Mike White, a structural engineer for six years, explains his work on the project to build a new extension at Jesus College, Cambridge, which has been shortlisted for The Structural Awards 2017.
The project is part of a wider scheme to update the West Court facilities owned by Jesus College in Cambridge. This new extension comprises a single-storey basement bar with a lightweight timber café structure above.
Probably the greatest challenge was achieving the pavilion’s simple, elegant design - the superstructure is completely on show so there’s nowhere to hide! On the other hand, as an engineer it’s especially gratifying to be able to walk into a building and see our work on show.
We succeeded by staying focussed on basic engineering principles, combined with a bit of innovative thinking. The structure is composed of basic structural elements - beams, columns and bracing - but the simplicity could easily be undone by over-complicated connections.
A lot of effort went into designing visually clean but effective connections, for example we 3D-printed a prototype component to help the team develop the design. The glulam oak timber was then fabricated using advanced computer-controlled manufacturing equipment to achieve the precise geometry of the pavilion’s cigar-shaped columns.
There were other challenges. The basement is close to a listed building and sited in tricky ground conditions, roughly 2.5m into the water table. Displacing all this water makes the building want to try and float; effectively it is a large concrete boat! Normally a basement would be weighed down by the building on top of it, but with only a single storey lightweight timber pavilion on top there was a risk that the building wouldn’t be heavy enough to stay sunk into the ground and would start to float upwards.
If the basement began to float it would cause the client all manner of problems, and you would expect to see a lot of cracking between the new basement and existing building. This could seriously damage any pipework or other services running between the two buildings. You wouldn’t want these problems with any building but especially not when joining onto a listed building.
We overcame this problem by adding weight to the building and also by tying the basement to the steel sheet piling around the perimeter. This gave enough resistance to flotation that the building should stay safely in the ground for years to come.
Part-way through the project we were surprised by a deep geological feature. Finding surprises in the ground is fairly common for engineers, which is why breaking ground is one of the riskiest times in any project. However, they’re normally fairly localised and don’t affect the overall philosophy of the design.
This site was exceptional because we had discovered an ancient river bed nearly 30m deep with very steep sides. Our original exploratory boreholes missed the extent of the issue and we had no choice but to reconsider the construction strategy for the basement.
Dealing with unexpected discoveries is a key part of the structural engineer’s role. Fortunately, we can find a solution to most challenges and this can be one of the most rewarding aspects of the job.
The client is extremely pleased with the pavilion and some of the other colleges in Cambridge are now keen to build something similar, so we’re very pleased with the result and thrilled to be shortlisted for The Structural Awards 2017.
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