projects /

Ilona Rose House

Location

111 – 119 Charring Cross Road

Client

Soho Estates

Architect

Matt Architecture

Completion

Autumn 2020

Project Summary & Objective

Ilona Rose is currently on site and when completed will be a 300,000 sq. ft new-build, mixed-use development spread over 13 storeys, including four below ground. The development will be predominantly office space with large garden terraces accessible from every floor. The basement office space will be naturally lit from above by a lightwell and will be the new home for Warner Bros’ post-production facility. The scheme will also provide new public realm spaces with cafes, restaurants, shops and a nightclub.

Key Challenges

One of the key challenges for Tier Consult presented by the development is creating the four-storey basement alongside the Northern Line tube tunnels to the east, Crossrail 1 tunnels to the north, whilst accommodating the future construction of Crossrail 2, running to the west of the site and connecting to the new Tottenham Court Road Crossrail station.

A further challenge is the formation of a new pedestrian walkway underneath the building, along Charing Cross road, to allow for a new loading bay off the main highway. As a result of this and the need to form the main retail entrance in the northeast corner, the primary corner column and façade columns will all finish / break at level two either stopping at that level or be set-back below to allow the required pedestrian access both into the building and along the walkway under the building.

Further constraints have been imposed on the structure by the Client’s requirement for column free accommodation and by the Planners’ requirement that the building both reflects the larger scale of development along Charing Cross road (to the east) and the smaller “Soho scale” to the west. A cascade of ‘set-backs’ with garden terracing creates this change of bulk and massing but a series of transfer structures is required to facilitate this change.

Solution

In order to properly assess the soil and heave pressures to be applied to the walls and base slab of the four storey basement and to predict the likely ground movements of the nearby buildings, brick sewers and tube & train tunnels, an extensive series of 2D and 3D finite element ground models were built. These models perform a time history analysis starting with ‘Greenfield’ conditions (stresses) in the ground on which is imposed the various development pressures including the changes of clay stresses resulting from the construction of the underground tunnels. These models continue the time history analysis through the basement formation, the construction of the building and into the future until the dissipation of excess pore water pressures in the clay has been achieved.

The retaining wall type and the numbers, levels and stiffnesses of any temporary propping are incorporated into the analytical models thus the excavation/construction sequence is determined by Tier and must be strictly adhered to by the contractor on site.

A ‘stiff response’ (minimised movement) to the excavation was required to limit the movement of , in particular, the Northern line tunnels and the listed Chapel of St. Barnabus. Three levels of propping were installed to provide this stiff response.

To allow the formation of the ground level walkway, under the main building above and the formation of the main entrance to the retail in the north east corner, the team designed a storey height vierendeel truss, cantilevered at each end, supported on four prefabricated box section transfer structures. This allowed the columns in the north-east and south-east corners of the building to stop at level 2 (the top of the truss) and the intermediate columns between them to continue down to basement level on a new in-set line within the building and behind the new pavement line.

The requirement for column free space necessitates the development of relatively deep long span beams with regular holes in the webs to allow the integration of building services within the depth of the beam.

The requirement also gives rise to the potential for a dynamic response to footfall excitation that is uncomfortable for certain building users. A design based on limiting each floor’s Response Factor ( a measure of floor acceleration) to a specific level has been carried out.

The transfer structures to facilitate the set-backs are created by enhancing the weight of the affected beams and reducing the perforations through the beams between the transfer column and the supporting column below.

Interestingly, whilst the strength requirement of the transfer beams is increased to support the column load above, the mass supported by the column and applied to the beam improves the dynamic performance of the floor plate in this area.

Piling and digging of the four-storey basement was completed in April 2019 with the following construction starting immediately thereafter. The project is due for completion in May 2021.

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