BARRETT STEEL BUILDINGS LTD
BARRETT STEEL BUILDINGS LTD
EAST MIDLANDS TRAINING (RYANAIR)
Not far from the main runway and within sight of the passenger terminal at Stansted Airport, a new hangar capable accommodating up to five Boeing 737s is up and running. A series of engineering and logistical challenges had to be overcome to lift four 125m long steel trusses on a design & build contract for the cavernous interior of the new maintenance hangar at the airport.
The design was progressed around the need to be able to lift, on a specific day, the major roof girders. The box girder had to be lifted and made secure in one day. It was recognised on day one that if the girders were erected out of tolerance it would be impossible to bring them back to true.
The design solution was to provide a 10m deep x 7.2m wide x 125m long box girder, pre-cambered for self weight and dead deflections. This would form the spine to the structure. Two further 125m trusses could then be erected in three 41.5m sections, and braced back to the spine box girder. The stiff spine would force the vertical trusses into position. Final adjustment of the door guides would take place after roof and wall cladding was complete. To do this a system of vertical and horizontal adjustment to the door guide support brackets was devised, which could be locked off once before handing over.
The erection method statement called for the girders to be transported “piece small” and built up on the ground in temporary stillages. The main contractor invested in the ground providing a high quality level erection platform capable of carrying the stillages with minimal settlement. The stillages were staged to allow a natural positive pre-camber to be built in. The completed box girder was checked and then locked by the application of TCB High Strength Friction Grip bolts.
On 16 April 2008 the box girder was hoisted into place using two 300t all-terrain mobile cranes. The girder was lifted between two pairs of 25m high lattice columns positioned 125m apart. The physical lift took 30 minutes, but all day to complete, from early morning briefings and safety checks to late in the evening tying back and making fast. Two further 50 tonne plain trusses were lifted end of April and braced back to the rigid box girder. The three 41.5m sections were then lifted individually by one of three 100t capacity mobile cranes and connected together and to the lattice columns while suspended in the air. Whilst the three sections of the truss were held at the right level and location, a fourth 25t capacity mobile crane traversed between the truss and box girder erecting tying in steelwork.
Only when the doors were installed and successfully commissioned did the project team celebrate a design well executed.
A fine example of an optimised long-span structure, at minimum cost with fast erection. The design & build criteria were limited to the volume contained, loadings and time of erection. Therefore the structural details were simplified to achieve economy, ease of transport and predictability of erection.
A text-book example of this direct approach.