The brief for 100 Bishopsgate was to develop a design that embodies the Brookfield brand, with 'best-in-class' offices that are ‘designed from the inside out’. The goal was
to create top-quality, flexible, comfortable, and aesthetically attractive commercial space that aligns with modern workplace trends and meets the diverse needs of its occupants.

In response, a tall building was devised with expansive open floor plates similar to those typically found in shorter, wider HQ buildings.

The tower showcases a spectacular 8-metre-high ground-floor lobby, creating an impressive and welcoming entrance. It is serviced by 26 passenger lifts, efficiently serving 36 column-free office floors from a central concrete core. The perimeter columns are spaced at 9-metre intervals, while a reduced depth edge beam allows for a recessed ceiling margin, ensuring minimal disruption to the full-height glazing surrounding the entire floor plate.

Project Challenges

The tower has a regular rectangular floor plate over the upper floors, splaying out over the lower half to form a parallelogram on plan when it meets the ground, with a maximum span of 23 metres. To achieve this dramatic form, perimeter columns are required to kick out from vertical to rake, and then to kick back to vertical at various levels. The longest of these rakes over 23 storeys, meeting ground level at an angle of eight degrees to the vertical. This geometry raises some key design challenges:

Enormous lateral forces are generated where the columns change between vertical and raking, which are tied back to the core.

Two tower columns are shorter than the rest, terminating at level 16, giving rise to uneven shortening during construction. This required an innovative de-jacking sequence to be developed, to shorten the columns as the frame is erected, keeping the floors even at completion.

Added Value

RBG devised a full construction sequence entailing top-down basement construction, but with a propped coffer dam excavation to enable early release of the tower core, which was on the critical path. However, the overall programme was still unacceptably long to secure a pre-let, so a ‘full top-down’ method was explored in tandem with Multiplex and the appointed concrete, steel and bulk excavation subcontractors.

This involved jump-starting the core by building it from a grid of plunge columns at the upper basement level and, later, casting the pile cap and infilling core walls as the construction above and below ground progressed. To enable accelerated construction of the tower basement and core pile cap, the walls of the 12m-deep basement were designed to be excavated with a single prop at ground floor level, while minimising the movements of the adjacent highways.

The modified construction sequence accelerated the programme by six months, allowing Brookfield to present a significantly enhanced offer to key tenants in the market. As a result, an anchor tenant was secured early in the construction phase, leading to the building being 70% let a full 20 months ahead of practical completion.

The detailed construction sequence was integrated into the permanent works design from an early stage, enhancing the certainty of tender and mitigating the potential impact on the design due to later changes related to the construction sequence.

Sustainable Methodologies and Outcomes

The primary objective was to design a building with a 'long life, loose fit' approach, facilitating flexible usage and maximising potential reuses over the building’s lifespan.

Additionally, all concrete used in the project was specified with a high percentage of GGBS cement replacement, maintaining acceptable curing rates and strengths.