Design Awards: 2016: Award

London Olympic Roof Conversion

London Olympic Roof Conversion

Architect
Populous

Structural Engineer
BuroHappold Engineering

Steelwork Contractor
William Hare

Main Contractor
Balfour Beatty Major Projects

Client
London Legacy Development Corporation

When the London Olympic Stadium was designed it was with an ethos of ‘embracing the temporary’ in the knowledge that, post- Games, its function would change and, as a result, the structure would need to change too. Such foresight paid dividends when it was announced that the stadium would become the new home of West Ham United football club at the beginning of the 2016/17 season.

One of the main stipulations for the future use of the stadium was that it would retain its running track. To prevent this from adversely affecting the atmosphere at football matches, an automated system of retractable seating was included in the new design, with all four sides of the lower bowl able to move over the running track when in football mode. To meet UEFA rules, the roof needed extending to fully cover the retractable seating.

Work began on the project to transform the venue in late 2013. The new structure included 8km of steel cables weighing 930 tonnes, 112 steel rafters, 2,308 purlins, 422 struts, 9,900 roof panels and 14 light paddles each weighing 43 tonnes, with the whole structure weighing in at around 4,700 tonnes which is nearly six times the weight of its predecessor.

In order to preserve some of the Olympic Stadium’s identity, the iconic triangular lighting tower design that used to stand over the old roof has been inverted and they now appear to hang underneath the new larger roof.

Early works involved the deconstruction of the old roof and the strengthening of the existing structure, foundations, V-columns and the perimeter compression truss.

Strengthening of the existing structure was one of the major challenges. Due to the additional weight of the new roof, it was necessary to replace and/or strengthen the existing V-columns and significant strengthening works were carried out to the existing compression truss.

For the compression truss strengthening work alone the amount of hierarchical complex calculations involved the steelwork contractor developing his own in-house software to process over 10,000 calculations – a task that would have been impossible using traditional methods.

The ambitious new cantilevered roof now stands as the world’s largest with every seat in the stadium now covered by the new roof.

The 14 new lighting paddles are positioned beneath the new roof. Each lighting paddle houses up to 41 lamps, many of which are the original lamps that shone over the stadium during the London 2012 games. Four 600 tonne capacity cranes operated in tandem to lift the lighting paddles and the other roof members into position.

The tolerance in the fabrication and quality of finish was expected to be very high and the design was made with security in mind. Most of the geometry was complex and specialised jigs were manufactured to fabricate some of the complex tubular nodes. A total station was employed to set out all of the brackets for the lighting paddles which all lean towards the pitch and are all slanted in three opposing planes.

Not least, the oval shape of the stadium and the movement and tolerance requirements only gave the opportunity for single pieces to be replicated twice, which meant that half of the stadium structure was fabricated with unique members.

Following the V-column and compression truss strengthening work, to maintain equilibrium until the oval was fully formed the erectors worked in two teams at opposite ends of the stadium working in a clockwise rotation constructing the back roof first, then the front roof complete with the lighting paddles and walkways.

To ensure the correct distribution of forces through the cable support structure to the compression truss, the front and back roof are completely independent of each other. However, for the installation of the lighting paddles, the front roof had to be temporarily tied to the back roof to ensure that the lighting paddles did not overturn until the full ring stiffness of a complete oval was achieved.

4D programming using BIM modelling was the key to delivering this successful project to a very high profile deadline, which was originally the 2015 Rugby World Cup taking place in September 2015. However, this was brought forward even more to fit in the Sainsbury’s Anniversary Games which took place in July 2015. This meant that all major construction had to be complete by May 2015.

The new structure now has a lifespan of over 60 years and is set to become the new national competition centre for UK Athletics, and in 2017 will host the IAAF World Athletics Championships and IPC World Championships. The stadium has already hosted five games of the 2015 Rugby World Cup and motor racing’s 2015 Race of Champions.

The stadium has also been upgraded to a 54,000 all-seater UEFA category 4 football stadium, which is the highest category of football stadium possible in the world.

Judges’ Comment

The need to modify the roof and seating of the 2012 Olympic athletics stadium to accommodate a multi-purpose sports venue posed formidable challenges. The geometry and behaviour of the original structure were very complex but, with extremely detailed study and fine engineering skill, most of the original elements have been re-incorporated.

