Lloyd's Building: Structural Report

Individual Report : Lloyd’s of London Joshua M. Bright 16119897

Contents Introduction Building Description Structural System Description Structural Technology Developments Influence between Materials, Structure and Architetcure Conclusions Citations & Bibliography

The Lloyd’s Building was designed by Richard Rodgers & Partners (Architects)(1) in conjunction with Arup (Structural Engineers) and Bovis (Main Contractor). Constructed started in 1978 and lasted 8 years until 1986(1) when the building was finally complete in the heart of London’s financial district, moments away from the London Stock Exchange and the Bank of England. The purpose of this report is to outline not only the structural system used with in the building, but also how the materials, architecture and technological advancements of the era were used in order to create what is described as the “Inside out” building(2) as well as his architectural and structural engineering influences that led him to create such a masterful structural system.

The Lloyd’s building is 68.4m by 46.8m, which is made up of 16.2m span floor plates. Due to the buildings rectangular doughnut shape, there is a 12 story full-height atrium space that is closed off by glass panes from the 4th floor upwards, with a number of escalators that gap the void at one end from the ground to the 4th floor(4). Made up of 33,510 cubic meters of concrete, 30,000 square meters of stainless steel cladding and 12,000 square meters of glass(3), all combined to create the stainless steel clad concrete framed building that Richard Rodgers had envisaged in 1978. The building takes influence from his earlier works on the Centre Pompidou by displaying the structural elements for all to see, these main elements include the floor plates, U-Beams, Brackets and columns(4). All of these combined help Rodgers to achieve mass voids of space by turning the building inside out, with the main services on the exterior of the building.

Compared to the Portland Stone buildings in the surrounding area, the Lloyd’s building was a revolutionary project that changed the face of London’s financial district, leading to building such as 30 St Mary Axe, The Shard and Rafael Viñoly’s 20 Fenchurch Street.

Lloyd’s of London Atrium Space

There are four main structural systems used in Rodgers design that combine to create a concrete framed structure that most Structural Engineers describe as “deceptive” due to its concrete slab upper section compared to its floor plates which can be seen from below. These main elements are as follows;

Yokes

Concrete Bracket Main Concrete Columns

In situ concrete was latter substituted. U-beams transfer the loads of the floor grid to the coumns via bracket system.

Lloyd’s of London Floor Slab (Lattice/Waffel)

Columns(4) There are 28 in situ columns, 20 along the façade and eight across the atrium, that are around 1 meter in diameter that have 10.8m centers. These columns are used to support loads exerted from the floor plates that are made of a 16.2m x 10.8m grid, including the 5.4m cantilevered corners. The columns along the façade lift the structure from the ground in some sections which allows people to walk below the structure and experience the building and its structural system from an entirely different perspective.

Floor Plates(4) The floor plates were made from in situ concrete beams, in a 1.8m square grid that include vertical concrete stubs on top of each intersection that were used to support a concrete slabbed floor. This technic was used in order to create a void space between the floor plate and slab were services could be easily laid. In order to speed up the process of creating these mass floor plates, a steel form was made in order to cast the concrete into the floor plates.

U-beams(4) The U-beams were formed by connecting two parallel pre-stressed beams in order to form a stronger connection between the columns. The use of pre-stressed beams allowed for shallower beams compared to normal reinforced beams. This techniques was employed in a number of different points throughout the building in order to reduce stress on loads and spans that were under mass amounts of stress. This technique also allowed Rodgers to maintain the visual appearance of the structure.

Brackets(4) There are 28 precast brackets per floor in order to support the weight exerted down from the columns. These brackets also extend into the building in order to support the floor plates by working in conjunction with the U-beams. The brackets are cast as a hollow cylinder that includes a ledge on which the U-beams can be clamped in place using the yoke, which is laid on top of the precast bracket. In order to connect the brackets with the columns, a precast column would be inserted into the hollow cylinder and secured in place by pouring concrete on top and around the column, creating a seamless joint between the columns and brackets. Due to the weight of the structure, it directly counteracts the weight of the floorplates and live/dead loads. The exterior brackets connect the column grid and the buildings main bracing together, which is made up of concrete-cased steel tubes, allowing for a smaller diameter member.

