BAA set itself the target of using technology to cut 10% off the cost of building Heathrow T5. It got the whole project team to use a single 3D computer model to design, build and ultimately maintain the terminal building. BAA also pursued standardisation, prefabrication and modular-isation as ways of driving costs down.

Conventionally, the architect designs the structure and passes CAD drawings to the engineer. The engineer then draws the structure again using a different program. This procedure cascades down the team to specialists, creating hundreds of sets of drawings of the same structure. Inevitable inconsistencies between these drawings have to be reconciled on site, leading to problems with delay, workmanship and cost.

When work commenced on design of T5, Mott MacDonald helped to implement a 3D design strategy. The same 3D model was used for construction and passed on to BAA for maintenance.

The objectives of using 3D were to:

• help visualise the structure and provide clarity before starting construction
• create consistency across the project team
• reduce errors, ambiguities and clashes
• provide fully co-ordinated information
• efficiently plan construction
• allow modularisation and prefabrication
• improve health and safety
• provide project savings

Process and software

The process involved producing a single 3D model using Architectural Desktop software. We used this to produce 2D plans, elevations and sections. Contractors used our 3D model to plan concrete pours, visualise reinforcement details and produce method statements. Architectural Desktop was supplemented by 3D Navis Works software for viewing, reviewing and detecting clashes. Other programs enabled services and steelwork design. Use of further software meant models could be ‘walked through’ in real time, turned into visualisations, used in animations, and linked to construction schedules. This helped produce a clear understanding of design intent, production planning and current project status.

Use of 3D in design planning and programming

Use of 3D design helped break the design process down into chunks. The whole of the substructure was broken down into 32 elements and each of these represented a delivery milestone. The 3D model was used by fabricators to factory produce building elements off-site. Because dimensions and orientations were downloaded directly from the single model, it meant that components could be guaranteed to fit when they were taken off the delivery lorry and onto site.

Clash detection

The model was extensively used for co-ordination and clash detection. Each wire, pillar and pipe was digitally modelled, enabling construction of every part of the building to be given a virtual dry run. This proved useful for preventing problems later on, as virtual mistakes are more easily rectified than real ones. The use of modelling helped prevent conflict and delay when it came to building T5 for real.

Similarly, examining the design in a virtual environment enabled potential hazards to be spotted and action taken to eliminate them.

For the cross passages on the airside road tunnel, Mott MacDonald produced animations to describe the excavation and lining procedures. As
a result we made the construction team fully aware of the entire process and the potential implications of deviating from the prescribed design and construction methods.