The concrete solution

A new project, refurbishing and re-working the Hayward Gallery, Queen Elizabeth Hall and Purcell Room at Southbank Centre, has breathed life into two key 20th Century buildings readying them for their next 50 years as an exquisite concrete home for the arts

Designed by a small team of ground-breaking architects at the London County Council Architect’s Department in the early 1960s, the spatially-complex buildings were engineered almost entirely using in-situ concrete by Arup. Extensive structural record information from the Arup archive enabled a creative and economical examination of the existing structure. This information, drawings and calculations, supported more elegant alterations to the existing reinforced concrete, and working carefully with the existing structure enhanced the quality of the design and considerably reduced the use of new materials and associated carbon costs.

The scope of the project was to significantly refurbish and rework the Queen Elizabeth Hall, QEH, Purcell Room, PR, and Hayward Gallery, HG. It is the services replacement and structural interventions that have had the most significant interaction with the concrete structure. Therefore, this article starts by describing the existing concrete and then delves into two specific structural works items where the concrete was carefully carved and cut to enable new routes and create better spaces.

The full scope of the project:

• Replacement of the building services and associated builders work
• New Artists’ entrance
• Opening up the corner of the QEH foyer to improve its public presence and bar
• New openings in the QEH Auditorium to add a door for level access and a flown lighting bridge
• New cast glass rooftop chiller enclosure on the PR plantroom
• New roof and rooflights on the HG with a matching ceiling, new art hanging walls and new floor finishes
• Internal concrete cleaning in galleries and auditoria

The existing 1960’s buildings
The existing 1960’s buildings were formed from 22,000m3 of concrete. At the peak of construction there were 180 carpenters working on the concrete shuttering; the formwork all constructed using two different thicknesses of tongue and grooved rip-sawn Baltic pine boards to give its distinctive stepped profile. The timber was selected following building visits and tests to give the best concrete surface and boards were reused wherever possible, often up to 12 times. To provide a blemish free surface all joints were sealed, and the formwork tested by being filled with water and left to stand before use. The end result of the care, extreme attention to detail and craftsmanship, in combination with a 15-strong team drawing all the formwork layouts before construction, is a pair of buildings of incredible surface refinement that take full advantage of the sculptural plasticity offered by in situ concrete.

Getting the buildings ready for their next 50 years; replacing all the existing services and adding the electrical and digital infrastructure necessary to support Southbank Centre’s varied artistic programming has required a deep understanding of the requirements in use, matched with a similar understanding of the complexities of the existing buildings. The start of this was a 3D model, developed in Revit from the Arup archive of original structural drawings, LCC and GLC architects’ drawings from Southbank Centre’s own archive and a 3D point cloud survey of the buildings. This enabled the buildings’ servicing to be unpicked and redesigned by Max Fordham, a considerable task given that there were 520 existing rooms across 40 different floor levels with most of the services integrated into the concrete structure.

Working with the concrete to enable the services installation: one thousand new openings in the existing reinforced concrete structure

One of the biggest structural challenges was to navigate through, checking, calculating and justifying over a thousand new openings in the existing reinforced concrete. During the design stages Max Fordham defined and scheduled the openings in Revit and this schedule was used to check the location of each opening and assign one of three structural opening classes which related to a specific approach and detail.

Many of the new openings in concrete were justified without additional structural support, reducing material and cost. This was completed either by inspection or further strut and tie calculations, to ensure the remaining structural element could support the original design load. This process ensured that there was no reduction in load allowances and allows maximum flexibility, key to Southbank Centre’s needs. It turns out you never know where the next five tonne sculpture might go.

Openings in more heavily loaded areas or critical structural elements required a new steel frame to be inserted in to the concrete. This was necessary to maintain the structural capacity of the building. Sequencing requirements for these openings were developed to minimise temporary works and working with BAM during the pre-construction phases a process of using UB stools to stage the installation was developed as a safe, time, and cost, efficient solution.

During construction, the Design and Construction Team set up a builderswork review process to capture new openings and ensure that the capacity of the existing structure was not compromised by the sheer number of openings. During this process communication between the Design Team and BAM was needed to find the best solution; often discussions on site and by phone enabled locations to be found which were better for both the structural integrity and the services installation. With over one thousand openings this co-ordination was critical to the success of the services installation, and to ensuring that the heritage features of the buildings were retained.

Adding a new accessible entrance to the Queen Elizabeth Hall: raising a 1.5 tonne concrete feature
Inside the QEH a series of concrete corbels cantilever out from the concrete walls to provide support for the large timber Helmholtz resonators that line the auditorium and moderate the acoustics. To enable a new accessible access route through the south wall one of the 1.5 tonne corbels needed to be raised. With the corbels being such significant interior features it was decided that matching new concrete to old would be near impossible and that moving the existing corbel would be more likely to succeed. The existing corbel was carefully cut out and enough of the wall above broken out to expose the reinforcement. This enabled new resin fixed reinforcement to be lapped with existing bars to support the old corbel in its new location.

During construction, the existing corbel reinforcement in the wall was cut in error and further structural analysis was required to identify additional bars that could be dowelled into the corbel to mitigate the error. Arup attended site frequently during this key period to ensure that the construction matched the design requirements.

These are just two examples of the careful structural interventions needed to prepare these iconic Brutalist buildings for an enduring future. This was made possible by; the engineers understanding the existing structural design and detailing, gaining an appreciation of the design principles and methods used at the time, and by applying a measure of first principles thinking. Strong relationships and close co-ordination between the project team during design and construction enabled practical, holistic solutions to be achieved when approaching the complex design problems during the refurbishment of the Southbank Centre.

Refurbishment project
Client: Southbank Centre
Architect: Feilden Clegg Bradley Studios
Structural Engineer: Arup
Services Engineer: Max Fordham LLP
Main Contractor: BAM

This article was written by Billy Field, Arup, Richard Henley, formerly Arup and Richard Battye, Feilden Clegg Bradley Studios