St James Theatre with Anthony McBride, August 2016

On Friday a few of us visited the St James Theatre in central Auckland, where a major refit is taking place. Anthony McBride of Compusoft Engineering took the group around the site.

Anthony McBride describes the structure of the theatre.

The major theme of the talk was how to deal with a large, crumbly, but precious building. The theatre is an inherently tricky shape: a large, empty box, with high slender walls, and a big span between them. It’s also inherently high-risk — if the building fails, a lot of people could be inside. (Anthony noted that the live load of the circles (galleries) is five times the dead load.) And, as it happens, the St James Theatre is a weak structure. Its concrete is drummy and crumbling–more on that in a moment. However, as is likely to be the case with heritage buildings, the fabric is beautiful, unique, and carries its own value. Trying to brace this big crumbly box with steel would mean obliterating a good deal of that fabric.

​View from backstage through the proscenium to the upper and lower circle.
​View from backstage through the proscenium to the upper and lower circle.

The solution that the engineers have decided upon is base isolation. If it’s impractical to strengthen the walls to resist strong shaking, the logical step is therefore to reduce the loads they experience by dissipating the quake energy. Anthony described the state-of-the-art triple pendulum bearing system which is being installed at the St James, which will allow the building to move up to 250mm in any direction. (Or perhaps it might be better to say, the ground moves and the building doesn’t move with it–its period is increased considerably.)

Looking down into the excavated floor from the upper gallery--the view from the gods.
Looking down into the excavated floor from the upper gallery–the view from the gods.

To illustrate the parlous state of the building, and also its charm, we had a thorough walk through the site. Starting in the lower circle, we filed down to the ground upon which the building stands. To get at the foundations in order to install the isolation, the floor has been removed. As I noted in the invitation, what was uncovered beneath the floor was a large section of nineteenth-century cobbled street, and what appeared to be the brick foundations of the butcher’s shop that stood on the site long before the theatre was built. A number of artefacts have been removed from the site, including bottles and china, and we were told that the floor slab of the restored theatre will include glass windows allowing visitors to inspect the cobblestones. It was eerie to stand right next to the paved street, while 25 metres above your head is an ornate ceiling complete with dome — the shabby-grand remains of a vaudeville house —  and to think of the different lives that have been lived inside this bubble of space. It’s true of any space in any city; but the enclosure and the contrasts are what make the thought hit home.

​​​The cobblestones, seen from the lower circle.
​​​The cobblestones, seen from the lower circle.
​​Looking up from the floor to the dome.
​​Looking up from the floor to the dome.

Looking up from the floor we saw the precarious south wall and the bulging brickwork of the proscenium arch. Looking down, Anthony showed us the foundations. The original design drawings of the theatre specified 6 metre deep solid foundations; but what was really built was more like 2.5 metres, tapering irregularly in a hand-dug caisson, and filled with building rubble. A real “oh shit” moment for the refit team. Even digging beneath these foundations looks like a no-go, as it might disrupt the skin friction between pile and soil, and you wouldn’t want to be there when that happens!

​The foundations as revealed by excavation.
​The foundations as revealed by excavation.
Passing through a basement that pre-dates the theatre, we climbed the scaffolding on the north wall, and paused to inspect the steel reinforcement that has been exposed by exploratory drilling. In a number of places, it was corroded, poorly interconnected, or simply inadequate, and considerable repairs will be required. We emerged onto the roof, where we could see the demolition crew working on the adjoining apartment tower, the profit from which is making the refit possible. I’ll spare you the detail of this, but we did get to hear (from the developer Steve Bielby) a little about the way that the development deal funds the heritage project, which was most interesting. From the roof we entered the upper circle, from where we could better see the ornate detailing of the decorative plasterwork and the dome. One day, but not soon, it will all be finished, and it will be glorious.
​Inspecting steel on the north wall.
​Inspecting steel on the north wall.