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BIM: Model behaviour

Reconstruction of the Golden Gate Bridge approach in San Francisco shows new possibilities for BIM methods in civil engineering.

Information modelling is now widespread in building work, but civil engineering has hung back, using 3D design tools perhaps, but not full modelling. Now, the capacities for BIM as a tool for not just design work, but also construction planning, scheduling and cost control may be beginning to take off.

Few projects showcase its capacities better than the reconstruction of Doyle Drive in San Francisco.

This large, six-lane elevated structure has long been an eyesore on the south side of the iconic Golden Gate Bridge. It is being replaced with a low-profile landscaped route, still using elevated sections to reach bridge deck level but dipping twice into a landscaped arch “tunnel” to hide traffic.

Consultants Parsons Brinckerhoff and Arup are at the design end of an eight-strong team on the project, which is bringing all its work together using a BIM system.

The complex design for this structure - the tunnels and the multi-level interchanges, the programme of long-term traffic diversions needed during the four years of construction, and the overlapping construction sequences with at-grade roads, tunnels and structure - make it an ideal test bed.

Not only is the design work being presented as a 3D information model but so too is sequencing and planning of the construction and diversions to create a “4D timeline” model to show it. A fifth dimension, costs, are added too and a sixth for quantities in the earthmove. These provide material for design, construction programming and public visualisations on a continuously live website.

“You can use Navis to break up the model into its 3D elements and attach each to a schedule of tasks like the construction sequence”

Brady Nadell

A full range of software is being used including a very old Autodesk program Caice, in which state road authority Caltrans prepared the basic alignment designs, Bentley’s InRoads, AutoCAD Civil 3D and Revit. Studio 3D Max is used to make the high-resolution visualisations straight from the 3D model.

At the centre is AutoDesk Navisworks programme. Originally developed for clash detection and layered visualisation of designs, this programme’s capacity to bring together a wide range of data and models is making it more and more important, says Doug Eberhard, a strategic development manager at AutoDesk.

Parsons Brinckerhoff design engineer Brady Nadell expands on how the process works: “We take the Caltrans data and convert to a 3D model. Inroads takes charge of the road surface and Civil 3D the rest.” Bentley software is used for bridge design work, he adds.

But swapping information from programme to programme is critical and a central system provides an excellent basis for design consultation with both the client and contractors. “It’s more comprehensible and particularly so for a design of this complexity,” says Nadell.

Navisworks allows partial 3D models to be assembled in one place in the same coordinates. Clash detection is important for design and later contractor interactions, and the programme highlights these automatically.

Navisworks is also the basis for timeline modelling. “You can use Navis to break up the model into its 3D elements and attach each to a schedule of tasks like the construction sequence,” says Nadell.

The multi-coloured sequence runs like a movie, day by day, showing the project growing. To that sequence can then be added quantities associated in a “resource loaded schedule”, which are displayed on the screen.

“Navisworks does not do that yet so we do it in an Excel spreadsheet and make a connection to show the numbers on the display,” says Nadell.

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