There were 5 main studies in the development of structural technology in, highlighted in Volume 56, issues 3, 8, 13, 14 and 15 of the Structural Engineer Journal 1978. These 5 studies look at the following developments: 3: Corrosion of Reinforcing Steel in Concrete and its Relation to Cracking 8: Correspondence on A Limit State Design Method for the Tension Region of Bolted Beam 13: Compression Laps of Reinforcement in Concrete Columns 14: Prestress Analysis for Continuous Beams: Developments in the Equivalent Load Method 15: Optimum Design of Reinforced Concrete Slabs From the above issues from Volume 56 of the structural engineer journal, we can see a clear emphasis on the relationship between analysis and consideration of both the methods used during a project, as well as the potential issues and failings that malpractice can cause. The above issues can be directly linked to the design of the structure of the Lloyd’s building when you consider the close link between all of the main aspects and how they all interlink to create one big structure, rather than numerous other buildings which are comprised of a number of different techniques.

From these issue, we can also see how there was a big emphasis on the use of concrete over steel in 1978, as when you look at issues 1 to 15, they are all closely related to the use of concrete, or uses of concrete in conjunction with other materials and reinforcements.

Looking back into the 1970’s when modernism was at it’s peak in architecture, we see a large number of brutalist buildings. Although Richard Rodgers used a large amount of concrete in the Lloyd’s of London building, it was covered in the façade of services and exterior lift shafts and stairwells. When considering the works of his close colleagues Renzo Piano, who he worked with on the Centre Pompidou) and Norman Foster, who’s 30 St Mary Axe can be seen from the Lloyd’s building, it is clear that a number of architects of this generation were starting to see into the future, past the brutalist movement, into their own era of modernism by covering the brutalist techniques of past architects in façade of mechanical wander.

The idea of covering something with a free façade, as well as the use of columns and large atrium like spaces can directly be linked to Le Corbusier’s 5 points of architecture which can be clearly seen in Rodgers Lloyd’s building. For example, the large floor slabs and concrete columns can be linked to Le Corbusier’s Pilotis, as well as the absence of supporting walls and the use of horizontal windows, which Rodgers turned to Vertical windows in his homage to Joseph Paxton’s Crystal Palace.

In conclusion, I feel that we can see a clear link between Rodgers influences in architecture, from Le Corbusier to his close colleague Renzo Piano and Norman Foster, as well as the Structural Technology developments of the 1970’s that directly impacted his design for the structural system of the Lloyd’s building.

The best example of this is his influence of Le Corbusier’s Pilotis, which led his to use a columned structure with floor plates, creating mass void spaces.

He then research this influence from which we can see from the Structural Engineering Journal would have influence his use of brackets and pre-stressed U-beams to form the lattice floor slabs and column joints. All of this was then bought together to create the structural system for the Lloyd’s building.

Citations & Bibliography (1) RIBA, The Brits who built the modern world, 2015; https://www.architecture.com/Explore/Buildings/Lloyds.aspx (2) Andrew Kroll, AD Classics: Lloyd’s of London Building / Richard Rogers, 2010; http:// www.archdaily.com/90668/ad-classics-lloyds-of-london-building-richard-rogers (3) Lloyd’s, About Lloyd’s, 2017; https://www.lloyds.com/lloyds/about-us/the-lloyds-building (4) Peter Rice (Associated Engineer: Ove Arup & Partners), Lloyd’s of London building (1986), 2006; http://www.engineering-timelines.com/scripts/engineeringItem.asp?id=244 (5) The Institution of Structural Engineers, Volume 56, issues 3, 8, 13, 14 & 15, 1978; https:// www.istructe.org/journal/volumes/volume-56-(published-in-1978) Atrium Photograph: https://s-media-cache-ak0.pinimg.com/originals/26/44/7f/26447fb57243e1e91639cf0faf230995.jpg Floor slab illustration: https://www.slideshare.net/Vishvendupandey/richard-rogerslloydslondon All unreferenced images were taken by myself on a visit to the case study.