The challenges have been met superbly and the project is a triumph for the team and for structural steelwork.

Harlech Castle Footbridge

Harlech Castle Footbridge

Concept Designer
Mott MacDonald

Structural Engineer
David Dexter Associates

Steelwork Contractor
S H Structures Ltd

Main Contractor
RL Davies & Son Ltd

Client
Cadw

Harlech Castle is one of the finest surviving 13th Century castles in Britain – it is a Grade I Listed Building, a Scheduled Ancient Monument and also part of a World Heritage Site. For many years access to the Castle had been via a series of timber steps, with no provision for those with impaired mobility. With the opening of a new visitor centre nearby, the vision was to connect this to the Castle via a new ‘floating’ bridge.

Due to the sensitive nature of the site, the aesthetics have been a particularly important consideration. Various concepts were explored to satisfy the constraints of functionality, alignment, heritage and visual impacts before finally opting for the ‘S’- shaped low profile Vierendeel truss design.

Both horizontal and vertical alignments were constrained by the need to connect straight through the Castle’s gatehouse, whilst maintaining a suitable gradient acceptable to those with impaired mobility.

To minimise the impact of the views of the distant mountains of Snowdonia, the profile of the bridge was reduced by tapering the bottom chords of the trusses and eliminating any diagonal bracing, thus avoiding a potentially more cluttered appearance. The visual lightness of the bridge is significantly improved by the selection of a stainless steel mesh infill to the parapets. The deck is 2m wide in general, however it widens up to 3m above the middle support to provide an area where people can enjoy the views.

To ensure that the bridge was future-proof provision was made for services to be run in a duct under the bridge deck, allowing the creation of a new venue within the castle where events and performances can be hosted.

Throughout the design process there was continuous dialogue between the project team using 3D BIM CAD modelling to explain design proposals and ensure the design developments were acceptable. The first key area for development was the truss and deck configuration. The original proposal had fin plates welded to the back of the CHS Vierendeel truss bracing elements, which then became the tee web in the handrail upright. This arrangement posed some fabrication challenges and raised the possibility of weld distortion in the fin plate attached to the CHS. An alternative solution was adopted whereby SHS bracing was used and the handrail fabricated tee upright orientation was reversed. The face of the SHS Vierendeel bracing then aligned with the flange of the tee to the balustrade which was tapered to give an elegant transition to the handrail, whilst the bracing also gives improved structural capacity particularly at the joint with the CHS chords for a given section width.

To maximise headroom clearances under the bridge, and to give a more efficient structural solution at the supporting columns, the depth of the truss profile was modified and the bottom chord form was achieved from a combination of curved and straight sections of tube.

The bridge’s dynamic performance required careful consideration in the design. The columns needed to be very stiff in the transverse direction so an elliptical section was used which, when partly filled with concrete, achieved the required result. This choice also had the added architectural benefit of the elliptical column being less obtrusive on elevation, whilst approximately matching the profile of the truss chord.

Before work started on site the existing façade was digitally scanned and the 3D survey was incorporated into the design model to ensure the critical dimensional interface between the Castle entrance and the bridge was achieved.

Bridge sections were set up in bespoke jigs to control weld distortion and maintain their geometry during welding.

The bridge is lit with a bespoke integrated LED lighting system that delivers bright white task lighting to the walkway, but has the added benefit of having a number of colour-changing effects that can be accessed for special events.

The bridge is finished with a timber deck and handrail for which FSC certified Ekki hardwood was selected, this requires no preservative treatment and little maintenance. The deck boards feature anti-slip inserts and seamlessly follow the curves of the bridge.

The biggest challenge to the installation team was the limited footprint of the site and the restricted access through Harlech. These challenges were overcome with the careful selection of the multi-wheel steer mobile crane and rear wheel steer transport trailers.

Steel erection required meticulous planning and attention to detail to ensure a smooth and safe installation process, however the unique historic nature of the site put even more responsibility onto the erection team. Following offsite matching of the deck units the fit-up on site was perfect and the three main spans were installed without any significant problems. With the bridge sections in place, the careful co-ordination of the fitting of the timber deck, parapets, lighting and services allowed the bridge to be completed in good time ready for its opening for the year’s summer visitors.

The new footbridge has been very well received and welcomed as an attractive addition to the historic site, whilst dramatically enhancing the visitors’ experience.

