Hopetoun Alpha with John O’Hagan of Compusoft Engineering, October 2017

Concrete classicism

A lightning-fast summary: Hopetoun Alpha was built in 1875. It’s mass concrete, meaning concrete with no internal reinforcing steel. Built for the Congregationalist church, this is a Neoclassical temple in the Doric order, with a charming and luminous timber interior. It’s in Beresford Square, close to the intersection of Pitt St and K Road.

Hopetoun Alpha, exterior

If you’re reading this, you likely know that concrete is pretty strong in compression, but not great in tension. It’s hard to crush, but it doesn’t like to bend. You’ll also have a pretty good idea that 140-year-old buildings can move around a bit: slowly, as the ground settles over the course of the years; and quickly, in extreme cases—for instance, when the ground shakes. So the task that John O’Hagan of Compusoft Engineering has accepted in assessing a building like this is twofold. Firstly, to evaluate how well the building has coped with all the slow movement and the vicissitudes of time, and secondly, to consider how well it might handle an earthquake or a severe weather event. John shared some of the process of making this assessment with us, as we walked around the building.

To understand how the building will perform, you need to know exactly what’s made from, and how the pieces are put together. Over the last few weeks, John and the owners of Hopetoun Alpha have carried out a number of investigations to establish this. They’ve been underneath the building, into the roof void, and everywhere in between. John began today’s tour by explaining the structural system of the building.

Alpha’s anatomy

The building is a long rectangle, shaped somewhat like a shoebox. Its two long walls, the side walls, get narrower in two steps as they get higher. At ground level, they’re about 640mm thick. The site slopes, but the walls come up to establish a level for the floor. At floor height, they step in to 420mm, creating a ledge both inside and out. On the outside, the ledge demarcates the plinth on which the building sits, and the walls change colour to emphasise this. On the inside, the step creates a handy support for the floor joists.

Hopetoun Alpha, basement. John indicates the ledge on which the floor joists rest

It’s a very common detail for “masonry” buildings of all kinds. As we’ve learnt on our tours, brick buildings often contain a similar step (or sometimes just a socket in the course) into which floor joists can be inserted. The problem is, of course, what happens when the walls move so much that the joists fall off their ledge or out of their sockets!

The walls step in at ceiling height, too, and there the step supports the ceiling trusses, which are likely made from jarrah. John shared a drawing of the trusses.

Hopetoun Alpha, drawing of ceiling trusses. Image courtesy John O’Hagan / Compusoft Engineering

He noted that although the trusses are statically indeterminate, they were well analysed by the designer for resisting gravity loads. The steel ties that you see connecting the vertical members to the bottom chord are wrapped around and pinned, forcing the verticals into tension. The diagonals carry compression. The trusses are sound and strong, and seem to have performed well. John mentioned that nails seem to have been a scarce resource at the time of construction, as there were very few to be seen in the timberwork! Fasteners of all kinds were clearly at a premium: a single bolt connects the front truss to the gable end. (As you can imagine, this is not ideal.)

The trusses span the main hall laterally, but there is far less roof structure in the longitudinal direction. What’s there is more or less entirely cosmetic—boxwork, panels, trim, ventilators. This meant that the engineers needed to wear abseiling harnesses to get up in the ceiling for a look—there’s not much to stand on and a fair way to fall.

Hopetoun Alpha, interior from mezzanine. Note bowed ceiling panels, and mezzanine cutting across windows.

As you can perhaps divine from the photo above, the mezzanine or gallery wasn’t part of the original build. The windows on the long walls would probably look different if this were the case (c.f. the smaller auditorium at the Auckland Town Hall.) The addition of the mezzanine meant some additional supports were needed underfloor. Cast iron columns carry the load down to neat brick piers—far neater than the original footings, which seem to have been pragmatically cast inside a few handy barrels!

Hopetoun Alpha, concrete footing (and extraneous foot, far right). Note the remains of barrel hoops and staves—easy formwork!

Mass (of) concrete

The entrance to the building presents the greatest challenge for modelling and analysis. There are large volumes of concrete in the pediment and the stairwells on either side, and, as noted, this section is poorly connected to the roof truss.

