.

201 Bishopsgate And The Broadgate Tower London

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Architect

SKIDMORE OWINGS & MERRILL

Structural Engineer

SKIDMORE OWINGS & MERRILL

Steelwork Contractor

WILLIAM HARE LTD

Main Contractor

BOVIS LEND LEASE LTD

Client

BRITISH LAND PLC

The development consists of a 12-storey office building known as 201 Bishopsgate and the 35-storey Broadgate Tower, which reaches a height of 165m above ground level. Between the two buildings is a Galleria area complete with a glazed roof which is supported as a cantilevered structure from the Broadgate Tower structure above level 5.

The development, which is located directly above the railway route at Liverpool Street station, was only structurally possible after significant enabling works were completed to create a raft structure over the live railway. Due to design changes the original 6,000 tonne raft structure needed extensive modification from the design constructed in the mid 1990’s, and resulted in an additional 1,000 tonnes of steelwork being incorporated.

In order to limit deflections and settlement it was necessary to distribute the resulting vertical forces from the two buildings evenly across the raft support structure, and thus the option of a heavy centralised RC core was not a viable structural solution for either building. Hence, the vertical load-path for the tower includes a series of raking A-frame legs that effectively prop the structure at level 5 and transfer the loads to strategically located transfer beams and columns within the raft structure.

The specification of 5-storey high raking struts provided a challenge during the construction of the frame, and an extensive arrangement of temporary props and trestles was required in order to build the structure up to level 5 before installation of the A-frame legs could begin. This included a sophisticated load transfer operation using a jacking system to transfer the loads from the temporary supports onto the permanent main raking columns. These raking columns and their associated bracing members were delivered as individual components of up to 26m in length.

The structural form of the Broadgate Tower is an elongated rhombus shape and the lateral stability is provided by a perimeter diagrid bracing system to all four sides of the structure located just inside the external cladding. The diagrid nodes occur at 6-storey increments, with plan bracing and RC diaphragm floor plates distributing the horizontal loadings into the external bracing lines.

Intermediate floor stability is provided by a secondary internal bracing system that spans between each 6-storey module.

The main service cores of the structure are constructed in steel and house the lift voids, staircases and service risers. The floor plates are RC on steel decking supported by long span cellular beams in the E-W direction.

In order to simplify the transport, handling and construction of the main perimeter members, the structure was constructed in 3- storey increments with the central welded splice being carried out on site to form the continuous 6-storey elements.

Wherever possible the main diagrid column and bracing connections were designed as a bolted joint but in certain locations, due to the resulting forces, it was necessary to site weld the joints. This detail required a robust temporary connection to be installed during erection in order that construction could continue above the splice location, and this methodology assisted in allowing control of the tower verticality during construction.

The building façade is designed to mimic the structural form so that the diagonal shape of the perimeter bracing system is visible from the outside. This gives the structure a unique feature that differentiates it from other buildings in and around the development.

Judges’ Comment

s:

These landmark offices are prominent and prestigious. The steel-framed Tower is sited above the Liverpool Street railway, above a bridging raft which had been constructed for an earlier, smaller scheme. The East façade has therefore been carried on large raking steel shores across to the raft abutment.

An heroic solution creating interesting spaces as a bonus.

Cabot Circus Footbridge Broadmead bristol

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Architect

WILKINSON EYRE

Concept Designer

WATERMAN CIVILS

Structural Engineer

DAVID DEXTER ASSOCIATES

Steelwork Contractor

S H STRUCTURES LTD

Main Contractor

SIR ROBERT MCALPINE LTD

Client

THE BRISTOL ALLIANCE

Cabot Circus Footbridge fulfils a utilitarian brief to provide the seamless linking of ‘satellite’ parking with new retail development. The bridge was planned as a continuation of a long sweeping pedestrian boulevard that cuts longitudinally through the new 2,500 space car park. Its long curving form is clearly related to the curving plan of the car park and can be read as having been ‘extruded’ out of the void created within the building.

Externally the bridge is viewed almost exclusively from Bond Street South below, and generally from the confines of vehicles passing beneath. The so-called ‘third’ elevation of a bridge – its underside – takes on particular significance in this context, and the design of the wide bridge soffit is critical in defining the visual signature of the structure. The careful use of concealed deck splices along the deck also provides the required continuity on plan.

The deck structure comprises a closed steel torsion box which is essentially triangular in section and provides a smooth soffit plane. The section varies along the bridge length such that the soffit seam meanders from side to side along the structure providing a fluid threedimensional form. Deck splices were bolted with TCB bolts which were accessed through hatches in the deck.

The deck is supported at mid span and at each end on tapered cantilevering raking steel columns, orientated in alternating directions such that the deck section at each support is identical but handed. These support arms from the main car park columns also house an arrangement of pot bearing, to accommodate differential movements on plan, while providing local vertical support to the bridge.

Internally, the changing deck geometry exerts an influence on the enclosure, defining the internal space of the bridge. The side plates of the deck are variable in inclination, and this variance is translated through to the steel portals, which incrementally ‘rotate’ relative to each other along the length of the bridge. These portal frames support wall and roof panels, which form warped planes of glass to provide a dynamic spatial experience for the bridge user.