Judges’ Comment

In a very sensitive setting this elegant bridge provides level access to the historic castle, whilst minimising its visual impact. The detailing and fabrication of the curved deck are exemplary. The erection was effected with a high degree of precision despite the limited site and extremely difficult access.

The modern shapes of the bridge create a beautiful counterpoint to the ancient castle it serves.

Thames Tower Redevelopment, Reading

Thames Tower Redevelopment

Architect
dn-a

Structural Engineer
Peter Brett Associates LLP

Steelwork Contractor
Shipley Structures Ltd

Main Contractor
Bowmer and Kirkland Ltd

Client
Landid Property Holdings Ltd

Located in the heart of Reading town centre, the existing Thames Tower concrete office block has been given a new lease of life with an enlarged footprint at each floor level in conjunction with a five-storey steel- framed extension above level 11.

The original scheme concept was to demolish the existing concrete-framed structure and replace it with a new 25- storey high tower, which would have necessitated the requirement for new supporting/up-rated concrete foundations.

However, through an innovative design proposal, the core of the existing structure was maintained and developed using a series of strengthening works throughout the height of the concrete frame, along with the provision of four additional steel- framed office floors to increase the nett usable internal areas. This also provided huge ‘value-engineering’ savings to the scheme as the basic core of the structure was maintained and no amendments or enhancements of the existing concrete foundations were necessary.

The refurbishment works included stripping the building back to its structural frame and the removal of the existing concrete cladding panels to all elevations, which were then replaced with a new terracotta tiling system to complement the local town centre surroundings.

In order to accommodate the increased dead and imposed loads from the new five-storey extension between levels 11 to 16, it was necessary to strengthen the columns and floors of the existing concrete-framed structure. This was achieved by the following:

  1. The supply and installation of 15mm thick stiffening plates to the full width of the concrete columns between levels 6 and 11. The columns were initially ultrasonically scanned to avoid clashes with the steel reinforcing bars. Following the bespoke fabrication of each of the 282no individual stiffening plates, these were fixed to the columns by means of 14no resin anchor bolts and subsequently bonded to the concrete face across the full plate area using a special ‘fast-curing’ resin.
  2. These were further complemented by fabricated ‘cruciform’ stiffening brackets at the column heads, in order to adequately disperse the upper load transfer.

An intermediate mezzanine steel-decked floor was also supplied and incorporated at level 01, using cellular beams to provide a lightweight steel solution with maximum integrated space for M&E equipment.

The above strengthening works, along with further stiffening plates and brackets at level 11, also facilitated the use of a roof- mounted tower crane for the installation of the new upper five-storey extension. The tower crane was installed approximately halfway through the steel site programme. Initially all of the internal steel members for the strengthening works had to be hoisted through the existing internal lift cores and ‘hand-balled’ into position.

The structure’s original design had the perimeter columns protruding beyond the main floor areas, along with splayed 45 degree corners throughout its full height.

As part of the building refurbishment, and to maximise the internal floor areas, the new design introduced a series of additional perimeter support beams which were connected to the external edge of the existing concrete columns. Metal decking and associated concrete floor infills then created an increase to the building footprint up to the exterior face of the perimeter columns.

The four corners of the building were also altered to create a now perfectly square structure, which has further increased each of the tower’s existing commercial floorplates. This was achieved by installing a new steel column to each of the building’s corners with secondary infill framing. These triangular corner infills were then subsequently metal-decked and concreted throughout the full height of the building. This has increased the tower’s floor space from 13,600m2 to approximately 17,000m2 of offices and 740m2 of restaurant/café space.

The new upper steelwork extension is connected to the existing concrete columns at the newly created level 11 and corner infill sections. Predominantly based around a 6.3m x 5.8m internal grid to match the existing columns below, each floor is formed with a series of cellular beams that accommodate services and support a metal deck flooring system.

The use of composite cellular beams has kept the steel weight to an absolute minimum, thus limiting the additional dead load on the existing structure below, and ultimately allowing M&E services to be distributed within the structural depth of the new steel members at all levels.

Due to limited storage space on site, vehicular restrictions on member lengths and the need to minimise the weight of mechanical plant on the roof structures, it was necessary to construct the upper extension on a floor-by-floor basis.

