29 August, 2014 | By David Rowlinson.
Hyder’s David Rowlinson explains the big technical challenges on the major station redevelopment and how they were overcome.
- Simple way to explain BIM
- Complex geometry at huge scale
- Benefits for whole supply chain
- Overcoming initial difficulties
- Changes to approvals
With Hyder Consulting being the lead designer for the redevelopment of Manchester Victoria Station, I have been part of the design team developing the new roof.
We have been working for principal contractor Morgan Sindall, Network Rail and Transport for Greater Manchester to transform the station into a transport interchange the city can be proud of.
Having previously worked on projects at London Paddington and London Bridge stations, I love the way Manchester Victoria’s 15 ribs, with their huge spans and lightweight ETFE covering, actually complement the historic façade of the Victorian frontage.
There is such contrast between the previous dark concourse and the proposed station that will be flooded with light.
Simple way to explain BIM
The term BIM gets heard a lot these days, which is great news, but when we started the design process more than a year ago, it wasn’t very well understood.
One of the first things I did was to put together a simple flowchart which showed how the information would pass between the various parties and in what format this would be.
BDP was the architect for the project, developing a preliminary Autocad 3D line model with the design team to suit the constraints of the site, the stakeholders and the engineering requirements.
I imported this line model into analysis software – Autocad Robot – and developed a complex 3D structural model, which included the detailed changes to the building articulation at critical stages in the project.
The graphical rendering from the structural analysis programme was the first interactive 3D model of the structure and was extremely useful during design team discussions about the interfaces with the various parts of the existing station.
This was, in effect, the first BIM model as it combined the geometry of structure and intelligent elements with information about section sizes and stress distributions.
After the geometry was agreed, and as I completed the structural analysis, Hyder’s 3D modellers began the task of creating an accurate BIM model using Autocad Revit.
Complex geometry at huge scale
Our team had experience of using Revit to deliver simple orthogonal structures, but never anything of the scale of what was proposed at Manchester Victoria, with its complex geometry.
The ribs are each based on arcs from one of three different ellipses. No member is the same length, in the same direction or inclination.
Often our senior technicians had to develop ways of modelling that our technical support specialists had never encountered previously.
After completing the structural model, the advantages of BIM really became apparent. Severfield (UK) was fabricating the steel and designing the connections and it was able to read the Robot model to inform the steel calculations.
Even better, the Severfield team was able to import our Revit model into its Tekla software which produces their fabrication data.
This process meant Hyder’s modelling efforts were used directly for fabrication, rather than the traditional process whereby designers draw up one design then fabricators then duplicate this work prior to construction.
In a project where the geometry is such a critical item, the BIM model delivered significant time, risk and quality advantages.
Benefits for whole supply chain
Other members of the supply chain were also able to use our BIM model to great effect. Morgan Sindall employed a specialist BIM provider (Rapid 5D) to add time, cost and resources to our model for use in managing the construction process.
The ETFE was supplied by Vector Foiltec, having previously supplied renowned schemes the Eden Project and the Beijing Water Cube.
Hyder saved the Revit model as a 3D CAD file, which Vector Foiltec used to produce the cutting patterns for each individual roof cushion.
Network Rail also agreed to take on our BIM model as part of the health and safety file, allowing future maintainers to know exactly how to keep the station in great shape.
As an engineer attending Network Rail Interdisciplinary Design Reviews, the BIM model was invaluable.
Instead of reviewing work on flat 2D paper drawings, trying to imagine exactly how the interfaces might work, we could actually fly around the model and see for ourselves how the space worked.
This didn’t just apply to clash detection and cable routing, but also to risk assessment.
It was so much easier to discuss constructability when elements can easily be turned on and off, and working at height was simple to identify when you can see the drop.
Overcoming initial difficulties
Working in BIM doesn’t make difficulties disappear – it isn’t some miracle cure. In some respects, it initially makes problems more difficult – the modelling process takes time and requires a great deal of accuracy.
However, the model ensures problems do get identified and are resolved thoroughly.
There is no moving a line on a drawing to avoid a clash; the whole member is modified and all the drawings and renders updated to demonstrate whether that modification has achieved the required results.
A further challenge was delivering in BIM while also meeting traditional construction expectations. For example, everybody starts a project with a topographical survey. But this is a 2D linework drawing.
For it to be useful in BIM, it needs to be converted into a 3D model.
This was something which needed to be done just as accurately as the modelling of the proposed structure, as anything on the topographical survey which wasn’t modelled was obviously Hyder’s risk.
Changes to approvals
Another aspect that took some getting used to was moving the drawings through the approval process.
With traditional 2D CAD, if there are no changes, you can simply change the drawing status. Job done.
Clients know this, so when we achieved category one sign-offs (accepted without any comments) in the BIM world, the model can develop in the meantime. New elements of structure may have been included.
As a result, my nice clean and clear drawing now has lots of additional information which needed to be removed and reviewed prior to issue.
There is only one model, one file, one source of truth. So achieving a staged delivery as required on a project on this scale requires careful planning.
Using BIM gives designers such confidence in their structures. Drawings are not just a collection of lines; they are the elements from the toolkit in engineers’ minds.
I think that is the strongest point about using BIM: it replicates the way that structures fit together in an engineer’s head, and allows them to deliver that visualisation in a collaborative manner.
David Rowlinson is an engineer at Hyder Consulting
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