Since the external and internal geometries of the bridge are visually complex the detailing of all elements is minimal to ensure a legible and ‘clean’ aesthetic. Services are subtly integrated, with lighting strips set flush into the portals internally and placed at varying heights to further accentuate the warping geometry.

The steel frames are portalised laterally to provide the principal axis of stability while, out of plane, the frames work compositely to antilever from the main deck. This stability system, with the aid of variable stiffness sealants, can accommodate the vertical and lateral deflections of the bridge, while maintaining stability of the glass panes required in an overhead condition.

The limited access and restricted number of road closures available during the construction phase meant that employing a structural steel solution enabled the bridge to be fabricated in large sections, which were trial assembled for fit and alignment before being delivered to site for installation.

Judges’ Comment

s:

The bridge provides a striking pedestrian approach to this major centre. The sweeping form of the box deck, sculpturally curved and twisted, supports the glass enclosure. The careful detailing, masking of the deck splices, the integration of the services and the high quality fabrication, all ensure an impressively clean appearance.

High standard of work has ensured an equally high quality result.

Ryanair Maintenance And Training Hangar Stansted

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Architect

CAPITA ARCHITECTURE

Structural Engineer

BARRETT STEEL BUILDINGS LTD

Steelwork Contractor

BARRETT STEEL BUILDINGS LTD

Main Contractor

KIER EASTERN

Client

EAST MIDLANDS TRAINING (RYANAIR)

Not far from the main runway and within sight of the passenger terminal at Stansted Airport, a new hangar capable accommodating up to five Boeing 737s is up and running. A series of engineering and logistical challenges had to be overcome to lift four 125m long steel trusses on a design & build contract for the cavernous interior of the new maintenance hangar at the airport.

The design was progressed around the need to be able to lift, on a specific day, the major roof girders. The box girder had to be lifted and made secure in one day. It was recognised on day one that if the girders were erected out of tolerance it would be impossible to bring them back to true.

The design solution was to provide a 10m deep x 7.2m wide x 125m long box girder, pre-cambered for self weight and dead deflections. This would form the spine to the structure. Two further 125m trusses could then be erected in three 41.5m sections, and braced back to the spine box girder. The stiff spine would force the vertical trusses into position. Final adjustment of the door guides would take place after roof and wall cladding was complete. To do this a system of vertical and horizontal adjustment to the door guide support brackets was devised, which could be locked off once before handing over.

The erection method statement called for the girders to be transported “piece small” and built up on the ground in temporary stillages. The main contractor invested in the ground providing a high quality level erection platform capable of carrying the stillages with minimal settlement. The stillages were staged to allow a natural positive pre-camber to be built in. The completed box girder was checked and then locked by the application of TCB High Strength Friction Grip bolts.

On 16 April 2008 the box girder was hoisted into place using two 300t all-terrain mobile cranes. The girder was lifted between two pairs of 25m high lattice columns positioned 125m apart. The physical lift took 30 minutes, but all day to complete, from early morning briefings and safety checks to late in the evening tying back and making fast. Two further 50 tonne plain trusses were lifted end of April and braced back to the rigid box girder. The three 41.5m sections were then lifted individually by one of three 100t capacity mobile cranes and connected together and to the lattice columns while suspended in the air. Whilst the three sections of the truss were held at the right level and location, a fourth 25t capacity mobile crane traversed between the truss and box girder erecting tying in steelwork.

Only when the doors were installed and successfully commissioned did the project team celebrate a design well executed.

Judges’ Comment

s:

A fine example of an optimised long-span structure, at minimum cost with fast erection. The design & build criteria were limited to the volume contained, loadings and time of erection. Therefore the structural details were simplified to achieve economy, ease of transport and predictability of erection.

A text-book example of this direct approach.

No 2 Spinningfields Square Manchester

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Architect

SHEPPARD ROBSON

Structural Engineer

CAPITA SYMONDS STRUCTURES

Steelwork Contractor

WILLIAM HARE LTD

Main Contractor

BOVIS LEND LEASE

Client

ALLIED LONDON PROPERTIES

The building provides 2,400m2 of high quality grade A office accommodation and 1,380m2 of restaurant and retail space over six floors within a new landmark structure at the entrance to the Spinningfields business and retail development in Manchester city centre.

The building takes the form of two parallelograms on plan, oppositely handed and positioned one above the other, creating at level 2 a roof terrace to the West elevation and a 23m long cantilever to the East. The external cladding and façade diagonal form reflect and complement the structural geometry of the building, drawing attention away from the horizontal plane of the floors.

The design of the building achieved an excellent BREEAM (2005) rating by taking a holistic approach considering all environmental factors. The high proportion of solid insulated panels within the façade benefited the energy demand of the building through a consequent reduction in solar gain.