This was sequentially constructed by means of the primary steel frame, followed by the metal deck flooring and associated concrete topping at each level. Following the adequate curing of the concrete deck at each level, the next level was subsequently constructed, up to level 15.

The steelwork for the new floors up to level 16 was completed in December 2015.

Judges’ Comment

This is a thorough and rigorous project which has been carried out with ingenuity and skill. With both painstaking analysis and inventive thought, a substantial but unloved city-centre concrete building has been enlarged upwards and horizontally by the creative use of steelwork.

The project was technically and logistically challenging, but teamwork and a committed client have achieved a solution which is exemplary in its calm elegance.

South Stand Expansion, Etihad Stadium

Final SSDA Brochure 2007

Architect
Populous

Structural Engineer
BuroHappold Engineering

Steelwork Contractor
Severfield

Main Contractor
Laing O’Rourke

Client
Manchester City Football Club

The South Stand expansion increased the capacity of the stadium during the 2014/15 football season, adding 6,000 new seats through a third tier on the terraces and 1,500 additional seats around the pitch. An architecturally sympathetic extension of an existing catenary ringed structure was needed, which did not compromise the integrity or capacity of the structure and ensured that the existing stadium remained operational during works.

The design was technically complex as the existing roof involved a cable net structure with a tension ring, from which steel roof rafters hung. The structural integrity of the existing tension ring relies on it running around the whole circumference of the roof; therefore any modification to the roof could not affect this, even in areas where roof rafters were removed. Protection of the existing cable was vital as there was no repair procedure in place, and damage would result in replacement and potentially the closure of the stadium for two years.

Extensive design optimisation exercises were undertaken, particularly for the steel roof and the stability cores. A whole series of geometric studies evaluated the effects of different stay and mast angles, concluding with a solution to satisfy both minimum material requirements and cost.

The stability cores were formed of steel vertical brace planes with the inclusion of outrigger bracing to add efficiency and, although a solution normally adopted on tall buildings, this approach proved effective for the project. A design and costing study of the original stays, which were formed of cable, revealed that bars could be introduced for the new stays. These had marginally more erection work associated with them, but overall were a more efficient solution. Combined 3D modelling allowed the integration of all services within the structural envelope, including the late addition of increased sports lighting requirements in accordance with new regulations.

The project contains a number of highly bespoke details tuned to the complex geometries and design challenges, including the multi-stay connection at the top of the masts and column bases formed of spherically machined plates and rotational bearings, which allow the new design to accommodate differential movements between the new and existing structures.

An area of complexity centred on the temporary modes of the stadium. For typical stadium conversions an additional tier can be built behind the existing building and a new roof constructed over the existing roof, with little interaction between old works and new. This was not the case with Etihad as the roof profile and supports at the end stands extended further back behind the seating and the new upper tier would therefore project through the existing roof profile.

The ‘interim roof’ solution involved cutting and removing the existing back of the roof, acknowledging that this meant cutting into roof rafters which had significant locked-in forces from the dead loading of the roof. Significant and complex temporary works were required for the project, with the remodelling of the existing roof completed in the first closed season alongside temporary propping to allow work to proceed above the existing roof. The existing roof was removed in the second closed season to reveal the new terrace behind. The new design respects the geometry of the existing stadium and, whilst the expanded South Stand is significantly larger than the previous one, blends into the original design.

Examples of innovation include bespoke designed solutions such as spherical bearings, cable protection frames, an upper MEWP platform, intermediate roof propping, tie bar installation lifting beams to include remote release features and hidden bolted splices in the rafters. The availability of a CTL 1600 crane, the largest crane of its type in the country, significantly influenced the lifting methodology as it permitted much larger lifts, speeded up construction and reduced the need for working at height splicing components.

In terms of sustainability the project focussed on re-use and recycling, rather than demolition. The team worked exceptionally hard to retain the existing cable net that supports the stadium roof. Much of the original building was retained during construction and existing components from the building’s façade re- used. Steel and aluminium crowd ‘flood gates’ were cleaned, repaired and repainted and the existing lower tier terracing was re-used following careful detailing of the connections to the new building. The client also received a masterplan design which enables the stadium capacity to be expanded further to the absolute limit of the existing cable net, and then only at that point does the roof need to be completely replaced.

A risk assessment considered potential fire loadings throughout the building and established specific design criteria. Intumescent paint was used extensively to enable steel to be exposed to view and corrosion protection is to a high standard and specification.

