A structure of light almost lost

Frank Gargano is a senior associate and structural engineer with engineering firm Arup. He specialises in the design and analysis of building structures, and was one of the lead engineers of the dome refurbishment.

The thing about the dome is that if you say to someone ‘I’ll meet you at the library’, everyone knows it and everybody knows the dome itself. Melbourne has got four or five really great old buildings, to me the dome is one of the greatest spaces there is.

Arches and domes have been around since the beginning: the Pantheon in Rome, St Peter’s Basilica. There are lots of great cathedrals that have domes but some are almost completely solid and might only have a lantern or a tiny bit of light right up the very top. Our dome is fully glazed – it’s light, you can see outside it. 

As an engineer, the biggest challenge was analysing and understanding how that actually works. It’s a dome and so it relies on arching to restrain the forces – but what actually takes them? The supporting vertical load (gravity) is easy to understand, it’s the walls. But at the very top, because of the shape of it, there are some thrust forces. I imagine the force coming down the face of the arch itself; ultimately it has to be resisted.

We found the answer as we climbed the cast-iron spiral staircases out onto the annular, from there we could get outside onto the roof at the base of the dome itself. From that vantage we could see there are eight external buttresses that actually do the restraining for the dome; that’s what provides the structural integrity. It’s very unusual.

My understanding is that there was some concern over whether the dome should be kept, back in the ’50s.

I suspect it was questioned because people couldn’t understand it.

Seeing it restored to its former glory and seeing people use it – looking up in awe, seeing that space returned to what it was originally meant to be – is fantastic. It’s absolutely full of light now.