Hopetoun Alpha, portico. John O’Hagan explains the structural system of the building

There are decent-sized spans between the columns—approaching two metres—and of course the concrete is being asked to cross that gap without tensile reinforcement. This part of the building may yet require more analysis.

She’ll be right

When the mezzanine was put in, Hopetoun Alpha was also extended at the rear. This allowed a stage to be built and an organ installed, and to accommodate this a large opening was made in the back wall of the existing hall. And the building didn’t fall down.

Hopetoun Alpha, model, showing the opening in the rear wall (the blue rectangle)

It didn’t fall down, but over the long years, a large crack has developed in the wall. This is probably the result of the foundations moving slightly outward, and of tension forces in the reduced thickness of wall above the stage. Whatever the cause, the crack extends from below a round window above the stage (not visible from inside) to the top of the proscenium. Then the crack starts again at the left-hand edge of the bottom of the stage aperture, and continues down to ground level.

Hopetoun Alpha, basement. John points out a deep crack in the transverse wall below the stage.

How significant the cracks are, structurally speaking, is yet to be determined. But it seems to me that some form of strengthening will be required to make up for the diminished capacity of the wall.

Solution, general form

I want to preface what follows by saying that John made it clear that he didn’t want to talk about specific solutions for Hopetoun Alpha. It’s too early for that—too early, even, to say for sure whether work is needed at all, until the NBS rating is determined. Instead, we talked about some hypothetical solutions for a building of this type. Please read the rest of this post in that spirit. Your mileage may vary.

Hopetoun Alpha, view from the mezzanine

The major concern in a building of this size and style would be the out-of-plane response of the long walls. This means, if an earthquake shook the building from side to side (as opposed to back and forth), how well would the long walls cope with being flexed?

It might be sufficient to support them by connecting the floor joists to the walls in the basement. (At the moment the joists are just resting on the ledge you saw in the picture above.) As well as that, you’d probably put a plywood diaphragm across above the ceiling panels to tie the walls together at the top. By doing this, you’d end up with the long walls far better supported by the in-plane elements of the building.

Hopetoun Alpha, longitudinal section showing position of mezzanine. Image courtesy John O’Hagan / Compusoft Engineering

But if floor and ceiling diaphragms weren’t enough, the mezzanine might present an opportunity. Site visitors may remember hearing about the truss inside the gallery at the Auckland Town Hall. There’s obviously no room, and no need, for a truss inside the mezzanine at Hopetoun Alpha. But the mezzanine itself has some inherent strength, aided by its tongue-and-groove flooring. This could be enhanced with some inserted material. If the mezzanine were then connected more securely to the wall, it would serve as a brace at about halfway up the wall height. The walls could then be modelled as rocking about the pivot of the mezzanine, improving their performance. Tying the structure together better would be completed by more securely fastening the pediment and the rest of the portico to the main building.

Thanks!

Grateful thanks to John O’Hagan for his time and enthusiasm. Thanks also to the Ashton Wylie Charitable Trust which owns the building, and to Paula King, who made it possible for us to go and see it. We’ll stay in touch with this project as it progresses.

The City Rail Link, Auckland Baptist Tabernacle, Mercury Theatre, Hopetoun Alpha, and the Pitt St Methodist Church with Edward Bennett and John Fellows, August 2017

Terry Gilliam’s 1985 film Brazil, designed by Norman Garwood, tells its story partly by creating contrasting spaces. There are cramped domestic interiors; imposing civic buildings; sparse and frightening chambers of horrors. The look of the film, Gilliam said, came from “looking at beautiful Regency houses, Nash terrace houses, where, smashing through the cornices, is the wastepipe from the loo… …all these times exist right now and people don’t notice them. They’re all there.*”

On Friday, as site visitors toured around four significant buildings in the Karangahape Road precinct, Brazil was on my mind. Mostly, this was because I knew we were going to go past the ghost of what used to be my favourite cafe in Auckland, named and themed after the film. But as we toured, it seemed to me that the film’s aesthetic echoed something about the sites we were looking at. All of them had hidden beauty; odd spaces; unexpected textures and histories to reveal. The face they show the street doesn’t always match what’s inside. And all of them exist in the anachronistic mish-mash that is K Road, a space that’s being opened up and re-invented by the imminent arrival of the City Rail Link tunnel.

