Careys’ concrete expertise enhances landmark 22 Bishopsgate project

One recent project that amply highlights our concrete abilities – including our characteristic meticulous planning, depth of knowledge, attention to detail and innovative approach – is the mixed-use 22 Bishopsgate development in the heart of London’s financial district. The newly completed skyscraper is the second tallest building in the UK, towering above its neighbours at 278m. The 62-storey building, which offers a gross floor area (including basements) of more than two million square feet, has transformed the capital’s skyline. It contains enough office space to accommodate 100 companies and hosts a number of different amenities and venues, such as restaurants, doctors’ surgeries, gyms and drycleaners. There is also a public viewing gallery and a two-storey restaurant and bar, located at the very top of the high-rise structure, which offers panoramic views of London.

Careys acted as concrete frame contractor on the 22 Bishopsgate project. In this capacity, we were responsible for the tower concrete construction and creation of the three-level basement. Overall, on this development, we poured 58,000m³ of concrete and installed 7,500 tonnes of reinforcement.

In order to complete this project safely and to the high standards of quality that we are known for, we used in-depth planning – which included deploying the latest BIM techniques – to examine project contingencies and trial the implementation of an innovative new jumpform system (the first of its kind in the UK). This approach enabled us to overcome a number of challenging circumstances at 22 Bishopsgate, such as incorporating elements from a previous, unfinished structure (Pinnacle Tower, which was abandoned due to the financial recession) and dealing with the restrictions of a space-limited urban location.

Deploying an innovative jumpform system to construct 22 Bishopsgate’s main core

Before commencing work at 22 Bishopsgate, Careys carried out a customarily thorough and detailed research and pre-planning process. This relied heavily upon the BIM and digital engineering input provided by the experts at our in house design team. As a result of this process, we decided to adapt and use a self-erecting jumpform system, the first of its type to be utilised in the UK, in order to construct the tower’s two concrete cores.

Whilst this type of jumpform system has been widely implemented in the Middle East for the construction of tall buildings, it had never been utilised in Europe until Careys deployed it – first on the nearby Principal Place project, and then at 22 Bishopsgate. Because UK construction standards are more stringent than those in the Middle East market, it was necessary for us to adapt the system to meet local requirements – especially from a health and safety perspective.

With the support of our in-house design team, which used cutting-edge 3D, 4D and virtual reality (VR) technology to trial each proposed adaptation in a variety of potential situations, we devised and carried out a series of careful design modifications aimed at:

• Improving the jumpform rig’s working environment
• Making the system more suitable for UK weather conditions
• Providing a high standard of safety

In order to implement these adaptations, it was necessary to completely remodel the rig and redesign the screens, equipment, ergonomics and access points. We were able to improve the design of the jumpform rig by using our design team's VR models to visually demonstrate the system’s potential features and capabilities to site operatives throughout the design process. This enabled them to give us valuable feedback, from a practical, site-based perspective, of what worked best and what could be enhanced on the rig.

Our eventual adaptations included:

• Fire and first aid points set in optimal locations
• A streamlined and spacious layout with ample storage area that created a cleaner, tidier more organised workspace
• Safe access, egress and evacuation of potential injured personnel from the rig procedures

Once we had reconfigured the system for maximum effectiveness and safety, Careys Design Team used the latest BIM techniques – including CGI – to develop a step-by-step guide for site workers to follow. These 3D visual depictions of the jumpform rig and system, included detailed methodology, sequence of assembly, steel rebar fixing, concreting, jacking and disassembly of the form panels in clear and concise cycles. We placed these large-scale, step-by-step displays on notice boards adjacent to the work areas, which gave site workers the opportunity to easily refer to them before their shifts, in order to ensure safe and efficient operation of the jumpform system.

