Bank of England rebuilding (1933)
Threadneedle Street, London, UK
date 1924 - 1933, onwards to 1942
era Modern |
category Building |
The rebuilding of the Bank of England in the City of London made Oscar Faber’s reputation as a multi-disciplinary engineer. It was a long-running project, lasting for some 18 years during which time considerable upheaval was caused by events such as the General Strike of 1926, the economic slump of 1931-2 and the start of World War II in 1939.
Faber formed a professional relationship with the Bank’s architect, Sir Herbert Baker, that was to continue throughout both their careers.
The Bank of England is an imposing Neo-Classical Grade I listed building that occupies the block bounded by Threadneedle Street, Prince's Street, Lothbury and Bartholomew Lane. The 1.6ha site lies diagonally opposite the Mansion House, official 'home' of the Lord Mayor, across the six-way intersection at the heart of the City.
The Bank's original architect, George Sampson, began the building in 1732-4. Sculptor and architect Sir Robert Taylor extended the façade and added the Rotunda between 1765 and his death in 1788. The Bank’s official Architect and Surveyor, Sir John Soane, completed the original buildings over the period 1788-1833 — part of the works included surrounding the site with a windowless perimeter wall (1828).
By the 1920s, the Bank was finding the building too small to cope with its increasing workload and consequent increase in staff numbers. Baker was appointed architect and he designed a building to replace the existing three storey complex, leaving its Soane walls in place. The new building has seven storeys above ground and three below, and it required the demolition of most of the earlier structure.
In the first instance, Faber was appointed structural and civil engineer for the works but Baker encouraged him to take on the mechanical and electrical design as well. So for this project Faber took on mechanical and electrical specialist Rob Kell, who was just 23 years old at the time. He would stay with Faber, and the firm Faber founded, for his whole career.
The rebuilding project had many complications. Work required included extensive underpinning, substantial retaining walls, the rebuilding of the banking halls to an open-plan layout and reconstructing the Soane domes forming the roof of the halls on the ground floor.
As the site is in one of the oldest parts of London, the below-ground conditions were bound to be complicated. London Underground train lines (in tunnels lined with brittle cast iron) run under Threadneedle Street and Prince's Street, and sewer and services lines abound. The site had to be excavated to a depth of 15.2m to accommodate the basements and foundation works, which meant that a new 2.44m thick reinforced concrete retaining wall had to be provided below the existing 180m length of Soane perimeter wall.
In such a congested site surrounded on all sides by vital infrastructure it would have been too dangerous to excavate long trenches for the retaining wall, so it was constructed in short sections of underpinning. To enable this, precast concrete wall panels were positioned and cross-braced by struts across the excavation. Jacking forces could then be controlled to provide stability for the retained walls above, allowing underpinning to take place. The Threadneedle Street portico is supported on a cantilevered projection from the retaining wall to keep the new work as far from the Tube line as possible.
The basement levels contain the secure vaults, divided into strong rooms typically 6.10m by 4.57m, and separated by 610mm thick reinforced concrete walls and floors with additional armour plating. All the vaults are also watertight.
The new building complex is steel framed, supported on a 1.22m thick reinforced concrete raft. The steel stanchion columns sit on 1.83m square, 230mm thick solid steel base plates weighing 6.1 tonnes each. This technique avoided the need for gusset plates, and saved considerably on cost and gained headroom.
The Bank was also the first important London building to have welded steel girders — riveting would have been too noisy. London City Council only approved electric welding for buildings in September 1934, though it had been used elsewhere in Europe for some time. The largest of the girders brought to site to be welded were up to 18.3m long and 3.66m deep, each weighing some 30 tonnes. In all 7,100 tonnes of steel was connected with welds.
To resist wind loading, knee bracing was applied to the multiple levels of stanchions above ground. In order to avoid excessive deflection in vertical members, Faber directed that the connections on the bracing struts (to the girders at the top and bottom of each floor level) were to be left loose until the building was complete before being secured. It was found that the gap between girder and strut closed by around 3mm due to dead weight loading. Temporary timber struts provided resistance to wind loading before the connections were bolted.
In general, heating was provided by passing hot water through copper pipes embedded in the concrete ceilings / floor slabs — particularly in the Soane domes — providing ‘panels’ of radiant heat. Faber had studied the convection currents generated by conventional radiators (he referred to them as ‘convectors’) in typical office situations, and preferred radiant heating, which he said prevented the spread of dirt and dust throughout the building.
Integration of mechanical and electrical work with civil and structural work became complicated. Faber designed a private electricity generating station within the complex capable of supplying power for all functions including the 48 lifts (elevators). He located an independent water supply by tapping an artesian well sunk below the basement level, and he considered air conditioning as an essential part of the concept. The Bank was seen as self-sufficient, and impervious to external forces.
Air distribution originated from a 2.44m square tunnel below the lowest vault, from which shafts rose up through the basement and superstructure. Circular copper branch ducts, concreted into the 610mm thick strong-room floors, conveyed air to each vault and on to the upper floors where the ducts extended into the office areas.
A separate exhaust system was enabled by the construction of an extraction vent for the basements. This was a tunnel 91mm wide and 2.44m high, set within the retaining wall on the four sides of the building, picking up each of the branch ducts and returning warm air to the air-conditioning plant. The superstructure system was served by 12 shafts rising vertically through the floors to a height of 45m. These shafts also serve to distribute wiring and other services.
The rebuilding of the Bank of England is considered to be Faber’s masterpiece. Both Kell and Stanley Vaughan, who would both become partners in 1948, were closely involved in the project. The three men formed a team that would work together in many later projects.
Architect: Sir Herbert Baker
Supervising engineer: Stanley Vaughan
M&E engineer: J.R. Kell
Heating contractor: Rosser & Russell
"Modern Buildings as Engineering Structures" by Oscar Faber, in The Structural Engineer, pp.42-54, London, February 1931
"Bank of England: Sentiment and Association in Building", in The Times, London, 20th June 1933
"The New Bank: Electric Welding of Steel Frame", in The Times, 23rd January 1935
"Oscar Faber, his work, his firm, & afterwards" by John Faber,
Quiller Press, London 1989