In company with Edward Bennett, K Road historian, and joined along the way by John Fellows of the City Rail Link, we learned a little more about the tunneling, discovered a couple of the loveliest interiors in Auckland, and even climbed through a trapdoor on a folding ladder—seemingly a recurring theme of these site visits. Follow me and I’ll show you some of what we saw.

Auckland Baptist Tabernacle

Auckland Baptist Tabernacle, Queen St.

The Auckland Baptist Tabernacle is a study in hierarchies. Front on, its Classical rigour is imposing—its design was based on the Pantheon in Rome. But from any other angle than dead centre, the building reveals its more prosaic brickwork—to me, generous and well crafted, but to Victorian tastes, horribly patchy and common. The walls were intended to be stucco’d to a shiny white, but this never happened.

Well-proportioned windows at the Auckland Baptist Tabernacle. Note the brick lintel and the irregular colour of the bricks.
Auckland Baptist Tabernacle, looking down into the main hall from the gallery.

Inside, the Tabernacle shifts gears again. The spaces are large—indeed, this was the largest room in Auckland when built in 1885—but not imposing. It’s perhaps not the authoritarian space that the portico might suggest. The authority, Edward explained, came from the moral rigour that the congregation practiced, and was intended to set clergy and flock on a more level footing.

Structurally, the room is noteworthy for the curved rear wall, intended to bounce sound back into the room. There are slender cast iron pillars supporting the gallery. But, most of all, this is a large span. And the span had to be crossed without the aid of structural steel. Luckily for the church’s builders, then, that they lived in a country where 2000-year old kauri grew strong and straight! Thirteen good-sized ‘uns were ordered up from the North, and were duly sawed to size. We climbed through a hatch in the ceiling to have a look. Here’s where it got a little Brazil.

In the ceiling, Auckland Baptist Tabernacle

As you can see above and at the top of this post, there’s a large-ish ceiling space above the main hall. Truthfully, I was a little preoccupied with my fear that a site visitor would put a foot wrong and crash sixty feet to their doom (“how can Santa Claus get in if we don’t have a chimney?”), but nevertheless I managed to cast an eye over the structure. There are large kauri rafters, long straight members which make up the top and bottom chords of the truss. The hall doesn’t run the length of the building—there are sizeable rooms behind for other kinds of functions, and so the building is divided about half way by a brick shear wall, which goes up through the whole building almost to the underside of the roof.

As the tour continued, I butted in to a conversation that Professor Jason Ingham was having about the Tabernacle. For those of you who don’t know him, Jason is responsible—among a number of other things!—for developing methods to analyse the strength of unreinforced masonry buildings. Jason explained that this kind of building is a classic example of a structure that isn’t explained well by conventional structural dynamics. Instead, said Jason, the ceiling has to be thought of as a flexible diaphragm (not a rigid one), and assessment and strengthening should be designed on that basis. That doesn’t, of course, solve the problem that (like most churches) you are dealing with a big empty box with long not-so-strong sides. Still, there may be more strength in the building than conventional analysis would suggest.

Mercury Theatre

Mercury Theatre, the stalls and the corner of the gallery. Showing the “restored” but perhaps over-garish colour scheme

Next stop was the Mercury Theatre, opened in 1910 and Auckland’s oldest surviving theatre. It has been through a number of reinventions in its time: as a picture palace; a 1970s black-box theatre; a church; a language school; and so on. Like the Tabernacle, it’s a brick building, but in the intervening 25 years between the Tab’ and the Mercury, structural steel was introduced: so the Mercury’s large roof is held up by I-beams, not kauri. [Edit (25 Aug 17): Thanks to Mike Skinner on the K Road Heritage Facebook page who pointed out that the Mercury’s roof beams are timber and provided a picture.]

The theatre is ornate, having kept most of its plasterwork intact even through the austerities of a 1970s all-black paintjob. When it was last restored, the paint was scraped back revealing the bright blues and reds you see in the photo. These colours were duly reinstated—but Edward’s opinion is that the bright colours would’ve been more muted in the original, overlaid with paint effects: in fact, he thinks the bright blue was probably an undercoat.

