Unlocking structures: Devonshire Square Building 7
Parmarbrook
A highly experienced civil and structural engineering studio with a passion for intelligent design.
London is abound with buildings ready to have their potential unlocked
London is a city with a rich history, filled with iconic architecture and buildings that tell a story. However, many of these structures are in need of modernisation and renovation to unlock their full potential. In this second instalment of our Unlocking Structures series, we’ll be focusing on the Devonshire Square masterplan.
Devonshire Square is a well-known area adjacent to Liverpool Street Station, one of London's busiest transport hubs. The redevelopment project, led by DSQ JVCo Sarl, aims to breathe new life into the area by refurbishing and modifying individual buildings as they become vacant and enhancing public spaces.
Building 7 in the masterplan was a particular focus of our team, where experienced Parmarbrook engineers were appointed by asset managers Nuveen, a TIAA company , to provide structural engineering consultancy on the development. The project, designed by Squire & Partners , comprised an extension to the ground and upper levels, the addition of external amenities such as balconies and terraces, the refurbishment of existing cores to meet new standards and requirements, and an upgrade of MEP and sustainability performance to meet BREEAM Excellent standards.
Unlocking the structure
To start, the key considerations for Building 7 were to understand and assess the following:
As a result of studying this, we were able to justify vertical extensions to the building which ranged between 2 and 5 stories (depending on the existing fa?ade setbacks), as the frame had suitable capacity from a load balance and stability perspective. However, this pushed the building over the key 30m threshold for fire engineering and escape. The outcome of this was that we needed to justify an increase in the building’s fire performance from 60 to 90 minutes, which was successfully completed with a focused suite of investigation works.
One of the major challenges we faced was justifying the interface between the new steel frame and the existing reinforced concrete frame for robustness and disproportionate collapse requirements.?This required a detailed analysis of the loads and load paths, and the concrete condition at each of the interfaces.
The limiting factor for the project was the existing piled foundations, and their original capacity and targeted new safe working load. To optimise this we worked with geotechnical engineers, CGL, to back-calculate the load capacity of the existing piles.
Using intelligent specification of materials, we were able to add 2-5 new floors over the existing reinforced concrete frame without any foundation strengthening works and no new piles. This was achieved by demolishing the reinforced concrete roof slab and various plant support additions, conducting extensive but cost-effective investigation works to existing foundations, and pile load assessments to justify a pile load increase of up to 20% – which was achieved with a detailed settlement and ground movement analysis.
Using steel trusses, we were able to reduce the weight of long-span transfer beams and long external balconies. Plus, we removed the existing reinforced concrete column at ground floor level to open up the entrance zone.
Another key move to optimise the scheme was to change the load paths to piles with a higher spare capacity. We applied a range of structural interventions to achieve this – such as installing new steel columns at lower levels with new ground beams, changing from cantilever reinforced concrete beams to direct the load path, introducing partially cantilevering floor beams at higher levels, and using lightweight construction for the courtyard’s horizontal extension.
The introduction of new shear walls around the new lift was crucial to increase the stiffness of the core globally and to keep wind induced deflections within acceptable cladding tolerances. We also increased the length of the main shear wall by 25% to increase its stiffness by 100%. At basement level, where we couldn't extend the wall, we doubled its thickness to achieve the same 100% stiffness increase. Working with the enhanced shear walls, we introduced a moment frame for the top two floors to minimise bracing, while not obstructing the windows or the office floor plate’s open plan layout – meeting the client’s architectural aspirations for the scheme, and ensuring the building is structurally sound and ‘unlocked’ for its next life cycle.
Externally, the masterplan aims to add significant greening to the estate both for carbon offset and wellness for the occupiers using the space. For us, this required a thorough analysis of the existing podium sandwich slabs – required to maximise the available depth of soil and associated planting. To keep things economic, we defined the landscaping build up zoning with the landscape architect in order to maximise the capacity of the existing structure with no additional strengthening.
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"Parmarbrook are a trusted partner of ours and they have been instrumental in realising our vision to reposition Building 7 as a cutting-edge, highly sustainable office building, which sits at the heart of our DSQ campus. Parmarbook’s experienced team exhibited exemplary attention to detail and were responsive in solution-finding when required throughout the project; skills that are invaluable in delivering a large-scale project on programme and within budget. Perhaps the highest compliment I can pay them is that I have only received positive feedback on Parmarbrook from the wider project team, who comprise of varied professionals and contractors.”
– Andrew Booth , Director at Nuveen
The collaboration
“The key to unlocking the structure was to understand the existing frame and foundations – achieved through a detailed archive drawing review and early investigation work. Nuveen’s aspiration was to optimise the potential of the building by maximising vertical and lateral volumes, and thus understood how an early expenditure with Parmarbrook would provide an overall cost saving, by de-risking the structural aspects of the project. We’re extremely proud of the end product, delivered by the design team, contractor and client, enhancing the existing structure by adding up to four additional floors – meeting the client’s vision and requirements.”
– Ben Paterson , Project Lead and Design Director at Parmarbrook
Through working with Nuveen, a TIAA company and the wider project team, we were able to deliver on the refurbishment of Devonshire Square building 7 – improving the public realm and providing more office space, while enhancing the building’s sustainability performance. We overcame the challenges retrofitting an existing structure brings through effective collaboration and the use of innovative techniques. We’re delighted with the results. The Devonshire Square project is a testament to the importance of modernising and renovating existing structures to meet the needs of the modern world.
Parmarbrook are experts in unlocking structures. Contact us to discuss how we can assist you in your redevelopment or refurbishment project.
Project team
Client: Nuveen, a TIAA company
Architect: Squire & Partners
Main Contractor: Built.
Project Manager: CogentBC LLP
Services: Hoare Lea
Landscape Contractors: Maylim
Cost Consultant: Arcadis