The extension, completed within 16 months, was opened on the 16 August 2015 in front of a record crowd of 54,331 people.

Judges’ Comment

This is a complex project which added 6,000 seats above the roof at one end of an existing stadium. The work tested all facets of steelwork construction to their limits, including design, fabrication and construction.

A stunning testimony to all concerned and to the capabilities of steelwork which merges seamlessly into the existing structure.

The Memorial Spire, International Bomber Command Centre, Lincoln

The Memorial Spire

Architect
Place Architecture

Structural Engineer
s h e d

Steelwork Contractor
S H Structures Ltd

Main Contractor
Lindum Group Ltd

Client
The Lincolnshire Bomber Command Memorial Trust

The International Bomber Command Centre (IBCC) is being created to provide a world- class facility to serve as a point for recognition, remembrance and reconciliation for Bomber Command. This is an ongoing project being driven by The Lincolnshire Bomber Command Memorial Trust, in partnership with the University of Lincoln, with the aim of opening the Centre in 2017.

Lincoln has been chosen as the site for the IBBC as Lincolnshire earned the title of Bomber County – it was the home of 27 operational bases which in itself was a third of the UK’s Bomber Command bases.
At the heart of the IBBC is the Memorial Spire which sits majestically above the City of Lincoln and acts as a beacon marking the courage and bravery of those who served in World War II.

The architectural references are taken from the airframe and wings of an Avro Lancaster Bomber. The structure represents two wing fragments tapering towards the sky, separated by perforated plates similar to those used in the aircraft’s frame construction. Further references can be found in the Spire’s dimensions, standing 31.9m high this represents the same span of a Lancaster’s wing and, at 5m wide at its base, is the same width of the aircraft’s wing.

The Spire’s orientation was carefully considered and it is placed so that visitors who walk through it will be rewarded with a framed view of Lincoln Cathedral. The Cathedral Spire was very familiar to the aircrew as it was a welcoming landmark to those who returned from their many sorties during World War II.

The facts and figures relating to the role of those young men who flew from airfields around Lincolnshire and other parts of the UK are thought provoking: 364,514 sorties flown, 3,491 aircraft lost and 25,611 aircrew losing their lives, with the average being 22 years old. To recognise the sacrifice of the aircrew the Spire is surrounded by a series of Memorial Walls. The weathering steel panels are laser cut with the names of those who lost their lives.

Steel was the obvious choice for the Spire and the weathering steel plate fulfilled all the structural and aesthetic requirements of the project. The selection of weathering steel gives the Spire a cold austere feel which, whilst not requiring applied surface treatments, will be maintenance-free throughout its lifespan.

The first part of the manufacturing process was to cut the individual plates. Using the information generated by the computer model the plates were carefully nested to minimise the overall waste of material. The external profiled plates had to be curved to create the wing-like form. This was achieved by press-braking the individual plates to the desired shape using files extracted from the 3D model.
The formed plates were built up in purpose-made jigs prior to being welded together to form the complete spire sections that would go to site as two loads. Due to the significant amount of welding, a great deal of care had to be put into the developing of the weld procedure to ensure there was no distortion in the plates, particularly along their leading edges where any defects would be most noticeable on the finished spire.

With fabrication complete the two sections of the spire were shot blasted – a process that would ensure any fabrication marks were removed and allow the structure to develop an even patina as the weathering steel gradually turned its familiar rusty colour.

On 2 October 2015 in front of an audience of 2,600 guests, including 312 Bomber Command veterans thought to be the largest gathering since 1945, the IBBC Memorial Spire was officially unveiled.

We all go about our working lives and spend time with our families and friends and it is easy to forget that the freedom we have today is thanks to those who gave so much during World War II. To be reminded about the sacrifices made by so many is a humbling experience. The Spire is a fitting memorial and, when further funding is in place, the construction of the Chadwick Centre will begin, which will house the Bomber Command archive and tell its story to future generations.

Judges’ Comment

This excellent project is a fitting testament to the memory of the World War II bomber crews that flew from Lincolnshire and other parts of the UK. The architectural arrangement of the various elements has been carefully considered, taking cues from the local context. The choice of weathering steel is most successful.

The detail design and particularly the execution of the monument are outstanding.