Pressed-metal ceiling, Mercury Theatre foyer

There’s a large expanse of lovely pressed-metal ceiling still to be seen in the entrance foyer, and Edward explained that at the time of construction, this was believed to be a fireproof material. Sadly, fires in other buildings with pressed-metal ceilings disproved this notion, and these ceilings were mostly torn out, becoming quite rare.

Complex forms beneath the gallery, Mercury Theatre

For my part, I enjoyed the profusion and contradiction of the forms and decorations of the theatre. It’s hard, on first sight, to get a sense of the exact extent of the space and its orientation, and this slightly warren-like quality is exacerbated by the theatre’s position, tucked down the lane, its façade declaiming bravely and boldly at an audience who are not there to watch.

John Fellows now took the stage at the Mercury. This was the perfect place for him to speak, as, come 2019, ground will be broken next door for the new Karangahape Station, part of the City Rail Link. The project involves digging a large pit at the south edge of the theatre, a pit which descends some ten stories. The station’s platforms will extend underneath the Mercury, underneath K Road, and underneath some of Pitt St on the other side.

It’s an audacious project, but of course one with plenty of precedents in all the major cities of the world. John explained that careful consideration has been given to minimising the impact that the CRL will have on the surrounding  buildings, both during construction and in operation. For example, the tunnels that will take passengers down from the Mercury Lane entrance to the station will veer out under the roadway, rather than passing under the theatre. This is to avoid noise and vibration passing up into the structures above.

John also explained that the results of subsurface core sampling have been encouraging. The soil, at the depth where the work has to be done, is East Coast Bays sandstone—common throughout Auckland. This soil can vary widely in its strength, but the good news is that the stuff underneath the Mercury is stronger than expected. This will make shoring up the pit next to the Mercury easier, and makes settlement less likely.

Decorative profusion, Mercury Theatre

As a sidenote, John described the system that is protecting the heritage buildings of Albert St, where the cut-and-cover tunnel work for the lower end of the line is currently proceeding. A network of over 1300 laser sensors is trained on the buildings’ exteriors, measuring in real time any deflections that might occur. If the movements of the buildings were to exceed the design parameters—hold the phone! The work stops immediately until the problem is resolved.

John had  plenty more to say about the plans for the station, about its design programme, mana whenua, use of local materials, bicycle integration, green design, and other topics. He said, just as Jeremy Salmond said at the Melanesian Mission, that he doesn’t see the purpose of trying to make a new building look like an old one just to “blend in” with its surroundings. Instead, John says, why not try to design a building that in 50-100 years will become a historic building in its own right? There was more to say and more to ask about all this, and the good news is that there will be an opportunity to hear more from John when he speaks at an ACE event in September. Keep an eye on their Facebook page for details.

We site visitors moved on to one of the loveliest hidden treasures in the city: the palm court in the disused K Road entranceway to the Mercury. To increase foot traffic to the Mercury, shortly after it was opened the owners purchased a narrow sliver of land and built a barrel-vaulted entranceway that took punters down into the theatre. As I mentioned, some will remember it as Brazil cafe. Now it’s a fast food joint. With brick-pattern wallpaper.

The Palm Court, Mercury Theatre

Tucked away, though, in between the Mercury and the now-disconnected entranceway, is the palm court. This was intended as a scene of Hollywood glamour to pass through on the way to the movies. Designed by Daniel Patterson, topped with a stunning leadlight dome, the room has retained its glamour and charm through decades of disuse. Fashionistas, artists, clairvoyants: what a studio space! Get in there, you muggs! (The author confesses to having once practiced one of the three professions listed above.)

Hopetoun Alpha

Hopetoun Alpha

Hopetoun Alpha is a delight. I felt the same sense of joy and astonishment as when I first entered St-Matthew-in-the-City, last year. It’s a light, delicate, finely-proportioned space—a Leipzig shoebox, just like Auckland Town Hall. Before you even get inside, the portico is unusual enough to warrant a better look. It’s painted a bold red with a pale blue soffit, creating a sense of interiority in comparison to the pale sides.

