William Hare Ltd
Bovis Lend Lease
The British Land Company PLC
Plantation Place South is the second commercial office building designed by Arup Associates for The British Land Company on a 2.5-acre site in the heart of the City of London. It joins the earlier larger building as part of a strategy to knit the new development into the City’s historical context, including the creation of new through pedestrian routes and views of Wren’s St Margaret Pattens church, while establishing a clear identity for itself on the southeast corner of the site.
The objective of the structural design, beyond satisfying the normal functional aspects, was to enhance the delivery and value of the project, these being the key objectives of a speculative commercial development, as well as to incorporate modern innovations where appropriate.
The plan layout was arranged with a central core and basement to mitigate the impact of perimeter site constraints, which were separately addressed in advance of construction. A substructure ring slab was configured to offer open basement construction and give immediate clear access to a slip form core for an early gain on critical path activity.
The structural frame system was optimised for efficiency and buildability. A detailed comparison with a comparable post-tensioned concrete flat slab, with the same overall structure/services depth, showed that the selected steel framed composite slab construction offered a 10% saving in the cost of foundations, a 6% saving in the frame cost, and a 5% saving on the programme time. Also, by taking into account the space between steel beams for services cross-overs and riser entries, additional services flexibility is in fact offered.
A distinction of the building is that it is the first building in the City of London to have been approved by the District Surveyor without applied fire protection to secondary steelwork. This has been achieved by appreciation of real fire behaviour and by state of the art finite element modelling of the mechanical response of the structure so that appropriate robustness can be designed in. The fire engineering approach has developed previous research into a real world practical application that can be applied to future steel framed buildings. A net reduction in total fire proofing costs was achieved, of the order of £5/m2.
An innovative prefabricated modular load-bearing stone façade was developed as a consequence of the urban context, as well as the new Part L building regulations which limit the potential extent of glass. The solution evolved from a pattern established in the first phase of the project, particularly in the use of projecting stone fins to provide self shading and a desire to exploit the high strength properties of the limestone approved by the Planners. The prefab component and infill window approach, incorporating stainless steel interconnections, offered an economically competitive alternative to the more usual and more limited curtain wall cladding market, as well as giving the building its distinctive character and appearance.
The design of this steel framed commercial office building situated in a prominent conservation area in the City has used innovation to optimise the design solution. The adoption of state-of-the-art thermo-mechanical analysis, justifying leaving the majority of the secondary steelwork unprotected, brought significant costs savings resulting in the first approved use of this approach for a building design in the City of London. The load bearing stone façade avoids column obstructions at the office perimeter.