Adaptive reuse has become an increasingly important development approach in the commercial sector. In cities such as London, where the planning landscape is focused on sustainable development, asset owners and property developers understand how making better use of existing building stock makes commercial sense. Adaptive reuse unlocks value in otherwise tired buildings, which are costly to operate and no longer attractive for the end user or property owner.
Delivering adaptive reuse projects requires innovative engineering solutions that balance heritage preservation, sustainability goals and modern performance requirements. Vertical and horizontal extensions employing lightweight clear-span solutions are often favoured.
In this article, we look at three landmark developments across London, where adaptive reuse has played a central role, and explore how Westok’s expertise helped give these buildings a second life.
5 Chancery Lane – A Sustainable Retrofit
Located in the heart of London, between Holborn and Fleet Street, 5 Chancery Lane is being sensitively retrofitted to deliver 100,000 sq ft of modern office space. The scheme includes a striking rooftop extension – two new floors and a terrace – that redefines the building’s presence on the London skyline.
The project adopts a number of key strategies to help make better use of the existing building. The existing atrium has been infilled from basement to fourth floor level and the building has been extended vertically with three new storeys.
Images courtesy of AFK Studios
Westok Solution
In many respects, the Westok solution for the new floor-plates mimics a new-build. The floor-plates comprise clear-span Westok beams from 9m to 13m in span, radiating from the new central core to the perimeter. This internal column-free solution delivers a flexible, lightweight low carbon sustainable development.
By retaining and reusing 86% of the original structure, the scheme will save an estimated 4,800 tonnes of CO₂, whilst also reducing construction waste. That circular approach to retrofit is also why this scheme is on course for BREEAM Excellent certification.
ASD Westok delivered a mix of both ribbon-cut and plated cellular beams to our customer B+K Hybrid Solutions.
10 King William Street – A Smarter Approach to Sustainable Office Space
Located directly above Bank Underground Station, 10 King William Street is set to become one of the City’s most considered new offices. Spanning over 140,000 sq ft, the scheme is respectful of its historic surroundings and designed around the people who will use it every day.
Its forward-thinking environmental ambition is targeting best-in-class credentials including BREEAM Outstanding, NABERS 5 Star, and WELL Platinum*.
Westok Solution
In order to achieve the flexible commercial spaces demanded by clients in this central London location, the structural design targeted lightweight clear spans from the outset.
Arranged around a central core, most floors comprise 14-16m span secondary beams at 3m spacing. Where the secondary beams cannot be supported directly on the core wall, loads are transferred via primary beams spanning between the core and the perimeter.
Following an early-stage review of the design requirements by the Westok team, ribbon-cut beams were selected as the most material-efficient option for the secondaries, with plate girders employing discreet cells for the primaries. Westok initially provided proposals for a typical floor plate, and Robert Bird Group engineers extended the design approach to the remainder of the structure as the scheme proceeded through detailed design. The design approach was supported by the Westok design team throughout the process.
In order to maximise structural efficiency and to reduce embodied carbon, most of the composite ribbon-cut beams were designed efficiently with a lighter section forming the top tee. Over the majority of the structure a standard beam depth of 650mm was adopted, with 400mm diameter cells facilitating the efficient expansion of UB457 and UB533 parent section ranges. As is typical for commercial office floor plates, almost all secondary beams feature at least one elongated opening.
In order to achieve the total deflection requirements of the floor-plate, pre-cambers between 40mm and 70mm were required; due to the ribbon-cutting process Westok provided these pre-cambers at no additional cost.
ASD Westok worked with our customer Bourne Steel to deliver 1000T of cellular beams for this landmark project for main contractor Mclaren Construction Group
75 London Wall – Engineering a low-carbon vertical extension in the City
75 London Wall is being reimagined to meet the demands of tomorrow’s workplace in a classic city-centre adaptive reuse design approach.
The scheme will deliver 450,000 sq ft of Grade A+ office space, achieving top-tier sustainability certifications including BREEAM ‘Outstanding’, WELL Core ‘Platinum’, and NABERS UK 5 Star Design for Performance**.
Image courtesy of Orms
Westok Solution
The existing structure, comprising reinforced concrete columns and reinforced / post tensioned slabs, was retained to 6th floor, with a new lightweight steel frame extending the structure to 14 floors in total.
The development targeted best in class flexible and adaptable spaces, with typical spans in the range 11-14m, matching the grid layout of the existing internal columns. Minimising the weight of the new structure was therefore critical to enable the existing columns to be utilised.
At the step-in terrace levels 7 and 10, plate girders were utilised at on-grid transfer beam positions, with the design switched to light-weight ribbon-cut beams for the intermediate secondaries.
Cells were typically 450mm diameter which facilitated the expansion of lightweight UB457s to a consistent beam depth of 650mm, maximising efficiency of steel use. Deeper profiles up to 850mm were designed at the level 10 transfer structure, where plate beams were used for the transfer beams carrying load from Levels 11 to 14. Deeper ribbon-cut beams were utilised for the intermediate secondaries. Most beams on the perimeter of the structure feature one or two elongated openings to facilitate the distribution of larger M&E services.
Westok worked closely with engineers at LSL, particularly at RIBA stage 3, providing detailed design options which clearly demonstrated the weight savings using the ribbon-cut manufacturing method. LSL took the knowledge gained to work-up the full detailed designs across the new frame. The final solution achieves a low embodied-carbon superstructure, whilst providing spaces which are practical, adaptable, and future-ready.
At fabrication stage Westok engineers worked with Bourne Steel to further review and optimise the use of stiffeners and cell infill plates.
In partnership with our customer Bourne Steel, Westok will supply 550t of ribbon-cut cellular beams for this landmark project, under construction by main contractor Multiplex.
ASD Westok Certificates and Accreditations
For all of the projects discussed in this news item, ASD Westok’s technical advisory engineers have played a key role: from identifying carbon saving strategies, assisting the design and construction teams throughout the process, delivering Continuing Professional Development (CPD) seminars and running design calculations.
ASD Westok is UKCA and CE qualified in S355 and S460 grade to Execution Class/EXC-4, the highest and most rigorous tier of structural steelwork fabrication to EN 1090. We implement a Welding Quality Management System (WQMS) compliant with EN ISO 3834.
Westok holds BES 6001, ISO 9001, ISO 14001 certification, qualifications with the Register of Qualified Steelwork Contractors (RQSC) Scheme for Buildings, and British Constructional Steelwork Association (BCSA) gold level sustainability charter status.
With experience delivering new build and adaptive reuse scheme, and projects involving steel reuse, ASD Westok is a key player in the London commercial market supporting cost-effective, flexible and low carbon solutions in structural steelwork.
ASD Technical Advisory Service
Speak with our team of engineers today to understand how our lean design approach can add value to your next steel framed project or to enquire about our free design software and CPD seminar offerings: +44 (0)113 2055270 or westok.design@asd.ltd
Reference:
*https://www.10kws.com/building
**https://www.multiplex.global/news/multiplex-awarded-250plus-million-construction-contract-to-deliver-75-london-wall/