The new £3.5bn Terminal 5 at London’s Heathrow Airport is one of the biggest and most complex building projects in recent times in the UK. DLT were responsible for conceptual and detailed design of the erection systems for the 18,500 tonne steel roof of the main terminal building and for the new 1100 tonne steel air traffic control tower. Both structures were fabricated off site and lifted into final position using strand jacks.
The main terminal roof was erected using methods more commonly found in major bridge construction. The main roof comprises a series of tied arch steel box rafters with a clear span of 156m, supported on tubular leg assemblies. The leg assemblies are erected first, onto DLT specially designed erection frames, followed by the box rafters. The rafters are assembled at ground level and then lifted to full height in groups of four using strand jacks. Each lift is 2,000 tonnes and is lifted with 16 No 185 tonne capacity strand jacks. The erection frames for the leg assemblies are designed to provide fully adjustable support to each of the leg components and to and skid between erection positions, avoiding the need to dismantle and re-erect.
The Control Tower consists of a 31m high accommodation pod and top mast section, the CAB, supported on a 56.5m guyed mast, total height 87.5m. The mast is stabilised using pairs of pretensions guys attached to the mast just below the CAB structure and positioned at 120º intervals.
The new tower is located adjacent to Terminal 3 and is surrounded by operational aircraft stands and taxiway. To minimise the impact of the airport’s operation an erection concept was developed to construct the CAB off-site before transporting it to the permanent site and lifted it to allow the insertion of the pre-fabrication sections of Mast.
Once delivered to the final site the CAB was temporarily put down on to the permanent foundation. The temporary steelwork used for the transportation operation was reconfigured and two systems of jacks in open hydraulic circuits were installed between the upper and lower Yoke. These were used to effectively form a structural pin between the permanent structure and the temporary works minimising the forces induced into the permanent works during lifting. Three 16m high Lifting Towers were assembled, one at each corner of the triangular lower Yoke, to support the lifting strand jacks. During lifting, lateral stability of the partially completed Control Tower was achieved by three 180 tonne capacity strand jack operated guys. An additional three 180 tonnes capacity strand jack guys were tensioned to provide additional stiffness to the guying system outside operational weather windows.
The lifting jacks lifted the CAB structure approximately 14m, allowing a section of steel mast to will be installed below. The structure was then put down allowing the lifting system to be reset. This lifting cycle was repeated five time until the final section of Mast was inserted. The completed Control Tower was then lowered onto its permanent foundation and the permanent guys installed.
Throughout the lifting operation a bespoke computer controlled system was used to synchronise the operation of the lifting and guying jacks and monitor loads. A separate geo-positioning system was used to constantly monitor the position of the top of the CAB, the lifting yoke and the lifting towers.