The office floors have been designed so that they can be fitted out on either an open plan or cellular basis, and the servicing has been provided so that each floor can be sub-divided into two separate tenancies. The floors also have built-in loading allowances for future storage capability and soft spots for tenant plant requirements.

Materials for the building components were selected for their durability and maintenance requirements. In particular the structure was specified for 60 years design life and major components of the envelope 25 years.

The use of steel was the only way such a demanding structure could be delivered economically. The integrated services solution meant that floor zones were minimised, the reduced self weight of the structure meant that the loads to be resolved by the cantilever and the foundations were kept as small as possible, and the high load capacity of steel meant that the cantilever elements could be kept as compact as possible.

The floor construction comprises a 150mm thick concrete slab on composite metal decking on a grid of secondary and primary Fabsec beams.

400mm diameter openings in the 550mm deep beams allowed for integration of the services within the structure zone. The cells were distributed in a regular grid through the irregular beam layout to aid coordination of the service provision. The Fabsec beams were also fire engineered to provide a least cost design considering both the beam weight and intumescent paint thickness.

The 23m cantilever was resolved by making the perimeter steelwork into a 3-storey deep truss, achieving the most economical frame solution possible. The truss philosophy was applied to all four elevations to provide both vertical support to the edge of the floor plate and lateral stability to the upper block. As a result it was possible to omit the concrete cores above second floor level saving money and time.

The structure was engineered to suit the cladding deflection requirements. The linearelastic properties of steel allowed for accurate 3D modeling and prediction of the behavior of the structure, which was then replicated in the on-site deflection measurements achieved by the frame.

The accuracy of construction which was achieved on site is a testament to the high level of skill and workmanship employed by the steelwork contractor in designing and fabricating the complex connections of the structure.

Judges’ Comment

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The building plan of two overlaying parallelograms produces a huge cantilever at the front, which provides a clear view of a notable historic building. The diagonal bracings of the 3-storey frame are cleverly aligned with the herring-bone pattern of the curtain walling, concealing the heavy cantilever trusses from the exterior.

A building of obvious quality in many respects.

A2/A282 Dartford Improvement Scheme

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Architect

JACOBS

Steelwork Contractor

FAIRFIELD-MABEY LTD

Main Contractor

COSTAIN

Client

HIGHWAYS AGENCY

The Highways Agency identified the need for a major road improvement programme at the A2/A282 intersection in north Kent. The aim of the project was to divert traffic away from the roundabout sitting below the M25 and above the A2. This was achieved by constructing a link to carry traffic from the A2 westbound onto the A282 northbound, and another from the A282 southbound to the A2 eastbound. A third dedicated lane on the A2 westbound funnels traffic to the southbound M25. These link roads required four new bridges to carry traffic over the existing highways.

More than 4,000t of weather resistant steel was used for the construction of the four new structures. One of the main considerations was that the bridges would need as little maintenance as possible due to access constraints. With weather resistant steel the rust ‘patina’ develops under conditions of alternate wetting and drying to produce a protective barrier, which impedes further access of oxygen and moisture and eliminates the need for it to be painted with safety, environmental and cost benefits.

The four structures consist of the main east to north link flyover, which is a 420m long nine span viaduct with more than 1,800t of steel. Two parallel five span bridges of 1,000t of steel each are both 250m long and run on either side of the existing A2. The fourth and final structure that was erected required 230t of steel and carries southbound A282 traffic over a small slip road before linking up with the A2.

Work on site for the east to north link flyover began in January 2007, with erection in February. Some sections were assembled on site with the majority of steelwork being lifted using a 1,000t telescopic crane. In May, a critical milestone was reached with the final section of the structure lifted in overnight to link the A2/A282 east-north viaduct. The middle section of the bridge was erected first, followed by the remaining spans toward the south abutment, completing six of the nine spans in one sequence. The remaining spans toward the north abutment were erected thereafter. The nine bridge spans carry the structure over eight piers. Five of the concrete formed piers have four columns while the three middle piers only have two columns. The middle three spans traverse open ground so there was enough room for temporary trestles to support the steelwork during erection.

All nine spans of the east to north link flyover vary in length from the longest at 59m to the shortest at 38m. The structure is curved in both plan and elevation. Steelwork for the bridge deck consists of two braced pairs of girders for each span which were paired on site and lifted into position using the AK680 crane. Cross members are situated at 8m intervals. Each pair of girders consists of four steel sections which were bolted together on site and prepared for erection.

At the design stage it was decided to fit the GRP permanent formwork onto the preassembled steelwork at ground level, which reduced the amount of working at height and meant fewer road closures. Seven optimum positions for one crane to lift all of the bridge decks into place during the steel erection process were worked out. The concrete deck was then poured following on three spans behind the steelwork.

The A2/A282 scheme was completed in December 2007, five months earlier than expected.

Judges’ Comment

s:

A large, busy interchange with one large bridge and three smaller ones. The composition of the bridges, with consistent architectural language, works well in the gently rolling landscape. The plate girder spans were pre-assembled with the decks, and exceptionally heavy lifts minimised traffic disruption.

The innovative use of weathering steel on this scale is practical and appropriate.