Our structural engineering design for this speculative office and retail development helped increase the project's earning potential as well as cutting costs significantly.
The scheme originally allowed for 17 storeys of flexible office space. We worked closely with the services engineers to save more than 100mm on the combined depth of the perforated steel beam, services and ceiling void between each floor; the total saving over 17 floors enabled the architects to add an eighteenth storey without increasing the overall building height.
The new building is a steel frame structure with concrete cores and curtain wall glazing set back from projected stainless steel-clad columns. It replaces a 1960s building on the same site.
We deepened the existing single basement, creating a new second basement set in from the first. By refining the design of the foundations, we were able to fit new piles between those of the previous building, obviating the need for costly removal. Stringent value engineering resulted in the use of Giken sheet piling for the retaining walls, which are not required to bear vertical loads.
fire & safety
Aldermanbury Square is an award-winning speculative office and retail development housed in an 18 storey steel frame structure with concrete cores and a double basement. Externally, the main columns are steel clad and project from curtain wall glazing.
Our fire consultants, SAFE, faced a number of challenges in relation to fire safety for this building. We worked hard to achieve the architect's vision and realise the required net lettable area. Window sprinklers have been located at the building's perimeters — fire boundary locations. This made it possible avoid the need for a façade step-back, or a secondary fire rated façade.
The particular floor layout in this building means that one fire fighting lift is adequate. Careful positioning of the of risers has meant that all parts of the floor plate can be reached within the required time. This situation has been used to reduce the structural fire rating from 120 minutes to 90 minutes, allowing the steel to be protected by intumescent paint and saving precious ceiling void space.
This office and retail development in the City greatly increased the usable space yielded by the site.
The footprint of the new building fills the site, doubling that of the 1960s building it replaces. A second, deeper basement was excavated and new foundations put in place. Our geotechnical engineers liaised with the party wall engineers, modelling the effects of elastic and swelling heave resulting from the development and monitoring adjacent buildings to satisfy all necessary criteria for their immediate and long term structural integrity.
An assessment of existing under-reamed piles confirmed that these were not suitable for re-use, due to the very different architectural layout of the new structure. New foundations were designed to avoid the existing piles — obviating the need for expensive and time-consuming removal — as well as respecting the exclusion zone of a disused post office tunnel that runs beneath the site.