Key Construction facts summary:
· Goal was to build a 40 storey, 180 metre office tower
· Construction programme January 2001 - September 2003
· Contract value for the shell & core of £131 million
· Creating 500,000 sq ft of net lettable space
· Incorporating 24,000m2 of external cladding
· 11,000 tonnes of structural steel
· Achieving sectional completion target dates to enable early access for fit out
Gary Clifford, Skanska Project Director, 30 St Mary Axe said:
‘The creation of this new London landmark has illustrated the very best of Skanska’s construction expertise in action. Rigorous planning, innovation throughout the construction process, a high degree of off-site prefabrication, collaborative working, and strict health & safety controls have all made real contributions to the success of this iconic building.’
David Fison, Skanska UK CEO commented:
‘We are delighted to have been involved with Swiss Re in this tremendous project to develop 30 St Mary Axe. Working closely together as an integrated team, with all professions and our client, we have produced a unique office building that sets new standards for London as a capital city in myriad ways.’
From solid foundations
Skanska UK Building started this unique project within the heart of the City of London in early December of 2000.
Working within the confined space of a Central London location, the demolition of the old Baltic Exchange Hall was the first activity to commence. Construction of new foundations started in early 2001 and consisted of 364 new permanent piles and 40 temporary piles, each 750mm in diameter and between 26 to 30 meters deep.
The first major challenge was the casting of the main pile cap on which the entire tower is founded. This necessitated a single pour of some 1,750m3 in one
eleven-hour shift. Concrete was delivered on a Saturday from three locations on the outskirts of the London and involved some 290 vehicle movements in and out of the site.
The superstructure of the building is entirely steel framed (including the core) forming an exterior diagrid from a series of two storey A-shaped frames. Absolute precision was required to create the diagrid and its unusual curved shape. By prefabricating components to rigorously tight dimensions prior to assembly, any issues regarding the complex angular relationships between components were resolved before erection.
The core was erected six floors in advance of the main floor plate, which allowed the ‘A’ frames for a particular two storey band to be lifted and positioned using the core for stability.
As the structure rose, Skanska Rashleigh Weatherfoil delivered the prefabricated service risers, again constructed off site and delivered at weekends, where they were hoisted into position using one of three site tower cranes. This method of construction was adopted for many areas of the project, which in turn added security for the overall construction programme.
Working ten floors below the steel diagrid superstructure, the cladding contractor installed the large diamond curtain wall components forming the exterior envelope of the tower. The prefabricated units were transported up the tower via an external scaffold tower with both material and passenger hoists connected. Once on a specific floor the panels were separated from the packaging and handled using equipment specially designed for the project and put in place with the external handrail in place, thus providing an almost risk-free operation.
From a higher floor, mobile floor cranes provided a hook, which would be lowered down to the cladding unit and connected. At this point the ‘Robota’ was released to get other units ready. The floor crane was then used to lower and finally position the unit into its location.
Tight site requires absolute planning precision
In a tight site where space was of at such a premium, all aspects of the construction had to be thought through with military precision. A large part of this planning was done ahead of arrival on site. Part of the process involved the use of Navisworks, a software programme to produce 3D models, not only of the structure and cladding, but also of the building services.
Creating these computer generated models gave several benefits in terms of sizing, positioning and handling of elements but also in the area of identifying design clashes between components, which if they had been discovered on site would have severely disrupted and hampered the overall construction programme.
Innovative responses to logistical challenges
One of the key successes of the project was the team’s approach to the logistical challenges. Three tower cranes were positioned outside the tower on the footprint of the site within 3.5m of the façade. These were carefully specified to suit capacity, reach, speed, climbing and dismantling criteria.
The ground floor plaza slab was structurally enhanced by Skanska to allow vehicles to drive onto site and thus remove any risk of local traffic congestion. This proved of great benefit and allowed steel to be delivered on one side and concrete to be brought in from the other side of site.
Quickly transporting people and materials up and down is absolutely vital in high-rise construction. So in addition to external hoisting an internal hoist was installed, covering 36 storeys. Together with a number of completed permanent lifts, it was used to carry men and materials up the building to the work faces after the external access was removed to make the building watertight.
Health and Safety a priority
Training was a major influence in achieving a high standard of Health and Safety performance throughout the project. All personnel attended an in depth induction course on their first day on site.
At the end of the induction all personnel sat a health and safety test with a minimum pass mark of 75%. Those not achieving the minimum standard were not given access to the site.
Throughout the project several Health and Safety courses took place, ranging from slinger signaller, mobile elevating work platforms, cherry pickers, site safety for supervisors, IOSH managing safely for managers, first aid, fire wardens, foundation one day health and safety awareness prior to sitting the CSCS touch screen test.
A major drive was implemented throughout the project to achieve full compliance with the Major Contractors Group Charter to employ a fully qualified workforce by the end of 2003. In general we achieved 85% across the board.
The accident frequency rate was well below the HSE National average.
Skanska UK is proud to have been able to supply an end-to-end service for our client including the expertise of:
Skanska UK Building - shell & core - Skanska Rashleigh Weatherfoil - shell & core M&E, Kontor Skanska - client fit out working with Skanska Rashleigh Weatherfoil, Clark & Fenn Skanska and Richard Lees Steel Decking.