Here’s a piece that Stacy Vallis & I wrote about the Kopu Bridge near Thames. It’s a 90-year-old swing-span bridge, quite lovely. Management of the bridge has recently been handed over to a community group who are going to open it up to walkers and cyclists.
Our source material for the article included some really interesting articles from Heritage NZ and Engineering New Zealand (formerly IPENZ). From an engineering perspective, I particularly enjoyed reading the 1930 article by AJ Baker on the construction of the bridge. It’s linked through from the bottom of the ENZ page.
Thanks to Engineering New Zealand, I recently had the opportunity to attend a site visit to the NZ International Convention Centre. The NZICC is being built in central Auckland across the road from SKYCITY. The site takes up most of the block, and on two of its corners there are heritage buildings.
The two buildings have required different treatment. The Albion Hotel, a five-storey URM building completed in 1873, is scheduled in the Auckland Unitary Plan as a Category B site. It has remained intact. Berlei House, (aka Nelson House), was designated a Category 2 Historic Place by Heritage NZ. To allow for sufficient land area for the conference centre, the developers were granted permission to demolish it, retaining the façade. You can read the Heritage Impact Statement prepared by Dave Pearson Architects on Auckland Council’s website.
Although the visit didn’t focus on the heritage sites, I was able to ask a few questions about Berlei House and the Albion. I thought that the treatment of the façade and of the retained building was interesting enough to merit a brief post.
Berlei House was completed in 1931. It was designed by Roy Lippincott, best known in these parts for the University of Auckland Clock Tower and for Smith & Caughey’s on Queen St. The Berlei House façade is brick at the base, with precast concrete panels forming the upper half. Large elaborate windows create slender piers over most of the wall height.
On both sides of the site, deep excavations have been made to allow for a capacious carpark. For the Berlei House façade, this meant that temporary works in the form of steel gantries were required to support it while the pit was dug.
And what a pit! As you can see above, the excavation went down and down, with the façade nimbly supported on the very edge. But the gantry wasn’t staying, and the façade wasn’t going to have to hover on the brink like this forever.
Richard Built, BECA Technical Fellow in Structural Engineering, was one of the tour presenters. As we passed through the Berlei house façade on our way into the site, Richard explained that a concrete structure had been constructed to support the façade and to direct perimeter loads into the foundations. The façade’s not taking any loads beyond its own self-weight. We were not permitted to photograph inside the site, but from the street I snapped a couple of shots, showing the new frame hiding behind the façade.
With the job still in progress, it’s possible to see the holes where steel rods have been inserted to connect the façade to the concrete structure. They are held in place with an epoxy grout. Lateral load resistance is now provided by the concrete frame.
I saw less of the Albion. In the later part of our tour, we went through a corner of the exhibition hall, which will be at street level on Hobson St, next to the Albion. We were able to see the plain, windowless North wall of the building. Barnabas Ilko of Fletcher Construction explained that there is 400mm of space between the Albion and the NZICC—which seems tight. Then he explained that the NZICC wall has to fit into that space, and it’s 225mm thick! Oh, and the precast panels are over 10m high. Piece of cake, right?
The Albion Hotel, like the Berlei House façade, is also sitting on the edge of an excavation. This one is deeper: the land at the site slopes down from Hobson St to Nelson St, so on this side where the slope is higher, the hole must go down further to make a level basement. Incidentally, Richard Built mentioned in his presentation that the lateral pressures on the structure from the slope are greater than the vertical forces from the weight of the building!
We were told that the Albion Hotel was permitted to settle a maximum of 20mm. Somehow, the work was completed without exceeding that limit—when you look at the depth of the wall below the building, the challenge of achieving this target seems enormous.
There was a lot more to know and to see at the NZICC. The structural design is on a fairly heroic scale (40m spans, 4m deep trusses, columns supporting 13MN loads, etc) but as interesting as it is, it’s not germane to the theme here. Engineers might like to keep an eye on the Engineering NZ newsletter, as Fletchers have promised opportunities for future visits.
Thanks to Mervin Tibay for organising the visit, and to Richard Built, Richard Archbold (the project architect, from Warren & Mahoney) and Barnabas Ilko of Fletcher Construction.