Once we began construction of the cores at 22 Bishopsgate, the jumpform system performed admirably and contributed greatly to the successful completion of the towering superstructure. One area in which it enhanced project performance was the installation of the large amount of embedment elements required by this project. The design of the building called for over 50 embed plates to be put in at each level of the core in order to connect steel beams to the core walls. On levels 25 through 26 and 41 to 42, we had to install three sets of double-height outrigger trusses designed to provide lateral stiffness to the structure.

We were able to use the jumpform system to more efficiently, quickly and safely manipulate the large structural steel sections of the trusses and incorporate them into the wall section. Additionally, because the jumpform system enabled us to install the large numbers of heavy embed elements at an increased pace, the site team had extra time to check and verify for accuracy before closing the form for concreting.

Our use of the jumpform system also helped us to achieve an excellent concrete finish on the core. The form linings were robust, and we were able to utilise the same linings to the full height of the core. Very few surface repairs were needed and the resulting finishes far exceeded the architect’s expectations. Indeed, due to the high-quality concrete results attained by our use of the jumpform system, the architects were able to omit the plasterboard linings to the inside of the stair shafts – a step which led to considerable savings on this part of the project.

This was because its elements are all fully reusable with minimal servicing needed. They are also easily adaptable and can be modified for other projects without undue effort. In fact, the system is currently being reused to construct another high-rise project – The Residence Manchester– thus making it cost-effective, as well as sustainable.

Employing a bespoke top-down methodology to maximise construction efficiency

In addition to our construction of the superstructure cores at 22 Bishopsgate, Careys was also tasked with developing and carrying out a strategy that would allow the core structure to be built simultaneously with basement demolition and construction works. This would allow the critical building works to begin without delay, whilst mitigating the critical path of the basement works.

With the aid of our design team, we devised and carried out a partial top-down method for the construction of the three-level basement. This methodology required us to precisely and effectively coordinate:

• Ongoing demolition
• Local breaking out of the existing pile raft for installation of additional piles
• Reconstruction of new portions of the raft
• Erection of the main core above ground-floor level

In order to construct the main core by top-down method, we built a double-height transfer structure under the footprint of the main core, below ground-floor level. We designed this transfer structure so that it could be supported by some of the existing steel columns that had been designed for the original Pinnacle Tower.

We chose to use reinforced concrete to create this transfer structure, rather than structural steel framing. We did this because our models suggested that the implementation of a structural steel transfer structure would have required the use of difficult-to-handle and hard-to-install heavy elements below the temporary retained existing ground-floor and basement slabs.

In addition, we made this choice because reinforced concrete, in this case, had the advantage of providing a much stiffer transfer structure for the heavy tall core above. To construct the transfer structure, we first manhandled and fixed rebar in place, and then pumped in concrete. We poured the transfer structure in three lifts, in order to ensure that the existing suspended basement slab only needed to support the first lift. After that, each new pour supported the level above.

Our successful top-down construction process, which we facilitated through the implementation of this transfer structure, allowed the core above ground level to be built at the same time as work was carried out on the existing basement. This enabled the project to progress at a much faster and more effective rate, resulting in greater overall efficiency and cost savings.

Careys’ proficient concrete capabilities facilitate the successful creation of outstanding projects

By calling upon our years of experience and our advanced capabilities working with concrete, Careys was able to overcome a number of logistical challenges in order to deliver excellent solutions and an optimal outcome on the complex and important 22 Bishopsgate project.

This is an approach that we are able to consistently replicate on all of our concrete works, across an array of projects. No matter the complexities or demands of a particular project, our expertise, planning ability and innovative approach – supported by the state-of-the-art modelling skills of Careys Design Team – enable us to routinely carry out high-quality concrete works that meet, and often exceed, the standards of excellence that we demand of ourselves and that our clients deserve.

In recognition of the high quality and innovativeness of our works at 22 Bishopsgate, the project has been shortlisted for this year’s prestigious Concrete Society Award. It would be a fitting tribute to the company’s contributions over the decades if we were to win one of the industry’s biggest prizes as we close out the year marks Careys’ 50^th anniversary.