Surveying the Gherkin

Soaring 180 metres into London ’s financial skyline, 30 St Mary Axe has been taking form since 2001, and has now become a regular feature on the world’s television screens. Unmistakable in its shape and variously referred to as a “cigar-shaped spaceship” and the “gherkin” (both “erotic” and “silver”) as well as the “Swiss Re Tower” it has been designed to be the Capital’s first environmentally progressive tall building.

Architects Foster and Partners say, “The building is radical – technically, architecturally, socially and spatially. Both from the outside and from within it will be unlike any office building so far conceived.” The tower rises 179.8 metres in 40 storeys from the site of the former Baltic Exchange at the heart of London’s financial centre; it will be the new London HQ of the Swiss Reinsurance Company.

One of the challenges faced by Foster and Partners was the relatively small (1.4 acres, 0.57 hectares) area of the site, the solution was to build with a circular plan that widens as it rises from the ground and then tapers towards the apex. This has the effect of allowing the building to appear less bulky than a traditional rectangular shape, its aerodynamic form minimises wind loads on the structure and increases the safety of ground-level pedestrians, as gusts are not deflected downwards.

There are many innovative features in the building’s design and construction, and consequently many tales to tell of engineering feats and creative thinking. We will focus here on the efforts of one company, specialist cladding company Schmidlin (UK) Ltd., and the way in which its personnel coped with very tight constructional tolerances using Trimble^®5601 total stations.

The tower is supported by a central core with a perimeter grid of diagonally interlocking steel elements, called a diagrid. Due to the inherent stiffness of the external diagrid, the central core needs to act only as a load-bearing element and is free from diagonal bracing, producing more flexible floor plates. Diamond-shaped cladding elements connected to the main frame via stub brackets provide one of the key elements of the building’s appearance. Each element had to be lifted from the horizontal using a manipulator and then rotated and lowered into position.

Schmidlin (UK) Ltd handled the building’s external curtain walling up to level 38, internal diagrid cladding, plus internal screen work and ground floor glazing. The company purchased two new Trimble 5601 total stations for this contract. Survey and Setting Out Manager, Jeremy Creeke commented, “The instruments perform well and are very efficient, very good indeed.” He explained that tolerances were set at ± 2mm on each floor and that his team were working, “Right on the boundaries of what can be achieved.”

Schmidlin was founded in Aesch, Switzerland in 1936; today it is a leading global company in the design, manufacture and installation of high-quality curtain wall systems.

30 St Mary Axe, night view of entrance

Photograph by Grant Smith

Keith Hofgartner, Manager Trimble Geomatics and Engineering Division – UK and Ireland - concludes, “The Trimble 5600 Total Station series offers the best, most-productive measuring methods available and is ideal for a wide range of applications. The 5600 total station with its innovative Servo, Autolock^®, and Robotic technology, plus three Direct Reflex EDM options, allows survey crews to work more productively than ever before.”

Contact Doug Williams

Trimble is a leading innovator of Global Positioning System (GPS) technology. In addition to providing advanced GPS components, Trimble augments GPS with other positioning technologies as well as wireless communications and software to create complete customer solutions. Trimble’s worldwide presence and unique capabilities position the Company for growth in emerging applications including surveying, automobile navigation, machine guidance, asset tracking, wireless platforms, and telecommunications infrastructure. Founded in 1978 and headquartered in Sunnyvale , California , Trimble has more than 2,200 employees in more than 20 countries worldwide.

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