Red portico, Hopetoun Alpha
Blue ceiling, portico, Hopetoun Alpha. Note the marked curvature of the wall.
The “oak” door, Hopetoun Alpha, in fact made of kauri. Note the “ashlar” lines on the wall, which is in fact made of concrete.

From the pictures above, you can see that the front wall is curved, once again to produce sound reflection and natural amplification inside. The wall looks a bit like ashlar, doesn’t it? But in fact it is mass concrete, unreinforced. Timber trusses span the walls, just like at the Tabernacle. Speaking of timber and things that look like other things, the main door to Hopetoun Alpha appears to be oak—but scratches on its surface show that the oak is a paint effect, and the door is kauri. Fashions have changed, and now real fake oak is rarely seen.

It’s inside that Hopetoun Alpha truly shines. We were all delighted with its lightness and grace.

Interior, Hopetoun Alpha
Interior, Hopetoun Alpha. Detail of decorative elements. Slender cast iron columns.

Like many other buildings of its age and general type, Hopetoun Alpha and its owners are now having to give consideration to earthquake strengthening. There’s some hope that the gallery or mezzanine could act as a diaphragm, strengthening the outer walls.  [Edit: Edward Bennett kindly corrected me: the gallery was inserted into the 1875 building in 1885, “which is why it rather awkwardly passes in front of the windows”. The point I was trying (and failing) to make is that perhaps a retrofit can strengthen the gallery or be concealed inside it, to brace the long walls. HT]

Visitors to the Auckland Town Hall will remember that its gallery conceals a large truss designed to brace the long walls. Subsequent to our visit, I spoke with John O’Hagan of Compusoft Engineering, a firm known to site visitors from the St James Theatre visit last year. John’s supervising some investigations into the materials, foundations, and structural members of the building. We may yet have the chance to return and learn more.

Pitt St Methodist Church

Pitt St Methodist Church, with the 1962 porch

Last but not least we arrived at the Pitt St Methodist Church, nipping in through the Wesley Bicentennial Hall, for which there’s sadly no more space in this post. The Pitt St Methodist is determinedly Neo-Gothic, echoing the style of an English parish church, and deliberately eschewing the Classical. It’s a brick building, spanned with timber arches, and incorporating wrought-iron tie rods to muscularly and pointedly restrain the springings of the arches. Edward explained that this style reflected the Neo-Gothic designers’ conception of the power of the Gothic—Gothic church-builders would have done this too if they’d had wrought iron.

Pitt St Methodist Church, interior

Earlier, I wrote about John Fellows’ contention that to design for a great historic building, you make a great contemporary design. Here at Pitt St, there are two shades of this theory in evidence. The first is the organ, which was rebuilt and rehoused in the 1960s into a large “tabernacle”, looking something like an enormous jukebox. Secondly, there is the porch, added on at the same time. The porch is concertina-folded, with windows and doors shaped as stylised versions of the Gothic ogive. It’s very likely inspired by the Coventry Cathedral of a similar date, says Edward. Both the organ and the porch inspired mixed feelings from visitors, some feeling that they added a new dimension, others that they detracted from the original form of the building.

Pitt St Methodist Church, the organ in its 1962 “Tabernacle” rehousing.

Heritage buildings are living things, truth to tell, and there’s no one point at which you can freeze them and say, that’s it. For me, the comment that resonated was Paula King’s—she works for the Trust that owns Hopetoun Alpha. Paula said that using Hopetoun Alpha for good things “keeps its battery charged”; and keeping it charged gives it the power to last longer and speak louder, perhaps loud enough that future generations will still be able to hear it.

Thanks!

Our thanks to Edward Bennett and to John Fellows. You can read more about K Road’s buildings and their history at the kroad.com site, written by Edward. You can also read about the plans for Karangahape Station on the City Rail Link’s site.

* The quotation at the start of this post is from Bob McCabe’s book Dark Knights and Holy Fools: The Art and Films of Terry Gilliam: From Before Python to Beyond Fear and Loathing 1999 p.141.

Disclaimer: all ideas, information, insight are Edward’s and John’s. Errors of fact or interpretation are all my own work. HT